[go: up one dir, main page]

US20090317285A1 - High strength steel plate superior in stretch flange formability and fatigue characteristics - Google Patents

High strength steel plate superior in stretch flange formability and fatigue characteristics Download PDF

Info

Publication number
US20090317285A1
US20090317285A1 US12/373,570 US37357007A US2009317285A1 US 20090317285 A1 US20090317285 A1 US 20090317285A1 US 37357007 A US37357007 A US 37357007A US 2009317285 A1 US2009317285 A1 US 2009317285A1
Authority
US
United States
Prior art keywords
steel plate
less
inclusions
mns
fatigue characteristics
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US12/373,570
Other languages
English (en)
Inventor
Katsuhiro Sasai
Wataru Ohashi
Kenichi Yamamoto
Kaoru Kawasaki
Hiroshi Harada
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Corp
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from JP2006193893A external-priority patent/JP4901346B2/ja
Application filed by Individual filed Critical Individual
Assigned to NIPPON STEEL CORPORATION reassignment NIPPON STEEL CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HARADA, HIROSHI, KAWASAKI, KAORU, OHASHI, WATARU, SASAI, KATSUHIRO, YAMAMOTO, KENICHI
Publication of US20090317285A1 publication Critical patent/US20090317285A1/en
Assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION reassignment NIPPON STEEL & SUMITOMO METAL CORPORATION MERGER (SEE DOCUMENT FOR DETAILS). Assignors: NIPPON STEEL CORPORATION
Abandoned legal-status Critical Current

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0426—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite

Definitions

  • the present invention relates to high strength hot rolled steel plate superior in stretch flange formability and fatigue characteristics suitable as a material for members of an automobile chassis.
  • chassis parts accounts for a high ratio of the weight of the vehicle as a whole, so the materials used for such locations are being made higher in strength and smaller in thickness to enable lighter weight. Further, the materials used for such chassis parts are required to have high fatigue characteristics from the viewpoint of durability with respect to the vibration during driving.
  • Japanese Patent Publication (A) No. 11-199973 proposes steel plate comprised of composite structure steel plate of a ferrite phase and a martensite phase in which fine Cu is precipitated or a solid solution is dispersed (in general called “DP steel plate”).
  • DP steel plate a solid solution is dispersed
  • DP steel plate is superior in the balance of strength and ductility and in the fatigue characteristics, but the stretch flange formability, evaluated by a hole expansion test, remains inferior.
  • DP steel plate is a composite of a soft ferrite phase and a hard martensite phase, so at the time of hole expansion, the boundary parts of the two phases cannot keep up with the deformation and easily become starting points for breakage.
  • High strength hot rolled steel plate having a steel plate structure of mainly a bainite phase and suppressing the formation of coarse carbides such as disclosed in said Japanese Patent Publication (A) No. 2001-200331 does indeed exhibit a superior stretch flange formability, but cannot necessarily be said to be superior in fatigue characteristics compared with DP steel plate containing Cu. Further, with just suppressing the formation of coarse carbides, it is not possible to prevent the occurrence of cracks at the time of extreme hole expansion. According to the research of the inventors, the cause is the presence of stretched sulfide-based inclusions mainly comprised of MnS in the steel plate.
  • Mn is an element effectively contributing to the increase in strength of a material along with C and Si, but with high strength steel plate, to secure strength, the general practice has been to set the concentration of Mn high. Furthermore, if not performing the overlapping treatment of desulfurization in the secondary refining process, an S concentration of 50 ppm or more ends up being included. For this reason, a cast slab usually contains MnS. If the cast slab is hot rolled and cold rolled, the MnS easily deforms, so becomes stretched MnS-based inclusions. These become causes lowering the fatigue characteristics and stretch flange formability (hole expandability). However, no example has been found proposing hot rolled steel plate superior in stretch flange formability and fatigue characteristics from the viewpoint of control of the precipitation and deformation of MnS.
  • the present invention was proposed in consideration of the above points and has as its object the provision of high strength steel plate superior in stretch flange formability and fatigue characteristics improving the stretch flange formability and the fatigue characteristics by causing the precipitation of fine MnS in the cast slab and making this disperse as fine spherical inclusions not deformed and not easily becoming starting points of cracking in the steel plate at the time of rolling.
  • the inventors engaged in in-depth studies on the method of making fine MnS precipitate in cast slabs and making this disperse as fine spherical inclusions not deformed and not easily becoming starting points of cracking at the time of rolling and to clarify the additive elements not causing deterioration of the fatigue characteristics.
  • MnS precipitates on the fine, hard Ce oxides, La oxides, cerium oxysulfides, and lanthanum oxysulfides formed due to deoxidation due to addition of Ce and La
  • the thus precipitated MnS is resistant to deformation at the time or rolling as well, so the amount of stretched coarse MnS in the steel plate is remarkably reduced and, at the time of repeated deformation or at the time of hole expansion, these MnS-based inclusions do not easily become starting points of cracking or routes for crack propagation and that this leads to an improvement in the fatigue resistance etc.
  • a high strength steel plate superior in stretch flange formability and fatigue characteristics characterized by comprising steel plate containing, by mass %, C: 0.03 to 0.20%, Si: 0.08 to 1.5%, Mn: 1.0 to 3.0%, P: 0.05% or less, S: 0.0005% or more, N: 0.0005 to 0.01%, acid soluble Al: 0.01% or less, acid soluble Ti: less than 0.008%, and a total of one or both of Ce or La: 0.0005 to 0.04%, having a balance of iron and unavoidable impurities, and having a number ratio of stretched inclusions present in the steel plate having a circle equivalent diameter of 1 ⁇ m or more and a long axis/short axis of 5 or more of 20% or less.
  • a high strength steel plate superior in stretch flange formability and fatigue characteristics characterized by comprising steel plate containing, by mass %, C: 0.03 to 0.20%, Si: 0.08 to 1.5%, Mn: 1.0 to 3.0%, P: 0.05% or less, S: 0.0005% or more, N: 0.0005 to 0.01%, acid soluble Al: 0.01% or less, acid soluble Ti: less than 0.008%, and a total of one or both of Ce or La: 0.0005 to 0.04%, having a balance of iron and unavoidable impurities, and having inclusions in the steel plate comprised of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated in a number ratio of 10% or more.
  • a high strength steel plate superior in stretch flange formability and fatigue characteristics characterized by comprising steel plate containing, by mass %, C: 0.03 to 0.20%, Si: 0.08 to 1.5%, Mn: 1.0 to 3.0%, P: 0.05% or less, S: 0.0005% or more, N: 0.0005 to 0.01%, acid soluble Al: 0.01% or less, acid soluble Ti: less than 0.008%, and a total of one or both of Ce or La: 0.0005 to 0.04%, having a balance of iron and unavoidable impurities, and having a volume number ratio of stretched inclusions present in the steel plate having a circle equivalent diameter of 1 ⁇ m or more and a long axis/short axis of 5 or more of 1.0 ⁇ 10 4 /mm 3 or less.
  • a high strength steel plate superior in stretch flange formability and fatigue characteristics characterized by comprising steel plate containing, by mass %, C: 0.03 to 0.20%, Si: 0.08 to 1.5%, Mn: 1.0 to 3.0%, P: 0.05% or less, S: 0.0005% or more, N: 0.0005 to 0.01%, acid soluble Al: 0.01% or less, acid soluble Ti: less than 0.008%, and a total of one or both of Ce or La: 0.0005 to 0.04%, having a balance of iron and unavoidable impurities, and having a volume number density of inclusions in the steel plate comprised of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated in a volume number density of 1.0 ⁇ 10 3 /mm 3 or more.
  • a high strength steel plate superior in stretch flange formability and fatigue characteristics characterized by comprising steel plate containing, by mass %, C: 0.03 to 0.20%, Si: 0.08 to 1.5%, Mn: 1.0 to 3.0%, P: 0.05% or less, S: 0.0005% or more, N: 0.0005 to 0.01%, acid soluble Al: 0.01% or less, acid soluble Ti: less than 0.008%, and a total of one or both of Ce or La: 0.0005 to 0.04%, having a balance of iron and unavoidable impurities, and having an average circle equivalent diameter of stretched inclusions present in the steel plate having a circle equivalent diameter of 1 ⁇ m or more and a long axis/short axis of 5 or more of 10 ⁇ m or less.
  • a high strength steel plate superior in stretch flange formability and fatigue characteristics characterized by comprising steel plate containing, by mass %, C: 0.03 to 0.20%, Si: 0.08 to 1.5%, Mn: 1.0 to 3.0%, P: 0.05% or less, S: 0.0005% or more, N: 0.0005 to 0.01%, acid soluble Al: 0.01% or less, acid soluble Ti: less than 0.008%, and a total of one or both of Ce or La: 0.0005 to 0.04%, having a balance of iron and unavoidable impurities, having inclusions present in the steel plate comprising an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated, and having the inclusions include, in average composition, a total of one or both of Ce or La in 0.5 to 50 mass %.
  • a high strength steel plate superior in stretch flange formability and fatigue characteristics characterized by comprising steel plate containing, by mass %, C: 0.03 to 0.20%, Si: 0.08 to 1.5%, Mn: 1.0 to 3.0%, P: 0.05% or less, S: 0.0005% or more, N: 0.0005 to 0.01%, acid soluble Al: 0.01% or less, acid soluble Ti: less than 0.008%, and a total of one or both of Ce or La: 0.0005 to 0.04%, having a balance of iron and unavoidable impurities, and having a (Ce+La)/S ratio of 0.1 to 70.
  • FIG. 1 is a view showing the relationship of Ce+La (%) and S (%).
  • the inventors deoxidized molten steel containing C, 0.07%, Si: 0.2%, Mn: 1.2%, P: 0.01% or less, S: 0.005%, and N: 0.003% and having a balance of Fe using various elements and produced steel ingots. They hot rolled the obtained steel ingots to obtain 3 mm hot rolled steel plate. They then used the thus produced hot rolled steel plate for hole expansion tests and fatigue tests and investigated the number density, form, and average composition of the inclusions in the steel plate.
  • the reason why the Ce oxides, La oxides, cerium oxysulfides, and lanthanum oxysulfides become finer is that the SiO 2 -based inclusions first formed by Si deoxidation are reduced and broken up by the later added Ce and La to form fine Ce oxides, La oxides, cerium oxysulfides, and lanthanum oxysulfides and, furthermore, the interfacial energy between the formed Ce oxides, La oxides, cerium oxysulfides, and lanthanum oxysulfides themselves and the molten steel is low, so clustering after formation is also suppressed.
  • C is the most basic element for controlling the quenchability and strength of steel. It increases the hardness and depth of the quenched hardened layer and effectively contributes to the improvement of the fatigue strength. That is, this C is an essential element for securing the strength of steel plate. To obtain high strength steel plate, at least 0.03% is necessary. However, if this C is excessively included, the C is fixed by the formation of Ti carbides like in the past or even if using cooling conditions, a cementite phase ends up being formed. This cementite phase causes work hardening of the steel plate and is not preferable for improvement of the stretch flange formability characteristics. For this reason, in the present invention, from the viewpoint of improving the workability, the concentration of C is made 0.20% or less.
  • Si becomes an important deoxidizing element in molten steel to which Al or Ti are not added as much as possible like in the present invention, so is extremely important in the present invention. Further, Si has the function of increasing the nucleation sites of austenite at the time of quenching heating and suppressing the grain growth of the austenite and of making the grain size of the quenched hardened layer finer. This Si suppresses carbide formation and suppresses the drop in grain boundary strength due to carbides. Furthermore, this Si is effective against the formation of a bainite structure as well and plays an important role in terms of securing the strength of the material as a whole.
  • the lower limit of Si was made 0.08%.
  • the Si concentration is too high, the concentration of SiO 2 in the inclusions becomes higher and large inclusions become easier to form or the toughness and ductility become extremely poor and the surface decarburization and surface flaws increase, so the fatigue characteristics conversely deteriorate.
  • the upper limit of the Si was made 1.5%.
  • Mn is an element useful for deoxidization in the steelmaking stage. Along with C and Si, it is an element effective for raising the strength of the steel plate. To obtain this effect, it is necessary to include this Mn in 1.0% or more. However, if Mn is included in an amount over 3.0%, the ductility drops due to the segregation of Mn and solution strengthening. Further, the weldability and matrix toughness also deteriorate, so the upper limit of Mn is made 3.0%.
  • P is effective in the point of acting as a substitution type solution strengthening element smaller than Fe atoms, but segregates at the grain boundaries of the austenite and causes a drop in the grain boundary strength, so causes a drop in the torsional fatigue strength. Deterioration of the workability is a concern, so the amount is made 0.05% or less. Further, if not necessary for solution strengthening, P does not have to be added. The lower limit value of P therefore includes 0%.
  • S segregates as an impurity.
  • S forms coarse stretched inclusions of MnS and causes deterioration in the stretch flange formability, so as low a concentration as possible is desirable.
  • concentration of S had to be made an ultralow one of less than 0.0005%.
  • fine MnS is made to precipitate on the hard Ce oxides, La oxides, cerium oxysulfides, and lanthanum oxysulfides to make deformation at the time of rolling difficult and prevent stretching of the inclusions, so the upper limit value of the concentration of S is not particularly defined.
  • N is an element which is unavoidably mixed in the steel since nitrogen in the air is taken in during the melting process. N forms nitrides together with Al, Ti, etc. to promote the increased fineness of the matrix structure. However, if overly adding this N, even with a fine amount of Al or a fine amount of Ti, coarse precipitates are formed and the stretch flange formability is degraded. For this reason, in the present invention, the upper limit of the concentration of N was made 0.01%. On the other hand, to make the concentration of N less than 0.0005%, the cost becomes high, so 0.0005% is made the lower limit.
  • Acid soluble Al 0.01% or less
  • the oxides With acid soluble Al, the oxides easily cluster and become coarse, so this is preferably suppressed as much as possible to prevent deterioration of the stretch flange formability and the fatigue characteristics.
  • use as a preliminary deoxidizing material up to 0.01% is allowed. This is because if the acid soluble Al concentration is over 0.01%, the Al 2 O 3 content in the inclusions exceeds 50% and the inclusions cluster. From the viewpoint of preventing clustering, the lower the acid soluble Al concentration the better.
  • the lower limit value includes 0%.
  • the “acid soluble Al concentration” measures the concentration of Al dissolved in an acid, so is a method of analysis utilizing the fact that solute Al dissolves in acid while Al 2 O 3 does not dissolve in acid.
  • the “acid” means, for example, a mixed acid of a mixture of hydrochloric acid in 1 part, nitric acid in 1 part, and water in 2 parts (mass ratio). Using such an acid, it is possible to separate acid soluble Al and Al 2 O 3 not dissolving in an acid and measure the acid soluble Al concentration.
  • Acid soluble Ti less than 0.008%
  • the acid soluble Ti concentration measures the concentration of Ti dissolved in an acid, so is a method of analysis utilizing the fact that solute Ti dissolved in acid, while Ti oxide does not dissolve in acid.
  • the “acid” means, for example, a mixed acid of a mixture of hydrochloric acid in 1 part, nitric acid in 1 part, and water in 2 parts (mass ratio). Using such an acid, it is possible to separate acid soluble Ti and Ti oxides not dissolving in an acid and measure the acid soluble Ti concentration.
  • Ce and La have the effect of reducing the SiO 2 produced by Si deoxidation and forming inclusions having Ce oxides (for example, Ce 2 O 3 , CeO 2 ), cerium oxysulfides (for example, Ce 2 O 2 S), La oxides (for example, La 2 O 3 , LaO 2 ), lanthanum oxysulfides (for example, La 2 O 2 S), Ce oxide-La oxides, or cerium oxysulfide-lanthanum oxysulfides as main phases (50% or more as a rule of thumb) which easily become Mn precipitating sites and are hard, fine, and resistant to deformation at the time of rolling.
  • Ce oxides for example, Ce 2 O 3 , CeO 2
  • cerium oxysulfides for example, Ce 2 O 2 S
  • La oxides for example, La 2 O 3 , LaO 2
  • lanthanum oxysulfides for example, La 2 O 2 S
  • Ce oxide-La oxides or cerium oxysulfide-
  • these inclusions sometimes also partially contain MnO, SiO 2 , or Al 2 O 3 depending on the deoxidizing conditions, but if the main phase is such an oxide, they will sufficiently function as MnS precipitating sites and the effect of increasing the fineness and hardness of the inclusions will not be impaired.
  • the total concentration of the one or both of Ce or La must be made 0.0005% to 0.04%. If the total concentration of the one or both of Ce or La is less than 0.0005%, the SiO 2 inclusions cannot be reduced, while if over 0.04%, large amounts of cerium oxysulfide and lanthanum oxysulfide are produced and form coarse inclusions which degrade the stretch flange formability and fatigue characteristics.
  • Nb forms carbides, nitrides, and carbonitrides with C or N to promote the increased fineness of the matrix structure.
  • at least 0.01% is necessary.
  • the effect is saturated and the cost becomes high, so 0.10% is made the upper limit.
  • V forms carbides, nitrides, and carbonitrides with C or N to promote the increased fineness of the matrix structure. To obtain this effect, at least 0.01% is necessary. However, even if included in a large amount over 0.05%, the effect is saturated and the cost becomes high, so 0.05% is made the upper limit.
  • Cr may be included as necessary to improve the quenchability of steel and secure strength of the steel plate. To obtain this effect, at least 0.01% is necessary. However, inclusion of a large amount conversely degrades the balance of strength and ductility. Therefore, 0.6% is made the upper limit.
  • Mo may be included as necessary to improve the quenchability of steel and secure strength of the steel plate. To obtain this effect, at least 0.01% is necessary. However, inclusion of a large amount conversely degrades the balance of strength and ductility. Therefore, 0.4% is made the upper limit.
  • B may be included as necessary to improve the quenchability of steel, strengthen the grain boundaries, and improve the workability. To obtain this effect, at least 0.0003% is necessary. However, inclusion of a large amount conversely detracts from the cleanliness of the steel and degrades the ductility. Therefore, 0.003% is made the upper limit.
  • the “steel plate” means the plate after rolling obtained by hot rolling or further cooling rolling.
  • the inventors discovered through experiments that MnS-based inclusions with a circle equivalent diameter of less than 1 ⁇ m are harmless as starting points of cracking and do not cause deterioration of the stretch flange formability or fatigue characteristics. Further, inclusions with a circle equivalent diameter of 1 ⁇ m or more are easily observed by a scan type electron microscope (SEM) etc., so the inventors investigated the shape and composition of inclusions in steel plate with a circle equivalent diameter of 1 ⁇ m or more and evaluated the state of distribution of the MnS-based inclusions.
  • the “circle equivalent diameter” is defined as the (long axis ⁇ short axis) 0.5 found from the long axis and short axis of inclusions observed in cross-section.
  • the upper limit of the circle equivalent diameter of the MnS-based inclusions is not particularly limited, but in practice MnS-based inclusions of about 1 mm are observed.
  • the number ratio of the stretched inclusions is found by analyzing the composition of a plurality of randomly selected inclusions (for example 50 or so) with a circle equivalent diameter of 1 ⁇ m or more using an SEM and measuring the long axes and short axes of the inclusions from the SEM image.
  • a circle equivalent diameter 1 ⁇ m or more
  • the number ratio of the stretched inclusions can be found by dividing the detected number of stretched inclusions by the total number of inclusions investigated (in the above example, 50 or so).
  • the stretch ratio of the inclusions was made 5 or more because the inclusions with a stretch ratio of 5 or more in comparative steel plate not containing La are almost all MnS-based inclusions. Further, the upper limit of the stretch ratio of the MnS-based inclusions is not particularly limited, but in practice MnS-based inclusions with a stretch ratio of 50 or so are sometimes observed.
  • the stretch flange formability and the fatigue characteristics are improved. That is, if the number ratio of the stretched inclusions with a stretch ratio of 5 or more exceeds 20%, the number of MnS-based stretched inclusions easily becoming starting points of cracking becomes too large and the stretch flange formability and the fatigue characteristics drop.
  • the number ratio of stretched inclusions with a stretch ratio of 5 or more is made 20% or less. Further, the stretch flange formability and the fatigue characteristics are better the small the number of stretched MnS-based inclusions, so the lower limit value of the number ratio of the stretched inclusions with a stretch ratio of 5 or more includes 0%.
  • the lower limit value of the number ratio of stretched inclusions with a circle equivalent diameter of 1 ⁇ m or more and with a stretch ratio of 5 or more being 0% means when there are inclusions with a circle equivalent diameter of 1 ⁇ m or more, but none with a stretch ratio of 5 or more or when there are stretched inclusions with a stretch ratio of 5 or more, but all have a circle equivalent diameter of less than 1 ⁇ m.
  • MnS precipitates on the oxide or oxysulfide of one or both of Ce or La.
  • the form of the inclusions is not particularly limited so long as MnS precipitates on an oxide or oxysulfide of one or both of Ce or La, but usually is an oxide or oxysulfide of one or both of Ce or La as core around which the MnS precipitates.
  • inclusions comprised of an oxide or oxysulfide of one or both of Ce or La on which MnS has precipitated are resistant to deformation even at the time of rolling, so become unstretched shapes even in the steel plate, that is, substantially spherical inclusions.
  • the spherical inclusions judged as not stretched are not particularly limited, but may be inclusions in the steel plate with a stretch ratio of 3 or less, preferably inclusions with a ratio of 2 or less. This is because at the cast slab stage before the rolling, the stretch ratio of the inclusions of a form of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated was 3 or less. Further, if spherical inclusions judged as not stretched are completely spherical, the stretch ratio would become 1, so the lower limit of the stretch ratio is 1.
  • the number ratio of the inclusions was investigated by a method similar to the investigation of the number ratio of the stretched inclusions. As a result, it was learned that in steel plate controlled in precipitation to have a number ratio of inclusions of a form of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated of 10% or more, the stretch flange formability and the fatigue characteristics are improved. If the number ratio of inclusions of a form of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated becomes less than 10%, in accordance with this, the number ratio of MnS-based stretched inclusions becomes too large and the stretch flange formability and the fatigue characteristics fall.
  • the number ratio of inclusions of a form of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated is made 10% or more. Further, the stretch flange formability and the fatigue characteristics become better with a large amount of MnS precipitated on oxides or oxysulfides of one or both of Ce or La, so the upper limit value of the number ratio includes 100%.
  • inclusions of a form of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated are resistant to deformation even at the time of rolling, so the circle equivalent diameter is not particularly limited, but may be 1 ⁇ m or more. However, if too large, the inclusions may form starting points of cracking, so the upper limit is preferably 50 ⁇ m or so.
  • the number density of inclusions per unit volume is defined.
  • the distribution of particle size of the inclusions was obtained by SEM evaluation of the electrolyzed surface by the speed method.
  • SEM evaluation of the electrolyzed surface by the speed method means polishing the surface of a sample piece, then electrolyzing it by the speed method and directly evaluating the sample surface by an SEM to evaluate the size and number density of the inclusions.
  • the “speed method” is the method of using 10% acetyl acetone-1% tetramethyl ammonium chloride-methanol to electrolyze the sample surface and extract the inclusions.
  • As the amount of electrolysis 1 C per 1 cm 2 area of the sample surface was electrolyzed.
  • An SEM image of the thus electrolyzed surface was processed to find the distribution of frequency (number) with respect to the circle equivalent diameter. From this distribution of frequency of the particle size, the average circle equivalent diameter was calculated. Further, the frequency was divided by the depth found by the area of the observed field and the amount of electrolysis to calculate the number density of inclusions per volume.
  • the inventors evaluated the volume number density of inclusions with a circle equivalent diameter of 1 ⁇ m or more and with a stretch ratio of 5 or more becoming starting points of cracking and degrading the stretch flange formability and the fatigue characteristics and as a result learned that if 1.0 ⁇ 10 4 /mm 3 or less, the stretch flange formability and the fatigue characteristics are improved.
  • the volume number density of stretched inclusions with a circle equivalent diameter of 1 ⁇ m or more and with a stretch ratio of 5 or more is over 1.0 ⁇ 10 4 /mm 3 , the number density of the MnS-based stretched inclusions easily becoming starting points of cracking becomes too large and the and the stretch flange formability and the fatigue characteristics fall, so the volume number density of stretched inclusions with a circle equivalent diameter of 1 ⁇ m or more and with a stretch ratio of 5 or more is made 1.0 ⁇ 10 4 /mm 3 or less. Further, the stretch flange formability and the fatigue characteristics are better the smaller the stretched MnS-based inclusions, so the lower limit value of the volume number density with a circle equivalent diameter 1 ⁇ m or more and with a stretch ratio of 5 or more includes 0%.
  • the lower limit value of the volume number density of stretched inclusions with a circle equivalent diameter of 1 ⁇ m or more and with a stretch ratio of 5 or more being 0% means the same as the above.
  • the unstretched MnS-based inclusions become a form of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated.
  • the shape was substantially spherical inclusions.
  • the form of the inclusions in the same way as the above, is not particularly limited so long as it is an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated, but usually it is an oxide or oxysulfide of one or both of Ce or La as a core around which MnS is precipitated.
  • the “spherical inclusions” is not particularly limited, but refers to inclusions in the steel plate with a stretch ratio of 3 or less, preferably inclusions with a ratio of 2 or less.
  • the stretch ratio becomes 1, so the lower limit of the stretch ratio is 1.
  • the inventors investigated the volume number density of such inclusions and as a result learned that with steel plate controlled in precipitation to give a volume number density of inclusions of a form of an oxide or oxysulfide of one or both of Ce or La as a core around which MnS is precipitated of 1.0 ⁇ 10 3 /mm 3 or more, the stretch flange formability and the fatigue characteristics are improved.
  • the volume number density of inclusions of a form of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated is less than 1.0 ⁇ 10 3 /mm 3 , in accordance with this, the number ratio of the MnS-based stretched inclusions becomes too large and the stretch flange formability and the fatigue characteristics fall, so the volume number density of inclusions of a form of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated is defined as 1.0 ⁇ 10 3 /mm 3 or more. Further, the stretch flange formability and the fatigue strength become better the more the MnS precipitated around cores of an oxide or oxysulfide of one or both of Ce or La, so the upper limit value of the volume number density is not particularly defined.
  • the circle equivalent diameter of inclusions of a form of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated is not particularly limited, but may be 1 ⁇ m or more. However, if this circle equivalent diameter is too large, the inclusions are liable to become starting points of cracking, so the upper limit is preferably 50 ⁇ m or so.
  • the upper limit of the circle equivalent diameter is defined. Specifically, the inventors evaluated the average circle equivalent diameter of inclusions with a circle equivalent diameter of 1 ⁇ m or more and with a stretch ratio of 5 or more forming starting points of cracking and degrading the stretch flange formability and fatigue characteristics and as a result learned that if the average circle equivalent diameter of the stretched inclusions is 10 ⁇ m or less, the stretch flange formability and fatigue characteristics are improved.
  • the inventors took note of the fact that along with an increase in the number ratio of the stretched inclusions with a circle equivalent diameter of 1 ⁇ m or more and with a stretch ratio of 5 or more, the average circle equivalent diameter of the stretched inclusions becomes larger and defined the average circle equivalent diameter of the stretched inclusions as an indicator. They guessed that as the amount of Mn or S in the steel increases, the number of MnS formed increases and the formed MnS becomes coarser in size.
  • the stretched inclusions with a circle equivalent diameter of 1 ⁇ m or more and with a stretch ratio of 5 or more exceed 10 ⁇ m, in accordance with this, the number ratio of the stretched inclusions exceeds 20%, so the number ratio of coarse MnS-based stretched inclusions easily becoming starting points of cracking becomes too large and the stretch flange formability and fatigue characteristics fall, therefore the average circle equivalent diameter of the stretched inclusions with a circle equivalent diameter of 1 ⁇ m or more and with a stretch ratio of 5 or more is made 10 ⁇ m or less.
  • the content of the average composition of Ce or La in the inclusions where MnS is precipitated is defined.
  • the form of the inclusions in the same way as the above, is not particularly limited so long as MnS precipitates on an oxide or oxysulfide of one or both of Ce or La, but in most cases it comprises an oxide or oxysulfide of one or both of Ce or La as a core around which MnS is precipitated.
  • the spherical inclusions are not particularly limited, but may be inclusions in the steel plate with a stretch ratio of 3 or less, preferably inclusions with a ratio of 2 or less.
  • the stretch ratio is 1, so the lower limit of the stretch ratio is 1.
  • the inventors analyzed the composition of inclusions of a form of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated.
  • the circle equivalent diameter of the inclusions is 1 ⁇ m or more, observation becomes easy, so for convenience they covered a circle equivalent diameter of 1 ⁇ m or more. However, if observation is possible, inclusions with a circle equivalent diameter of less than 1 ⁇ m may also be included.
  • inclusions of a form of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated do not stretch, so it was confirmed that the stretch ratio was 3 or less in all of the inclusions. Therefore, the inventors analyzed the composition of inclusions with a circle equivalent diameter of 1 ⁇ m or more and with a stretch ratio of 3 or less.
  • the average content of the total of one or both of Ce or La in the inclusions with a circle equivalent diameter of 1 ⁇ m or more and a stretch ratio of 3 or less becomes less than 0.5 mass %, the number ratio of the inclusions of a form of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated is greatly reduced and, in accordance with this, the number ratio of MnS-based stretched inclusions easily becoming starting points of cracking becomes too large and the stretch flange formability and fatigue characteristics fall.
  • the chemical ingredient (Ce+La)/S ratio of the steel plate is defined.
  • the ratio of chemical ingredients for making MnS precipitate on an oxide or oxysulfide of one or both of Ce or La and preventing stretching of the MnS is important.
  • the inventors changed the (Ce+La)/S ratio of the steel plate and evaluated the form of the inclusions, stretch flange formability, and fatigue characteristics ( FIG. 1 ). As a result, they learned that when the (Ce+La)/S ratio is 0.1 to 70, the stretch flange formability and the fatigue characteristics are improved.
  • cerium oxysulfides and lanthanum oxysulfides are formed in large amounts and form coarse inclusions with a circle equivalent diameter of 50 ⁇ m or so or more, so the stretch flange formability and the fatigue characteristics are degraded.
  • the present invention improves the stretch flange formability and fatigue characteristics by control of the MnS-based inclusions.
  • the microstructure of the steel plate is not particularly limited.
  • the effect of the present invention is obtained in any steel plate of steel plate of a structure with bainitic ferrite as a main phase, composite structure steel plate having a ferrite phase as a main phase and having a martensite phase or bainite phase as a second phase, and composite structure steel plate comprised of ferrite, residual austenite, and a low temperature transformed phase (martensite or bainite), but to obtain a superior stretch flange formability, making the structure one having bainitic ferrite as its main phase is preferred.
  • the bainitic ferrite or bainite phase is the largest phase in terms of area ratio.
  • the area rate of the bainitic ferrite phase is preferably 50% or more, more preferably 80% or more, still more preferably 100%.
  • the balance may be made a bainite phase or polygonal ferrite phase contained in an amount of 20% or more.
  • the molten steel is blow refined in a converter to decarburize it and is further decarburized by using a vacuum degassing apparatus to make the C concentration 0.03 to 0.1%.
  • Si, Mn, P, and other alloys are added to this molten steel for deoxidation and adjustment of the ingredients.
  • Al and Ti are not added or, when adjustment of the oxygen is necessary, a small amount of Al or Ti of an extent whereby a small amount of acid soluble Al or acid soluble Ti remains is added, then one or both of Ce or La is added to adjust the composition.
  • the thus produced molten steel is continuously cast to produce a cast slab.
  • the invention may be applied to continuous casting of slabs of an extent of the usually 250 mm thickness, but it may also be sufficiently applied to continuous casting of blooms or billets or of thin slabs produced by slab continuous casting machine with thicknesses of the casting molds thinner than usual, for example, 150 mm or less.
  • the hot rolling conditions for producing high strength hot rolled steel plate will be explained next.
  • the heating temperature of the slabs before hot rolling is preferably 1150° C. or more for making the carbonitrides etc. in the steel enter solid solution. By making these enter solid solution, the formation of polygonal ferrite is suppressed in the cooling process after rolling and a structure mainly comprised of a bainitic ferrite phase preferable for the stretch flange formability is obtained.
  • the heating temperature of the slab before hot rolling exceeds 1250° C., the oxidation of the slab surface becomes remarkable. In particular, the grain boundaries are selectively oxidized. Due to this, wedge-shaped surface defects remain after descaling. This detracts from the surface quality after rolling, so the upper limit is preferably made 1250° C.
  • the finish rolling end temperature is important when controlling the structure of the steel plate.
  • the finish rolling end temperature is less than the Ar 3 point+30° C.
  • the crystal grains at the surface layer easily become coarser. This is not preferable for the fatigue characteristics.
  • the upper limit is preferably made the Ar 3 point+200° C.
  • making the average cooling rate of the steel plate after finish rolling 40° C./s or more and cooling in the range up to 300 to 500° C. is effective for suppressing the formation of the polygonal ferrite phase and obtaining a structure mainly comprised of a bainitic ferrite phase.
  • the average cooling rate is less than 40° C./s, polygonal ferrite phase forms more easily, so this is not preferred.
  • the upper limit of the cooling rate is preferably made 100° C./s.
  • the coiling temperature of the hot rolled coil is preferably made 300° C. or more for suppressing the formation of a martensite phase causing extreme deterioration of the stretch flange formability.
  • the coiling temperature is preferably made 500° C. or less. Therefore, by coiling at 500° C. or less, carbonitrides are precipitated in the subsequent cooling process so reduce the amounts of solid solution C and N in the ferrite phase and cause an improvement in the stretch flange formability.
  • Step Nos. Steel Numbers (hereinafter referred to as “Steel Nos.”) 1, 3, 5, 7, 9, 11, and 13 are made compositions in the range of high strength steel plate according to the present invention, while Steel Nos. 2, 4, 6, 8, 10, 12, and 14 are made comparative steels outside the range of high strength steel plate according to the present invention.
  • Steel Nos. 2, 4, and 6 were made slabs containing acid soluble Al in over 0.01%, while Steel Nos. 8, 10, 12, and 14 were made slabs with the total of one or both of Ce or La reduced to less than 0.0005.
  • the Conditions A were made a heating temperature of 1250° C., a finish rolling end temperature of 845° C., a cooling rate after finish rolling of 75° C./s, and a coiling temperature of 450° C.
  • the Conditions B were made a heating temperature of 1200° C., a finish rolling end temperature of 825° C., a cooling rate after finish rolling of 45° C./s, and a coiling temperature of 450° C.
  • the Conditions A were applied, further for the Steel No. 3 and the Steel No. 4, the Conditions B were applied, for the Steel No. 5 and the Steel No. 6, the Conditions A were applied, and for the Steel No. 7 and the Steel No. 8, the Steel No. 9 and the Steel No. 10, the Steel No. 11 and the Steel No. 12, and the Steel No. 13 and the Steel No. 14, the Conditions B were applied to enable the effects of the chemical compositions to be compared under the same production conditions.
  • the inventors investigated the strength, ductility, stretch flange formability, and fatigue strength ratio.
  • the inventors investigated the number ratio, volume number density, and average circle equivalent diameter of inclusions having a stretch ratio of 5 or more for all inclusions of 1 ⁇ m or more.
  • the inventors investigated the number ratio and volume number density of inclusions comprised of an oxide or oxysulfide of one or both of Ce or La on which MnS has precipitated for all inclusions of 1 ⁇ m or more and the average value of contents of the total of one or both of Ce or La in the inclusions with a stretch ratio of 3 or less.
  • the strength and ductility were found by a tensile test of a JIS No. 5 test piece taken in parallel with the rolling direction.
  • the fatigue strength ratio used as an indicator showing the fatigue characteristics was evaluated by the value of the fatigue strength at 2 ⁇ 10 6 cycles ( ⁇ W) found by the method based on JIS Z 2275 divided by the strength ( ⁇ B) of the steel plate ( ⁇ W/ ⁇ B).
  • test piece used was a No. 1 test piece defined in the specification having a parallel part of 25 mm, a radius of curvature R of 100 mm, and a thickness after equally grinding the two surfaces of the original plate (hot rolled plate) of 3.0 mm.
  • the inclusions were observed under a SEM. Fifty randomly selected inclusions with a circle equivalent diameter of 1 ⁇ m or more were measured for their long axes and short axes. Furthermore, the quantitative analysis function of an SEM was used to analyze the composition of 50 randomly selected inclusions with a circle equivalent diameter of 1 ⁇ m or more. Using these results, the number ratio of inclusions with a stretch ratio of 5 or more, the average circle equivalent diameter of inclusions with a stretch ratio of 5 or more, the number ratio of inclusions comprised of an oxide or oxysulfide of one or both of Ce or La on which MnS has precipitated, and furthermore an average value of the total of one or both of Ce or La in the inclusions with a stretch ratio of 3 or less were found. Further, the volume number density by type of inclusions was calculated by evaluation of the electrolyzed surface by SEM evaluation by the speed method.
  • the number ratio of inclusions comprised of an oxide or oxysulfide of one or both of Ce or La on which MnS is precipitated in the steel plate 10% or more, making the volume number density of the inclusions 1.0 ⁇ 10 3 /mm 3 or more, and making the average content of the total of one or both of Ce or La in the inclusions with a stretch ratio of 3 or less present in the steel plate 0.5% to 50%, it was possible to make the number ratio of the stretched inclusions with a circle equivalent diameter 1 ⁇ m or more and with a stretch ratio of 5 or more 20% or less, make the volume number density of the inclusions 1.0 ⁇ 10 4 /mm 3 or less, and make the average circle equivalent diameter of the inclusions 10 ⁇ m or less.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
US12/373,570 2006-07-14 2007-03-02 High strength steel plate superior in stretch flange formability and fatigue characteristics Abandoned US20090317285A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2006193893A JP4901346B2 (ja) 2005-11-07 2006-07-14 伸びフランジ性と疲労特性に優れた高強度鋼板
PCT/JP2007/054614 WO2008007477A1 (fr) 2006-07-14 2007-03-02 Feuille d'acier à haute résistance excellente en termes d'aptitude à l'étirement des bordures et de tenue à la fatigue

Publications (1)

Publication Number Publication Date
US20090317285A1 true US20090317285A1 (en) 2009-12-24

Family

ID=38923047

Family Applications (1)

Application Number Title Priority Date Filing Date
US12/373,570 Abandoned US20090317285A1 (en) 2006-07-14 2007-03-02 High strength steel plate superior in stretch flange formability and fatigue characteristics

Country Status (8)

Country Link
US (1) US20090317285A1 (fr)
EP (1) EP2048254B1 (fr)
KR (1) KR20090018167A (fr)
CN (1) CN101490295B (fr)
AU (1) AU2007273767B2 (fr)
CA (1) CA2657587C (fr)
TW (1) TWI424069B (fr)
WO (1) WO2008007477A1 (fr)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4431185B2 (ja) 2008-06-13 2010-03-10 新日本製鐵株式会社 伸びフランジ性と疲労特性に優れた高強度鋼板およびその溶鋼の溶製方法
TWI362424B (en) * 2009-03-27 2012-04-21 Nippon Steel Corp Carbon steel sheet hiving high carburizing quenching property and manufacturing method thereof
US9238848B2 (en) 2010-05-10 2016-01-19 Nippon Steel & Sumitomo Metal Corporation High-strength steel sheet and method for producing same
JP5765080B2 (ja) * 2010-06-25 2015-08-19 Ｊｆｅスチール株式会社 伸びフランジ性に優れた高強度熱延鋼板およびその製造方法
CN103080358B (zh) * 2011-02-24 2015-12-23 新日铁住金株式会社 延伸凸缘性和弯曲加工性优良的高强度钢板及其钢水的熔炼方法
RU2556253C1 (ru) * 2011-07-29 2015-07-10 Ниппон Стил Энд Сумитомо Метал Корпорейшн Высокопрочный стальной лист и высокопрочный оцинкованный стальной лист с превосходной формуемостью, и способы их получения
CN108350542B (zh) * 2015-09-22 2020-03-10 塔塔钢铁艾默伊登有限责任公司 具有优异的拉伸凸缘成形性的热轧高强度可轧制成形钢片材和制造所述钢的方法
CN107400824A (zh) * 2016-05-18 2017-11-28 鞍钢股份有限公司 一种延伸凸缘性优异的高强度汽车车轮用钢及其生产方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2287519A1 (fr) * 1974-10-07 1976-05-07 Kobe Steel Ltd Acier structural de bonne aptitude au soudage avec grand apport de chaleur et son procede de fabrication
JP2005307342A (ja) * 2004-03-25 2005-11-04 Jfe Steel Kk 厚肉低降伏比高張力鋼板の製造方法
US20060260719A1 (en) * 2002-07-23 2006-11-23 Toshiaki Mizoguchi Steels product reduced in amount of alumina cluster

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3619359B2 (ja) 1998-01-19 2005-02-09 新日本製鐵株式会社 疲労特性に優れた複合組織高強度冷延鋼板およびその製造方法
JP4258934B2 (ja) 2000-01-17 2009-04-30 Ｊｆｅスチール株式会社 加工性と疲労特性に優れた高強度熱延鋼板およびその製造方法
JP3650601B2 (ja) * 2001-12-07 2005-05-25 新日本製鐵株式会社 伸びフランジ性と疲労特性に優れた高強度熱延鋼板およびその製造方法
JP4050991B2 (ja) * 2003-02-28 2008-02-20 新日本製鐵株式会社 伸びフランジ成形性に優れた高強度鋼板およびその製造方法
JP4105974B2 (ja) * 2003-04-16 2008-06-25 新日本製鐵株式会社 打ち抜き端面の疲労特性と伸びフランジ性に優れた高強度熱延鋼板およびその製造方法
JP2005256115A (ja) * 2004-03-12 2005-09-22 Nippon Steel Corp 伸びフランジ性と疲労特性に優れた高強度熱延鋼板
JP4268559B2 (ja) * 2004-04-23 2009-05-27 新日本製鐵株式会社 伸びフランジ性に優れた高強度鋼板
JP4291761B2 (ja) * 2004-08-31 2009-07-08 新日本製鐵株式会社 伸びフランジ性と疲労特性に優れた高強度熱延鋼板

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2287519A1 (fr) * 1974-10-07 1976-05-07 Kobe Steel Ltd Acier structural de bonne aptitude au soudage avec grand apport de chaleur et son procede de fabrication
US20060260719A1 (en) * 2002-07-23 2006-11-23 Toshiaki Mizoguchi Steels product reduced in amount of alumina cluster
JP2005307342A (ja) * 2004-03-25 2005-11-04 Jfe Steel Kk 厚肉低降伏比高張力鋼板の製造方法

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
Hayashi et al., English machine translation of JP 2005-307342, 11-2005, p. 1-15. *
Kasamatsu et al., English machine translation fo FR 2287519A1, 05-1976, p. 1-24. *

Also Published As

Publication number Publication date
CN101490295B (zh) 2012-09-19
CA2657587A1 (fr) 2008-01-17
AU2007273767B2 (en) 2010-08-12
KR20090018167A (ko) 2009-02-19
CA2657587C (fr) 2013-11-26
TWI424069B (zh) 2014-01-21
CN101490295A (zh) 2009-07-22
EP2048254A4 (fr) 2012-11-07
EP2048254A1 (fr) 2009-04-15
AU2007273767A1 (en) 2008-01-17
WO2008007477A1 (fr) 2008-01-17
EP2048254B1 (fr) 2020-08-19
TW200804607A (en) 2008-01-16

Similar Documents

Publication Publication Date Title
JP5093422B2 (ja) 高強度鋼板及びその製造方法
JP4431185B2 (ja) 伸びフランジ性と疲労特性に優れた高強度鋼板およびその溶鋼の溶製方法
JP6293997B2 (ja) 伸びフランジ性、曲げ加工性に優れた高強度鋼板およびその鋼板用の溶鋼の溶製方法
JP5053186B2 (ja) 伸びフランジ性と疲労特性に優れた高強度鋼板およびその溶鋼の溶製方法
JP5158272B2 (ja) 伸びフランジ性と曲げ加工性に優れた高強度鋼板およびその溶鋼の溶製方法
EP2048254B1 (fr) Tole d'acier à haute résistance supérieure dans la formabilité des bords d'étirage et les carastéristiques de fatigue
WO2016148037A1 (fr) Tôle d'acier destinée à la cémentation possédant d'excellentes aptitudes au façonnage à froid et ténacité après traitement thermique de cémentation
JP5158271B2 (ja) 伸びフランジ性と曲げ加工性に優れた高強度鋼板およびその溶鋼の溶製方法
WO2012115181A1 (fr) Feuille d'acier à haute résistance présentant une déformabilité de bordage par étirage supérieure et une aptitude supérieure à la flexion, et procédé de préparation d'acier de lingot
JP5696359B2 (ja) 高強度鋼板およびその溶鋼の溶製方法
JP5205795B2 (ja) 伸びフランジ性と疲労特性に優れた高強度鋼板およびその溶鋼の溶製方法
JP4901346B2 (ja) 伸びフランジ性と疲労特性に優れた高強度鋼板
JP5157235B2 (ja) 伸びフランジ性と疲労特性に優れた高強度鋼板およびその溶鋼の溶製方法
JP5058892B2 (ja) 伸びフランジ性に優れたｄｐ鋼板およびその製造方法

Legal Events

Date Code Title Description
AS Assignment

Owner name: NIPPON STEEL CORPORATION, JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SASAI, KATSUHIRO;OHASHI, WATARU;YAMAMOTO, KENICHI;AND OTHERS;REEL/FRAME:022107/0524

Effective date: 20081225

AS Assignment

Owner name: NIPPON STEEL & SUMITOMO METAL CORPORATION, JAPAN

Free format text: MERGER;ASSIGNOR:NIPPON STEEL CORPORATION;REEL/FRAME:029885/0388

Effective date: 20121001

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION