TWI650435B - Steel sheet and manufacturing method thereof - Google Patents
Steel sheet and manufacturing method thereof Download PDFInfo
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- TWI650435B TWI650435B TW107111354A TW107111354A TWI650435B TW I650435 B TWI650435 B TW I650435B TW 107111354 A TW107111354 A TW 107111354A TW 107111354 A TW107111354 A TW 107111354A TW I650435 B TWI650435 B TW I650435B
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 523
- 239000010959 steel Substances 0.000 title claims abstract description 523
- 238000004519 manufacturing process Methods 0.000 title claims description 22
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 559
- 229910052742 iron Inorganic materials 0.000 claims abstract description 278
- 239000000126 substance Substances 0.000 claims abstract description 44
- 239000013078 crystal Substances 0.000 claims abstract description 31
- 239000000203 mixture Substances 0.000 claims abstract description 27
- 229940116364 hard fat Drugs 0.000 claims abstract description 13
- 229910001035 Soft ferrite Inorganic materials 0.000 claims abstract description 11
- 238000010438 heat treatment Methods 0.000 claims description 287
- 238000001816 cooling Methods 0.000 claims description 64
- 238000000034 method Methods 0.000 claims description 39
- 238000011282 treatment Methods 0.000 claims description 38
- 238000004458 analytical method Methods 0.000 claims description 20
- 238000005246 galvanizing Methods 0.000 claims description 16
- 239000007789 gas Substances 0.000 claims description 15
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 15
- 229910052684 Cerium Inorganic materials 0.000 claims description 14
- 229910052749 magnesium Inorganic materials 0.000 claims description 12
- 229910052797 bismuth Inorganic materials 0.000 claims description 11
- 239000010960 cold rolled steel Substances 0.000 claims description 11
- 238000004020 luminiscence type Methods 0.000 claims description 11
- 229910052748 manganese Inorganic materials 0.000 claims description 11
- 229910052726 zirconium Inorganic materials 0.000 claims description 11
- 229910052799 carbon Inorganic materials 0.000 claims description 10
- 229910052791 calcium Inorganic materials 0.000 claims description 9
- 229910052739 hydrogen Inorganic materials 0.000 claims description 9
- 239000012535 impurity Substances 0.000 claims description 9
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 8
- 229910052710 silicon Inorganic materials 0.000 claims description 8
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 7
- 229910052796 boron Inorganic materials 0.000 claims description 7
- 239000001257 hydrogen Substances 0.000 claims description 7
- 229910052746 lanthanum Inorganic materials 0.000 claims description 7
- 229910052758 niobium Inorganic materials 0.000 claims description 7
- 229910052782 aluminium Inorganic materials 0.000 claims description 6
- 229910052787 antimony Inorganic materials 0.000 claims description 6
- 229910052802 copper Inorganic materials 0.000 claims description 6
- 229910052750 molybdenum Inorganic materials 0.000 claims description 6
- 229910052759 nickel Inorganic materials 0.000 claims description 6
- 229910052721 tungsten Inorganic materials 0.000 claims description 6
- 229910052720 vanadium Inorganic materials 0.000 claims description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 238000005266 casting Methods 0.000 claims description 5
- 229910052804 chromium Inorganic materials 0.000 claims description 5
- 229910052719 titanium Inorganic materials 0.000 claims description 5
- 229910052735 hafnium Inorganic materials 0.000 claims description 4
- 229910052718 tin Inorganic materials 0.000 claims description 4
- 229910052760 oxygen Inorganic materials 0.000 claims description 3
- 229910052757 nitrogen Inorganic materials 0.000 claims description 2
- 230000008520 organization Effects 0.000 claims description 2
- 229910052717 sulfur Inorganic materials 0.000 claims description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims 1
- 125000003636 chemical group Chemical group 0.000 claims 1
- 229910052698 phosphorus Inorganic materials 0.000 claims 1
- QMQXDJATSGGYDR-UHFFFAOYSA-N methylidyneiron Chemical compound [C].[Fe] QMQXDJATSGGYDR-UHFFFAOYSA-N 0.000 abstract description 11
- 239000010410 layer Substances 0.000 description 121
- 230000000694 effects Effects 0.000 description 40
- 229910000859 α-Fe Inorganic materials 0.000 description 40
- 230000001965 increasing effect Effects 0.000 description 36
- 238000006243 chemical reaction Methods 0.000 description 34
- 238000007747 plating Methods 0.000 description 34
- 239000002344 surface layer Substances 0.000 description 31
- 238000005452 bending Methods 0.000 description 25
- 238000005096 rolling process Methods 0.000 description 25
- 238000012545 processing Methods 0.000 description 24
- 238000005275 alloying Methods 0.000 description 23
- 239000002245 particle Substances 0.000 description 23
- 238000005098 hot rolling Methods 0.000 description 17
- 239000010955 niobium Substances 0.000 description 16
- 238000005097 cold rolling Methods 0.000 description 15
- 239000000463 material Substances 0.000 description 15
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- 238000007254 oxidation reaction Methods 0.000 description 10
- 238000001887 electron backscatter diffraction Methods 0.000 description 9
- 238000012360 testing method Methods 0.000 description 9
- 229910001335 Galvanized steel Inorganic materials 0.000 description 8
- 239000008397 galvanized steel Substances 0.000 description 8
- 230000001771 impaired effect Effects 0.000 description 8
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- 238000005554 pickling Methods 0.000 description 8
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- NAWXUBYGYWOOIX-SFHVURJKSA-N (2s)-2-[[4-[2-(2,4-diaminoquinazolin-6-yl)ethyl]benzoyl]amino]-4-methylidenepentanedioic acid Chemical compound C1=CC2=NC(N)=NC(N)=C2C=C1CCC1=CC=C(C(=O)N[C@@H](CC(=C)C(O)=O)C(O)=O)C=C1 NAWXUBYGYWOOIX-SFHVURJKSA-N 0.000 description 5
- 229910000794 TRIP steel Inorganic materials 0.000 description 5
- 239000003337 fertilizer Substances 0.000 description 5
- 238000000445 field-emission scanning electron microscopy Methods 0.000 description 5
- 238000001556 precipitation Methods 0.000 description 5
- 238000004544 sputter deposition Methods 0.000 description 5
- LRXTYHSAJDENHV-UHFFFAOYSA-H zinc phosphate Chemical compound [Zn+2].[Zn+2].[Zn+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O LRXTYHSAJDENHV-UHFFFAOYSA-H 0.000 description 5
- 229910000165 zinc phosphate Inorganic materials 0.000 description 5
- 229910001208 Crucible steel Inorganic materials 0.000 description 4
- 229910001047 Hard ferrite Inorganic materials 0.000 description 4
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- 238000002441 X-ray diffraction Methods 0.000 description 3
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 3
- 239000012141 concentrate Substances 0.000 description 3
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- 229910052725 zinc Inorganic materials 0.000 description 3
- 239000011701 zinc Substances 0.000 description 3
- TUSDEZXZIZRFGC-UHFFFAOYSA-N 1-O-galloyl-3,6-(R)-HHDP-beta-D-glucose Natural products OC1C(O2)COC(=O)C3=CC(O)=C(O)C(O)=C3C3=C(O)C(O)=C(O)C=C3C(=O)OC1C(O)C2OC(=O)C1=CC(O)=C(O)C(O)=C1 TUSDEZXZIZRFGC-UHFFFAOYSA-N 0.000 description 2
- 239000001263 FEMA 3042 Substances 0.000 description 2
- 206010020751 Hypersensitivity Diseases 0.000 description 2
- LRBQNJMCXXYXIU-PPKXGCFTSA-N Penta-digallate-beta-D-glucose Natural products OC1=C(O)C(O)=CC(C(=O)OC=2C(=C(O)C=C(C=2)C(=O)OC[C@@H]2[C@H]([C@H](OC(=O)C=3C=C(OC(=O)C=4C=C(O)C(O)=C(O)C=4)C(O)=C(O)C=3)[C@@H](OC(=O)C=3C=C(OC(=O)C=4C=C(O)C(O)=C(O)C=4)C(O)=C(O)C=3)[C@H](OC(=O)C=3C=C(OC(=O)C=4C=C(O)C(O)=C(O)C=4)C(O)=C(O)C=3)O2)OC(=O)C=2C=C(OC(=O)C=3C=C(O)C(O)=C(O)C=3)C(O)=C(O)C=2)O)=C1 LRBQNJMCXXYXIU-PPKXGCFTSA-N 0.000 description 2
- 229910001347 Stellite Inorganic materials 0.000 description 2
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 2
- 208000026935 allergic disease Diseases 0.000 description 2
- 230000007815 allergy Effects 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 239000010953 base metal Substances 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- AHICWQREWHDHHF-UHFFFAOYSA-N chromium;cobalt;iron;manganese;methane;molybdenum;nickel;silicon;tungsten Chemical compound C.[Si].[Cr].[Mn].[Fe].[Co].[Ni].[Mo].[W] AHICWQREWHDHHF-UHFFFAOYSA-N 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
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- 238000007542 hardness measurement Methods 0.000 description 2
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- 229910052747 lanthanoid Inorganic materials 0.000 description 2
- 150000002602 lanthanoids Chemical class 0.000 description 2
- 229910052745 lead Inorganic materials 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 150000002910 rare earth metals Chemical class 0.000 description 2
- LRBQNJMCXXYXIU-NRMVVENXSA-N tannic acid Chemical compound OC1=C(O)C(O)=CC(C(=O)OC=2C(=C(O)C=C(C=2)C(=O)OC[C@@H]2[C@H]([C@H](OC(=O)C=3C=C(OC(=O)C=4C=C(O)C(O)=C(O)C=4)C(O)=C(O)C=3)[C@@H](OC(=O)C=3C=C(OC(=O)C=4C=C(O)C(O)=C(O)C=4)C(O)=C(O)C=3)[C@@H](OC(=O)C=3C=C(OC(=O)C=4C=C(O)C(O)=C(O)C=4)C(O)=C(O)C=3)O2)OC(=O)C=2C=C(OC(=O)C=3C=C(O)C(O)=C(O)C=3)C(O)=C(O)C=2)O)=C1 LRBQNJMCXXYXIU-NRMVVENXSA-N 0.000 description 2
- 229940033123 tannic acid Drugs 0.000 description 2
- 235000015523 tannic acid Nutrition 0.000 description 2
- 229920002258 tannic acid Polymers 0.000 description 2
- 238000005496 tempering Methods 0.000 description 2
- 239000011800 void material Substances 0.000 description 2
- 238000003466 welding Methods 0.000 description 2
- 229910000885 Dual-phase steel Inorganic materials 0.000 description 1
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 1
- 240000004282 Grewia occidentalis Species 0.000 description 1
- 101000582320 Homo sapiens Neurogenic differentiation factor 6 Proteins 0.000 description 1
- 102100030589 Neurogenic differentiation factor 6 Human genes 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- 238000007545 Vickers hardness test Methods 0.000 description 1
- 229910000754 Wrought iron Inorganic materials 0.000 description 1
- 241000276425 Xiphophorus maculatus Species 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910052785 arsenic Inorganic materials 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- ZDVYABSQRRRIOJ-UHFFFAOYSA-N boron;iron Chemical compound [Fe]#B ZDVYABSQRRRIOJ-UHFFFAOYSA-N 0.000 description 1
- 229910052793 cadmium Inorganic materials 0.000 description 1
- 238000012993 chemical processing Methods 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
- ZCDOYSPFYFSLEW-UHFFFAOYSA-N chromate(2-) Chemical compound [O-][Cr]([O-])(=O)=O ZCDOYSPFYFSLEW-UHFFFAOYSA-N 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
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- 239000000446 fuel Substances 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- 229910052732 germanium Inorganic materials 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 239000005431 greenhouse gas Substances 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
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- 229910052738 indium Inorganic materials 0.000 description 1
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- 150000002601 lanthanoid compounds Chemical class 0.000 description 1
- 238000001748 luminescence spectrum Methods 0.000 description 1
- 229910052754 neon Inorganic materials 0.000 description 1
- GKAOGPIIYCISHV-UHFFFAOYSA-N neon atom Chemical compound [Ne] GKAOGPIIYCISHV-UHFFFAOYSA-N 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
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- 229910052762 osmium Inorganic materials 0.000 description 1
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- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
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- 229910052713 technetium Inorganic materials 0.000 description 1
- 238000010792 warming Methods 0.000 description 1
Landscapes
- Heat Treatment Of Sheet Steel (AREA)
Abstract
此鋼板具有預定化學組成，且鋼板內部之鋼組織以體積分率計含有：軟質肥粒鐵：0~30%、殘留沃斯田鐵：3%~40%、新生麻田散鐵：0~30%、波來鐵與雪明碳鐵之合計：0~10%，且剩餘部分含有硬質肥粒鐵；鋼板內部中，長寬比2.0以上之殘留沃斯田鐵佔總殘留沃斯田鐵之個數比率為50%以上，自前述表面起於板厚方向上存在厚度為1~100μm之軟質層，前述軟質層所含肥粒鐵中，長寬比小於3.0之晶粒的體積分率為50%以上，前述軟質層中之殘留沃斯田鐵的體積分率小於鋼板內部之殘留沃斯田鐵的體積分率的50%，自前述表面起於大於0.2μm且在5.0μm以下之範圍出現前述顯示Si之波長的發光強度之波峰。The steel plate has a predetermined chemical composition, and the steel structure inside the steel plate contains, by volume fraction, soft ferrite: 0~30%, residual Worthite iron: 3%~40%, new mata loose iron: 0~30 %, the total of Bora iron and Xueming carbon iron: 0~10%, and the remaining part contains hard fat iron; in the interior of the steel plate, the residual Worth iron with an aspect ratio of 2.0 or more accounts for the total residual Worthite iron. The number ratio is 50% or more, and a soft layer having a thickness of 1 to 100 μm exists in the thickness direction from the surface, and the volume fraction of crystal grains having an aspect ratio of less than 3.0 in the soft layer of the soft layer is 50% or more, the volume fraction of the residual Worthite iron in the soft layer is less than 50% of the volume fraction of the residual Worth iron in the steel sheet, and is larger than 0.2 μm and less than 5.0 μm from the surface. The aforementioned peak of the luminous intensity showing the wavelength of Si appears.
Description
本發明涉及一種鋼板及其製造方法。The present invention relates to a steel sheet and a method of manufacturing the same.
背景技術 近年來，由伴隨地球暖化對策之溫室氣體排出量規制之觀點，係尋求汽車進一步之油耗改善。而為了使車體輕量化並確保衝撞安全性，汽車用零件應用高強度鋼板有愈趨擴展之傾向。 想當然耳，供於汽車用零件之鋼板不僅強度，還要求壓製加工性及熔接性等於零件成形時所要求之各種施工性。具體而言，由壓製加工性之觀點，對鋼板多要求具優異之延伸率(拉伸試驗中之總延伸率；El)、延伸率凸緣性(擴孔率；λ)。Background Art In recent years, from the viewpoint of regulation of greenhouse gas emissions associated with measures for global warming, it is sought to further improve fuel consumption of automobiles. In order to reduce the weight of the vehicle body and ensure the safety of collision, high-strength steel sheets for automotive parts tend to expand. Of course, the steel plate for automotive parts is not only strong, but also requires press workability and weldability equal to the various workability required for part forming. Specifically, from the viewpoint of press workability, the steel sheet is required to have an excellent elongation (total elongation in tensile test; El) and elongation flangeability (hole expansion ratio; λ).
壓製加工性高之高強度鋼板已知有具有肥粒鐵相與麻田散鐵相之DP鋼(Dual Phase鋼)(例如可參照專利文獻1)。DP鋼具有優異的延展性。然，DP鋼之硬質相卻會成為空隙形成之起點故擴孔性差。A DP steel (Dual Phase steel) having a ferrite iron phase and a granulated iron phase is known as a high-strength steel sheet having high press workability (for example, refer to Patent Document 1). DP steel has excellent ductility. However, the hard phase of DP steel becomes the starting point of void formation, so the hole expandability is poor.
又，延展性佳的高強度鋼板已知有使鋼組織中殘存有沃斯田鐵相以利用TRIP(變態誘發塑性)效果之TRIP鋼(例如參照專利文獻2)。TRIP鋼的延展性比DP鋼更高。但，TRIP鋼的擴孔性差。而且，TRIP鋼因使沃斯田鐵殘存，故必須含有大量的Si等合金。因此，TRIP鋼之化學轉化處理性及鍍敷密著性較差。Further, a high-strength steel sheet having excellent ductility is known as a TRIP steel in which a Worstian iron phase remains in a steel structure to utilize a TRIP (allergy-induced plasticity) effect (for example, see Patent Document 2). TRIP steel has higher ductility than DP steel. However, TRIP steel has poor hole expandability. Moreover, TRIP steel must contain a large amount of alloy such as Si because it retains the Worthite iron. Therefore, the chemical conversion treatability and plating adhesion of TRIP steel are inferior.
專利文獻3中記載了一種擴孔性優異之高強度鋼板，其微觀組織以面積率計含有70%以上之變韌鐵或變韌肥粒鐵，且拉伸強度在800MPa以上。專利文獻4中則係記載了一種拉伸強度在800MPa以上且擴孔性及延展性佳之高強度鋼板，其微觀組織係以變韌鐵或變韌肥粒鐵為主相，第2相為沃斯田鐵，且剩餘部分為肥粒鐵或麻田散鐵。Patent Document 3 describes a high-strength steel sheet having excellent hole expandability, and the microstructure thereof contains 70% or more of toughened iron or toughened ferrite iron in an area ratio, and the tensile strength is 800 MPa or more. Patent Document 4 describes a high-strength steel sheet having a tensile strength of 800 MPa or more and excellent hole expandability and ductility, and the microstructure is mainly composed of toughened iron or toughened ferrite iron, and the second phase is a flame.斯田铁, and the rest is ferrite iron or 麻田散铁.
且，非專利文獻1中揭示了藉由應用將鋼板進行2次退火之2次退火法，來提升鋼板之延伸率及擴孔性。Further, Non-Patent Document 1 discloses that the elongation of the steel sheet and the hole expandability are improved by applying a secondary annealing method in which the steel sheet is annealed twice.
但，以往之高強度鋼板的延展性及擴孔性仍無法充分滿足近年來汽車公司之需求。 且，由確保乘客安全性之觀點，對汽車用高強度鋼板要求零件在加工後於衝撞變形時不會發生破裂。零件在衝撞時所受變形主要情況多為彎曲變形，故要求作為其素材之鋼板具有彎曲性。此處所言彎曲性係指鋼板因壓製加工等受應變後之彎曲性。因此，對作為零件之素材的鋼板要求在加工後仍具有良好之彎曲性。 然，至今仍未有針對改善加工後之彎曲性的檢討。However, the ductility and hole expandability of the conventional high-strength steel sheets cannot fully satisfy the demand of automobile companies in recent years. Moreover, from the viewpoint of ensuring passenger safety, it is required that the high-strength steel sheet for automobiles does not crack when subjected to collision deformation after processing. The main deformation of the parts during the collision is mostly bending deformation, so the steel plate as the material is required to have flexibility. The term "bendability" as used herein refers to the flexibility of a steel sheet after being subjected to straining by press working or the like. Therefore, the steel sheet as the material of the part is required to have good bending property after processing. However, there has been no review to improve the flexibility after processing.
先前技術文獻 專利文獻 專利文獻1：日本專利特開平6-128688號公報 專利文獻2：日本專利特開2006-274418號公報 專利文獻3：日本專利特開2003-193194號公報 專利文獻4：日本專利特開2003-193193號公報 非專利文獻[Patent Document 1] Japanese Patent Laid-Open No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. Japanese Patent Laid-Open No. 2003-193193, Non-Patent Literature
非專利文獻1：K.Sugimoto et al., ISIJ International, Vol.33(1993), No.7, pp775-782Non-Patent Document 1: K. Sugimoto et al., ISIJ International, Vol. 33 (1993), No. 7, pp775-782
發明概要 發明欲解決之課題 本發明係鑑於上述情事而成者。本發明之課題在於提供一種具優異延展性及擴孔性且加工後之彎曲性良好的高強度鋼板及其製造方法。Disclosure of the Invention Problems to be Solved by the Invention The present invention has been made in view of the above circumstances. An object of the present invention is to provide a high-strength steel sheet having excellent ductility and hole expandability and excellent bending property after processing, and a method for producing the same.
用以解決課題之手段 本發明人等為解決上述課題反覆積極努力檢討。 結果發現，對具有預定化學組成之熱軋鋼板或冷軋鋼板進行條件相異之2次熱處理(退火)，藉此可有效將鋼板內部製成預定鋼組織且可有效形成具預定厚度及鋼組織之表層。而且發現了，藉由於預定深度形成含Si氧化物之內部氧化層，亦可確保汽車用鋼板所尋求之鍍敷密著性及化學轉化處理性。Means for Solving the Problem The present inventors have actively reviewed the problem in order to solve the above problems. As a result, it has been found that the hot-rolled steel sheet or the cold-rolled steel sheet having a predetermined chemical composition is subjected to two heat treatments (annealing) which are different in conditions, whereby the inside of the steel sheet can be effectively made into a predetermined steel structure and can be effectively formed into a predetermined thickness and steel structure. The surface layer. Further, it has been found that by forming an internal oxide layer containing Si oxide at a predetermined depth, it is possible to ensure plating adhesion and chemical conversion treatability sought for a steel sheet for automobiles.
具體來說，藉由第1次的熱處理，使鋼板內部之鋼組織以麻田散鐵等板條狀組織為主體，並使表層之鋼組織以肥粒鐵為主體。然後，於第2次的熱處理中，將最高加熱溫度設於α(肥粒鐵)與γ(沃斯田鐵)之二相區域，並同時施行脫碳處理。結果，2次熱處理後製得之鋼板其鋼板內部為分散有針狀殘留沃斯田鐵之鋼組織，表層之鋼組織以肥粒鐵為主體且具有預定厚度。上述鋼板強度高、延展性及擴孔性佳、加工後之彎曲性良好。且，以上述鋼板為母材並施行熔融鍍鋅之鍍鋅鋼板亦具有優異之延展性及擴孔性且加工後之彎曲性良好。Specifically, in the first heat treatment, the steel structure inside the steel sheet is mainly composed of a lath-like structure such as a granulated iron, and the steel structure of the surface layer is mainly composed of ferrite iron. Then, in the second heat treatment, the maximum heating temperature is set in the two-phase region of α (fertilizer iron) and γ (Worstian iron), and decarburization treatment is simultaneously performed. As a result, the steel sheet obtained after the two heat treatments had a steel structure in which the needle-like residual Worth iron was dispersed inside the steel sheet, and the steel structure of the surface layer was mainly composed of the ferrite iron and had a predetermined thickness. The steel sheet has high strength, good ductility and hole expandability, and good bending property after processing. Further, the galvanized steel sheet which is subjected to hot-dip galvanizing using the above-mentioned steel sheet as a base material also has excellent ductility and hole expandability and is excellent in bending property after processing.
並且在上述第1次及第2次的熱處理中，可抑制鋼中所含Si等合金元素在鋼板外部氧化，而於預定深度形成含Si氧化物之內部氧化層，從而獲得優異的化學轉化處理性。並且，於鋼板在表面形成鍍敷層時，可獲得優異的鍍敷密著性。 本發明即係根據上述見解而完成。本發明主旨如下。Further, in the first and second heat treatments, it is possible to suppress oxidation of the alloying elements such as Si contained in the steel to the outside of the steel sheet, and to form an internal oxide layer containing Si oxide at a predetermined depth, thereby obtaining an excellent chemical conversion treatment. Sex. Further, when the steel sheet is formed on the surface of the plating layer, excellent plating adhesion can be obtained. The present invention has been completed based on the above findings. The gist of the present invention is as follows.
(1)本發明之一態樣之鋼板，其特徵在於：具有以下化學組成：以質量%計含有：C：0.050%~0.500%、Si：0.01%~3.00%、Mn：0.50%~5.00%、P：0.0001%~0.1000%、S：0.0001%~0.0100%、Al：0.001%~2.500%、N：0.0001%~0.0100%、O：0.0001%~0.0100%、Ti：0%~0.300%、V：0%~1.00%、Nb：0%~0.100%、Cr：0%~2.00%、Ni：0%~2.00%、Cu：0%~2.00%、Co：0%~2.00%、Mo：0%~1.00%、W：0%~1.00%、B：0%~0.0100%、Sn：0%~1.00%、Sb：0%~1.00%、Ca：0%~0.0100%、Mg：0%~0.0100%、Ce：0%~0.0100%、Zr：0%~0.0100%、La：0%~0.0100%、Hf：0%~0.0100%、Bi：0%~0.0100%、REM：0%~0.0100%，且剩餘部分由Fe及不純物構成；自表面起以1/4厚度之位置為中心之1/8厚度~3/8厚度之範圍的鋼組織，以體積分率計含有：軟質肥粒鐵：0%~30%、殘留沃斯田鐵：3%~40%、新生麻田散鐵：0%~30%、波來鐵與雪明碳鐵之合計：0%~10%，且剩餘部分含有硬質肥粒鐵；前述1/8厚度~3/8厚度之前述範圍中，長寬比2.0以上之殘留沃斯田鐵佔總殘留沃斯田鐵之個數比率為50%以上，將具有硬度在前述1/8厚度~3/8厚度之前述範圍之硬度的80%以下之區域定義為軟質層時，自前述表面起於板厚方向上存在厚度為1~100μm之軟質層，前述軟質層所含肥粒鐵中，長寬比小於3.0之晶粒的體積分率為50%以上，前述軟質層中之殘留沃斯田鐵的體積分率小於前述1/8厚度~3/8厚度之前述範圍中的殘留沃斯田鐵的體積分率的50%，自前述表面起於前述板厚方向上以高頻輝光放電分析法分析顯示Si之波長的發光強度時，自前述表面起於大於0.2μm且在5.0μm以下之範圍中出現前述顯示Si之波長的發光強度之波峰。(1) A steel sheet according to an aspect of the present invention, comprising: the following chemical composition: C: 0.050% to 0.500%, Si: 0.01% to 3.00%, Mn: 0.50% to 5.00% by mass% , P: 0.0001%~0.1000%, S: 0.0001%~0.0100%, Al: 0.001%~2.500%, N: 0.0001%~0.0100%, O: 0.0001%~0.0100%, Ti: 0%~0.300%, V :0%~1.00%, Nb: 0%~0.100%, Cr: 0%~2.00%, Ni: 0%~2.00%, Cu: 0%~2.00%, Co: 0%~2.00%, Mo:0 %~1.00%, W: 0%~1.00%, B: 0%~0.0100%, Sn: 0%~1.00%, Sb: 0%~1.00%, Ca: 0%~0.0100%, Mg: 0%~ 0.0100%, Ce: 0%~0.0100%, Zr: 0%~0.0100%, La: 0%~0.0100%, Hf: 0%~0.0100%, Bi: 0%~0.0100%, REM: 0%~0.0100% And the remaining part is composed of Fe and impurities; the steel structure in the range of 1/8 thickness to 3/8 thickness centered on the surface at a position of 1/4 thickness from the surface contains, by volume fraction, soft ferrite: 0%~30%, residual Worthite iron: 3%~40%, new Matian loose iron: 0%~30%, total of Bora and ferrem carbon iron: 0%~10%, and the remaining part contains Hard fat iron; in the aforementioned range of 1/8 thickness to 3/8 thickness, the aspect ratio is 2.0 or more The residual Worthite iron accounts for 50% or more of the total residual Worth iron, and defines a soft layer having a hardness of 80% or less of the hardness of the aforementioned range of 1/8 thickness to 3/8 thickness. When there is a soft layer having a thickness of 1 to 100 μm in the thickness direction from the surface, the volume fraction of crystal grains having an aspect ratio of less than 3.0 in the soft layer of the soft layer is 50% or more, the softness The volume fraction of the residual Worthite iron in the layer is less than 50% of the volume fraction of the residual Worthite iron in the aforementioned range of 1/8th thickness to 3/8 of the thickness, from the aforementioned surface in the aforementioned plate thickness direction When the luminescence intensity indicating the wavelength of Si is analyzed by the high-frequency glow discharge analysis method, the peak of the luminescence intensity showing the wavelength of Si appears from the surface at a range of more than 0.2 μm and 5.0 μm or less.
(2)上述(1)之鋼板中，前述化學組成亦可含有以下中之一種或二種以上元素：Ti：0.001%~0.300%、V：0.001%~1.00%、及Nb：0.001%~0.100%。(2) The steel sheet according to (1) above, wherein the chemical composition may further contain one or more of the following elements: Ti: 0.001% to 0.300%, V: 0.001% to 1.00%, and Nb: 0.001% to 0.100 %.
(3)上述(1)或(2)之鋼板中，前述化學組成亦可含有以下中之一種或二種以上元素：Cr：0.001%~2.00%、Ni：0.001%~2.00%、Cu：0.001%~2.00%、Co：0.001%~2.00%、Mo：0.001%~1.00%、W：0.001%~1.00%、及B：0.0001%~0.0100%。(3) The steel sheet according to (1) or (2) above, wherein the chemical composition may further contain one or more of the following elements: Cr: 0.001% to 2.00%, Ni: 0.001% to 2.00%, Cu: 0.001 %~2.00%, Co: 0.001%~2.00%, Mo: 0.001%~1.00%, W: 0.001%~1.00%, and B: 0.0001%~0.0100%.
(4)上述(1)~(3)中任一項之鋼板中，前述化學組成亦可含有以下中之一種或二種元素：Sn：0.001%~1.00%、Sb：0.001%~1.00%。(4) The steel sheet according to any one of the above (1) to (3), wherein the chemical composition may further contain one or two of the following elements: Sn: 0.001% to 1.00%, and Sb: 0.001% to 1.00%.
(5)上述(1)~(4)中任一項之鋼板中，前述化學組成亦可含有以下中之一種或二種以上元素：Ca：0.0001%~0.0100%、Mg：0.0001%~0.0100%、Ce：0.0001%~0.0100%、Zr：0.0001%~0.0100%、La：0.0001%~0.0100%、Hf：0.0001%~0.0100%、Bi：0.0001%~0.0100%、及REM：0.0001%~0.0100%。(5) The steel sheet according to any one of the above (1) to (4), wherein the chemical composition may further contain one or more of the following elements: Ca: 0.0001% to 0.0100%, Mg: 0.0001% to 0.0100% Ce: 0.0001% to 0.0100%, Zr: 0.0001% to 0.0100%, La: 0.0001% to 0.0100%, Hf: 0.0001% to 0.0100%, Bi: 0.0001% to 0.0100%, and REM: 0.0001% to 0.0100%.
(6)上述(1)~(5)中任一項之鋼板中，前述化學組成亦可滿足下述式(1)。 Si+0.1×Mn+0.6×Al≧0.35・・・(1) (式(1)中之Si、Mn及Al表示各元素以質量%計之含量)。(6) In the steel sheet according to any one of the above (1) to (5), the chemical composition may satisfy the following formula (1). Si + 0.1 × Mn + 0.6 × Al ≧ 0.35 (1) (Si, Mn, and Al in the formula (1) represent the content of each element in mass%).
(7)上述(1)~(6)中任一項之鋼板亦可於表面具有熔融鍍鋅層或電鍍鋅層。(7) The steel sheet according to any one of the above (1) to (6) may have a hot-dip galvanized layer or an electrogalvanized layer on the surface.
(8)本發明之另一態樣之鋼板之製造方法，係製造如上述(1)~(6)中任一項之鋼板的方法，該方法之特徵在於：對熱軋鋼板或冷軋鋼板施行滿足下述(a)~(e)之第1熱處理後，施行滿足下述(A)~(E)之第2熱處理，前述熱軋鋼板係將具有如(1)~(6)中任一項之化學組成的鋼胚進行熱軋延並酸洗而製得，前述冷軋鋼板係將前述熱軋鋼板進行冷軋延而製得。 (a)於650℃達至最高加熱溫度為止之期間，設成含有0.1體積%以上之H 2且滿足下述式(3)之氣體環境。 (b)於A c3-30℃~1000℃之最高加熱溫度下保持1秒~1000秒。 (c)以650℃至最高加熱溫度為止之溫度範圍的平均加熱速度為0.5℃/秒~500℃/秒之方式進行加熱。 (d)於最高加熱溫度下保持後，以700℃至Ms為止之溫度範圍的平均冷卻速度為5℃/秒以上之方式進行冷卻。 (e)將以平均冷卻速度5℃/秒以上之冷卻進行至Ms以下之冷卻停止溫度為止。 (A)於650℃達至最高加熱溫度為止之期間，設成H 2為0.1體積%以上、O 2為0.020體積%以下且log(PH 2O/PH 2)滿足下述式(3)之氣體環境。 (B)於A c1+25℃~A c3-10℃之最高加熱溫度下保持1秒~1000秒。 (C)以650℃至最高加熱溫度為止之平均加熱速度為0.5℃/秒~500℃/秒之方式進行加熱。 (D)以700至600℃為止之溫度範圍的平均冷卻速度為3℃/秒以上之方式進行冷卻。 (E)以平均冷卻速度3℃/秒以上進行冷卻後，於300℃~480℃之間保持10秒以上。 -1.1≦log(PH 2O/PH 2)≦-0.07・・・(3) (式(3)中，PH 2O表示水蒸氣分壓，PH 2表示氫分壓)。 (8) A method of producing a steel sheet according to another aspect of the present invention, which is characterized in that the method of producing a steel sheet according to any one of the above (1) to (6) is characterized in that: the hot rolled steel sheet or the cold rolled steel sheet After performing the first heat treatment satisfying the following (a) to (e), the second heat treatment satisfying the following (A) to (E) is performed, and the hot-rolled steel sheet has the following (1) to (6) A steel composition of a chemical composition is obtained by hot rolling and pickling, and the cold-rolled steel sheet is obtained by cold rolling the hot-rolled steel sheet. (a) A gas atmosphere containing 0.1% by volume or more of H 2 and satisfying the following formula (3) at a temperature of 650 ° C up to the maximum heating temperature. (b) Hold at a maximum heating temperature of A c3 -30 ° C to 1000 ° C for 1 second to 1000 seconds. (c) heating is performed in such a manner that the average heating rate in the temperature range from 650 ° C to the highest heating temperature is from 0.5 ° C / sec to 500 ° C / sec. (d) After being held at the highest heating temperature, the film is cooled so that the average cooling rate in the temperature range from 700 ° C to Ms is 5 ° C /sec or more. (e) Cooling at an average cooling rate of 5 ° C /sec or more is carried out until the cooling stop temperature of Ms or less. (A) In the period from 650 ° C to the maximum heating temperature, H 2 is 0.1% by volume or more, O 2 is 0.020% by volume or less, and log (PH 2 O/PH 2 ) satisfies the following formula (3). Gas environment. (B) Hold at a maximum heating temperature of A c1 +25 ° C to A c3 -10 ° C for 1 second to 1000 seconds. (C) Heating is performed at an average heating rate of from 650 ° C to the maximum heating temperature of from 0.5 ° C / sec to 500 ° C / sec. (D) Cooling is performed so that the average cooling rate in the temperature range from 700 to 600 ° C is 3 ° C /sec or more. (E) After cooling at an average cooling rate of 3 ° C /sec or more, it is maintained at 300 ° C to 480 ° C for 10 seconds or longer. -1.1 ≦ log (PH 2 O/PH 2 ) ≦ -0.07 (3) (In the formula (3), PH 2 O represents a partial pressure of water vapor, and PH 2 represents a partial pressure of hydrogen).
(9)上述(8)之鋼板之製造方法亦可於前述(D)之後的階段施行熔融鍍鋅處理。(9) The method for producing a steel sheet according to the above (8) may be subjected to a hot-dip galvanizing treatment at a stage after the above (D).
發明效果 依據本發明之上述態樣，可提供一種具優異延展性及擴孔性、且化學轉化處理性、鍍敷密著性佳、並且加工後之彎曲性良好之高強度鋼板及其製造方法。 本發明之鋼板因延展性及擴孔性優異、且加工後之彎曲性良好，故可適用作可利用壓製加工等成形成各種形狀之汽車用鋼板。且，本發明之鋼板因化學轉化處理性、鍍敷密著性佳，故適於在表面形成化學轉化處理皮膜或鍍敷層之鋼板。Advantageous Effects of Invention According to the above aspect of the present invention, it is possible to provide a high-strength steel sheet having excellent ductility and hole expandability, chemical conversion treatability, good plating adhesion, and good bending property after processing, and a method for producing the same . Since the steel sheet of the present invention is excellent in ductility and hole expandability and has good flexibility after processing, it can be suitably used as a steel sheet for automobiles which can be formed into various shapes by press working. Further, since the steel sheet of the present invention is excellent in chemical conversion treatability and plating adhesion, it is suitable for forming a steel sheet having a chemical conversion treatment film or a plating layer on the surface.
用以實施發明之形態 「鋼板」 以下，詳細說明本發明之一實施形態之鋼板(本實施形態之鋼板)。 首先，說明本實施形態之鋼板具有之化學組成。以下說明中，表示元素含量之[%]意指[質量%]。In the embodiment of the present invention, a steel sheet (a steel sheet according to the embodiment) of the present invention will be described in detail. First, the chemical composition of the steel sheet of the present embodiment will be described. In the following description, [%] indicating the element content means [% by mass].
「C：0.050~0.500%」 C係可大幅提高鋼板強度之元素。且，C可使沃斯田鐵穩定化，故為獲得有助於提升延展性之殘留沃斯田鐵所需之元素。因此，C可有效兼顧強度與成形性。C含量若少於0.050%，則無法充分獲得殘留沃斯田鐵，而難以確保充分的強度及成形性。故設C含量為0.050%以上。為了更提升強度與成形性，C含量宜為0.075%以上，且0.100%以上更佳。 另一方面，C含量若大於0.500%，熔接性會顯著變差。因此設C含量為0.500%以下。由點熔接性之觀點，C含量宜為0.350%以下，且0.250%以下更佳。"C: 0.050~0.500%" The C system can greatly improve the strength of the steel plate. Moreover, C stabilizes the Worthite iron, so it is required to obtain the residual Worthite iron that contributes to the improvement of ductility. Therefore, C can effectively balance strength and formability. When the C content is less than 0.050%, the residual Worthite iron cannot be sufficiently obtained, and it is difficult to ensure sufficient strength and formability. Therefore, the C content is set to be 0.050% or more. In order to further improve the strength and formability, the C content is preferably 0.075% or more, and more preferably 0.100% or more. On the other hand, if the C content is more than 0.500%, the weldability is remarkably deteriorated. Therefore, the C content is made 0.500% or less. From the viewpoint of spot weldability, the C content is preferably 0.350% or less, and more preferably 0.250% or less.
「Si：0.01~3.00%」 Si係可抑制於鋼板中生成鐵系碳化物以使殘留沃斯田鐵穩定化，以提高強度與成形性之元素。Si含量小於0.01%時，會大量生成粗大的鐵系碳化物，使強度及成形性變差。因此，將Si含量設在0.01%以上。由此觀點來看，Si的下限值宜為0.10%以上，且以0.25%以上為佳。 另一方面，Si係會使鋼材脆化之元素。Si含量若大於3.00%，會使鋼板的擴孔性不充分。且，Si含量若大於3.00%，會易發生鑄造出的鋼胚破裂等問題。因此，將Si含量設在3.00%以下。並且，Si會損害鋼板的耐衝撃特性。故Si含量宜為2.50%以下，且2.00%以下較佳。"Si: 0.01 to 3.00%" The Si system suppresses the formation of iron-based carbides in the steel sheet to stabilize the residual Worthite iron, thereby improving the strength and formability. When the Si content is less than 0.01%, coarse iron-based carbides are formed in a large amount, which deteriorates strength and formability. Therefore, the Si content is set to 0.01% or more. From this point of view, the lower limit of Si is preferably 0.10% or more, and preferably 0.25% or more. On the other hand, Si is an element that makes the steel brittle. When the Si content is more than 3.00%, the hole expandability of the steel sheet is insufficient. Further, if the Si content is more than 3.00%, problems such as cracking of the cast steel blank may occur. Therefore, the Si content is set to 3.00% or less. Moreover, Si impairs the punching resistance of the steel sheet. Therefore, the Si content is preferably 2.50% or less, and preferably 2.00% or less.
「Mn：0.50~5.00%」 Mn因可提高鋼板的淬火性以提升強度而含有。Mn含量若小於0.50%，則於退火後的冷卻中會大量形成軟質的組織，從而難以確保夠高的拉伸強度。因此，須設Mn含量為0.50%以上。為了更提高強度，Mn含量宜為0.80%以上，且1.00%以上更佳。 另一方面，Mn含量若大於5.00%，會使鋼板的延伸率及擴孔性不充分。且，Mn含量若大於5.00%，會使鋼板板厚中央部生成粗大的Mn濃化部，易引起脆化，而易發生鑄造出的鋼胚破裂等問題。因此，將Mn含量設在5.00%以下。且，若Mn含量增加亦會使點熔接性變差，故Mn含量宜為3.50%以下，且3.00%以下更佳。"Mn: 0.50 to 5.00%" Mn is contained because it can improve the hardenability of the steel sheet and increase the strength. When the Mn content is less than 0.50%, a large amount of soft structure is formed during cooling after annealing, and it is difficult to ensure a sufficiently high tensile strength. Therefore, the Mn content must be 0.50% or more. In order to further increase the strength, the Mn content is preferably 0.80% or more, and more preferably 1.00% or more. On the other hand, when the Mn content is more than 5.00%, the elongation and the hole expandability of the steel sheet are insufficient. Further, when the Mn content is more than 5.00%, a coarse Mn-concentrated portion is formed in the central portion of the steel sheet thickness, which is liable to cause embrittlement, and problems such as cracking of the cast steel blank are liable to occur. Therefore, the Mn content is set to 5.00% or less. Further, if the Mn content is increased, the spot weldability is deteriorated, so the Mn content is preferably 3.50% or less, and more preferably 3.00% or less.
「P：0.0001~0.1000%」 P係會使鋼材脆化之元素。P含量若大於0.1000%，鋼板的延伸率及擴孔性不充分。且，P含量若大於0.1000%，會易發生鑄造出的鋼胚破裂等問題。因此，將P含量設在0.1000%以下。且，P係會使由點熔接生成之熔融部脆化之元素。為獲得充分的熔接接頭強度，P含量宜設為0.0400%以下，且設為0.0200%以下更佳。 另一方面，設P含量低於0.0001%會伴隨製造成本的大幅增加。因此，設P含量為0.0001%以上。且P含量宜設為0.0010%以上。"P: 0.0001~0.1000%" P is an element that makes the steel brittle. When the P content is more than 0.1000%, the elongation and the hole expandability of the steel sheet are insufficient. Further, if the P content is more than 0.1000%, problems such as cracking of the cast steel blank may occur. Therefore, the P content is set to 0.1000% or less. Further, P is an element which causes embrittlement of the molten portion formed by spot welding. In order to obtain sufficient weld joint strength, the P content is preferably set to 0.0400% or less, and more preferably set to 0.0200% or less. On the other hand, setting the P content to less than 0.0001% is accompanied by a large increase in manufacturing cost. Therefore, the P content is made 0.0001% or more. Further, the P content is preferably set to 0.0010% or more.
「S：0.0001~0.0100%」 S係會與Mn連結形成粗大的MnS，使延展性、擴孔性(延伸率凸緣性)及彎曲性等成形性降低之元素。因此，設S含量在0.0100%以下。又，S會使點熔接性變差。故宜設S含量在0.0070%以下，且設為0.0050%以下更佳。 另一方面，將S含量設為小於0.0001%時，會伴隨製造成本的大幅增加。因此，設S含量在0.0001%以上。S含量宜設為0.0003%以上，且0.0006%以上更佳。"S: 0.0001 to 0.0100%" S is an element that forms a coarse MnS with Mn and reduces the formability such as ductility, hole expandability (elongation flangeability) and flexibility. Therefore, the S content is set to be 0.0100% or less. Also, S deteriorates the spot weldability. Therefore, it is preferable to set the S content to 0.0070% or less and to set it to 0.0050% or less. On the other hand, when the S content is less than 0.0001%, the manufacturing cost is greatly increased. Therefore, the S content is made 0.0001% or more. The S content is preferably set to 0.0003% or more, and more preferably 0.0006% or more.
「Al：0.001~2.500%」 Al係會使鋼材脆化的元素。Al含量若大於2.500%，會易發生鑄造出的鋼胚破裂等問題。因此，設Al含量在2.500%以下。且，Al含量若增加會使點熔接性變差。因此，宜設Al含量在2.000%以下，且設為1.500%以下更佳。 另一方面，不特別限定Al含量的下限雖亦可獲得效果，但Al係在原料中微量存在之不純物，而若設其含量小於0.001%則會伴隨製造成本的大幅增加。因此，設Al含量為0.001%以上。Al亦為可有效作為脫氧材之元素，故為充分獲得脫氧效果，宜設Al含量為0.010%以上。並且，Al係可抑制粗大的碳化物生成之元素，故亦可為了使殘留沃斯田鐵穩定化而含有。為使殘留沃斯田鐵穩定化，宜設Al含量為0.100%以上，且設為0.250%以上更佳。"Al: 0.001 to 2.500%" Al is an element that makes the steel brittle. If the Al content is more than 2.500%, problems such as cracking of the cast steel blank may occur. Therefore, the Al content is set to 2.500% or less. Further, if the Al content is increased, the spot weldability is deteriorated. Therefore, it is preferable to set the Al content to 2.000% or less and to set it to 1.500% or less. On the other hand, although the lower limit of the Al content is not particularly limited, an effect can be obtained. However, Al is an impurity which is present in a small amount in the raw material, and if the content is less than 0.001%, the production cost is greatly increased. Therefore, the Al content is made 0.001% or more. Al is also an element which can be effectively used as a deoxidizing material. Therefore, in order to sufficiently obtain the deoxidizing effect, it is preferable to set the Al content to be 0.010% or more. Further, since the Al system can suppress the element of coarse carbide formation, it can be contained in order to stabilize the residual Worth iron. In order to stabilize the residual Worthite iron, it is preferable to set the Al content to 0.100% or more and more preferably 0.250% or more.
「N：0.0001~0.0100%」 N會形成粗大的氮化物，使延展性、擴孔性(延伸率凸緣性)及彎曲性等成形性變差，故必須抑制其含量。N含量若大於0.0100%，會使成形性劣化明顯。因此，設N含量在0.0100%以下。且，N會造成熔接時產生氣孔，故其含量宜少。N含量在0.0075%以下為佳，在0.0060%以下較佳。 N含量的下限不特別限定雖亦可獲得效果，但若設N含量小於0.0001%會招致製造成本大幅增加。因此，設N含量為0.0001%以上。N含量宜為0.0003%以上，更宜為0.0005%以上。"N: 0.0001 to 0.0100%" N forms a coarse nitride and deteriorates formability such as ductility, hole expandability (elongation flangeability) and bendability. Therefore, it is necessary to suppress the content. When the N content is more than 0.0100%, the formability is deteriorated remarkably. Therefore, the N content is made 0.0100% or less. Moreover, N causes pores to be formed during welding, so the content thereof is preferably small. The N content is preferably 0.0075% or less, more preferably 0.0060% or less. Although the lower limit of the N content is not particularly limited, an effect can be obtained, but if the N content is less than 0.0001%, the manufacturing cost is greatly increased. Therefore, the N content is made 0.0001% or more. The N content is preferably 0.0003% or more, more preferably 0.0005% or more.
「O：0.0001~0.0100%」 O會形成氧化物，使延展性、擴孔性(延伸率凸緣性)及彎曲性等成形性變差，故必須抑制其含量。O含量若大於0.0100%，會使成形性劣化明顯，故宜設O含量的上限為0.0100%。O含量宜為0.0050%以下，且0.0030%以下更佳。 O含量的下限不特別限定雖亦可獲得效果，但若設O含量小於0.0001%會伴隨製造成本的大幅增加，故宜設下限為0.0001%。"O: 0.0001 to 0.0100%" O forms an oxide and deteriorates formability such as ductility, hole expandability (elongation flangeability) and flexibility, and therefore it is necessary to suppress the content. When the O content is more than 0.0100%, the formability is deteriorated remarkably. Therefore, the upper limit of the O content is preferably made 0.0100%. The O content is preferably 0.0050% or less, and more preferably 0.0030% or less. Although the lower limit of the O content is not particularly limited, an effect can be obtained. However, if the O content is less than 0.0001%, the manufacturing cost is greatly increased, so the lower limit is preferably made 0.0001%.
「Si+0.1×Mn+0.6×Al≧0.35」 殘留沃斯田鐵有於熱處理中分解成變韌鐵、波來鐵或粗大的雪明碳鐵之虞。而為抑制殘留沃斯田鐵分解、提升成形性，Si、Mn及Al即為特別重要之元素。為抑制殘留沃斯田鐵之分解，宜滿足下述式(1)。式(1)左邊的值宜為0.60以上，且0.80以上更佳。 Si+0.1×Mn+0.6×Al≧0.35 ・・・(1) (式(1)中之Si、Mn及Al表示各元素以質量%計之含量)。"Si+0.1×Mn+0.6×Al≧0.35” The residual Worthite iron is decomposed into a toughened iron, a ferritic iron or a coarse ferritic carbon iron during heat treatment. In order to suppress the decomposition of the residual Worthite iron and improve the formability, Si, Mn and Al are particularly important elements. In order to suppress the decomposition of the residual Worthite iron, the following formula (1) should be satisfied. The value on the left side of the formula (1) is preferably 0.60 or more, and more preferably 0.80 or more. Si + 0.1 × Mn + 0.6 × Al ≧ 0.35 (1) (Si, Mn, and Al in the formula (1) represent the content of each element in mass%).
本實施形態之鋼板基本係包含上述元素，但亦可因應需要含有選自於Ti、V、Nb、Cr、Ni、Cu、Co、Mo、W、B、Sn、Sb、Ca、Mg、Ce、Zr、La、Hf、Bi、REM之一種或二種以上之元素。該等元素為任意元素且非必須含有，故下限為0%。The steel sheet according to the embodiment basically contains the above elements, but may be selected from the group consisting of Ti, V, Nb, Cr, Ni, Cu, Co, Mo, W, B, Sn, Sb, Ca, Mg, Ce, and One or more of Zr, La, Hf, Bi, and REM. These elements are arbitrary elements and are not necessarily included, so the lower limit is 0%.
「Ti：0~0.300%」 Ti係可透過析出強化、抑制肥粒鐵晶粒的成長使細粒強化、及抑制再結晶所行之差排強化而有助於提高鋼板強度的元素。但Ti含量若大於0.300%，則碳氮化物的析出會變多而使成形性變差。因此於含有時，Ti含量宜為0.300%以下。又，從成形性的觀點來看，Ti含量在0.150%以下較佳。 Ti含量的下限不特別限定雖亦可獲得效果，但為充分獲得含有Ti而使強度提升之效果，Ti含量宜為0.001%以上。為使鋼板更高強度化，Ti含量以0.010%以上更佳。"Ti: 0 to 0.300%" Ti is an element that contributes to the strength of the steel sheet by strengthening the precipitation and suppressing the growth of the iron grains of the ferrite grains, strengthening the fine particles, and suppressing the difference in recrystallization. However, when the Ti content is more than 0.300%, precipitation of carbonitrides increases, and moldability is deteriorated. Therefore, when contained, the Ti content is preferably 0.300% or less. Further, from the viewpoint of moldability, the Ti content is preferably 0.150% or less. The lower limit of the Ti content is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of improving the strength by containing Ti, the Ti content is preferably 0.001% or more. In order to increase the strength of the steel sheet, the Ti content is preferably 0.010% or more.
「V：0~1.00%」 V係可透過析出強化、抑制肥粒鐵晶粒的成長使細粒強化、及抑制再結晶所行之差排強化而有助於提高鋼板強度的元素。但V含量若大於1.00%，則碳氮化物會過度析出而使成形性變差。因此於含有時，V含量宜為1.00%以下，且0.50%以下更佳。V含量的下限不特別限定雖亦可獲得效果，但為充分獲得含有V而使強度提升之效果，V含量宜為0.001%以上，且0.010%以上更佳。"V: 0 to 1.00%" V is an element that contributes to the strength of the steel sheet by strengthening the precipitation and suppressing the growth of the iron grains of the ferrite grains, strengthening the fine particles, and suppressing the difference in recrystallization. However, if the V content is more than 1.00%, the carbonitride will be excessively precipitated to deteriorate the formability. Therefore, when it is contained, the V content is preferably 1.00% or less, and more preferably 0.50% or less. The lower limit of the V content is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of increasing the strength by containing V, the V content is preferably 0.001% or more, and more preferably 0.010% or more.
「Nb：0~0.100%」 Nb係可透過析出強化、抑制肥粒鐵晶粒的成長使細粒強化、及抑制再結晶所行之差排強化而有助於提高熔融鍍鋅鋼板之強度的元素。但Nb含量若大於0.100%，則碳氮化物的析出會變多而使成形性變差。因此於含有時，Nb含量宜為0.100%以下。從成形性的觀點來看，Nb含量在0.060%以下較佳。Nb含量的下限不特別限定雖亦可獲得效果，但為充分獲得含有Nb而使強度提升之效果，Nb含量宜為0.001%以上。為使鋼板更高強度化，Nb含量以0.005%以上更佳。"Nb: 0 to 0.100%" Nb can enhance the strength of the hot-dip galvanized steel sheet by strengthening the precipitation and suppressing the growth of the ferrite-grained iron crystal grains, strengthening the fine particles, and suppressing the difference in recrystallization. element. However, when the Nb content is more than 0.100%, precipitation of carbonitrides increases, and moldability is deteriorated. Therefore, when it is contained, the Nb content is preferably 0.100% or less. From the viewpoint of moldability, the Nb content is preferably 0.060% or less. The lower limit of the Nb content is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of enhancing the strength by containing Nb, the Nb content is preferably 0.001% or more. In order to increase the strength of the steel sheet, the Nb content is preferably 0.005% or more.
「Cr：0~2.00%」 Cr係可提高鋼板之淬火性而有效高強度化之元素。但Cr含量若大於2.00%，會損及熱處理中之加工性而使生產性降低。基於此，於含有時Cr含量宜設為2.00%以下，且1.20%以下更佳。 Cr含量的下限不特別限定雖亦可獲得效果，但為充分獲得含有Cr所帶來之高強度化的效果，Cr含量宜為0.001%以上，且0.010%以上更佳。"Cr: 0 to 2.00%" Cr is an element that can improve the hardenability of the steel sheet and effectively increase the strength. However, if the Cr content is more than 2.00%, the workability in the heat treatment is impaired and the productivity is lowered. Based on this, the Cr content is preferably set to 2.00% or less and more preferably 1.20% or less. The lower limit of the Cr content is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of increasing the strength by Cr, the Cr content is preferably 0.001% or more, and more preferably 0.010% or more.
「Ni：0~2.00%」 Ni係可抑制在高溫下之相變態而對鋼板之高強度化有效之元素。但Ni含量若大於2.00%，會損及熔接性。基於此，於含有時Ni含量宜設為2.00%以下，且1.20%以下更佳。 Ni含量的下限不特別限定雖亦可獲得效果，但為充分獲得含有Ni所帶來之高強度化的效果，Ni含量宜為0.001%以上，且0.010%以上更佳。"Ni: 0 to 2.00%" Ni is an element which suppresses the phase transformation at a high temperature and is effective for increasing the strength of the steel sheet. However, if the Ni content is more than 2.00%, the weldability may be impaired. Based on this, the Ni content is preferably set to 2.00% or less and more preferably 1.20% or less. The lower limit of the Ni content is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of increasing the strength by Ni, the Ni content is preferably 0.001% or more, and more preferably 0.010% or more.
「Cu：0~2.00%」 Cu係可作為微細粒子存在於鋼中以提高鋼板強度之元素。但Cu含量若大於2.00%，會損及熔接性。因此於含有時，Cu含量宜設為2.00%以下，且1.20%以下更佳。Cu含量的下限不特別限定雖亦可獲得效果，但為充分獲得含有Cu所帶來之高強度化的效果，Cu含量宜為0.001%以上，且0.010%以上更佳。"Cu: 0 to 2.00%" Cu is an element in which fine particles are present in steel to increase the strength of the steel sheet. However, if the Cu content is more than 2.00%, the weldability may be impaired. Therefore, when it is contained, the Cu content is preferably set to 2.00% or less, and more preferably 1.20% or less. The lower limit of the Cu content is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of increasing the strength of Cu, the Cu content is preferably 0.001% or more, and more preferably 0.010% or more.
「Co：0~2.00%」 Co係可提高淬火性而對鋼板之高強度化有效之元素。但Co含量若大於2.00%，會損及熱處理中之加工性而使生產性降低。基於此，於含有時Co含量宜設為2.00%以下，且1.20%以下更佳。 Co含量的下限不特別限定雖亦可獲得效果，但為充分獲得含有Co所帶來之高強度化的效果，Co含量宜為0.001%以上，且0.010%以上更佳。"Co: 0 to 2.00%" Co is an element that improves the hardenability and is effective for increasing the strength of the steel sheet. However, if the Co content is more than 2.00%, the workability in the heat treatment is impaired and the productivity is lowered. Based on this, the Co content is preferably set to 2.00% or less and more preferably 1.20% or less. The lower limit of the Co content is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of increasing the strength of Co, the Co content is preferably 0.001% or more, and more preferably 0.010% or more.
「Mo：0~1.00%」 Mo係可抑制在高溫下之相變態而對鋼板之高強度化有效之元素。但Mo含量若大於1.00%，會損及熱處理中之加工性而使生產性降低。基於此，於含有時Mo含量宜設為1.00%以下，且0.50%以下更佳。 Mo含量的下限不特別限定雖亦可獲得效果，但為充分獲得含有Mo所帶來之高強度化的效果，Mo含量宜為0.001%以上，且0.005%以上更佳。"Mo: 0 to 1.00%" Mo is an element which suppresses the phase transformation at a high temperature and is effective for increasing the strength of the steel sheet. However, if the Mo content is more than 1.00%, the workability in the heat treatment is impaired and the productivity is lowered. Based on this, the Mo content is preferably 1.00% or less and more preferably 0.50% or less at the time of containing. The lower limit of the Mo content is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of increasing the strength by Mo, the Mo content is preferably 0.001% or more, and more preferably 0.005% or more.
「W：0~1.00%」 W係可抑制在高溫下之相變態而對鋼板之高強度化有效之元素。但W含量若大於1.00%，會損及熱處理中之加工性而使生產性降低。基於此，於含有時W含量1.00%以下，且0.50%以下更佳。 W含量的下限不特別限定雖亦可獲得效果，但為充分獲得W所帶來之高強度化的效果，W含量宜為0.001%以上，且0.010%以上更佳。"W: 0 to 1.00%" W is an element that suppresses the phase transformation at high temperatures and is effective for increasing the strength of the steel sheet. However, if the W content is more than 1.00%, the workability in the heat treatment is impaired and the productivity is lowered. Based on this, the content of W is 1.00% or less and more preferably 0.50% or less. The lower limit of the W content is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of increasing the strength by W, the W content is preferably 0.001% or more, and more preferably 0.010% or more.
「B：0~0.0100%」 B係可抑制在高溫下之相變態而對鋼板之高強度化有效之元素。但B含量若大於0.0100%，會損及熱處理中之加工性而使生產性降低。基於此，於含有時B含量宜設為0.0100%以下。從生產性的觀點來看，B含量在0.0050%以下較佳。 B含量的下限不特別限定雖亦可獲得效果，但為充分獲得含有B所帶來之高強度化的效果，宜設B含量為0.0001%以上。為更高強度化，B含量以0.0005%以上更佳。"B: 0 to 0.0100%" B is an element that suppresses the phase transformation at high temperatures and is effective for increasing the strength of the steel sheet. However, if the B content is more than 0.0100%, the workability in the heat treatment is impaired and the productivity is lowered. Based on this, the B content is preferably set to 0.0100% or less when it is contained. From the viewpoint of productivity, the B content is preferably 0.0050% or less. The lower limit of the B content is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of increasing the strength by B, it is preferable to set the B content to 0.0001% or more. For higher strength, the B content is more preferably 0.0005% or more.
「Sn：0~1.00%」 Sn係可抑制組織之粗大化而對鋼板之高強度化有效之元素。但Sn含量若大於1.00%，會使鋼板過度脆化而有鋼板於軋延時斷裂的情形。因此於含有時，Sn含量宜為1.00%以下。 Sn含量的下限不特別限定雖亦可獲得效果，但為充分獲得Sn所帶來之高強度化的效果，Sn含量宜為0.001%以上，且0.010%以上更佳。"Sn: 0 to 1.00%" Sn is an element that suppresses the coarsening of the structure and is effective for increasing the strength of the steel sheet. However, if the Sn content is more than 1.00%, the steel sheet may be excessively embrittled and the steel sheet may be broken at the time of rolling. Therefore, when it is contained, the Sn content is preferably 1.00% or less. The lower limit of the Sn content is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of increasing the strength of Sn, the Sn content is preferably 0.001% or more, and more preferably 0.010% or more.
「Sb：0~1.00%」 Sb係可抑制組織之粗大化而對鋼板之高強度化有效之元素。但Sb含量若大於1.00%，會使鋼板過度脆化而有鋼板於軋延時斷裂的情形。因此於含有時，Sb含量宜為1.00%以下。 Sb含量的下限不特別限定雖亦可獲得效果，但為充分獲得Sb所帶來之高強度化的效果，Sb含量宜為0.001%以上，且0.005%以上更佳。"Sb: 0 to 1.00%" Sb is an element that suppresses the coarsening of the structure and is effective for increasing the strength of the steel sheet. However, if the Sb content is more than 1.00%, the steel sheet may be excessively embrittled and the steel sheet may be broken at the time of rolling. Therefore, when it is contained, the Sb content is preferably 1.00% or less. The lower limit of the Sb content is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of increasing the strength of Sb, the Sb content is preferably 0.001% or more, and more preferably 0.005% or more.
「Ca、Mg、Ce、Zr、La、Hf、Bi、REM之一種或二種以上分別為0~0.0100%」 REM係Rare Earth Metal之簡稱，於本實施形態中係指除Ce、La外屬鑭系列之元素。於本實施形態中，REM、Ce、La大多係以稀土金屬型態作添加，且有時會複合含有鑭系元素。而即便將La及/或Ce以外之鑭系元素作為不純物來含有亦可獲得其效果。且，即便添加金屬La及/或Ce亦可獲得其效果。於本實施形態中，REM之含量係除Ce、La外屬鑭系元素之含量的合計值。"One or more of Ca, Mg, Ce, Zr, La, Hf, Bi, and REM are 0 to 0.0100%, respectively." REM is an abbreviation for Rare Earth Metal. In this embodiment, it refers to a group other than Ce and La. The elements of the 镧 series. In the present embodiment, REM, Ce, and La are often added in a rare earth metal form, and may contain a lanthanoid compound in combination. Even if a lanthanide element other than La and/or Ce is contained as an impurity, the effect can be obtained. Moreover, the effect can be obtained even if metal La and/or Ce are added. In the present embodiment, the content of REM is a total value of the content of the lanthanoid elements other than Ce and La.
使含有該等元素之理由如下。 Ca、Mg、Ce、Zr、La、Hf、Bi、REM係可有效改善成形性之元素，而可各以0.0001%~0.0100%含有一種或二種以上。Ca、Mg、Ce、Zr、La、Hf、Bi、REM之一種或二種以上之各含量若大於0.0100%，則有延展性降低之虞。因此於含有時，上述各元素含量宜為0.0100%以下，且0.0070%以下更佳。又，含有二種以上上述元素時，Ca、Mg、Ce、Zr、La、Hf、Bi、REM含量合計宜設為0.0100%以下。 上述各元素含量的下限不特別限定雖亦可獲得效果，但為充分獲得改善鋼板成形性之效果，各元素含量宜為0.0001%以上。由成形性之觀點，Ca、Mg、Ce、Zr、La、Hf、Bi、REM之一種或二種以上之含量合計以0.0010%以上更佳。The reasons for including these elements are as follows. Ca, Mg, Ce, Zr, La, Hf, Bi, and REM are elements which can effectively improve formability, and may be contained in one form or two or more types from 0.0001% to 0.0100%. When the content of one or more of Ca, Mg, Ce, Zr, La, Hf, Bi, and REM is more than 0.0100%, the ductility is lowered. Therefore, when it is contained, the content of each of the above elements is preferably 0.0100% or less, and more preferably 0.0070% or less. Further, when two or more of the above elements are contained, the total content of Ca, Mg, Ce, Zr, La, Hf, Bi, and REM is preferably set to 0.0100% or less. The lower limit of the content of each of the above elements is not particularly limited, and an effect can be obtained. However, in order to sufficiently obtain the effect of improving the formability of the steel sheet, the content of each element is preferably 0.0001% or more. From the viewpoint of moldability, the total content of one or two or more of Ca, Mg, Ce, Zr, La, Hf, Bi, and REM is preferably 0.0010% or more.
本實施形態之鋼板包含上述元素且剩餘部分為Fe及不純物。前述Ti、V、Nb、Cr、Ni、Cu、Co、Mo、W、B、Sn、Sb皆可允許以低於前述下限值之微量含有作為不純物。 且，Ca、Mg、Ce、Zr、La、Hf、Bi、REM皆可允許以低於前述下限值之極微量含有作為不純物。 且，可允許以合計0.0100%以下含有H、Na、Cl、Sc、Zn、Ga、Ge、As、Se、Y、Tc、Ru、Rh、Pd、Ag、Cd、In、Te、Cs、Ta、Re、Os、Ir、Pt、Au、Pb作為不純物。The steel sheet of the present embodiment contains the above elements and the remainder is Fe and impurities. The aforementioned Ti, V, Nb, Cr, Ni, Cu, Co, Mo, W, B, Sn, and Sb may be allowed to be contained in a trace amount lower than the above lower limit as an impurity. Further, Ca, Mg, Ce, Zr, La, Hf, Bi, and REM may be allowed to be contained in an extremely small amount lower than the aforementioned lower limit value as an impurity. Further, it is allowed to contain H, Na, Cl, Sc, Zn, Ga, Ge, As, Se, Y, Tc, Ru, Rh, Pd, Ag, Cd, In, Te, Cs, Ta in a total amount of 0.0100% or less. Re, Os, Ir, Pt, Au, Pb are used as impurities.
接下來，說明本實施形態之鋼板的鋼組織(微觀組織)。各組織含量說明中的[%]為[體積%]。 (鋼板內部的鋼組織) 如圖1所示，本實施形態之鋼板1中，自鋼板1之表面起以板厚1/4厚度之位置(從表面起於板厚方向上板厚1/4之位置)為中心之1/8厚度~3/8厚度之範圍11的鋼組織(以下稱為「鋼板內部的鋼組織」)，含有0~30%之軟質肥粒鐵、3%~40%之殘留沃斯田鐵、0~30%之新生麻田散鐵、波來鐵與雪明碳鐵織之合計為0~10%，且長寬比2.0以上之殘留沃斯田鐵佔總殘留沃斯田鐵之個數比率為50%以上。Next, the steel structure (microstructure) of the steel sheet of the present embodiment will be described. [%] in the description of the content of each tissue is [% by volume]. (Steel structure inside the steel sheet) As shown in Fig. 1, the steel sheet 1 of the present embodiment has a thickness of 1/4 of the thickness from the surface of the steel sheet 1 (the thickness is 1/4 of the thickness in the thickness direction from the surface) The position is 1% of the thickness of the steel structure of the range of 1/8 thickness to 3/8 thickness (hereinafter referred to as "steel structure inside the steel plate"), containing 0 to 30% of soft ferrite, 3% to 40% The remaining Worthfield iron, 0~30% of the new Ma Tian loose iron, the Bora iron and the Xueming carbon iron weave are 0~10%, and the residual Worthite iron with an aspect ratio of 2.0 or more accounts for the total residual Wo The ratio of the number of the stars is more than 50%.
「軟質肥粒鐵：0~30%」 肥粒鐵係具有優異延展性之組織。但因肥粒鐵之強度低，故對高強度鋼板來說為難以活用之組織。本實施形態之鋼板中，鋼板內部的鋼組織(鋼板內部的微觀組織)含有0%~30%之軟質肥粒鐵。 本實施形態之「軟質肥粒鐵」意指晶粒內不含殘留沃斯田鐵之肥粒鐵。軟質肥粒鐵之強度低，相較於周邊部應變易集中而易發生破壞。軟質肥粒鐵之體積分率若大於30%，會使強度與成形性之平衡顯著變差。因此，將軟質肥粒鐵限制在30%以下。將軟質肥粒鐵限制在15%以下更佳，0%亦無妨。"Soft Fertilizer Iron: 0~30%" Fermented iron is a tissue with excellent ductility. However, due to the low strength of the ferrite iron, it is a structure that is difficult to use for high-strength steel sheets. In the steel sheet according to the embodiment, the steel structure inside the steel sheet (the microstructure inside the steel sheet) contains 0% to 30% of soft ferrite. The "soft fat iron" in the present embodiment means that the ferrite iron containing no residual Worthite iron is contained in the crystal grains. The soft ferrite has a low strength and is prone to damage compared to the peripheral strain. If the volume fraction of the soft fat iron is more than 30%, the balance between strength and formability is significantly deteriorated. Therefore, the soft fat iron is limited to 30% or less. It is better to limit the soft ferrite iron to 15% or less, and 0%.
「殘留沃斯田鐵：3%~40%」 殘留沃斯田鐵係可提高強度-延展性平衡之組織。本實施形態之鋼板中，鋼板內部的鋼組織含有3%~40%之殘留沃斯田鐵。由成形性之觀點，鋼板內部中的殘留沃斯田鐵的體積分率設為3%以上，且宜設為5%以上，設為7%以上更佳。 另一方面，要設殘留沃斯田鐵之體積分率大於40%時，則需含有大量的C、Mn及/或Ni。而此時會使熔接性顯著變差。因此，設殘留沃斯田鐵的體積分率為40%以下。為提高鋼板的熔接性、提高便利性，宜設殘留沃斯田鐵的體積分率為30%以下，設為20%以下更佳。"Residual Vostian Iron: 3% to 40%" Residual Worth Iron can improve the strength-extension balance of the organization. In the steel sheet according to the embodiment, the steel structure inside the steel sheet contains 3% to 40% of the remaining Worthite iron. From the viewpoint of moldability, the volume fraction of the residual Worth iron in the inside of the steel sheet is set to 3% or more, and is preferably 5% or more, and more preferably 7% or more. On the other hand, if the volume fraction of the residual Worthite iron is greater than 40%, it is necessary to contain a large amount of C, Mn and/or Ni. At this time, the weldability is significantly deteriorated. Therefore, the volume fraction of the residual Worthite iron is 40% or less. In order to improve the weldability of the steel sheet and to improve the convenience, it is preferable to set the volume fraction of the residual Worthite iron to 30% or less, and more preferably 20% or less.
「新生麻田散鐵：0~30%」 新生麻田散鐵可大幅提升拉伸強度。另一方面，新生麻田散鐵會成為破壞的起點使耐衝撃特性顯著變差。因此，設新生麻田散鐵的體積分率為30%以下。尤其為了提升耐衝撃特性，宜設新生麻田散鐵的體積分率為15%以下，設為7%以下更佳。新生麻田散鐵亦可為0%，但為確保鋼板的強度，宜為2%以上。"New Ma Tian loose iron: 0~30%" New Ma Tian loose iron can greatly increase the tensile strength. On the other hand, the new Ma Tian loose iron will become the starting point of damage and the impact resistance characteristics will be significantly deteriorated. Therefore, the volume fraction of the new Ma Tian loose iron is 30% or less. In particular, in order to improve the impact resistance characteristics, it is preferable to set the volume fraction of the new Ma Tian loose iron to 15% or less, and to set it to 7% or less. The new Ma Tian loose iron can also be 0%, but to ensure the strength of the steel plate, it should be 2% or more.
「波來鐵與雪明碳鐵之合計：0~10%」 鋼板內部的鋼組織中亦可含有波來鐵及/或雪明碳鐵。但，波來鐵及/或雪明碳鐵的體積分率一多，延展性即會變差。因此，宜將波來鐵及/或雪明碳鐵的體積分率以合計計限制在10%以下。波來鐵及/或雪明碳鐵的體積分率較佳為合計為5%以下，0%亦無妨。"Total of Bora and Schönming Carbon: 0~10%" The steel inside the steel plate may also contain Borne and/or ferritic carbon. However, if the volume fraction of the Bora and/or the ferritic carbon iron is too large, the ductility will deteriorate. Therefore, it is preferable to limit the volume fraction of the Boron iron and/or the ferritic carbon iron to 10% or less in total. The volume fraction of the Bora iron and/or the ferritic carbon iron is preferably 5% or less in total, and 0% is also no problem.
「長寬比2.0以上的殘留沃斯田鐵的個數比率為總殘留沃斯田鐵的50%以上」 本實施形態中，鋼板內部的鋼組織中之殘留沃斯田鐵粒的長寬比很重要。長寬比大、即延伸過的殘留沃斯田鐵在鋼板經加工之變形初期係穩定的。但長寬比大的殘留沃斯田鐵伴隨加工的進展會使應變集中於前端部分，適度地變態而產生TRIP(變態誘發塑性)效果。因此，鋼板內部的鋼組織藉由含有長寬比大的殘留沃斯田鐵，可在不損及靭性、耐氫脆化特性、擴孔性等下改善延展性。由以上觀點，本實施形態之鋼板中，係設長寬比2.0以上的殘留沃斯田鐵佔總殘留沃斯田鐵之個數比率為50%以上。長寬比2.0以上的殘留沃斯田鐵的個數比率宜為70%以上，更宜為80%以上。"The ratio of the number of residual Worthite irons with an aspect ratio of 2.0 or more is 50% or more of the total residual Worthite iron." In this embodiment, the aspect ratio of the Worstian iron particles remaining in the steel structure inside the steel plate Very important. The residual Worthite iron, which has a large aspect ratio and is extended, is stable in the initial stage of deformation of the steel sheet. However, the progress of the processing of the residual Worthite iron with a large aspect ratio causes the strain to concentrate on the front end portion, and moderately deforms to produce a TRIP (allergy-induced plasticity) effect. Therefore, the steel structure inside the steel sheet contains the residual Worth iron having a large aspect ratio, and the ductility can be improved without impairing toughness, hydrogen embrittlement resistance, hole expandability, and the like. From the above viewpoints, in the steel sheet according to the present embodiment, the ratio of the number of residual Worthite irons having a total aspect ratio of Worthite iron of an aspect ratio of 2.0 or more is 50% or more. The ratio of the number of residual Worthite iron having an aspect ratio of 2.0 or more is preferably 70% or more, more preferably 80% or more.
「回火麻田散鐵」 回火麻田散鐵係可在不損耐衝撃特性下大幅提升鋼板的拉伸強度之組織，而含於鋼板內部的鋼組織中亦無妨。但，若使鋼板內部生成大量回火麻田散鐵，則有無法充分獲得殘留沃斯田鐵之情形。因此，宜將回火麻田散鐵的體積分率限制在50%以下，且限制在30%以下更佳。"Returning the Ma Tian loose iron" The tempering Ma Tian loose iron system can greatly increase the tensile strength of the steel sheet without damaging the impact resistance characteristics, and it is also possible to include the steel structure inside the steel sheet. However, if a large amount of tempered granulated iron is generated inside the steel sheet, the residual Worthite iron may not be sufficiently obtained. Therefore, it is preferable to limit the volume fraction of the tempered granulated iron to 50% or less, and it is more preferable to limit it to 30% or less.
本實施形態之鋼板中，鋼板內部的鋼組織中之剩餘部分組織主要為將殘留沃斯田鐵內包於晶粒內之「硬質肥粒鐵」。所謂主要為係指剩餘部分組織中硬質肥粒鐵具有最大體積分率。 硬質肥粒鐵係藉由對具有包含由變韌鐵、回火麻田散鐵、新生麻田散鐵之1種或2種以上所構成之板條狀組織的鋼組織之熱處理用鋼板進行後述第2熱處理而形成。硬質肥粒鐵因將殘留沃斯田鐵內包於晶粒內，故具有高強度。且，相較於肥粒鐵晶界存在有殘留沃斯田鐵之情況，硬質肥粒鐵其不易發生肥粒鐵與殘留沃斯田鐵之界面剝離，故具有良好的成形性。In the steel sheet according to the present embodiment, the remaining portion of the steel structure in the steel sheet is mainly a "hard fat iron" in which the remaining Worth iron is contained in the crystal grains. The so-called mainly means that the hard fat iron in the remaining part of the tissue has the largest volume fraction. The hard fat-grain iron is the second steel material for heat treatment which has a steel structure including a lath-like structure composed of one or two or more types of wrought iron, tempered granulated iron, and new granulated iron. Formed by heat treatment. The hard fat iron has high strength because it contains the remaining Worth iron in the grain. Moreover, compared with the case where there is a residual Worthite iron in the ferrite grain boundary, the hard fat iron is less likely to cause the interface peeling between the ferrite iron and the residual Worth iron, so that it has good formability.
又，鋼板內部的鋼組織中之剩餘部分組織中除上述硬質肥粒鐵外含有變韌鐵亦無妨。本實施形態之變韌鐵包含：由微細的BCC結晶與粗大的鐵系碳化物構成之粒狀變韌鐵、由板條狀BCC結晶與粗大的鐵系碳化物構成之上變韌鐵、由板狀BCC結晶與排列成與其內部平行之微細的鐵系碳化物構成之下變韌鐵、及不包含鐵系碳化物之變韌肥粒鐵。Further, the remaining portion of the steel structure in the steel sheet may contain toughened iron in addition to the hard fat iron. The toughened iron according to the present embodiment includes: a granular tough iron composed of fine BCC crystals and coarse iron-based carbides, and a toughened iron composed of lath-shaped BCC crystals and coarse iron-based carbides. The plate-shaped BCC crystals and the fine iron-based carbides arranged in parallel with the inside thereof constitute a toughened iron, and a toughened ferrite iron which does not contain iron-based carbide.
(表層的微觀組織) 接下來，說明鋼板表層的鋼組織(微觀組織)。(Microstructure of surface layer) Next, the steel structure (microstructure) of the surface layer of the steel sheet will be described.
「將具有硬度在1/8厚度~3/8厚度之範圍(鋼板內部)之硬度的80%以下之區域定義為軟質層時，表層存在厚度為1~100μm之軟質層」 為改善加工後的彎曲性，必要要件之一為使鋼板表層軟質化。本實施形態之鋼板中，當將硬度在鋼板內部之硬度(平均硬度)的80%以下之區域定義為軟質層時，從鋼板表面起於板厚方向上具有厚度為1~100μm之軟質層。換言之，鋼板表層部存在硬度在鋼板內部之平均硬度的80%以下之軟質層，且該軟質層的厚度為1~100μm。"When a region having a hardness of 80% or less of the hardness in the range of 1/8 thickness to 3/8 thickness (inside the steel sheet) is defined as a soft layer, the surface layer has a soft layer having a thickness of 1 to 100 μm". Flexibility, one of the necessary requirements is to soften the surface layer of the steel sheet. In the steel sheet of the present embodiment, when a region having a hardness of 80% or less of the hardness (average hardness) inside the steel sheet is defined as a soft layer, a soft layer having a thickness of 1 to 100 μm is formed from the surface of the steel sheet in the thickness direction. In other words, the surface layer portion of the steel sheet has a soft layer having a hardness of 80% or less of the average hardness inside the steel sheet, and the thickness of the soft layer is 1 to 100 μm.
軟質層之厚度若從表面起於深度方向(板厚方向)上小於1μm，會無法充分獲得加工後的彎曲性。軟質層之厚度(從表面起算的深度範圍)宜為5μm以上，10μm以上更佳。 另一方面，軟質層之厚度若大於100μm，會使鋼板強度大幅降低。因此，設軟質層之厚度為100μm以下。軟質層之厚度宜為70μm以下。When the thickness of the soft layer is less than 1 μm from the surface in the depth direction (thickness direction), the bending property after the processing cannot be sufficiently obtained. The thickness of the soft layer (the depth range from the surface) is preferably 5 μm or more, more preferably 10 μm or more. On the other hand, if the thickness of the soft layer is more than 100 μm, the strength of the steel sheet is greatly lowered. Therefore, the thickness of the soft layer is set to 100 μm or less. The thickness of the soft layer is preferably 70 μm or less.
「軟質層所含肥粒鐵中，長寬比小於3.0之晶粒的體積分率在50%以上」 軟質層所含肥粒鐵中長寬比小於3.0之晶粒(肥粒鐵之晶粒)的體積分率(相對於肥粒鐵之總晶粒佔軟質層之體積分率，長寬比小於3.0之肥粒鐵晶粒的比率)若小於50%，則加工後之彎曲性會變差。因此，設軟質層所含肥粒鐵中長寬比小於3.0之晶粒的體積分率為50%以上。理想為60%以上，較理想為70%以上。於此，所欲目標之肥粒鐵包含軟質肥粒鐵及硬質肥粒鐵。"In the soft layer of ferrite, the volume fraction of grains with an aspect ratio of less than 3.0 is more than 50%." The grain size of the ferrite in the soft layer is less than 3.0 (the grain of the ferrite grain) The volume fraction (relative to the ratio of the total grain size of the ferrite grain to the soft layer, and the ratio of the grain size of the ferrite grain to the aspect ratio of less than 3.0) is less than 50%, and the bending property after processing changes. difference. Therefore, it is assumed that the volume fraction of crystal grains having an aspect ratio of less than 3.0 in the ferrite-rich iron contained in the soft layer is 50% or more. The ideal is 60% or more, and more preferably 70% or more. Here, the fertilized iron of the desired target comprises soft ferrite iron and hard ferrite iron.
「軟質層中之殘留沃斯田鐵的體積分率小於鋼板內部中之殘留沃斯田鐵的體積分率的50%」 軟質層所含殘留沃斯田鐵經加工會變態成硬質的麻田散鐵，而有在加工後於彎曲加工時成為破裂發生之起點的情形。因此，軟質層所含殘留沃斯田鐵的體積分率宜越小越好。軟質層所含殘留沃斯田鐵的體積分率係設為小於鋼板內部中之殘留沃斯田鐵的體積分率的50%。較理想為小於30%。 鋼板內部中之殘留沃斯田鐵的體積分率係指從表面起以鋼板板厚1/4厚度之位置為中心之1/8厚度~3/8厚度之範圍所含殘留沃斯田鐵的體積分率。"The volume fraction of the residual Worth iron in the soft layer is less than 50% of the volume fraction of the residual Worth iron in the inner layer of the steel sheet." The residual Worthite iron contained in the soft layer will be transformed into a hard Ma Tiansan. Iron, and there is a case where the crack starts to occur at the time of bending. Therefore, the volume fraction of the remaining Worth iron contained in the soft layer should be as small as possible. The volume fraction of the residual Worth iron contained in the soft layer was set to be less than 50% of the volume fraction of the residual Worth iron in the inside of the steel sheet. More preferably less than 30%. The volume fraction of the residual Worthite iron in the inside of the steel plate refers to the residual Worthite iron contained in the range of 1/8 thickness to 3/8 thickness centering on the surface of the steel plate with a thickness of 1/4 of the thickness of the steel plate. Volume fraction.
「含Si氧化物之內部氧化層」 本實施形態之鋼板利用高頻輝光放電(高頻GDS)分析法自表面起於深度方向(板厚方向)上分析顯示Si之波長的發光強度時，從表面起於大於0.2μm且在5.0μm以下之範圍中會出現顯示Si之波長的發光強度的波峰。表從表面起於大於0.2μm且在5.0μm以下之範圍中出現顯示Si之波長的發光強度的波峰係表示鋼板內部氧化，而從鋼板表面起於大於0.2μm且在5.0μm以下之範圍中具有含Si氧化物之內部氧化層。於上述深度範圍中具有內部氧化層之鋼板因製造時之熱處理伴隨產生之鋼板表面的Si氧化物等氧化膜的生成受到抑制，故具有優異的化學轉化處理性及鍍敷密著性。"Internal Oxide Layer Containing Si Oxide" When the steel sheet of the present embodiment is analyzed by a high-frequency glow discharge (high-frequency GDS) method from the surface in the depth direction (thickness direction), the intensity of Si is displayed. When the surface is larger than 0.2 μm and in the range of 5.0 μm or less, a peak showing the luminescence intensity of the wavelength of Si appears. The peak of the luminescence intensity showing the wavelength of Si from the surface in the range of more than 0.2 μm and in the range of 5.0 μm or less represents the internal oxidation of the steel sheet, and has a range of more than 0.2 μm and less than 5.0 μm from the surface of the steel sheet. An internal oxide layer containing Si oxide. In the steel sheet having the internal oxide layer in the above-described depth range, the formation of an oxide film such as Si oxide on the surface of the steel sheet accompanying the heat treatment at the time of production is suppressed, so that it has excellent chemical conversion treatability and plating adhesion.
本實施形態之鋼板利用高頻輝光放電分析法自表面起於深度方向上分析時，亦可於從表面起於大於0.2μm且在5.0μm以下之範圍、與從表面起0μm~0.2μm之範圍(比深度0.2μm淺之區域)之兩範圍中，具有顯示Si之波長的發光強度的波峰。於兩範圍中具有波峰表示不僅鋼板具有內部氧化層，還於表面具有含Si氧化物之外部氧化層。When the steel sheet according to the present embodiment is analyzed in the depth direction from the surface by the high-frequency glow discharge analysis method, it may be in a range of more than 0.2 μm and 5.0 μm or less from the surface, and a range of 0 μm to 0.2 μm from the surface. In the two ranges (area which is shallower than the depth of 0.2 μm), there is a peak of the luminous intensity showing the wavelength of Si. The presence of peaks in both ranges means that not only the steel sheet has an internal oxide layer but also an external oxide layer containing Si oxide on the surface.
圖2係顯示本實施形態之鋼板利用高頻輝光放電分析法自表面起於深度方向上分析顯示Si之波長的發光強度時，自表面起算之深度與顯示Si之波長的發光強度(Intensity)之關係的圖表。圖2所示之本實施形態之鋼板中，從表面起於大於0.2μm且至5.0μm以下之範圍中有出現顯示Si之波長的發光強度的波峰(來自內部氧化層)。並且，從表面起0(最表面)~0.2μm之範圍中亦有出現顯示Si之波長的光強度的波峰(來自外部氧化層(I MAX))。因此可知，圖2所示之鋼板不僅具有內部氧化層還具有外部氧化層。 2 is a view showing the depth from the surface and the intensity of the display of the wavelength of Si when the steel sheet of the present embodiment is analyzed by the high-frequency glow discharge analysis method from the surface in the depth direction. Relationship chart. In the steel sheet according to the embodiment shown in Fig. 2, a peak (from the internal oxide layer) exhibiting an emission intensity of a wavelength of Si appears in a range of more than 0.2 μm to 5.0 μm or less from the surface. Further, a peak of light intensity (from the external oxide layer (I MAX )) showing a wavelength of Si appears in the range of 0 (the outermost surface) to 0.2 μm from the surface. Therefore, it is understood that the steel sheet shown in Fig. 2 has not only an internal oxide layer but also an external oxide layer.
圖3係顯示與本實施形態相異之鋼板利用高頻輝光放電分析法自表面起於深度方向上分析時，自表面起算之深度與顯示Si之波長的發光強度(Intensity)之關係的圖表。圖3所示鋼板中，顯示Si之波長的光強度的波峰係出現於自表面起0(最表面)~0.2μm之範圍中，但未出現於大於0.2μm且至5.0μm以下之深度範圍中。該情形表示鋼板不具有內部氧化層而僅具有外部氧化層。Fig. 3 is a graph showing the relationship between the depth from the surface and the intensity of the display of the wavelength of Si when the steel sheet different from the present embodiment is analyzed in the depth direction from the surface by the high-frequency glow discharge analysis method. In the steel sheet shown in Fig. 3, the peak of the light intensity showing the wavelength of Si appears in the range of 0 (the outermost surface) to 0.2 μm from the surface, but does not appear in the depth range of more than 0.2 μm and less than 5.0 μm. . This case indicates that the steel sheet does not have an internal oxide layer but only has an outer oxide layer.
「自表面起板厚1/8之厚度的硬度變化率」 且，本實施形態之鋼板自表面起至板厚1/8之厚度(1/8厚度)為止以10μm間距測定硬度後算出之每厚度10μm之硬度的變化量的最大值宜為100Hv以下(硬度的變化率在100Hv/10μm以下，換言之為100Hv/0.01mm以下)。藉此，可更提升加工後之彎曲性。其理由雖尚不明瞭，但吾等推測藉由消除硬度急遽變化之區域，可提高鋼板內部之鋼組織(母材組織)與表層之鋼組織的親和性，從而抑制表層之組織與母材組織之邊界部在彎曲加工時產生空隙之故。"The rate of change in hardness of the thickness of the surface from the surface of the plate is 1/8", and the hardness of the steel plate of the present embodiment is measured at a pitch of 10 μm from the surface to a thickness of 1/8 (1/8 thickness). The maximum value of the amount of change in hardness of 10 μm is preferably 100 Hv or less (the rate of change in hardness is 100 Hv/10 μm or less, in other words, 100 Hv/0.01 mm or less). Thereby, the bending property after processing can be further improved. Although the reason for this is not clear, we have estimated that by eliminating the region where the hardness changes rapidly, the affinity between the steel structure (base metal structure) inside the steel sheet and the steel structure of the surface layer can be improved, thereby suppressing the structure of the surface layer and the base metal structure. The boundary portion creates a void during the bending process.
「鍍鋅層」 本實施形態之鋼板表面(兩面或單面)亦可形成有鍍鋅層(熔融鍍鋅層或電鍍鋅層)。熔融鍍鋅層亦可為熔融鍍鋅層合金化而成之合金化熔融鍍鋅層。 當熔融鍍鋅層為未合金化者時，熔融鍍鋅層中之Fe含量宜小於7.0質量%。 而當熔融鍍鋅層為經合金化而成之合金化熔融鍍鋅層時，Fe含量宜為6.0質量%以上。合金化熔融鍍鋅鋼板具有比熔融鍍鋅鋼板更佳之熔接性。"Zinc-plated layer" A galvanized layer (a hot-dip galvanized layer or an electrogalvanized layer) may be formed on the surface (both sides or one side) of the steel sheet of the present embodiment. The molten galvanized layer may also be an alloyed hot-dip galvanized layer obtained by alloying a hot-dip galvanized layer. When the hot-dip galvanized layer is unalloyed, the Fe content in the hot-dip galvanized layer is preferably less than 7.0% by mass. When the hot-dip galvanized layer is an alloyed hot-dip galvanized layer which is alloyed, the Fe content is preferably 6.0% by mass or more. The alloyed hot-dip galvanized steel sheet has better weldability than the hot-dip galvanized steel sheet.
鍍鋅層的鍍敷附著量並無特別限制，而由耐蝕性之觀點宜為每單面5g/m 2以上，且為20~120g/m 2之範圍內，並且宜為25~75g/m 2之範圍內。 The plating amount of the galvanized layer is not particularly limited, but is preferably 5 g/m 2 or more per one side and 20 to 120 g/m 2 from the viewpoint of corrosion resistance, and is preferably 25 to 75 g/m. Within the scope of 2 .
本實施形態之鋼板亦可設有鍍鋅層並且為了改善塗裝性、熔接性等進一步於鍍鋅層上設置上層鍍敷層。且，亦可對經鍍鋅之鋼板施行各種處理，例如鉻酸鹽處理、磷酸鹽處理、潤滑性提升處理、熔接性提升處理等。The steel sheet according to the embodiment may be provided with a galvanized layer, and an upper plating layer may be further provided on the galvanized layer in order to improve coating properties and weldability. Further, various treatments may be performed on the galvanized steel sheet, such as chromate treatment, phosphate treatment, lubricity lifting treatment, weldability lifting treatment, and the like.
本實施形態之鋼板係對經包含第1熱處理之步驟所製得之以下之鋼板(第2熱處理前之素材：以下記載為“熱處理用鋼板”)進行後述第2熱處理而形成。In the steel sheet of the present embodiment, the steel sheet (the material before the second heat treatment: the steel sheet for heat treatment described below) which is obtained by the step including the first heat treatment is formed by a second heat treatment which will be described later.
「熱處理用鋼板」 本實施形態之熱處理用鋼板可用作本實施形態之鋼板的素材。 具體而言，作為本實施形態之鋼板的素材之熱處理用鋼板宜具有與上述本實施形態之鋼板相同之化學組成，且具有以下所示鋼組織(微觀組織)。各組織含量說明中之[%]只要無特別限制即表示[體積%]。"Steel sheet for heat treatment" The steel sheet for heat treatment of the present embodiment can be used as the material of the steel sheet of the present embodiment. Specifically, the steel sheet for heat treatment of the material of the steel sheet according to the present embodiment preferably has the same chemical composition as the steel sheet of the above-described embodiment, and has the steel structure (microstructure) shown below. [%] in the description of the content of each tissue means [% by volume] unless otherwise specified.
亦即宜為：自表面起以鋼板板厚1/4厚度之位置為中心之1/8厚度~3/8厚度之範圍的鋼組織(鋼板內部的鋼組織)以體積分率計含有合計70%以上之由變韌鐵、回火麻田散鐵、新生麻田散鐵之1種或2種以上所構成之板條狀組織，且含有殘留沃斯田鐵，長寬比小於1.3且長徑大於2.5μm之殘留沃斯田鐵粒的個數密度為1.0×10 -2個/μm 2以下，自表面起於深度方向上形成有由以體積分率計包含80%以上之肥粒鐵的軟質層所構成之表層，軟質層的厚度為1μm~50μm，利用高頻輝光放電分析法自表面起於深度方向上分析時，於大於0.2μm且在5.0μm以下之深度之間出現顯示Si之波長的發光強度的波峰。變韌鐵包含：由微細的BCC結晶與粗大的鐵系碳化物構成之粒狀變韌鐵、由板條狀BCC結晶與粗大的鐵系碳化物構成之上變韌鐵、由板狀BCC結晶與排列成與其內部平行之微細的鐵系碳化物構成之下變韌鐵、及不包含鐵系碳化物之變韌肥粒鐵。 In other words, it is preferable that the steel structure (steel structure inside the steel sheet) having a thickness of 1/8 thickness to 3/8 of the center of the steel plate thickness of 1/4 of the thickness of the steel sheet is contained in a volume fraction of 70 in total. More than % of the slat-like structure consisting of one or more of toughened iron, tempered granian iron, and new granulated iron, and containing residual Worth iron, aspect ratio less than 1.3 and longer diameter greater than The number density of the remaining Worstian iron particles of 2.5 μm is 1.0×10 −2 /μm 2 or less, and a soft material containing 80% or more of the ferrite iron by volume fraction is formed in the depth direction from the surface. The surface layer composed of the layers, the thickness of the soft layer is 1 μm to 50 μm, and the wavelength of Si is displayed between the depths greater than 0.2 μm and below 5.0 μm when analyzed by the high-frequency glow discharge analysis from the surface in the depth direction. The peak of the luminous intensity. The toughened iron comprises: granular tough iron composed of fine BCC crystals and coarse iron-based carbides, slab-like BCC crystals and coarse iron-based carbides composed of toughened iron, crystallized by platy BCC A toughened iron composed of fine iron-based carbides arranged in parallel with the inside thereof, and a toughened ferrite iron not containing iron-based carbides.
以下詳細說明作為本實施形態鋼板的素材之熱處理用鋼板的較佳鋼組織(微觀組織)。The preferred steel structure (microstructure) of the steel sheet for heat treatment which is the material of the steel sheet of the present embodiment will be described in detail below.
(熱處理用鋼板之內部的鋼組織) 「以體積分率計含有合計70%以上之板條狀組織」 本實施形態之熱處理用鋼板從表面起以鋼板板厚1/4厚度之位置為中心之1/8厚度~3/8厚度之範圍的鋼組織(鋼板內部的鋼組織)，宜以體積分率計含有合計70%以上之由變韌鐵、回火麻田散鐵、新生麻田散鐵之1種或2種以上構成之板條狀組織。(Steel structure in the inside of the steel sheet for heat treatment) "The strip-shaped structure containing 70% or more in total by volume fraction" The steel sheet for heat treatment of the present embodiment is centered on the surface of the steel sheet with a thickness of 1/4 of the thickness of the steel sheet. Steel structure in the range of 1/8 thickness to 3/8 thickness (steel structure inside the steel plate), it is preferable to contain 70% or more of the toughening iron, the tempering Ma Tian loose iron, and the new Ma Tian loose iron by volume fraction. One or two or more kinds of lath-like structures.
藉由以體積分率計含有合計70%以上之上述板條狀組織，對熱處理用鋼板施行後述第2熱處理而製得之鋼板其鋼板內部的鋼組織會以硬質肥粒鐵為主體。當上述板條狀組織之合計體積分率小於70%時，對熱處理用鋼板施行第2熱處理而製得之鋼板其鋼板內部的鋼組織會變成含大量軟質肥粒鐵者，而無法製得本實施形態之鋼板。熱處理用鋼板之鋼板內部的鋼組織宜以體積分率計含有合計80%以上之上述板條狀組織，且含有合計90%以上更佳，100%亦無妨。The steel sheet obtained by performing the second heat treatment described later on the steel sheet for heat treatment by the above-described lath-like structure containing a total of 70% or more by volume fraction is mainly composed of hard fat iron. When the total volume fraction of the lath-like structure is less than 70%, the steel sheet obtained by performing the second heat treatment on the steel sheet for heat treatment may become a steel containing a large amount of soft fat iron, and the steel sheet cannot be obtained. Steel plate of the embodiment. The steel structure inside the steel sheet for the steel sheet for heat treatment preferably contains 80% or more of the above-mentioned lath-like structure in a volume fraction, and is preferably 90% or more in total, and 100%.
「長寬比小於1.3且長徑大於2.5μm之殘留沃斯田鐵粒的個數密度」 熱處理用鋼板之鋼板內部的鋼組織除上述板條狀組織外亦可含有殘留沃斯田鐵。惟，含有殘留沃斯田鐵時，宜將長寬比小於1.3且長徑大於2.5μm的殘留沃斯田鐵粒的個數密度限制為1.0×10 -2個/μm 2以下。 "Number density of residual Worthfield iron particles having an aspect ratio of less than 1.3 and a long diameter of more than 2.5 μm" The steel structure inside the steel sheet of the steel sheet for heat treatment may contain residual Worthite iron in addition to the above-mentioned lath-like structure. However, when the residual Worthite iron is contained, the number density of the residual Worstian iron particles having an aspect ratio of less than 1.3 and a long diameter of more than 2.5 μm is preferably limited to 1.0 × 10 -2 / μm 2 or less.
存在於鋼板內部的鋼組織之殘留沃斯田鐵若為粗大塊狀，對熱處理用鋼板施行第2熱處理而製得之鋼板的內部會存在粗大塊狀的殘留沃斯田鐵粒，而有難以充分確保長寬比在2.0以上的殘留沃斯田鐵的個數比率之情形。因此，設長寬比小於1.3且長徑大於2.5μm之粗大塊狀的殘留沃斯田鐵粒的個數密度為1.0×10-2個/μm2以下。粗大塊狀之的殘留沃斯田鐵粒的個數密度宜越低越好，0.5×10 -2個/μm 2以下為佳。 If the Worstian iron in the steel structure existing inside the steel sheet is in the form of a large block, the steel sheet obtained by performing the second heat treatment on the steel sheet for heat treatment may have coarse residual Vorstian iron grains in the inside of the steel sheet, and it is difficult to sufficiently secure the steel sheet. The case where the aspect ratio of the residual Worthite iron having an aspect ratio of 2.0 or more. Therefore, the number density of the coarse-grained residual Worthfield iron particles having an aspect ratio of less than 1.3 and a long diameter of more than 2.5 μm is 1.0 × 10 -2 / μm 2 or less. The number density of the coarse-grained residual Worthfield iron particles is preferably as low as possible, preferably 0.5 × 10 -2 / μm 2 or less.
且，若熱處理用鋼板的鋼板內部過度存在殘留沃斯田鐵，對熱處理用鋼板施行後述第2熱處理會使一部分的殘留沃斯田鐵各向同性化。結果，會有無法於第2熱處理後製得之鋼板的內部充分確保長寬比在2.0以上的殘留沃斯田鐵之情形。因此，熱處理用鋼板之鋼板內部的鋼組織所含殘留沃斯田鐵的體積分率宜為10%以下。In addition, when the steel sheet for heat treatment is excessively left with the Worthite iron, the second heat treatment described later is applied to the steel sheet for heat treatment to partially homogenize the remaining Worthite iron. As a result, there is a case where the inside of the steel sheet which cannot be obtained after the second heat treatment sufficiently ensures the Worstian iron having an aspect ratio of 2.0 or more. Therefore, the volume fraction of the remaining Worthite iron contained in the steel structure inside the steel sheet for the steel sheet for heat treatment is preferably 10% or less.
(熱處理用鋼板表層的微觀組織) 「以體積分率計包含80%以上之肥粒鐵的軟質層」 作為本實施形態鋼板的素材之熱處理用鋼板宜自表面起於深度方向(板厚方向)上形成有由以體積分率計包含80%以上之肥粒鐵的軟質層所構成之表層。軟質層之厚度宜為1μm~50μm。軟質層之厚度自表面起於深度方向上若小於1μm，則形成於對熱處理用鋼板施行第2熱處理而製得之鋼板的軟質層之厚度會不夠。 另一方面，軟質層之厚度自表面起於深度方向上大於50μm的話，形成於對熱處理用鋼板施行第2熱處理而製得之鋼板的軟質層之厚度(自表面起算之深度範圍)會過多，而使鋼板強度降低。因此，軟質層之厚度宜為50μm以下，且10μm以下更佳。(The microstructure of the surface layer of the steel sheet for heat treatment) "The soft layer containing 80% or more of the ferrite iron in the volume fraction" The steel sheet for heat treatment of the material of the steel sheet of the present embodiment is preferably in the depth direction (thickness direction) from the surface. A surface layer composed of a soft layer containing 80% or more of ferrite iron in a volume fraction is formed thereon. The thickness of the soft layer is preferably from 1 μm to 50 μm. When the thickness of the soft layer is less than 1 μm in the depth direction from the surface, the thickness of the soft layer formed on the steel sheet obtained by performing the second heat treatment on the steel sheet for heat treatment may be insufficient. On the other hand, when the thickness of the soft layer is more than 50 μm in the depth direction from the surface, the thickness of the soft layer (the depth range from the surface) of the steel sheet formed by performing the second heat treatment on the steel sheet for heat treatment is excessive. The strength of the steel sheet is lowered. Therefore, the thickness of the soft layer is preferably 50 μm or less, and more preferably 10 μm or less.
「含Si氧化物之內部氧化層」 本實施形態之熱處理用鋼板利用高頻輝光放電(高頻GDS)分析法自表面於深度方向上分析時，從表面起於大於0.2μm且在5.0μm以下之範圍中宜出現顯示Si之波長的發光強度的波峰。於該位置出現波峰表示熱處理用鋼板內部氧化，而從表面起於大於0.2μm且在5.0μm以下之範圍中具有含Si氧化物之內部氧化層。自表面起於上述深度具有內部氧化層之熱處理用鋼板已抑制了於製造時之熱處理所伴隨之鋼板表面中生成Si氧化物等氧化膜。"Internal Oxide Layer Containing Si Oxide" The steel sheet for heat treatment of the present embodiment is characterized by a high-frequency glow discharge (high-frequency GDS) analysis method when the surface is analyzed in the depth direction, and is larger than 0.2 μm and 5.0 μm or less from the surface. A peak showing the luminescence intensity of the wavelength of Si should appear in the range. The occurrence of a peak at this position indicates internal oxidation of the steel sheet for heat treatment, and an internal oxide layer containing Si oxide in a range of more than 0.2 μm from the surface and 5.0 μm or less. The steel sheet for heat treatment having the internal oxide layer at the above-described depth from the surface has suppressed the formation of an oxide film such as Si oxide in the surface of the steel sheet accompanying the heat treatment at the time of production.
熱處理用鋼板利用高頻輝光放電分析法自表面起於深度方向上分析時，亦可於從表面起於大於0.2μm且在5.0μm以下之範圍、與0μm~0.2μm之範圍(比深度0.2μm淺之區域)之兩範圍中，具有顯示Si之波長的發光強度的波峰。於兩範圍中具有顯示Si之波長的發光強度的波峰係表示熱處理用鋼板具有內部氧化層，且於表面具有含Si氧化物之外部氧化層。When the steel sheet for heat treatment is analyzed from the surface in the depth direction by high-frequency glow discharge analysis, it may be in a range of more than 0.2 μm and 5.0 μm or less from the surface, and a range of 0 μm to 0.2 μm (0.2 μm in specific depth). In the two ranges of the shallow region, there is a peak of the luminous intensity showing the wavelength of Si. The peak having an emission intensity indicating the wavelength of Si in both ranges indicates that the steel sheet for heat treatment has an internal oxide layer and has an external oxide layer containing Si oxide on the surface.
「本實施形態之鋼板之製造方法」 接下來說明本實施形態之鋼板之製造方法。"Method for Producing Steel Sheet According to Present Embodiment" Next, a method for producing a steel sheet according to the present embodiment will be described.
本實施形態之鋼板之製造方法，係對具有上述化學組成之鋼胚經熱軋延且酸洗而得之熱軋鋼板、或對熱軋鋼板經冷軋延而得之冷軋鋼板，施行以下所示第1熱處理來製造熱處理用鋼板。之後，對熱處理用鋼板施行以下所示第2熱處理。第1熱處理及/或第2熱處理可使用專用之熱處理產線來實施，而使用以往之退火產線亦無妨。In the method for producing a steel sheet according to the present embodiment, the hot-rolled steel sheet obtained by hot rolling and pickling the steel sheet having the chemical composition or the cold-rolled steel sheet obtained by cold rolling the hot-rolled steel sheet is subjected to the following The first heat treatment is shown to produce a steel sheet for heat treatment. Thereafter, the second heat treatment shown below was applied to the steel sheet for heat treatment. The first heat treatment and/or the second heat treatment can be carried out using a dedicated heat treatment line, and it is also possible to use a conventional annealing line.
(鑄造步驟) 製造本實施形態之鋼板時，首先係鑄造具有上述化學成分(組成)之鋼胚。供於熱軋延之鋼胚可使用連續鑄造鋼胚或利用薄鋼胚連鑄機等所製出者。鑄造後之鋼胚可先暫時冷卻至常溫後再進行熱軋延，亦可在高溫狀態下直接進行熱軋延。將鑄造後之鋼胚在高溫狀態下直接供於熱軋延因可削減熱軋延加熱所需之能量故而為佳。(Casting Step) When the steel sheet of the present embodiment is produced, first, a steel slab having the above chemical composition (composition) is cast. The steel blank for hot rolling can be produced by continuously casting steel or by using a thin steel continuous casting machine or the like. The steel slab after casting can be temporarily cooled to normal temperature and then hot rolled, or directly rolled at a high temperature. It is preferable to directly supply the steel preform after casting to the hot rolling extension at a high temperature to reduce the energy required for heating the hot rolling.
(鋼胚加熱) 熱軋延前先將鋼胚加熱。製造本實施形態之鋼板時，宜選定滿足以下所示式(4)之鋼胚加熱條件。(steel embryo heating) The steel embryo is heated before the hot rolling. When manufacturing the steel sheet of the present embodiment, it is preferable to select a steel slab heating condition that satisfies the following formula (4).
[數學式1] (式(4)中，fγ係下述式(5)所示之值，WMnγ係下述式(6)所示之值，D係下述式(7)所示之值，A c1係下述式(8)所示之值，A c3係下述式(9)所示之值，ts(T)係鋼胚加熱溫度T之鋼胚滯留時間(sec))。 [Math 1] (In the formula (4), fγ is a value represented by the following formula (5), WMnγ is a value represented by the following formula (6), and D is a value represented by the following formula (7), and is under the A c1 system. The value shown in the formula (8), A c3 is a value represented by the following formula (9), and ts (T) is a steel embryo retention time (sec) of the steel embryo heating temperature T.
[數學式2] (式(5)中，T係鋼胚加熱溫度(℃)，WC係鋼中之C含量(質量%)，A c1係下述式(8)所示之值，A c3係下述式(9)所示之值)。 [Math 2] (In the formula (5), the T-type steel embryo heating temperature (°C), the C content (% by mass) in the WC-based steel, A c1 is a value represented by the following formula (8), and A c3 is a following formula ( 9) The value shown).
[數學式3] (式(6)中，T係鋼胚加熱溫度(℃)，WMn係鋼中之Mn含量(質量%)，A c1係下述式(8)所示之值，A c3係下述式(9)所示之值)。 [Math 3] (In the formula (6), the T-type steel slab heating temperature (°C), the Mn content (% by mass) in the WMn-based steel, A c1 is a value represented by the following formula (8), and A c3 is a following formula ( 9) The value shown).
[數學式4] (式(7)中，T係鋼胚加熱溫度(℃)，R係氣體常數；8.314J/mol)。 [Math 4] (In the formula (7), the T-type steel embryo heating temperature (°C), the R-system gas constant; 8.314 J/mol).
A c1=723-10.7×Mn-16.9×Ni+29.1×Si+16.9×Cr・・(8) (式(8)式中之元素符號為該元素在鋼中之質量%)。 A c3=879-346×C+65×Si-18×Mn+54×Al・・(9) (式(9)式中之元素符號為該元素在鋼中之質量%)。 A c1 = 723-10.7 × Mn - 16.9 × Ni + 29.1 × Si + 16.9 × Cr (8) (The symbol of the element in the formula (8) is the mass % of the element in the steel). A c3 = 879 - 346 × C + 65 × Si - 18 × Mn + 54 × Al (9) (The element symbol in the formula (9) is the mass % of the element in the steel).
式(4)之分子係表示於α(肥粒鐵)與γ(沃斯田鐵)之二相區域滯留中α分配到γ之Mn含量的程度。式(4)之分子越大，鋼中之Mn濃度分布越不均質化。 式(4)之分母係對應於γ單相區域滯留中在γ中擴散之Mn原子的距離之項次。式(4)之分母越大，Mn濃度分布越均質化。為使鋼中之Mn濃度分布充分均質化，宜選定鋼胚加熱條件使式(4)之值為1.0以下。式(4)之值越小，越可降低熱處理用鋼板及對熱處理用鋼板進行第2熱處理後製得之鋼板的鋼板內部中之粗大塊狀的沃斯田鐵粒的個數密度。The molecular formula of the formula (4) indicates the degree to which α is assigned to the Mn content of γ in the two-phase region retention of α (fertilizer iron) and γ (Worstian iron). The larger the molecule of formula (4), the more heterogeneous the Mn concentration distribution in the steel. The denominator of the formula (4) corresponds to the distance of the Mn atom diffused in γ in the γ single-phase region retention. The larger the denominator of the formula (4), the more homogenous the Mn concentration distribution. In order to sufficiently homogenize the Mn concentration distribution in the steel, it is preferable to select the steel embryo heating condition so that the value of the formula (4) is 1.0 or less. The smaller the value of the formula (4), the lower the number density of the coarse bulk Worthite iron particles in the steel sheet of the steel sheet obtained by the second heat treatment of the steel sheet for heat treatment and the steel sheet for heat treatment.
(熱軋延) 加熱鋼胚後進行熱軋延。熱軋延之完成溫度(完工溫度)若低於850℃，則軋延反作用力會提高，而難以穩定製得指定之板厚。因此，宜設熱軋延之完成溫度為850℃以上。由軋延反作用力之觀點，熱軋延之完成溫度宜設為870℃以上。另一方面，若設熱軋延之完成溫度高於1050℃，則於從鋼胚加熱結束至熱軋延完成為止之步驟中，必須使用加熱裝置等加熱鋼板，造成需高成本。因此，宜設熱軋延之完成溫度在1050℃以下。為易確保熱軋延中之鋼板溫度，宜設熱軋延之完成溫度在1000℃以下，且設980℃以下更佳。(Hot rolling) After heating the steel embryo, hot rolling is performed. If the completion temperature (completion temperature) of the hot rolling is lower than 850 ° C, the rolling reaction force is increased, and it is difficult to stably obtain the specified plate thickness. Therefore, it is preferable to set the completion temperature of the hot rolling to be 850 ° C or higher. From the viewpoint of the rolling reaction force, the completion temperature of the hot rolling is preferably set to 870 ° C or higher. On the other hand, if the completion temperature of the hot rolling is higher than 1050 ° C, it is necessary to heat the steel sheet by using a heating device or the like in the step from the end of the heating of the steel slab to the completion of the hot rolling, resulting in high cost. Therefore, it is preferable to set the completion temperature of the hot rolling to be below 1050 °C. In order to easily ensure the temperature of the steel sheet in the hot rolling, it is preferable to set the completion temperature of the hot rolling to be below 1000 ° C, and it is more preferable to set it below 980 ° C.
(酸洗步驟) 接著，將依上述製出之熱軋鋼板進行酸洗。酸洗係去除熱軋鋼板表面之氧化物的步驟，對用以提升鋼板之化學轉化處理性、鍍敷密著性很重要。熱軋鋼板之酸洗可為一次，亦可分數次進行。(Pickling Step) Next, the hot-rolled steel sheet produced as described above was pickled. The step of pickling to remove the oxide on the surface of the hot-rolled steel sheet is important for improving the chemical conversion treatability and plating adhesion of the steel sheet. The pickling of the hot rolled steel sheet may be carried out once or in fractions.
(冷軋延) 將酸洗後之熱軋鋼板進行冷軋延而製成冷軋鋼板亦無妨。藉由對熱軋鋼板進行冷軋延可高精度製造具有預定板厚之鋼板。冷軋延中，軋縮率合計(冷軋延中之累積軋縮率)若大於85%，會使鋼板喪失延展性，從而提高鋼板在冷軋延中斷裂之危險性。因此，宜設軋縮率合計在85%以下，且設為75%以下更佳。冷軋延步驟中之合計軋縮率的下限並無特別限定，不施行冷軋延亦無妨。為提升鋼板之形狀均質性以獲得良好之外觀、且使第1熱處理中及第2熱處理中之鋼板溫度均一以獲得良好之延展性，冷軋延之軋縮率以合計計宜設為0.5%以上，且設為1.0%以上更佳。(Cold Rolling) It is also possible to cold-roll a hot-rolled steel sheet after pickling to obtain a cold-rolled steel sheet. The steel sheet having a predetermined thickness can be produced with high precision by cold rolling the hot rolled steel sheet. In the cold rolling process, if the total rolling reduction ratio (accumulated rolling reduction ratio in the cold rolling) is more than 85%, the steel sheet loses ductility, thereby increasing the risk of the steel sheet breaking in the cold rolling. Therefore, it is preferable to set the total reduction ratio to 85% or less, and it is more preferable to set it as 75% or less. The lower limit of the total rolling reduction ratio in the cold rolling step is not particularly limited, and it is not necessary to carry out cold rolling. In order to improve the shape homogeneity of the steel sheet to obtain a good appearance, and to uniformize the temperature of the steel sheet in the first heat treatment and the second heat treatment to obtain good ductility, the rolling reduction ratio of the cold rolling is set to 0.5% in total. The above is more preferably 1.0% or more.
(第1熱處理) 接著，對酸洗後之熱軋鋼板、或對熱軋鋼板經冷軋延所得之冷軋鋼板進行第1熱處理來製造熱處理用鋼板。第1熱處理係以滿足下述(a)~(e)之條件來進行。 (a)於650℃達至最高加熱溫度為止之期間，設成含有0.1體積%以上之H 2且滿足下述式(3)之氣體環境。 -1.1≦log(PH 2O/PH 2)≦-0.07・・・(3) (式(3)中，log表示常用對數，PH 2O表示水蒸氣分壓，PH 2表示氫分壓)。 (First heat treatment) Next, a hot-rolled steel sheet after pickling or a cold-rolled steel sheet obtained by cold rolling a hot-rolled steel sheet is subjected to a first heat treatment to produce a steel sheet for heat treatment. The first heat treatment is carried out under the conditions (a) to (e) below. (a) A gas atmosphere containing 0.1% by volume or more of H 2 and satisfying the following formula (3) at a temperature of 650 ° C up to the maximum heating temperature. -1.1≦log(PH 2 O/PH 2 )≦-0.07・・・(3) (In the formula (3), log indicates a common logarithm, PH 2 O indicates a partial pressure of water vapor, and PH 2 indicates a partial pressure of hydrogen).
第1熱處理中，藉由滿足上述(a)，可抑制在鋼板外部之氧化反應且同時可促進鋼板表層部之脫碳反應。In the first heat treatment, by satisfying the above (a), the oxidation reaction outside the steel sheet can be suppressed and the decarburization reaction in the surface layer portion of the steel sheet can be promoted.
氣體環境中之H 2若小於0.1體積%，則無法充分使存在於鋼板表面之氧化膜還原，而於鋼板上形成氧化膜。因此，會使第2熱處理後製得之鋼板的化學轉化處理性及鍍敷密著性降低。 另一方面，氣體環境中之H 2含量若大於20體積%，則效果會飽和。且，氣體環境中之H 2含量若大於20體積%，會增加操作上氫爆之危險性。因此，宜設氣體環境中之H 2含量在20體積%以下。 When the H 2 in the gas atmosphere is less than 0.1% by volume, the oxide film existing on the surface of the steel sheet cannot be sufficiently reduced, and an oxide film is formed on the steel sheet. Therefore, the chemical conversion treatability and the plating adhesion of the steel sheet obtained after the second heat treatment are lowered. On the other hand, if the H 2 content in the gas atmosphere is more than 20% by volume, the effect is saturated. Moreover, if the H 2 content in the gaseous environment is more than 20% by volume, the risk of hydrogen explosion in operation is increased. Therefore, it is preferable to set the H 2 content in a gaseous environment to be 20% by volume or less.
且，log(PH 2O/PH 2)小於-1.1時，會發生鋼板表層之Si、Mn的外部氧化，使脫碳反應不充分，致使形成於熱處理用鋼板之表層部的軟質層之厚度變薄。結果，第2熱處理後之鋼板的軟質層厚度仍不足。 另一方面，log(PH 2O/PH 2)若大於-0.07，則脫碳反應會過度進行從而使第2熱處理後製得之鋼板強度不充分。結果，第2熱處理後之鋼板的強度仍不足。 Further, when log (PH 2 O/PH 2 ) is less than -1.1, external oxidation of Si and Mn in the surface layer of the steel sheet occurs, and the decarburization reaction is insufficient, so that the thickness of the soft layer formed in the surface layer portion of the steel sheet for heat treatment becomes thin. As a result, the thickness of the soft layer of the steel sheet after the second heat treatment was still insufficient. On the other hand, if the log (PH 2 O/PH 2 ) is more than -0.07, the decarburization reaction proceeds excessively, so that the strength of the steel sheet obtained after the second heat treatment is insufficient. As a result, the strength of the steel sheet after the second heat treatment was still insufficient.
(b)於A c3-30℃~1000℃之最高加熱溫度下保持1秒~1000秒。 第1熱處理中，係設最高加熱溫度為A c3-30℃以上。最高加熱溫度低於A c3-30℃時，熱處理用鋼板之鋼板內部的鋼組織中會殘存塊狀粗大的肥粒鐵。結果，熱處理用鋼板之第2熱處理後所得之鋼板的軟質肥粒鐵的體積分率會過多，且長寬比2.0以上之殘留沃斯田鐵的個數比率會不夠，致使特性變差。最高加熱溫度宜為A c3-15℃以上，且設為A c3+5℃以上更佳。 另一方面，若過度加熱至高溫，不僅會有表層脫碳過度進行之虞，加熱所需成本亦會增加。因此，最高加熱溫度是設為1000℃以下。 (b) Hold at a maximum heating temperature of A c3 -30 ° C to 1000 ° C for 1 second to 1000 seconds. In the first heat treatment, the maximum heating temperature is set to A c3 -30 ° C or higher. When the maximum heating temperature is lower than A c3 -30 ° C, massive coarse ferrite iron remains in the steel structure inside the steel sheet of the steel sheet for heat treatment. As a result, the volume fraction of the soft ferrite iron of the steel sheet obtained after the second heat treatment of the steel sheet for heat treatment is excessive, and the ratio of the number of remaining Worthite iron having an aspect ratio of 2.0 or more is insufficient, resulting in deterioration of characteristics. The maximum heating temperature is preferably A c3 -15 ° C or more, and is preferably set to A c3 + 5 ° C or more. On the other hand, if it is excessively heated to a high temperature, not only the excessive decarburization of the surface layer but also the cost of heating will increase. Therefore, the maximum heating temperature is set to 1000 ° C or lower.
第1熱處理中，設最高加熱溫度下之保持時間為1秒~1000秒。保持時間若少於1秒，熱處理用鋼板之鋼板內部的鋼組織中會殘存塊狀粗大的肥粒鐵。結果，第2熱處理後製得之鋼板的軟質肥粒鐵的體積分率會過多而使特性變差。保持時間宜為10秒以上，且50秒以上更佳。 另一方面，保持時間若過長，則不僅加熱至最高加熱溫度所帶來之效果會飽和，還會損及生產性。因此，保持時間設為1000秒以下。In the first heat treatment, the holding time at the highest heating temperature is set to 1 second to 1000 seconds. If the holding time is less than 1 second, massive coarse ferrite iron remains in the steel structure inside the steel sheet of the steel sheet for heat treatment. As a result, the volume fraction of the soft fat iron of the steel sheet obtained after the second heat treatment is excessive and the characteristics are deteriorated. The holding time should be 10 seconds or more, and more preferably 50 seconds or more. On the other hand, if the holding time is too long, not only the effect of heating to the highest heating temperature is saturated, but also the productivity is impaired. Therefore, the hold time is set to 1000 seconds or less.
(c)以650℃至最高加熱溫度為止之溫度範圍的平均加熱速度為0.5℃/秒~500℃/秒之方式進行加熱。 第1熱處理中，加熱時，於650℃至最高加熱溫度為止之溫度範圍中，平均加熱速度若小於0.5℃/秒，則於加熱處理中會促使Mn偏析，而形成粗大塊狀Mn濃化區域。此時，會使第2熱處理後製得之鋼板特性變差。為抑制塊狀沃斯田鐵的生成，設650℃~最高加熱溫度之平均加熱速度為0.5℃/秒以上。且宜為1.5℃/秒以上。 另一方面，平均加熱速度若大於500℃/秒，則無法充分進行脫碳反應。因此設平均加熱速度為500℃/秒以下。 650℃至最高加熱溫度為止之平均加熱速度係以鋼板表面溫度從650℃至最高加熱溫度為止之經過時間除以650℃與最高加熱溫度之差而得。(c) heating is performed in such a manner that the average heating rate in the temperature range from 650 ° C to the highest heating temperature is from 0.5 ° C / sec to 500 ° C / sec. In the first heat treatment, in the temperature range from 650 ° C to the maximum heating temperature during heating, if the average heating rate is less than 0.5 ° C / sec, Mn segregation is promoted in the heat treatment to form a coarse bulk Mn-concentrated region. . At this time, the characteristics of the steel sheet obtained after the second heat treatment are deteriorated. In order to suppress the formation of the bulk Worthite iron, the average heating rate of 650 ° C to the highest heating temperature is set to 0.5 ° C / sec or more. And it is preferably 1.5 ° C / sec or more. On the other hand, if the average heating rate is more than 500 ° C / sec, the decarburization reaction cannot be sufficiently performed. Therefore, the average heating rate is set to 500 ° C / sec or less. The average heating rate from 650 ° C to the highest heating temperature is obtained by dividing the elapsed time from the surface temperature of the steel sheet from 650 ° C to the highest heating temperature by the difference between the maximum heating temperature of 650 ° C and the maximum heating temperature.
(d)於最高加熱溫度下保持後，以700℃至Ms為止之溫度範圍的平均冷卻速度為5℃/秒以上之方式進行冷卻。 第1熱處理中，為使熱處理用鋼板之鋼板內部的鋼組織以板條狀組織為主體，於最高加熱溫度下保持後，700℃至下述式(10)所示Ms為止之溫度範圍的冷卻速度係以平均冷卻速度為5℃/秒以上之方式進行冷卻。平均冷卻速度若低於5℃/秒，則熱處理用鋼板中會有生成塊狀肥粒鐵之情形。此時，第2熱處理後中，所製得之鋼板的軟質肥粒鐵的體積分率會過多，使拉伸強度等特性變差。平均冷卻速度宜設為10℃/秒以上，且設為30℃/秒以上更佳。 平均冷卻速度的上限雖無須特別限定，但若以大於500℃/秒之平均冷卻速度進行冷卻則須特別之設備。因此，宜設平均冷卻速度在500℃/秒以下。700℃至Ms以下為止之溫度範圍的平均冷卻速度係以鋼板表面溫度從700℃至Ms為止之經過時間除以700℃與Ms之差而得。(d) After being held at the highest heating temperature, the film is cooled so that the average cooling rate in the temperature range from 700 ° C to Ms is 5 ° C /sec or more. In the first heat treatment, the steel structure in the steel sheet for the heat treatment steel sheet is mainly composed of a lath-like structure, and is cooled at a temperature of 700 ° C to a temperature range of Ms represented by the following formula (10) after being held at the highest heating temperature. The speed was cooled so that the average cooling rate was 5 ° C / sec or more. When the average cooling rate is less than 5 ° C / sec, a block-shaped fat iron may be formed in the steel sheet for heat treatment. At this time, after the second heat treatment, the volume fraction of the soft fat iron of the obtained steel sheet is excessive, and the characteristics such as tensile strength are deteriorated. The average cooling rate is preferably set to 10 ° C / sec or more, and more preferably 30 ° C / sec or more. Although the upper limit of the average cooling rate is not particularly limited, if it is cooled at an average cooling rate of more than 500 ° C / sec, special equipment is required. Therefore, it is desirable to set the average cooling rate to be 500 ° C / sec or less. The average cooling rate in the temperature range from 700 ° C to less than Ms is obtained by dividing the elapsed time from the surface temperature of the steel sheet from 700 ° C to Ms by the difference between 700 ° C and Ms.
Ms=561-407×C-7.3×Si-37.8×Mn-20.5×Cu-19.5×Ni-19.8×Cr-4.5×Mo・・(10) (式(10)式中之元素符號為該元素在鋼中之質量%)。Ms=561-407×C-7.3×Si-37.8×Mn-20.5×Cu-19.5×Ni-19.8×Cr-4.5×Mo・(10) (The symbol of the element in the formula (10) is that the element % by mass in steel).
(e)在上述平均冷卻速度5℃/秒以上之冷卻係進行至Ms以下之冷卻停止溫度為止。 第1熱處理中，700℃至Ms為止之溫度範圍的平均冷卻速度為5℃/秒以上之冷卻係進行至式(10)所示Ms以下之冷卻停止溫度為止。冷卻停止溫度亦可為室溫(25℃)。藉由設冷卻停止溫度在Ms以下，可得第1熱處理後製得之熱處理用鋼板的鋼板內部的鋼組織以板條狀組織為主體者。(e) The cooling system having the above average cooling rate of 5 ° C /sec or more is performed until the cooling stop temperature of Ms or less. In the first heat treatment, the cooling system in which the average cooling rate in the temperature range from 700 ° C to Ms is 5 ° C /sec or more is performed until the cooling stop temperature of Ms or less represented by the formula (10). The cooling stop temperature can also be room temperature (25 ° C). When the cooling stop temperature is equal to or less than Ms, the steel structure inside the steel sheet of the steel sheet for heat treatment obtained after the first heat treatment is mainly composed of a lath-like structure.
本實施形態之製造方法中，於第1熱處理中，亦可對經冷卻至Ms以下且室溫以上之冷卻停止溫度的鋼板接續進行以下所示第2熱處理。又，第1熱處理中亦可於冷卻至室溫為止並捲取後進行以下所示第2熱處理。In the manufacturing method of the present embodiment, in the first heat treatment, the second heat treatment shown below may be continued to the steel sheet cooled to a cooling stop temperature of Ms or lower and room temperature or higher. Further, in the first heat treatment, the second heat treatment shown below may be performed after being cooled to room temperature and wound up.
於第1熱處理中冷卻至室溫為止之鋼板係上述本實施形態之熱處理用鋼板。藉由對熱處理用鋼板進行以下所示第2熱處理可製成本實施形態之鋼板。 本實施形態中，亦可對進行第2熱處理前之熱處理用鋼板施行各種處理。例如，為矯正熱處理用鋼板之形狀，亦可對熱處理用鋼板施行調質軋延處理。又，為去除熱處理用鋼板表面存在之氧化物，對熱處理用鋼板施行酸洗處理亦無妨。The steel sheet which was cooled to room temperature in the first heat treatment is the steel sheet for heat treatment of the above-described embodiment. The steel sheet of this embodiment can be produced by performing the second heat treatment shown below on the steel sheet for heat treatment. In the present embodiment, various treatments may be performed on the steel sheet for heat treatment before the second heat treatment. For example, in order to correct the shape of the steel sheet for heat treatment, the steel sheet for heat treatment may be subjected to a temper rolling process. Further, in order to remove the oxide existing on the surface of the steel sheet for heat treatment, the steel sheet for heat treatment may be subjected to pickling treatment.
(第2熱處理) 對施行第1熱處理後之鋼板(熱處理用鋼板)施行第2熱處理。第2熱處理係以滿足下述(A)~(E)之條件下進行。 (A)於650℃達至最高加熱溫度為止之期間，設成H 2為0.1體積%以上、O 2為0.020體積%以下且log(PH 2O/PH 2)滿足下述式(3)之氣體環境。 -1.1≦log(PH 2O/PH 2)≦-0.07・・・(3) (式(3)中，log表示常用對數，PH 2O表示水蒸氣分壓，PH 2表示氫分壓)。 第2熱處理中，藉由滿足上述(A)，可抑制在鋼板外部之氧化反應，並促進表層部之脫碳反應。 (Second Heat Treatment) The second heat treatment is performed on the steel sheet (the steel sheet for heat treatment) after the first heat treatment. The second heat treatment is carried out under the conditions of the following (A) to (E). (A) In the period from 650 ° C to the maximum heating temperature, H 2 is 0.1% by volume or more, O 2 is 0.020% by volume or less, and log (PH 2 O/PH 2 ) satisfies the following formula (3). Gas environment. -1.1≦log(PH 2 O/PH 2 )≦-0.07・・・(3) (In the formula (3), log indicates a common logarithm, PH 2 O indicates a partial pressure of water vapor, and PH 2 indicates a partial pressure of hydrogen). In the second heat treatment, by satisfying the above (A), the oxidation reaction outside the steel sheet can be suppressed, and the decarburization reaction in the surface layer portion can be promoted.
氣體環境中之H 2若小於0.1體積%、或O 2大於0.020體積%，則無法充分使存在於鋼板表面之氧化膜還原，而於鋼板上形成氧化膜。結果，會使第2熱處理後製得之鋼板的化學轉化處理性及鍍敷密著性降低。較佳H 2之範圍為1.0%體積以上，且2.0體積%以上更佳。較佳O 2之範圍為0.010體積%以下，且0.005體積%以下更佳。 又，氣體環境中之H 2含量若大於20體積%，則效果會飽和。且，氣體環境中之H 2含量若大於20體積%，會增加操作上氫爆之危險性。因此，宜設氣體環境中之H 2含量在20體積%以下。 When the H 2 in the gas atmosphere is less than 0.1% by volume or the O 2 is more than 0.020% by volume, the oxide film existing on the surface of the steel sheet cannot be sufficiently reduced, and an oxide film is formed on the steel sheet. As a result, the chemical conversion treatability and the plating adhesion of the steel sheet obtained after the second heat treatment are lowered. Preferably, the range of H 2 is 1.0% by volume or more, and more preferably 2.0% by volume or more. Preferably, the range of O 2 is 0.010% by volume or less, and more preferably 0.005% by volume or less. Further, if the H 2 content in the gas atmosphere is more than 20% by volume, the effect is saturated. Moreover, if the H 2 content in the gaseous environment is more than 20% by volume, the risk of hydrogen explosion in operation is increased. Therefore, it is preferable to set the H 2 content in a gaseous environment to be 20% by volume or less.
log(PH 2O/PH 2)小於-1.1時，會發生鋼板表層之Si、Mn的外部氧化，使脫碳反應不充分，致使形成第2熱處理後製得之鋼板表層的軟質層之厚度變薄。因此，設log(PH 2O/PH 2)為-1.1以上。log(PH 2O/PH 2)若為-0.8以上，則第2熱處理後製得之鋼板其自表面起至1/8厚度為止之硬度的變化率會成為較佳範圍故而為佳。吾等認為其係因藉由設log(PH 2O/PH 2)在-0.8以上，可連鋼板之深部亦進行脫碳反應，且使於第1熱處理中未發生脫碳反應之區域亦進行脫碳反應。 另一方面，log(PH 2O/PH 2)若大於-0.07，則脫碳反應會過度進行從而使第2熱處理後製得之鋼板強度不充分。因此，設log(PH 2O/PH 2)在-0.07以下。 When the log (PH 2 O/PH 2 ) is less than -1.1, external oxidation of Si and Mn in the surface layer of the steel sheet occurs, and the decarburization reaction is insufficient, so that the thickness of the soft layer of the surface layer of the steel sheet obtained after the second heat treatment is changed. thin. Therefore, it is assumed that log (PH 2 O/PH 2 ) is -1.1 or more. When the log (PH 2 O/PH 2 ) is -0.8 or more, the rate of change in hardness of the steel sheet obtained after the second heat treatment from the surface to the thickness of 1/8 is preferably in a preferable range. We believe that because the log (PH 2 O/PH 2 ) is above -0.8, the decarburization reaction can be carried out in the deep part of the steel sheet, and the area where the decarburization reaction does not occur in the first heat treatment is also carried out. Decarburization reaction. On the other hand, if the log (PH 2 O/PH 2 ) is more than -0.07, the decarburization reaction proceeds excessively, so that the strength of the steel sheet obtained after the second heat treatment is insufficient. Therefore, it is assumed that log (PH 2 O/PH 2 ) is -0.07 or less.
(B)於(A c1+25)℃~(A c3-10)℃之最高加熱溫度下保持1秒~1000秒。 於第2熱處理中，係設最高加熱溫度為(A c1+25)℃~(A c3-10)℃。最高加熱溫度若低於(A c1+25)℃，鋼中的雪明碳鐵會熔融殘留，使第2熱處理後製得之鋼板的內部組織中之殘留沃斯田鐵分率不夠，致使特性變差。為提高第2熱處理後製得之鋼板中的硬質組織分率以獲得更高強度之鋼板，宜設最高加熱溫度為(A c1+40)℃以上。 (B) Hold at the highest heating temperature of (A c1 +25) ° C ~ (A c3 -10) ° C for 1 second to 1000 seconds. In the second heat treatment, the maximum heating temperature is (A c1 +25) ° C ~ (A c3 -10) ° C. If the maximum heating temperature is lower than (A c1 +25) ° C, the ferritic carbon in the steel will melt and remain, so that the residual Worstian iron fraction in the internal structure of the steel sheet obtained after the second heat treatment is insufficient, resulting in characteristics. Getting worse. In order to increase the hard tissue fraction in the steel sheet obtained after the second heat treatment to obtain a steel sheet having a higher strength, it is preferable to set the maximum heating temperature to be (A c1 + 40) ° C or more.
另一方面，最高加熱溫度若高於(A c3-10)℃，則內部鋼組織幾乎或全部會變成沃斯田鐵，而第2熱處理前之鋼板(熱處理用鋼板)中的板條狀組織會消失，致使第2熱處理前之鋼板的板條狀組織無法存於第2熱處理後之鋼板中。結果，第2熱處理後製得之鋼板的內部組織中之殘留沃斯田鐵分率會不夠，且長寬比2.0以上之殘留沃斯田鐵的個數比率亦會不夠，致使特性大幅變差。因此，設最高加熱溫度為(A c3-10)℃以下。為使第2熱處理前之鋼板中的板條狀組織可充分持續存在，更提升鋼板之特性，宜設最高加熱溫度在(A c3-20)℃以下，且設在(A c3-30)℃以下更佳。 On the other hand, if the maximum heating temperature is higher than (A c3 -10) ° C, the inner steel structure becomes almost or all of the Worth iron, and the lath-like structure in the steel plate (the steel plate for heat treatment) before the second heat treatment It will disappear, and the lath-like structure of the steel sheet before the second heat treatment cannot be stored in the steel sheet after the second heat treatment. As a result, the residual Worthite iron fraction in the internal structure of the steel sheet obtained after the second heat treatment may be insufficient, and the ratio of the number of residual Worthite irons having an aspect ratio of 2.0 or more may be insufficient, resulting in greatly deteriorated characteristics. . Therefore, the maximum heating temperature is set to be (A c3 -10) ° C or less. In order to make the lath-like structure in the steel sheet before the second heat treatment sufficiently persist, and to improve the characteristics of the steel sheet, it is preferable to set the maximum heating temperature below (A c3 -20) ° C and at (A c3 -30) ° C. The following is better.
第2熱處理中，係設最高加熱溫度下之保持時間為1秒~1000秒。保持時間若少於1秒，鋼中的雪明碳鐵會熔融殘留，而有鋼板特性變差之虞。保持時間宜設為30秒以上。另一方面，若保持時間過長，則加熱至最高加熱溫度所帶來之效果會達飽和，且會使生產性降低。因此，保持時間設為1000秒以下。In the second heat treatment, the holding time at the highest heating temperature is set to be 1 second to 1000 seconds. If the holding time is less than 1 second, the stellite in the steel will melt and remain, and the characteristics of the steel sheet will deteriorate. The holding time should be set to 30 seconds or more. On the other hand, if the holding time is too long, the effect of heating to the highest heating temperature will be saturated, and the productivity will be lowered. Therefore, the hold time is set to 1000 seconds or less.
(C)以650℃至最高加熱溫度為止之平均加熱速度為0.5℃/秒~500℃/秒之方式進行加熱。 第2熱處理中650℃至最高加熱溫度為止之平均加熱速度若小於0.5℃/秒，會促使於第1熱處理作成之板條狀組織回復，使晶粒內不具有沃斯田鐵粒之軟質肥粒鐵的體積分率增加。另一方面，平均加熱速度若大於500℃/秒，則無法充分進行脫碳反應。(C) Heating is performed at an average heating rate of from 650 ° C to the maximum heating temperature of from 0.5 ° C / sec to 500 ° C / sec. In the second heat treatment, if the average heating rate from 650 ° C to the maximum heating temperature is less than 0.5 ° C / sec, the lath-like structure produced by the first heat treatment is promoted to be restored, so that the soft fertilizer of the Worthite iron particles is not contained in the crystal grains. The volume fraction of granular iron increases. On the other hand, if the average heating rate is more than 500 ° C / sec, the decarburization reaction cannot be sufficiently performed.
(D)以700至600℃為止之平均冷卻速度為3℃/秒以上之方式從最高加熱溫度冷卻至480℃以下。 於第2熱處理中，從最高加熱溫度冷卻至480℃以下為止。此時，設700~600℃之間之平均冷卻速度為3℃/秒以上。若以平均冷卻速度小於3℃/秒於上述範圍中冷卻，會生成粗大的碳化物使鋼板特性降低。平均冷卻速度宜設為10℃/秒以上。平均冷卻速度的上限無特別限定亦無妨，但若大於200℃/秒需特殊的冷卻裝置，故設為200℃/秒以下。(D) Cooling from the highest heating temperature to 480 ° C or less in such a manner that the average cooling rate from 700 to 600 ° C is 3 ° C /sec or more. In the second heat treatment, it is cooled from the maximum heating temperature to 480 ° C or lower. At this time, the average cooling rate between 700 and 600 ° C is set to be 3 ° C / sec or more. When the average cooling rate is less than 3 ° C / sec in the above range, coarse carbides are formed to lower the characteristics of the steel sheet. The average cooling rate should be set to 10 ° C / sec or more. The upper limit of the average cooling rate is not particularly limited. However, if a special cooling device is required for more than 200 ° C / sec, it is set to 200 ° C / sec or less.
(E)在300℃~480℃之間保持10秒以上。 接著，在300℃~480℃之間的溫度區域中將鋼板保持10秒以上。保持時間若少於10秒，則無法使碳於未變態沃斯田鐵中充分濃化。此時，層狀肥粒鐵無法充分成長而無法使C於沃斯田鐵濃化。結果，上述保持後於最終冷卻時會生成新生麻田散鐵，造成鋼板特性大大變差。為充分使碳往沃斯田鐵中濃化、降低麻田散鐵之生成量以改善鋼板特性，宜設保持時間在100秒以上。雖無須限定保持時間的上限，但過長亦會使生產性降低，故亦可設保持時間在1000秒以下。 冷卻停止溫度低於300℃時，亦可再加熱至300~480℃後進行保持。(E) Hold at 300 ° C to 480 ° C for more than 10 seconds. Next, the steel sheet is held in a temperature range of between 300 ° C and 480 ° C for 10 seconds or longer. If the holding time is less than 10 seconds, the carbon cannot be sufficiently concentrated in the untransformed Worth iron. At this time, the layered ferrite iron cannot be sufficiently grown to concentrate the C in the Vostian iron. As a result, the newly-created kenian loose iron is generated upon the final cooling after the above-mentioned holding, and the characteristics of the steel sheet are greatly deteriorated. In order to fully concentrate the carbon into the Vostian iron and reduce the amount of granulated iron to improve the characteristics of the steel sheet, it is preferable to set the holding time to 100 seconds or more. Although it is not necessary to limit the upper limit of the holding time, if the length is too long, the productivity is lowered, so that the holding time may be set to 1000 seconds or less. When the cooling stop temperature is lower than 300 ° C, it can be further heated to 300 to 480 ° C and then held.
＜鍍鋅步驟＞ 亦可對第2熱處理後之鋼板進行用以於表面形成熔融鍍鋅層之熔融鍍鋅。且，熔融鍍鋅層形成後亦可接著進行鍍敷層之合金化處理。 又，亦可對第2熱處理後之鋼板進行用以於表面形成電鍍鋅層之電鍍鋅。<Zinc plating step> The steel sheet after the second heat treatment may be subjected to hot-dip galvanizing for forming a hot-dip galvanized layer on the surface. Further, after the formation of the hot-dip galvanized layer, the alloying treatment of the plating layer may be performed. Further, the steel sheet after the second heat treatment may be subjected to electrogalvanization for forming an electrogalvanized layer on the surface.
熔融鍍鋅及合金化處理以及電鍍鋅只要滿足本發明規定之條件，則可於第2熱處理之冷卻步驟(D)完成之後於任一時間點進行。例如，如圖4所示模式[1]，冷卻步驟(D)、等溫保持步驟(E)後亦可施行鍍敷處理(可進一步因應需要施行合金化處理)，且如圖5所示模式[2]，冷卻步驟(D)後亦可施行鍍敷處理(可進一步因應需要施行合金化處理)，之後再施行等溫保持(E)。或是，如圖6所示模式[3]，冷卻步驟(D)、等溫保持步驟(E)後可先暫時冷卻至室溫為止，之後再施行鍍敷處理(可進一步因應需要施行合金化處理)。The hot-dip galvanizing, the alloying treatment, and the electrogalvanizing can be performed at any time after completion of the cooling step (D) of the second heat treatment as long as the conditions specified in the present invention are satisfied. For example, as shown in FIG. 4, the mode [1], the cooling step (D), and the isothermal holding step (E) may also be subjected to a plating treatment (which may be further subjected to alloying treatment as needed), and the mode is as shown in FIG. [2] After the cooling step (D), a plating treatment may be performed (the alloying treatment may be further performed as needed), and then isothermal holding (E) is performed. Alternatively, as shown in Fig. 6, the mode [3], the cooling step (D), and the isothermal holding step (E) may be temporarily cooled to room temperature, and then subjected to a plating treatment (the alloying may be further performed as needed). deal with).
熔融鍍鋅步驟中之鍍鋅浴溫度及鍍鋅浴組成等之鍍敷條件可使用一般條件，並無特別限制。例如鍍敷浴溫可為420~500℃、鋼板進入鍍敷浴之進入板溫可為420~500℃、浸漬時間可為5秒以下。鍍敷浴宜為含有0.08~0.2%之Al的鍍敷浴，且其他亦可含有不可避免之不純物的Fe、Si、Mg、Mn、Cr、Ti、Pb。又，熔融鍍鋅之單位面積量宜可以氣體擦拭等公知方法來控制。單位面量通常只要每單面5g/m 2以上即可，但宜為20~120g/m 2，且以25~75g/m 2更佳。 The plating conditions such as the galvanizing bath temperature and the composition of the galvanizing bath in the hot-dip galvanizing step can be used in general conditions, and are not particularly limited. For example, the plating bath temperature may be 420 to 500 ° C, the entry temperature of the steel sheet into the plating bath may be 420 to 500 ° C, and the immersion time may be 5 seconds or less. The plating bath is preferably a plating bath containing 0.08 to 0.2% of Al, and the other may contain Fe, Si, Mg, Mn, Cr, Ti, and Pb which are unavoidable impurities. Further, the amount of the unit area of the hot-dip galvanizing is preferably controlled by a known method such as gas wiping. The unit amount is usually 5 g/m 2 or more per one side, but is preferably 20 to 120 g/m 2 and more preferably 25 to 75 g/m 2 .
對形成有熔融鍍鋅層之高強度熔融鍍鋅鋼板可如前述因應需要進行合金化處理。 合金化處理中宜設合金化處理溫度為460~600℃。合金化處理若低於460℃，則合金化速度會變慢，故不僅生產性會降低還會發生合金化處理不均。 另一方面，合金化處理溫度若高於600℃，則合金化會過度進行而使鋼板的鍍敷密著性變差。合金化處理溫度宜為480~580℃。合金化處理之加熱時間宜設為5~60秒。 且，合金化處理宜以可使熔融鍍鋅層中之鐵濃度成為6.0質量%以上之條件來進行。The high-strength hot-dip galvanized steel sheet on which the hot-dip galvanized layer is formed can be alloyed as needed. In the alloying treatment, the alloying treatment temperature should be 460~600 °C. When the alloying treatment is lower than 460 ° C, the alloying speed is slowed, so that not only the productivity is lowered but also the alloying treatment is uneven. On the other hand, when the alloying treatment temperature is higher than 600 ° C, the alloying progresses excessively, and the plating adhesion of the steel sheet deteriorates. The alloying treatment temperature is preferably 480 to 580 °C. The heating time of the alloying treatment should be set to 5 to 60 seconds. Further, the alloying treatment is preferably carried out under the conditions that the iron concentration in the hot-dip galvanized layer is 6.0% by mass or more.
進行電鍍鋅時無特別限定其條件。The conditions for electroplating are not particularly limited.
藉由進行以上說明之第2熱處理可製得上述本實施形態之鋼板。 本實施形態中，可為了矯正形狀對鋼板施行冷軋延。冷軋延可於進行第1熱處理後施行，亦可於進行第2熱處理後施行。又，亦可於進行第1熱處理後與於進行第2熱處理後之兩者後施行。以冷軋延之軋縮率來說，軋縮率宜設為3.0%以下，且設為1.2%以下更佳。冷軋延之軋縮率若大於3.0%，則一部分之殘留沃斯田鐵會因加工誘發變態而變態成麻田散鐵，致使殘留沃斯田鐵的體積分率降低，而有損及特性之虞。另一方面，冷軋延之軋延率的下限值並無特別限定，不施行冷軋延仍能獲得本實施形態之鋼板的特性。The steel sheet of the above-described embodiment can be obtained by performing the second heat treatment described above. In the present embodiment, the steel sheet can be cold rolled for correcting the shape. The cold rolling may be performed after the first heat treatment or after the second heat treatment. Further, it may be performed after the first heat treatment and after the second heat treatment. In terms of the rolling reduction ratio of the cold rolling, the rolling reduction ratio is preferably set to 3.0% or less, and more preferably 1.2% or less. If the rolling reduction ratio of the cold rolling is more than 3.0%, a part of the residual Worthite iron will be metamorphosed into a granulated iron due to processing induced metamorphism, resulting in a decrease in the volume fraction of the residual Worth iron, which is detrimental to the characteristics. Hey. On the other hand, the lower limit of the rolling ratio of the cold rolling is not particularly limited, and the characteristics of the steel sheet of the present embodiment can be obtained without performing the cold rolling.
接下來，說明本實施形態之鋼板及本實施形態之熱處理用鋼板所具有之各構成的測定方法。 「鋼組織之測定」 鋼板內部及軟質層的鋼組織所含肥粒鐵(軟質肥粒鐵、硬質肥粒鐵)、變韌鐵、回火麻田散鐵、新生麻田散鐵、波來鐵、雪明碳鐵、殘留沃斯田鐵的體積分率可用以下所示方法測定。Next, a method of measuring each structure of the steel sheet according to the embodiment and the steel sheet for heat treatment of the present embodiment will be described. "Measurement of steel structure" The steel structure inside the steel plate and the soft layer contains ferrite iron (soft ferrite iron, hard ferrite iron), toughened iron, tempered Ma Tian loose iron, new Ma Tian loose iron, and Bora iron. The volume fraction of Xueming carbon iron and residual Worth iron can be measured by the method shown below.
以與鋼板之軋延方向平行之板厚截面為觀察面採取試料，研磨觀察面後進行硝太蝕刻。接著，於觀察鋼板內部的鋼組織時，係在觀察面中自表面起以1/4厚度之位置為中心之1/8厚度~3/8厚度之範圍中之一個或多個觀察視野中，而於觀察軟質層的鋼組織時，係自鋼板的最表層起包含軟質層深度範圍之區域中之一個或多個觀察視野中，以場發射掃描式電子顯微鏡(FE-SEM：Field Emission Scanning Electron Microscope)觀察合計2.0×10 -9m 2以上之面積。然後，分別測定肥粒鐵、變韌鐵、回火麻田散鐵、新生麻田散鐵、波來鐵、雪明碳鐵、殘留沃斯田鐵之面積分率並將其作為體積分率。 A sample was taken with a plate thickness section parallel to the rolling direction of the steel sheet as an observation surface, and the observation surface was polished to perform a niobium etching. Next, when observing the steel structure inside the steel sheet, in one or more observation fields in the range of 1/8 thickness to 3/8 thickness centering on the position of 1/4 thickness from the surface in the observation surface, When observing the steel structure of the soft layer, the field emission scanning electron microscope (FE-SEM: Field Emission Scanning Electron) is used in one or more observation fields including the depth range of the soft layer from the outermost layer of the steel sheet. Microscope) Observe a total area of 2.0 × 10 -9 m 2 or more. Then, the area fractions of ferrite iron, toughened iron, tempered granulated iron, granulated iron, neon ferritic, ferritic, and residual Worth iron were determined and used as volume fractions.
在此，晶粒內具有下部組織且碳化物以多個變形體析出之區域判斷為回火麻田散鐵。又，雪明碳鐵析出成層狀之區域判斷為波來鐵或雪明碳鐵。亮度小且無法觀察到下部組織之區域判斷為肥粒鐵(軟質肥粒鐵或硬質肥粒鐵)。亮度大且未因蝕刻而出現下部組織之區域判斷為新生麻田散鐵或殘留沃斯田鐵。剩餘部分判斷為變韌鐵。藉由將各體積分率用點計數法算出作為各組織之體積分率。Here, the region having the lower structure in the crystal grain and the carbide precipitated in the plurality of deformed bodies is determined as the tempered granulated iron. Further, the region in which the stellite carbon iron precipitated into a layer was judged to be a ferritic or ferritic carbon iron. The area where the brightness is small and the lower structure cannot be observed is judged to be ferrite iron (soft fat iron or hard fat iron). The area where the brightness is large and the lower structure is not formed by etching is judged to be a new granulated loose iron or a residual Worth iron. The remaining part is judged to be toughened iron. The volume fraction of each tissue was calculated by dot counting method for each volume fraction.
硬質肥粒鐵及軟質肥粒鐵的體積分率係以測得之肥粒鐵的體積分率為基礎，利用後述方法求出個別之體積分率。新生麻田散鐵的體積分率係從新生麻田散鐵或殘留沃斯田鐵之體積分率減去利用後述X射線繞射法求得之殘留沃斯田鐵的體積分率而求得。The volume fraction of the hard fat iron and the soft fat iron is based on the measured volume fraction of the ferrite iron, and the individual volume fraction is obtained by the method described later. The volume fraction of the granulated iron in the new kenian is obtained by subtracting the volume fraction of the residual Worthite iron obtained by the X-ray diffraction method described later from the volume fraction of the granulated iron or the residual Worth iron.
本實施形態之鋼板及作為其素材之熱處理用鋼板中，鋼板內部所含殘留沃斯田鐵的體積分率係利用X射線繞射法評估。具體而言，於自板厚表面起以1/4厚度之位置為中心之1/8厚度~3/8厚度之範圍中，將與板面平行之面佳工成鏡面，並用X射線繞射法測定FCC鐵的面積分率，並以此作為殘留沃斯田鐵的體積分率。In the steel sheet according to the present embodiment and the steel sheet for heat treatment as the material, the volume fraction of the remaining Worth iron contained in the steel sheet is evaluated by an X-ray diffraction method. Specifically, in the range of 1/8 thickness to 3/8 thickness centering on the surface of the plate thickness at a position of 1/4 thickness, the surface parallel to the plate surface is mirrored and X-ray diffraction is used. The method determines the area fraction of FCC iron and uses this as the volume fraction of residual Worth iron.
「軟質層中所含殘留沃斯田鐵體積分率與鋼板內部所含殘留沃斯田鐵體積分率之比率」 本實施形態之鋼板中，軟質層所含殘留沃斯田鐵的體積分率與鋼板內部的殘留沃斯田鐵的體積分率之比率係利用EBSD法(電子背向散射繞射法)進行高解析度結晶結構解析來評估。具體來說，係以與鋼板之軋延方向平行之板厚截面為觀察面採取試料，研磨觀察面加工成鏡面。並為去除表層的加工層而進行電解研磨或使用矽酸膠進行機械研磨。接著，對包含軟質層之鋼板的表層部及鋼板內部(自表面起以1/4厚度之位置為中心之1/8厚度~3/8厚度之範圍)，利用EBSD法以觀察視野的總面積合計為2.0×10 -9m 2以上(多個視野或同一視野皆可)進行結晶結構解析。測定時利用EBSD法測得之數據解析係使用TSL公司製之「OIM Analysys 6.0」。又，評點間距離(step)設為0.01~0.20μm。由觀察結果將判斷為FCC鐵之區域判斷為殘留沃斯田鐵，並個別算出軟質層及鋼板內部的殘留沃斯田鐵的體積分率。 "The ratio of the volume fraction of the residual Worthfield iron contained in the soft layer to the volume fraction of the residual Worthite contained in the steel sheet". The volume fraction of the Worstian iron contained in the soft layer in the steel sheet of the present embodiment. The ratio of the volume fraction of the residual Worthite iron inside the steel sheet was evaluated by the EBSD method (electron backscatter diffraction method) for high-resolution crystal structure analysis. Specifically, the sample is taken as a viewing surface with a plate thickness section parallel to the rolling direction of the steel sheet, and the polishing observation surface is processed into a mirror surface. It is electrolytically ground to remove the processed layer of the surface layer or mechanically ground using a tannic acid gel. Next, the EBSD method is used to observe the total area of the field of view of the surface layer of the steel sheet including the soft layer and the inside of the steel sheet (the range of 1/8 thickness to 3/8 thickness centered on the surface at a position of 1/4 thickness). The crystal structure analysis is performed in a total of 2.0 × 10 -9 m 2 or more (multiple fields of view or the same field of view). The data analysis system measured by the EBSD method at the time of measurement was "OIM Analysys 6.0" manufactured by TSL Corporation. Further, the distance between the evaluation points is set to 0.01 to 0.20 μm. From the observation results, it was judged that the FCC iron region was judged as the residual Worthite iron, and the volume fraction of the residual Worthite iron in the soft layer and the steel plate was calculated individually.
「殘留沃斯田鐵粒之長寬比及長徑之測定」 鋼板內部的鋼組織所含殘留沃斯田鐵粒的長寬比及長徑係用FE-SEM觀察晶粒，並利用EBSD法(電子背向散射繞射法)進行高解析度結晶方位解析來評估。 具體來說，係以與鋼板之軋延方向平行之板厚截面為觀察面採取試料，研磨觀察面加工成鏡面。接著，在觀察面中自表面起以1/4厚度之位置為中心之1/8厚度~3/8厚度之範圍中之一個或多個觀察視野中，利用FE-SEM觀察合計2.0×10 -9m 2以上之面積。由觀察結果將判斷為FCC鐵之區域視為殘留沃斯田鐵。 "Measurement of the aspect ratio and long diameter of the residual Worthite iron grain" The aspect ratio and the long diameter of the Worstian iron particles contained in the steel structure inside the steel plate are observed by FE-SEM, and the EBSD method is used. (Electronic Backscatter Diffraction Method) The high-resolution crystal orientation analysis was performed to evaluate. Specifically, the sample is taken as a viewing surface with a plate thickness section parallel to the rolling direction of the steel sheet, and the polishing observation surface is processed into a mirror surface. Next, in the observation surface, one or more observation fields in the range of 1/8 thickness to 3/8 thickness centered on the position of 1/4 thickness from the surface, the total observation by the FE-SEM is 2.0×10 − Area of 9 m 2 or more. From the observation results, it is judged that the area of the FCC iron is regarded as the residual Worthite iron.
接著，為避免測定錯誤，自經利用上述方法測得之殘留沃斯田鐵的結晶方位僅描繪長軸長度為0.1μm以上之沃斯田鐵粒的結晶方位分布圖。並將產生10°以上結晶方位差之邊界視為殘留沃斯田鐵粒之晶界。長寬比係殘留沃斯田鐵粒之長軸長度除以短軸長度而得之值。長徑設為殘留沃斯田鐵粒之長軸長度。由該結果求出長寬比2.0以上的殘留沃斯田鐵佔總殘留沃斯田鐵之個數比率。利用EBSD法測得之數據解析係使用TSL公司製之「OIM Analysys 6.0」。又，評點間距離(step)設為0.03~0.20μm。Next, in order to avoid measurement errors, only the crystal orientation of the Worstian iron particles having a long axis length of 0.1 μm or more was plotted from the crystal orientation of the residual Worth iron measured by the above method. The boundary which produces a crystal orientation difference of 10 or more is regarded as the grain boundary of the residual Worthfield iron grain. The aspect ratio is the value obtained by dividing the length of the long axis of the Worstian iron particles by the length of the short axis. The long diameter is set to the length of the long axis of the remaining Worthfield iron particles. From this result, the ratio of the number of residual Worthite irons having an aspect ratio of 2.0 or more to the total residual Worthite iron was determined. The data analysis system measured by the EBSD method uses "OIM Analysys 6.0" manufactured by TSL Corporation. Further, the distance between the points is set to 0.03 to 0.20 μm.
「包含沃斯田鐵粒之肥粒鐵粒(硬質肥粒鐵)/不包含沃斯田鐵粒之肥粒鐵粒(軟質肥粒鐵)」 針對分離肥粒鐵中包含(內包)沃斯田鐵粒之晶粒與不包含沃斯田鐵粒之晶粒的手法進行說明。首先，利用FE-SEM觀察晶粒並用EBSD法進行高解析度結晶方位解析。具體來說，係以與鋼板之軋延方向平行之板厚截面為觀察面採取試料，研磨觀察面加工成鏡面。並為去除表層的加工層而進行電解研磨或使用矽酸膠進行機械研磨。然後，對自BCC鐵測得之數據以產生15°以上結晶方位差之邊境為晶界，描繪肥粒鐵粒之晶界分布。接著，為避免測定錯誤，自FCC鐵測得之數據僅描繪長軸長度為0.1μm以上之沃斯田鐵粒的晶粒分布圖後，與肥粒鐵粒之晶界分布圖重疊。 一個肥粒鐵粒中，只要有一個以上沃斯田鐵粒完全組入其內部即視為「包含沃斯田鐵粒之肥粒鐵粒」。而未鄰接沃斯田鐵粒或僅於與其他晶粒之邊界與沃斯田鐵隣接時視為「不包含沃斯田鐵粒之肥粒鐵粒」。"Fermented iron particles (hard fat iron) containing Worthfield iron particles / fermented iron particles (soft fat iron) not containing Worthian iron particles" The crystal grains of the Stones and the methods of not including the grains of the Worthite iron grains are explained. First, the crystal grains were observed by FE-SEM and high-resolution crystal orientation analysis was performed by the EBSD method. Specifically, the sample is taken as a viewing surface with a plate thickness section parallel to the rolling direction of the steel sheet, and the polishing observation surface is processed into a mirror surface. It is electrolytically ground to remove the processed layer of the surface layer or mechanically ground using a tannic acid gel. Then, the data measured from the BCC iron is used as a grain boundary to produce a grain boundary of 15° or more, and the grain boundary distribution of the ferrite grains is depicted. Next, in order to avoid measurement errors, the data measured from the FCC iron only maps the grain distribution map of the Worthfield iron particles having a long axis length of 0.1 μm or more, and overlaps with the grain boundary distribution map of the ferrite grains. In a ferrite grain, as long as more than one Worthfield iron particle is completely incorporated into the inside, it is considered to be "fertilizer iron particles containing Worthfield iron particles". It is considered to be “a ferrite grain that does not contain Worthite iron particles” when it is not adjacent to the Worthite iron or just adjacent to the Worthite iron at the boundary with other grains.
「表層~鋼板內部之硬度」 用以決定軟質層厚度之表層~鋼板內部的硬度分布例如可用以下手法求得。 以與鋼板之軋延方向平行之板厚截面為觀察面採取試料，研磨觀察面加工成鏡面，並為去除表層的加工層而使用矽酸膠進行化學研磨。針對製得試料之觀察面用微小硬度測定裝置以自最表層起5μm深度之位置為起點，從表面起至板厚1/8厚度之位置為止，沿鋼板厚度方向以10μm間距壓入頂角136°之四角錐狀維氏壓頭。此時，壓入荷重設成各維氏壓痕不會互相影響。例如為2gf。然後，用光學顯微鏡或掃描式電子顯微鏡等測定壓痕之對角線長度並轉換成維氏硬度(Hv)。 接著，將測定位置沿軋延方向移動10μm以上，並以自最表層起10μm深度位置為起點，至板厚1/8厚度之位置為止進行相同測定。然後，再將測定位置沿軋延方向移動10μm以上，並以自最表層起5μm深度之位置為起點，從表面起至板厚1/8厚度之位置為止進行相同測定。接著，將測定位置沿軋延方向移動10μm以上，並以自最表層起10μm深度位置為起點，至板厚1/8厚度之位置為止進行相同測定。如圖7所示，藉由反覆進行而就各厚度位置測定各5點之維氏硬度。如此一來，事實上即可獲得於深度方向上5μm間距之硬度測定數據。為避免壓痕彼此影響故而不僅將測定間隔設為5μm間距。將5點的平均值作為在該厚度位置上之硬度。各數據間藉由用直線插補而獲得深度方向的硬度分布圖。從硬度分布圖讀取硬度在母材硬度的80%以下之深度位置來求取軟質層的厚度。 同樣地，硬度變化率的最大值亦可從上述深度方向之硬度分布圖算出。 另一方面，鋼板內部的硬度係針對以1/4厚度位置為中心之1/8厚度~3/8厚度之範圍，依與上述相同重點用微小硬度測定裝置測定至少5點硬度並將該值平均而求得。 微小硬度測定裝置例如可使用FISCHERSCOPE(註冊商標)HM2000 XYp。"The hardness of the surface layer to the inside of the steel sheet" The hardness distribution of the surface layer to the thickness of the steel sheet to determine the thickness of the soft layer can be obtained, for example, by the following method. The sample was taken with a plate thickness section parallel to the rolling direction of the steel sheet as a viewing surface, and the polishing observation surface was processed into a mirror surface, and chemically polished using a citric acid gel to remove the processed layer of the surface layer. The observation surface of the prepared sample was pressed into the apex angle 136 at a pitch of 10 μm in the thickness direction of the steel sheet from the surface to the thickness of 1/8 of the thickness from the surface at a position of 5 μm from the surface layer as a starting point. ° Four-corner tapered Vickers indenter. At this time, the press-in load is set so that the Vickers indentations do not affect each other. For example, 2gf. Then, the diagonal length of the indentation is measured by an optical microscope or a scanning electron microscope or the like and converted into Vickers hardness (Hv). Next, the measurement position was moved by 10 μm or more in the rolling direction, and the same measurement was performed from the position of the depth of 10 μm from the outermost layer to the position of the thickness of 1/8 of the thickness. Then, the measurement position was further moved by 10 μm or more in the rolling direction, and the same measurement was performed from the surface to the position of the thickness of 1/8 from the surface at a position of 5 μm from the outermost layer. Next, the measurement position was moved by 10 μm or more in the rolling direction, and the same measurement was performed from the position of the depth of 10 μm from the outermost layer to the position of the thickness of 1/8 of the thickness. As shown in Fig. 7, the Vickers hardness of each of five points was measured for each thickness position by repeating. In this way, hardness measurement data at a pitch of 5 μm in the depth direction can be obtained in fact. In order to avoid the influence of the indentations on each other, not only the measurement interval was set to a pitch of 5 μm. The average value of 5 points is taken as the hardness at the thickness position. A hardness distribution map in the depth direction is obtained by linear interpolation between the data. The thickness of the soft layer was determined by reading the hardness at a depth of 80% or less of the hardness of the base material from the hardness profile. Similarly, the maximum value of the hardness change rate can also be calculated from the hardness profile in the depth direction described above. On the other hand, the hardness inside the steel sheet is in the range of 1/8 thickness to 3/8 thickness centering on the 1/4 thickness position, and at least 5 points of hardness are measured by the micro hardness measuring device in accordance with the above-mentioned same emphasis and the value is Averaged. For the minute hardness measuring device, for example, FISCHERSCOPE (registered trademark) HM2000 XYp can be used.
「軟質層所含肥粒鐵之晶粒的長寬比與長寬比小於3.0之晶粒的比率」 軟質層中之肥粒鐵的長寬比係用FE-SEM觀察晶粒，並用EBSD法(電子背向散射繞射法)進行高解析度結晶方位解析來評估。利用EBSD法測得之數據解析係使用TSL公司製之「OIM Analysys 6.0」。又，評點間距離(step)設為0.01~0.20μm。 自觀察結果將判斷為BCC鐵之區域視為肥粒鐵並描繪結晶方位分布圖。然後，將產生15°以上結晶方位差之邊境視為晶界。長寬比係各肥粒鐵粒之長軸長度除以短軸長度而得之值。 求出軟質層所含肥粒鐵中長寬比小於3.0之晶粒的比率(體積分率)。"The aspect ratio of the grain size of the ferrite-rich iron in the soft layer to the grain ratio of the aspect ratio of less than 3.0." The aspect ratio of the ferrite-grained iron in the soft layer is observed by FE-SEM, and the EBSD method is used. (Electronic Backscatter Diffraction Method) The high-resolution crystal orientation analysis was performed to evaluate. The data analysis system measured by the EBSD method uses "OIM Analysys 6.0" manufactured by TSL Corporation. Further, the distance between the evaluation points is set to 0.01 to 0.20 μm. From the observation results, it is judged that the area of BCC iron is regarded as the ferrite iron and the crystal orientation distribution map is drawn. Then, a border which produces a crystal orientation difference of 15 or more is regarded as a grain boundary. The aspect ratio is the value obtained by dividing the length of the long axis of each of the ferrite particles by the length of the short axis. The ratio (volume fraction) of crystal grains having an aspect ratio of less than 3.0 in the ferrite iron contained in the soft layer was determined.
「高頻輝光放電(高頻GDS)分析」 用高頻輝光放電分析法分析本實施形態之鋼板及熱處理用鋼板時，可使用公知之高頻GDS分析法。 具體來說係使用以下方法：將鋼板表面置於Ar氣體環境，且於施加電壓以產生輝光電漿之狀態下，一邊濺鍍鋼板表面一邊於深度方向上分析之方法。然後，自輝光電漿中原子可被激發之元素特有的發光光譜波長鑑定材料(鋼板)所含元素，並從所鑑定之元素的發光強度估算材料所含元素之量。深度方向之數據可從濺鍍時間估算。具體來說，可事先用標準試樣先求取濺鍍時間與濺鍍深度之關係，以將濺鍍時間變換成濺鍍深度。因此，可將從濺鍍時間變換而得之濺鍍深度定義為自材料表面起算之深度。 高頻GDS分析可使用市售之分析裝置。本實施形態中，係使用堀場製作所公司製之高頻輝光放電發光分析裝置GD-Profiler2。 實施例"High-frequency glow discharge (high-frequency GDS) analysis" When the steel sheet for the present embodiment and the steel sheet for heat treatment are analyzed by the high-frequency glow discharge analysis method, a known high-frequency GDS analysis method can be used. Specifically, a method in which the surface of the steel sheet is placed in an Ar gas atmosphere and the surface of the steel sheet is sputtered while being subjected to a voltage to generate a glow plasma is used. Then, the element contained in the material (steel plate) is identified from the wavelength of the luminescence spectrum peculiar to the element in which the atom can be excited in the luminescence paste, and the amount of the element contained in the material is estimated from the luminescence intensity of the identified element. Data in the depth direction can be estimated from the sputtering time. Specifically, the relationship between the sputtering time and the sputtering depth can be determined in advance using a standard sample to convert the sputtering time into a sputtering depth. Therefore, the sputter depth that can be converted from the sputter time is defined as the depth from the surface of the material. A high frequency GDS analysis can use a commercially available analytical device. In the present embodiment, a high-frequency glow discharge luminescence analyzer GD-Profiler 2 manufactured by Horiba, Ltd. is used. Example
接下來，說明本發明之實施例。實施例中之條件為用以確認本發明可實施性及效果所採用之一條件例。本發明並不受限於該一條件例。只要不脫離本發明要旨而可達成本發明之目的，本發明即可採用各種條件。Next, an embodiment of the present invention will be described. The conditions in the examples are examples of conditions used to confirm the workability and effects of the present invention. The present invention is not limited to this one conditional example. The present invention can be applied to various conditions without departing from the gist of the present invention for the purpose of the invention.
熔製具有表1所示化學組成之鋼製出鋼胚。將該鋼胚進行以下熱軋延而製出熱軋鋼板：以表2~表5所示鋼胚加熱溫度、鋼胚加熱條件進行加熱，且軋延完成溫度設為表2~表5所示溫度。之後，酸洗熱軋鋼板去除表面鏽皮。然後對一部份的熱軋鋼板進行冷軋延製成冷軋鋼板。A steel-made steel embryo having the chemical composition shown in Table 1 was melted. The steel preform is subjected to the following hot rolling to produce a hot-rolled steel sheet: heating is carried out under the steel embryo heating temperature and steel embryo heating conditions shown in Tables 2 to 5, and the rolling completion temperature is set as shown in Table 2 to Table 5. temperature. Thereafter, the hot-rolled steel sheet is pickled to remove surface scale. Then, a part of the hot rolled steel sheet is cold rolled to form a cold rolled steel sheet.
[表1] [Table 1]
[表2] [Table 2]
[表3] [table 3]
[表4] [Table 4]
[表5] [table 5]
對依上述所製得之板厚1.2mm之熱軋鋼板或板厚1.2mm之冷軋鋼板施行以下所示第1熱處理及/或第2熱處理。此外，一部份的實施例係將已於第1熱處理中冷卻至表6~表9所示冷卻停止溫度為止之冷軋鋼板不冷卻至室溫即接著進行第2熱處理。其他實施例則係於第1熱處理中冷卻至冷卻停止溫度為止後，冷卻至室溫為止後再進行第2熱處理。而一部份的實施例係不進行第1熱處理即進行第2熱處理。The first heat treatment and/or the second heat treatment shown below were carried out on the hot-rolled steel sheet having a thickness of 1.2 mm and the cold-rolled steel sheet having a thickness of 1.2 mm. Further, in some embodiments, the cold-rolled steel sheet which has been cooled to the cooling stop temperature shown in Tables 6 to 9 in the first heat treatment is not cooled to room temperature, and then the second heat treatment is performed. In the other embodiment, after cooling to the cooling stop temperature in the first heat treatment, the second heat treatment is performed after cooling to room temperature. In some embodiments, the second heat treatment is performed without performing the first heat treatment.
(第1熱處理) 以表6~表9所示條件加熱至最高加熱溫度並在最高加熱溫度下保持。之後，以表6~9所示平均冷卻速度在700℃~Ms中冷卻至冷卻停止溫度為止。於第1熱處理中，在以表6~表9所示濃度含有H 2、log(PH 2O/PH 2)為表6~表9所示數值之氣體環境下，從650℃加熱達至最高加熱溫度為止。 (First heat treatment) The mixture was heated to the highest heating temperature under the conditions shown in Tables 6 to 9 and maintained at the highest heating temperature. Thereafter, the average cooling rate shown in Tables 6 to 9 was cooled to a cooling stop temperature in the range of 700 ° C to Ms. In the first heat treatment, the gas was heated from 650 ° C to the highest in a gas atmosphere containing H 2 and log (PH 2 O/PH 2 ) as shown in Tables 6 to 9 at the concentrations shown in Tables 6 to 9. Heating temperature up to now.
A c3係利用下述式(9)求出，Ms係利用下述式(10)求出。 A c3=879-346×C+65×Si-18×Mn+54×Al・・(9) (式(9)式中之元素符號為該元素在鋼中之質量%)。 Ms=561-407×C-7.3×Si-37.8×Mn-20.5×Cu-19.5×Ni-19.8×Cr-4.5×Mo・・(10) (式(10)式中之元素符號為該元素在鋼中之質量%)。 A c3 is obtained by the following formula (9), and Ms is obtained by the following formula (10). A c3 = 879 - 346 × C + 65 × Si - 18 × Mn + 54 × Al (9) (The element symbol in the formula (9) is the mass % of the element in the steel). Ms=561-407×C-7.3×Si-37.8×Mn-20.5×Cu-19.5×Ni-19.8×Cr-4.5×Mo・(10) (The symbol of the element in the formula (10) is that the element % by mass in steel).
[表6] [Table 6]
[表7] [Table 7]
[表8] [Table 8]
[表9] [Table 9]
(第2熱處理) 以650℃至最高加熱溫度為止之平均加熱速度為表10~表13所示條件，加熱至最高加熱溫度並於最高加熱溫度下保持。然後，以700~600℃之冷卻速度為表10~表13所示平均冷卻速度，冷卻至冷卻停止溫度為止。第2熱處理中，係於表10~表13所示氣體環境下從650℃加熱達至最高加熱溫度為止。(Second Heat Treatment) The average heating rate from 650 ° C to the maximum heating temperature was as shown in Tables 10 to 13 and was heated to the highest heating temperature and maintained at the highest heating temperature. Then, the cooling rate at 700 to 600 ° C is the average cooling rate shown in Tables 10 to 13 and is cooled to the cooling stop temperature. In the second heat treatment, it was heated from 650 ° C to the maximum heating temperature in the gas atmosphere shown in Tables 10 to 13.
接著，對第2熱處理後之一部分的高強度鋼板進行電鍍鋅步驟，於高強度鋼板兩面表面形成電鍍鋅層而製得電鍍鋅鋼板(EG)。 而各實驗例中，實驗例No.1’~80’係於以表8及表9所示條件進行冷卻、等溫保持後之時間點(即於圖4之模式[1]所示時間點)施行合金化熔融鍍鋅。此外，該等實驗例No.1’~80’中，實驗例1’~16’、18’~58’、60’~73’，75’~80’係於熔融鍍鋅後進行合金化處理，實驗例17’、59’、74’係未於熔融鍍鋅後進行合金化處理。Next, a high-strength steel sheet of one part after the second heat treatment is subjected to an electrogalvanizing step to form an electrogalvanized layer on both surfaces of the high-strength steel sheet to obtain an electrogalvanized steel sheet (EG). In each of the experimental examples, the experimental examples No. 1' to 80' were at the time point after cooling and isothermal holding under the conditions shown in Tables 8 and 9 (i.e., at the time point shown in the mode [1] of Fig. 4 ) Alloying hot-dip galvanizing. Further, in the experimental examples No. 1' to 80', the experimental examples 1' to 16', 18' to 58', 60' to 73', and 75' to 80' were alloyed after hot-dip galvanizing. Experimental Examples 17', 59', and 74' were not alloyed after hot-dip galvanizing.
實驗例No.81’~88’係依圖5所示模式[2]，以表13所示條件加熱、冷卻、鍍敷，及除實驗例No.86外施行合金化處理並進行冷卻、等溫保持。Experimental Example No. 81'-88' was heated, cooled, plated under the conditions shown in Table 13, and subjected to alloying treatment except for Experimental Example No. 86, and cooled, according to the mode [2] shown in FIG. Keep warm.
而實驗例No.89’係依圖6所示模式[3]，以表13所示條件進行加熱、冷卻、等溫保持後，暫時先冷卻至室溫為止，之後再進行合金化熔融鍍鋅、合金化處理。In the experimental example No. 89', the pattern [3] shown in Fig. 6 was heated, cooled, and isothermally held under the conditions shown in Table 13, and then temporarily cooled to room temperature, and then alloyed by hot-dip galvanizing. Alloying treatment.
熔融鍍鋅係各例皆浸漬於460℃之熔融鋅浴中，對鋼板兩面以每單面單位面積量50g/m 2來實施。 Each of the hot-dip galvanizing systems was immersed in a molten zinc bath at 460 ° C, and was applied to both sides of the steel sheet in an amount of 50 g/m 2 per one-sided unit area.
A c1係利用下述式(8)求得，A c3係利用上述式(9)求得。 A c1=723-10.7×Mn-16.9×Ni+29.1×Si+16.9×Cr・・(8)(式(8)式中之元素符號為該元素在鋼中之質量%)。 A c1 is obtained by the following formula (8), and A c3 is obtained by the above formula (9). A c1 = 723-10.7 × Mn - 16.9 × Ni + 29.1 × Si + 16.9 × Cr (8) (The element symbol in the formula (8) is the mass % of the element in the steel).
[表10] [Table 10]
[表11] [Table 11]
[表12] [Table 12]
[表13] [Table 13]
接著，經上述而製得之實驗例No.1~No.78及實驗例No.1’~No.89’之鋼板係利用上述方法測定自表面起以1/4厚度之位置為中心之1/8厚度~3/8厚度之範圍中之鋼組織(鋼板內部的鋼組織)，分別調查軟質肥粒鐵、殘留沃斯田鐵、回火麻田散鐵、新生麻田散鐵、波來鐵與雪明碳鐵之合計、硬質肥粒鐵、變韌鐵之各體積分率。Next, the steel sheets of Experimental Examples No. 1 to No. 78 and Experimental Examples No. 1' to No. 89' obtained as described above were measured by the above method, and the center of the 1/4 thickness was measured from the surface. /8 steel thickness in the range of thickness ~3/8 (steel structure inside the steel plate), respectively investigated soft ferrite iron, residual Worth iron, tempered Ma Tian loose iron, new Ma Tian loose iron, Bora iron and The total volume fraction of Xueming carbon and iron, hard fat iron, and toughened iron.
而實驗例No.1~No.78及實驗例No.1’~No.89’之鋼板的鋼板內部係利用上述方法調查長寬比2.0以上的殘留沃斯田鐵佔總殘留沃斯田鐵之個數比率。 這些結果顯示於表14~表17中。In the steel sheets of the steel sheets of Experimental Examples No. 1 to No. 78 and Experimental Examples No. 1' to No. 89', the residual Worthite iron having an aspect ratio of 2.0 or more was investigated by the above method. The ratio of the number. These results are shown in Tables 14 to 17.
[表14] [Table 14]
[表15] [Table 15]
[表16] [Table 16]
[表17] [Table 17]
接著，對實驗例No.1~No.78及實驗例No.1’~No.89’之鋼板利用上述方法測定鋼組織、硬度，調查軟質層之厚度(自表面起算之深度範圍)。同時利用上述方法調查自表面起至1/8厚度為止之硬度的變化率的最大值。 且，對實驗例No.1~No.78及實驗例No.1’~No.89’之鋼板利用上述方法調查軟質層所含肥粒鐵之晶粒中長寬比小於3.0之晶粒的個數比率、軟質層所含殘留沃斯田鐵與內部組織所含殘留沃斯田鐵之比率。 將結果顯示於表18~表21中。Next, the steel sheets and the hardness of the steel sheets of Experimental Examples No. 1 to No. 78 and Experimental Examples No. 1' to No. 89' were measured by the above method, and the thickness of the soft layer (depth range from the surface) was examined. At the same time, the maximum value of the change rate of the hardness from the surface to the thickness of 1/8 was investigated by the above method. Further, in the steel sheets of Experimental Examples No. 1 to No. 78 and Experimental Examples No. 1' to No. 89', the above-described method was used to investigate the crystal grains having a grain length-width ratio of less than 3.0 in the grain of the ferrite in the soft layer. The ratio of the number of layers, the ratio of the remaining Worth iron contained in the soft layer to the residual Worth iron contained in the internal structure. The results are shown in Tables 18 to 21.
並且，對實驗例No.1~No.78及實驗例No.1’~No.89’之鋼板利用上述方法以高頻輝光放電分析法自表面起於深度方向上分析顯示Si之波長的發光強度的波峰，調查於大於0.2μm且在5.0μm以下之深度範圍中是否有出現顯示Si之波長的發光強度的波峰(顯示具有含Si氧化物之內部氧化層的波峰)。 而實驗例No.1~No.78及實驗例No.1’~No.89’之鋼板中，自表面起於深度方向上於大於0.2μm且在5.0μm以下之深度範圍中，有出現顯示Si之波長的發光強度的波峰者評估內部氧化波峰為「有」，未出現波峰者評估內部氧化波峰為「無」。將結果顯示於表18~表21中。Further, the steel sheets of Experimental Examples No. 1 to No. 78 and Experimental Examples No. 1' to No. 89' were analyzed by high-frequency glow discharge analysis from the surface in the depth direction by the above method to show the wavelength of Si. The peak of the intensity was investigated for whether or not a peak showing an emission intensity of a wavelength of Si (showing a peak having an internal oxide layer containing Si oxide) was observed in a depth range of more than 0.2 μm and less than 5.0 μm. In the steel sheets of Experimental Examples No. 1 to No. 78 and Experimental Examples No. 1' to No. 89', the display appeared in the depth range of more than 0.2 μm and 5.0 μm or less in the depth direction from the surface. The peak of the luminescence intensity of the wavelength of Si was evaluated as "present", and the peak of the internal oxidation was evaluated as "none". The results are shown in Tables 18 to 21.
[表18] [Table 18]
[表19] [Table 19]
[表20] [Table 20]
[表21] [Table 21]
且，對實驗例No.1~No.78及實驗例No.1’~No.89’之鋼板利用以下所示方法調查最大拉伸應力(TS)、延伸率(El)、擴孔性(擴孔率)、加工後之彎曲性(預應變後最小彎曲半徑)、化學轉化處理性、鍍敷密著性。將結果顯示於表22~表25中。Further, the steel sheets of Experimental Examples No. 1 to No. 78 and Experimental Examples No. 1' to No. 89' were subjected to the following methods to investigate the maximum tensile stress (TS), elongation (El), and hole expandability ( The hole expansion ratio), the bending property after the processing (the minimum bending radius after the pre-strain), the chemical conversion treatability, and the plating adhesion. The results are shown in Table 22 to Table 25.
以對軋延方向呈直角方向為拉伸方向採取JIS5號拉伸試驗片，並依JIS Z2241測定最大拉伸應力及延伸率，且依JIS Z2256測定擴孔性。然後，將最大拉伸應力為700MPa以上者評估為良好。A JIS No. 5 tensile test piece was taken in a direction perpendicular to the rolling direction, and the maximum tensile stress and elongation were measured in accordance with JIS Z2241, and the hole expandability was measured in accordance with JIS Z2256. Then, the one having the maximum tensile stress of 700 MPa or more was evaluated as good.
又，為評估強度、延伸率與擴孔性之平衡，用經上述方法測得之最大拉伸應力(TS)、延伸率(El)、擴孔性(擴孔率)之結果算出下述式(11)所示之值。式(11)所示之值越大，強度與延伸率與擴孔性之平衡越佳。將式(11)之值為80×10 -7以上者評估為良好。 TS 2×El×λ・・・(11) (式(11)中，TS表示最大拉伸應力(MPa)，El表示延伸率(%)，λ表示擴孔性(%))。 將結果顯示於表22~表25中。 Further, in order to evaluate the balance between the strength, the elongation, and the hole expandability, the following formula was calculated from the results of the maximum tensile stress (TS), elongation (El), and hole expandability (hole expansion ratio) measured by the above method. (11) The value shown. The larger the value shown by the formula (11), the better the balance between the strength and the elongation and the hole expandability. The value of the formula (11) of 80 × 10 -7 or more was evaluated as good. TS 2 × El × λ (11) (In the formula (11), TS represents the maximum tensile stress (MPa), El represents the elongation (%), and λ represents the hole expandability (%)). The results are shown in Table 22 to Table 25.
加工後之彎曲性係利用以下手法來評估。以對軋延方向呈直角方向為拉伸方向採取JIS5號拉伸試驗片，並以十字頭速度2mm/分鐘之速度賦予4%之預應變。然後，自拉伸試驗片之平行部採取25mm×60mm之試驗片，用前端之R為1~6mm之90°的衝模與衝頭進行90度V彎曲試驗。用放大鏡觀察彎曲試驗後之試驗片表面，將無破裂之最小彎曲半徑定義為預應變後最小彎曲半徑。將最小彎曲半徑在3.0mm以下者評估為良好。The bending after processing is evaluated by the following methods. A JIS No. 5 tensile test piece was taken in a direction perpendicular to the rolling direction, and a pre-strain of 4% was applied at a crosshead speed of 2 mm/min. Then, a test piece of 25 mm × 60 mm was taken from the parallel portion of the tensile test piece, and a 90-degree V bending test was performed using a punch having a front end of R of 1 to 6 mm and a punch of 90°. The surface of the test piece after the bending test was observed with a magnifying glass, and the minimum bending radius without crack was defined as the minimum bending radius after the pre-strain. Those with a minimum bending radius of 3.0 mm or less were evaluated as good.
又，除實驗例No.54、No.69外之No.1~No.78之鋼板係利用以下所示方法測定化學轉化處理性。 將鋼板切成70mm×150mm，並對其於40℃下噴塗Nihon Parkerizing Co., Ltd.製之脫脂劑(商品名：Fine Cleaner E2083)之18g/l水溶液120秒。然後，水洗經塗佈脫脂劑後之鋼板並脫脂，將其於常溫下浸漬於Nihon Parkerizing Co., Ltd.製之表面調整劑(商品名：PREPALENE XG)的0.5g/l水溶液中60秒。之後，將塗佈表面調整劑後之鋼板浸漬於Nihon Parkerizing Co., Ltd.製之磷酸鋅處理劑(商品名：PALBOND L3065)中120秒並水洗、乾燥。藉此，而於鋼板表面形成由磷酸鋅被膜構成之化學轉化處理膜。Further, the steel sheets of No. 1 to No. 78 other than Experimental Examples No. 54 and No. 69 were measured for chemical conversion treatability by the methods described below. The steel plate was cut into 70 mm × 150 mm, and an 18 g/l aqueous solution of a degreaser (trade name: Fine Cleaner E2083) manufactured by Nihon Parkerizing Co., Ltd. was sprayed at 40 ° C for 120 seconds. Then, the steel sheet coated with the degreaser was washed with water and degreased, and immersed in a 0.5 g/liter aqueous solution of a surface conditioner (trade name: PREPARENE XG) manufactured by Nihon Parkerizing Co., Ltd. at room temperature for 60 seconds. Thereafter, the steel sheet coated with the surface conditioning agent was immersed in a zinc phosphate treating agent (trade name: PALBOND L3065) manufactured by Nihon Parkerizing Co., Ltd. for 120 seconds, washed with water, and dried. Thereby, a chemical conversion treatment film composed of a zinc phosphate coating film is formed on the surface of the steel sheet.
自形成有化學轉化處理膜之鋼板採取寬度70mm×長度150mm之試驗片。然後，使用掃描式電子顯微鏡(SEM)以1000倍之倍率觀察沿試驗片長度方向之3處(中央部及兩端部)。並對各試驗片依以下基準評估化學轉化處理膜之晶粒附著程度。A test piece having a width of 70 mm and a length of 150 mm was taken from the steel sheet on which the chemical conversion treatment film was formed. Then, three points (center portion and both end portions) along the longitudinal direction of the test piece were observed at a magnification of 1000 times using a scanning electron microscope (SEM). The degree of grain adhesion of the chemical conversion treatment film was evaluated for each test piece according to the following criteria.
「Ex」表面緊密附著有化學轉化處理膜之磷酸鋅結晶。 「G」磷酸鋅結晶疏散、且於相鄰結晶間發現些微間隙(未附著磷酸鋅被膜，一般稱為「露出」之部分)。 「B」於表面明顯發現到有未被化學轉化處理被膜被覆之處。The surface of "Ex" is closely adhered to the zinc phosphate crystal of the chemical conversion treatment film. The "G" zinc phosphate crystals are scattered, and some micro-gap is found between adjacent crystals (the zinc phosphate film is not attached, which is generally called "exposed"). "B" was clearly found on the surface where it was not covered by the chemical conversion coating.
表21~表25之表面所記載之「EG」表示電鍍鋅鋼板、「GI」表示熔融鍍鋅鋼板、「GA」表示合金化熔融鍍鋅鋼板。"EG" described on the surface of Tables 21 to 25 indicates an electrogalvanized steel sheet, "GI" indicates a hot-dip galvanized steel sheet, and "GA" indicates an alloyed hot-dip galvanized steel sheet.
又，實驗例No.54、No.69、No.1’~No.89’之鋼板係利用以下所示方法測定鍍敷密著性。Further, in the steel sheets of Experimental Examples No. 54, No. 69, and No. 1' to No. 89', the plating adhesion was measured by the method described below.
自該等鋼板採取30mm×100mm之試驗片並進行90°V彎曲試驗。然後，將市售之SELLOTAPE(註冊商標)沿彎曲稜線貼附，並測定附著於膠帶上之鍍敷寬度作為剝離寬度。評估如下。 Ex：鍍敷剝離小(剝離寬度小於5mm) G：不影響實際使用之程度的剝離(剝離寬度在5mm以上且小於10mm) B：剝離嚴重(剝離寬度10mm以上) 鍍敷密著性係以Ex、G為合格。Test pieces of 30 mm × 100 mm were taken from the steel sheets and subjected to a 90 ° V bending test. Then, a commercially available SELLOTAPE (registered trademark) was attached along a curved ridge line, and the plating width attached to the tape was measured as the peeling width. The assessment is as follows. Ex: small plating peeling (peeling width is less than 5 mm) G: peeling that does not affect the actual use (peeling width is 5 mm or more and less than 10 mm) B: severe peeling (peeling width: 10 mm or more) plating adhesion is Ex G is qualified.
以下就各實驗例之評估結果進行說明。The evaluation results of the respective experimental examples are described below.
[表22] [Table 22]
[表23] [Table 23]
[表24] [Table 24]
[表25] [Table 25]
屬本發明例之實驗例No.1、4、7、10、12~14、18、19、21~23、27、28、30~34、36、37、39~42、44~46、49、50、52~63、66~70、76~78、1’、4’、7’、10’~14’、16’~19’、23’、24’、26’~28’、32’、33’、35’~39’、41’、42’、44’~47’、49’~51’、54’、55’、57’~68’、71’~75’、81’~89’之鋼板具高強度且延展性及擴孔性佳、並且加工後之彎曲性及化學轉化處理性或鍍敷密著性良好。Experimental examples No. 1, 4, 7, 10, 12 to 14, 18, 19, 21 to 23, 27, 28, 30 to 34, 36, 37, 39 to 42, 44 to 46, 49 belonging to the examples of the present invention. , 50, 52~63, 66~70, 76~78, 1', 4', 7', 10'~14', 16'~19', 23', 24', 26'~28', 32' , 33', 35'~39', 41', 42', 44'~47', 49'~51', 54', 55', 57'~68', 71'~75', 81'~89 'The steel sheet has high strength, good ductility and hole expandability, and good bending property after chemical processing, chemical conversion treatment property, or plating adhesion.
實驗例No.11、17、29、47、48之鋼板因未施行第1熱處理，故金屬組織中未含有硬質肥粒鐵，結果強度、延伸率、擴孔率的平衡差。 實驗例No.2之鋼板因第1熱處理中之最高加熱溫度低，故長寬比2.0以上之殘留沃斯田鐵的個數比率不足，而強度、延伸率、擴孔率的平衡差。 實驗例No.3之鋼板因第1熱處理中之最高加熱溫度高，故鋼板中之軟質層厚度變厚，使鋼板強度降低。In the steel sheets of Experimental Examples Nos. 11, 17, 29, 47, and 48, since the first heat treatment was not performed, the hard ferrite was not contained in the metal structure, and the balance between the strength, the elongation, and the hole expansion ratio was poor. In the steel sheet of Experimental Example No. 2, since the highest heating temperature in the first heat treatment was low, the ratio of the number of remaining Worth irons having an aspect ratio of 2.0 or more was insufficient, and the balance between strength, elongation, and hole expansion ratio was poor. In the steel sheet of Experimental Example No. 3, since the highest heating temperature in the first heat treatment was high, the thickness of the soft layer in the steel sheet became thick, and the strength of the steel sheet was lowered.
實驗例No.5之鋼板鋼板因第1熱處理中之650℃至最高加熱溫度為止之平均加熱速度慢，故長寬比2.0以上之殘留沃斯田鐵的個數比率不足，而強度、延伸率、擴孔率的平衡差。 實驗例No.6、16之鋼板因第1熱處理中之log(PH 2O/PH 2)低，故軟質層中之長寬比小於3.0之肥粒鐵比率變小，而加工後之彎曲性差。 In the steel plate of Experimental Example No. 5, since the average heating rate is 750 ° C to the highest heating temperature in the first heat treatment, the ratio of the number of residual Worth irons having an aspect ratio of 2.0 or more is insufficient, and the strength and elongation are insufficient. The balance of the hole expansion ratio is poor. In the steel sheets of Experimental Examples Nos. 6 and 16, since the log (PH 2 O/PH 2 ) in the first heat treatment was low, the ratio of the ratio of the ratio of the ratio of the ratio of the ratio of the aspect ratio to the ratio of the ratio of the ratio of the ratio of the aspect ratio to the thickness of the soft layer in the soft layer was small, and the bending property after the processing was poor. .
實驗例No.8之鋼板因第1熱處理中之冷卻速度慢，故鋼板的內部組織中之軟質肥粒鐵的分率變多。因此，實驗例No.8之鋼板之強度、延伸率、擴孔率的平衡差。 實驗例No.9、15、20、25、51之鋼板因第2熱處理中之log(PH 2O/PH 2)低，故軟質層中之殘留γ分率/鋼板內部之殘留γ分率變大，而加工後之彎曲性差。 In the steel sheet of Experimental Example No. 8, since the cooling rate in the first heat treatment was slow, the fraction of the soft fat iron in the internal structure of the steel sheet increased. Therefore, the balance of the strength, elongation, and hole expansion ratio of the steel sheet of Experimental Example No. 8 was poor. In the steel sheets of Experimental Examples No. 9, 15, 20, 25, and 51, since the log (PH 2 O/PH 2 ) in the second heat treatment is low, the residual γ fraction in the soft layer/the residual γ fraction in the steel sheet becomes Large, and the bending after processing is poor.
實驗例No.24之鋼板因第1熱處理及第2熱處理中之log(PH 2O/PH 2)低，故鋼板中之軟質層厚度不足，而加工後之彎曲性差。 實驗例No.17、24、48之鋼板因鋼板之表層組織未形成軟質層而無內部氧化波峰，故化學轉化處理性之評估為「B」。 In the steel sheet of Experimental Example No. 24, since the log (PH 2 O/PH 2 ) in the first heat treatment and the second heat treatment was low, the thickness of the soft layer in the steel sheet was insufficient, and the flexibility after the processing was poor. In the steel sheets of Experimental Examples Nos. 17, 24, and 48, since the surface layer structure of the steel sheet did not form a soft layer and there was no internal oxidation peak, the chemical conversion treatability was evaluated as "B".
實驗例No.26之鋼板因第2熱處理中之最高加熱溫度高，故殘留沃斯田鐵不足，而強度、延伸率、擴孔率的平衡差。 實驗例No.35之鋼板因第2熱處理中之在300℃~480℃之間的保持時間不夠，故內部組織的新生麻田散鐵分率變多，而強度、延伸率、擴孔率的平衡差。In the steel sheet of Experimental Example No. 26, since the highest heating temperature in the second heat treatment was high, the Worstian iron remained insufficient, and the balance of strength, elongation, and hole expansion ratio was poor. In the case of the steel sheet of the experimental example No. 35, the holding time between 300 ° C and 480 ° C in the second heat treatment was insufficient, so that the distribution of the iron content of the new tissue in the internal structure was increased, and the balance of the strength, the elongation, and the hole expansion ratio was increased. difference.
實驗例No.38之鋼板因第1熱處理中之冷卻停止溫度高，故長寬比2.0以上之殘留沃斯田鐵的個數比率不足，而強度、延伸率、擴孔率的平衡差。 實驗例No.43之鋼板因第2熱處理中之冷卻速度慢，故鋼板的內部組織中之波來鐵與雪明碳鐵的合計分率變多，而強度、延伸率、擴孔率的平衡差。In the steel sheet of the experimental example No. 38, since the cooling stop temperature in the first heat treatment was high, the ratio of the number of remaining Worth irons having an aspect ratio of 2.0 or more was insufficient, and the balance between the strength, the elongation, and the hole expansion ratio was poor. In the steel sheet of the experimental example No. 43, since the cooling rate in the second heat treatment is slow, the total fraction of the pulverized iron and the swarf carbon iron in the internal structure of the steel sheet increases, and the balance of the strength, the elongation, and the hole expansion ratio is increased. difference.
實驗例No.64之鋼板因第2熱處理中之最高加熱溫度低，故鋼板的內部組織中之殘留沃斯田鐵分率不足，而強度、延伸率、擴孔率的平衡差。 實驗例No.65之鋼板因第2熱處理中之log(PH 2O/PH 2)大，故鋼板的表層組織中之軟質層厚度變厚，而使最大拉伸應力(TS)不充分。 In the steel sheet of Experimental Example No. 64, since the highest heating temperature in the second heat treatment was low, the residual Worstian iron fraction in the internal structure of the steel sheet was insufficient, and the balance of strength, elongation, and hole expansion ratio was poor. In the steel sheet of Experimental Example No. 65, since the log (PH 2 O/PH 2 ) in the second heat treatment was large, the thickness of the soft layer in the surface layer structure of the steel sheet was increased, and the maximum tensile stress (TS) was insufficient.
實驗例No.71~75之鋼板的化學組成在本發明範圍外。實驗例No.71之鋼板因C含量不足，故最大拉伸應力(TS)不充分。實驗例No.72之鋼板因Nb含量多，故加工後之彎曲性差。實驗例No.73之鋼板因Mn含量不足，故最大拉伸應力(TS)不充分。實驗例No.74之鋼板因Si含量多，故擴孔性差。實驗例No.75之鋼板因Mn含量及P含量多，故延伸率及擴孔性差。The chemical compositions of the steel sheets of Experimental Examples Nos. 71 to 75 are outside the scope of the present invention. The steel sheet of Experimental Example No. 71 was insufficient in C content, so the maximum tensile stress (TS) was insufficient. The steel sheet of Experimental Example No. 72 had a large Nb content, so that the flexibility after processing was poor. The steel sheet of Experimental Example No. 73 was insufficient in Mn content, so the maximum tensile stress (TS) was insufficient. The steel sheet of Experimental Example No. 74 had a large content of Si, so that the hole expandability was poor. In the steel sheet of Experimental Example No. 75, since the Mn content and the P content were large, the elongation and the hole expandability were inferior.
實驗例No.15’、22’、34’、52’、53’之鋼板因未施行第1熱處理，故金屬組織中未含有硬質肥粒鐵，結果強度、延伸率、擴孔率的平衡差。In the steel sheets of Experimental Examples No. 15', 22', 34', 52', and 53', since the first heat treatment was not performed, the hard ferrite was not contained in the metal structure, and the balance between the strength, the elongation, and the hole expansion ratio was poor. .
實驗例No.2’之鋼板因第1熱處理中之最高加熱溫度低，故長寬比2.0以上之殘留沃斯田鐵的個數比率不足，而強度、延伸率、擴孔率的平衡差。In the steel sheet of Experimental Example No. 2', since the highest heating temperature in the first heat treatment was low, the ratio of the number of remaining Worthite iron having an aspect ratio of 2.0 or more was insufficient, and the balance of strength, elongation, and hole expansion ratio was poor.
實驗例No.3’之鋼板因第1熱處理中之最高加熱溫度高，故軟質層厚度變厚，使強度變低。In the steel sheet of Experimental Example No. 3', since the highest heating temperature in the first heat treatment was high, the thickness of the soft layer became thick, and the strength was lowered.
實驗例No.5’之鋼板因第1熱處理中之650℃至最高加熱溫度為止之平均加熱速度慢，故長寬比2.0以上之殘留沃斯田鐵的個數比率不足，而強度、延伸率、擴孔率的平衡差。In the steel sheet of the experimental example No. 5', since the average heating rate of 650 ° C to the highest heating temperature in the first heat treatment is slow, the ratio of the number of residual Worth irons having an aspect ratio of 2.0 or more is insufficient, and the strength and elongation are insufficient. The balance of the hole expansion ratio is poor.
實驗例No.6’、21’之鋼板因第1熱處理中之log(PH 2O/PH 2)低，故軟質層中長寬比小於3.0之肥粒鐵比率變小，而加工後之彎曲性差。 In the steel sheets of Experimental Examples No. 6' and 21', since the log (PH 2 O/PH 2 ) in the first heat treatment is low, the ratio of the ferrite-grain ratio in the soft layer having an aspect ratio of less than 3.0 becomes small, and the bending after processing is small. Poor sex.
實驗例No.8’之鋼板因第1熱處理中之冷卻速度慢，故軟質肥粒鐵分率變多。因此，強度、延伸率、擴孔率的平衡差。In the steel sheet of Experimental Example No. 8', since the cooling rate in the first heat treatment was slow, the iron content of the soft fat particles increased. Therefore, the balance of strength, elongation, and hole expansion ratio is poor.
實驗例No.9’、20’、22’、25’、29’、30’、56’之鋼板因第2熱處理中之log(PH 2O/PH 2)低，故軟質層中之殘留γ分率/鋼板內部之殘留γ分率變大，而加工後之彎曲性差。 In the steel sheets of Experimental Examples Nos. 9', 20', 22', 25', 29', 30', 56', the log (PH 2 O/PH 2 ) in the second heat treatment was low, so the residual γ in the soft layer The fractional/residual gamma fraction inside the steel sheet becomes large, and the flexibility after processing is poor.
實驗例No.22’、29’、53’之鋼板因鋼板之表層組織未形成軟質層而無內部氧化波峰，故鍍敷密著性之評估為「B」。In the steel sheets of Experimental Examples No. 22', 29', and 53', since the surface layer structure of the steel sheet did not form a soft layer and there was no internal oxidation peak, the evaluation of the plating adhesion was "B".
實驗例No.31’之鋼板因第2熱處理中之最高到達溫度高，故長寬比2.0以上之殘留沃斯田鐵的個數比率不足，而強度、延伸率、擴孔率的平衡差。In the steel sheet of the experimental example No. 31', since the highest temperature reached in the second heat treatment was high, the ratio of the number of remaining Worth irons having an aspect ratio of 2.0 or more was insufficient, and the balance between the strength, the elongation, and the hole expansion ratio was poor.
實驗例No.40’之鋼板因第2熱處理中之在300℃~480℃之間的保持時間不夠，故內部組織的新生麻田散鐵分率變多，而強度、延伸率、擴孔率的平衡差。In the case of the steel sheet of the experimental example No. 40', the holding time between 300 ° C and 480 ° C in the second heat treatment was insufficient, so that the distribution rate of the new generation of the field was increased, and the strength, the elongation, and the hole expansion ratio were increased. Poor balance.
實驗例No.43’之鋼板因第1熱處理中之冷卻停止溫度高，故長寬比2.0以上之殘留沃斯田鐵的個數比率不足，而強度、延伸率、擴孔率的平衡差。In the steel sheet of the experimental example No. 43', since the cooling stop temperature in the first heat treatment was high, the ratio of the number of remaining Worth irons having an aspect ratio of 2.0 or more was insufficient, and the balance between the strength, the elongation, and the hole expansion ratio was poor.
實驗例No.48’之鋼板因第2熱處理中之冷卻速度慢，故鋼板的內部組織中之波來鐵與雪明碳鐵的合計分率變多，而強度、延伸率、擴孔率的平衡差。In the steel sheet of the experimental example No. 48', since the cooling rate in the second heat treatment is slow, the total fraction of the ferrite and the ferritic carbon in the internal structure of the steel sheet increases, and the strength, the elongation, and the hole expansion ratio are increased. Poor balance.
實驗例No.69’之鋼板因第2熱處理中之最高到達溫度低，故鋼板的內部組織中之殘留沃斯田鐵分率不足，而強度、延伸率、擴孔率的平衡差。In the steel sheet of Experimental Example No. 69', since the highest temperature reached in the second heat treatment was low, the residual Worthstone iron fraction in the internal structure of the steel sheet was insufficient, and the balance of strength, elongation, and hole expansion ratio was poor.
實驗例No.70’之鋼板因第2熱處理中之log(PH 2O/PH 2)大，故鋼板的表層組織中之軟質層厚度變厚，而最大拉伸應力(TS)不充分。 In the steel sheet of Experimental Example No. 70', since the log (PH 2 O/PH 2 ) in the second heat treatment was large, the thickness of the soft layer in the surface layer structure of the steel sheet became thick, and the maximum tensile stress (TS) was insufficient.
實驗例No.76’~80’之鋼板的化學組成在本發明範圍外。該等中，實驗例No.76’之鋼板因C含量不足，故最大拉伸應力(TS)不充分。實驗例No.77’之鋼板因Nb含量多，故加工後之彎曲性差。實驗例No.78’之鋼板因Mn含量不足，故最大拉伸應力(TS)不充分。實驗例No.79’之鋼板因Si含量多，故擴孔性差。實驗例No.80’之鋼板因Mn含量及P含量多，故延伸率及擴孔性差。The chemical composition of the steel sheets of Experimental Examples No. 76' to 80' is outside the scope of the present invention. In these cases, the steel sheet of Experimental Example No. 76' was insufficient in the C content, so the maximum tensile stress (TS) was insufficient. The steel sheet of Experimental Example No. 77' had a large Nb content, so that the flexibility after processing was poor. Since the steel sheet of Experimental Example No. 78' was insufficient in Mn content, the maximum tensile stress (TS) was insufficient. The steel sheet of Experimental Example No. 79' had a large content of Si, so that the hole expandability was poor. In the steel sheet of Experimental Example No. 80', since the Mn content and the P content were large, the elongation and the hole expandability were inferior.
以上已就本發明之較佳實施形態及實施例進行說明，惟該等實施形態、實施例僅為本發明要旨範圍內之一例，只要於不脫離本發明要旨之範圍內即可進行構成之附加、省略、取代其他變更。亦即，本發明並不受限於前述說明，僅受所附申請專利範圍之限，且於其範圍內可適當變更。The preferred embodiments and examples of the present invention have been described above, but the embodiments and examples are merely examples within the scope of the present invention, and may be added as long as they do not depart from the gist of the present invention. , omit, replace other changes. That is, the present invention is not limited to the foregoing description, but is only limited by the scope of the appended claims, and may be appropriately modified within the scope thereof.
產業上之可利用性 根據本發明，可提供一種延展性及擴孔性優異、化學轉化處理性、鍍敷密著性佳、並且加工後之彎曲性良好之高強度鋼板及其製造方法。 本發明之鋼板因延展性及擴孔性優異、且加工後之彎曲性良好，故可適用作可利用壓製加工等成形成各種形狀之汽車用鋼板。且，本發明之鋼板因化學轉化處理性、鍍敷密著性佳，故適於在表面形成化學轉化處理皮膜或鍍敷層之鋼板。Industrial Applicability According to the present invention, it is possible to provide a high-strength steel sheet excellent in ductility and hole expandability, chemical conversion treatability, and good plating adhesion, and excellent in bending property after processing, and a method for producing the same. Since the steel sheet of the present invention is excellent in ductility and hole expandability and has good flexibility after processing, it can be suitably used as a steel sheet for automobiles which can be formed into various shapes by press working. Further, since the steel sheet of the present invention is excellent in chemical conversion treatability and plating adhesion, it is suitable for forming a steel sheet having a chemical conversion treatment film or a plating layer on the surface.
1‧‧‧鋼板1‧‧‧ steel plate
11‧‧‧自鋼板表面起以1/4厚度之位置為中心之1/8厚度~3/8厚度之範圍(鋼板內部)11‧‧‧1/8 thickness to 3/8 thickness from the surface of the steel plate at a position of 1/4 thickness (inside the steel plate)
12‧‧‧軟質層12‧‧‧Soft layer
圖1係本實施形態之鋼板之與軋延方向及板厚方向平行的截面圖。 圖2係顯示本實施形態之鋼板以高頻輝光放電分析法自表面起於深度方向(板厚方向)上分析時，自表面起算之深度與顯示Si之波長的發光強度(Intensity)之關係的圖表。 圖3係顯示與本實施形態相異之鋼板(比較鋼板)以高頻輝光放電分析法自表面起於深度方向(板厚方向)上分析時，自表面起算之深度與顯示Si之波長的發光強度(Intensity)之關係的圖表。 圖4係顯示本實施形態之鋼板之製造方法中第2熱處理~熔融鍍鋅、合金化處理之溫度/時間的模式之第1例的線圖。 圖5係顯示本實施形態之鋼板之製造方法中第2熱處理~熔融鍍鋅、合金化處理之溫度/時間的模式之第2例的線圖。 圖6係顯示本實施形態之鋼板之製造方法中第2熱處理~熔融鍍鋅、合金化處理之溫度/時間的模式之第3例的線圖。 圖7係顯示本實施形態之鋼板的硬度測定之例的示意圖。Fig. 1 is a cross-sectional view showing a steel sheet according to the embodiment in parallel with a rolling direction and a thickness direction. Fig. 2 is a view showing the relationship between the depth from the surface and the intensity of the display of the wavelength of Si when the steel sheet according to the present embodiment is analyzed in the depth direction (thickness direction) from the surface by the high-frequency glow discharge analysis method. chart. Fig. 3 is a view showing the difference between the depth from the surface and the wavelength of the display Si when the steel sheet (comparative steel sheet) different from the present embodiment is analyzed from the surface in the depth direction (plate thickness direction) by the high-frequency glow discharge analysis method. A graph of the relationship between intensity and intensity. Fig. 4 is a diagram showing a first example of a mode of temperature/time of the second heat treatment to the hot-dip galvanizing and the alloying treatment in the method for producing a steel sheet according to the embodiment. Fig. 5 is a diagram showing a second example of a mode of temperature/time of the second heat treatment to the hot-dip galvanization and the alloying treatment in the method for producing a steel sheet according to the embodiment. Fig. 6 is a diagram showing a third example of a mode of temperature/time of the second heat treatment to the hot-dip galvanizing and the alloying treatment in the method for producing a steel sheet according to the embodiment. Fig. 7 is a schematic view showing an example of hardness measurement of the steel sheet of the embodiment.
Claims (10)
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| CN103827336A (en) * | 2011-09-30 | 2014-05-28 | 新日铁住金株式会社 | High-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet having tensile strength of 980MPa or more and excellent in coating adhesion, formability, and hole expansibility, and methods for producing the same |
| TW201713778A (en) * | 2015-06-11 | 2017-04-16 | 新日鐵住金股份有限公司 | Alloyed hot-dip galvanized steel sheet and manufacturing method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103827336A (en) * | 2011-09-30 | 2014-05-28 | 新日铁住金株式会社 | High-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet having tensile strength of 980MPa or more and excellent in coating adhesion, formability, and hole expansibility, and methods for producing the same |
| TW201713778A (en) * | 2015-06-11 | 2017-04-16 | 新日鐵住金股份有限公司 | Alloyed hot-dip galvanized steel sheet and manufacturing method thereof |
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