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WO2018088421A1 - Tôle d'acier mince haute résistance laminée à froid et procédé de production de tôle d'acier mince haute résistance laminée à froid - Google Patents

Tôle d'acier mince haute résistance laminée à froid et procédé de production de tôle d'acier mince haute résistance laminée à froid Download PDF

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Publication number
WO2018088421A1
WO2018088421A1 PCT/JP2017/040219 JP2017040219W WO2018088421A1 WO 2018088421 A1 WO2018088421 A1 WO 2018088421A1 JP 2017040219 W JP2017040219 W JP 2017040219W WO 2018088421 A1 WO2018088421 A1 WO 2018088421A1
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Prior art keywords
less
rolled
cold
steel sheet
hot
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PCT/JP2017/040219
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English (en)
Japanese (ja)
Inventor
美絵 小幡
植田　圭治
金子　真次郎
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JFE Steel Corp
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JFE Steel Corp
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Priority to JP2018512636A priority Critical patent/JP6597889B2/ja
Publication of WO2018088421A1 publication Critical patent/WO2018088421A1/fr
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    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

  • the present invention relates to a high-strength cold-rolled steel sheet and a method for producing a high-strength cold-rolled steel sheet. More specifically, the present invention relates to a high-strength cold-rolled thin steel sheet having a tensile strength TS of 980 MPa or more and suitable for automobile parts and a method for producing the same.
  • Patent Documents 1 to 3 In recent years, from the viewpoint of preservation of the global environment, there has been a demand for improved fuel economy of automobiles, and it has been promoted to apply high-strength cold-rolled thin steel sheets having a tensile strength of 980 MPa or more to body parts and the like (for example, Patent Documents 1 to 3). Furthermore, recently, there has been an increasing demand for improving the collision safety of automobiles, and from the viewpoint of ensuring the safety of passengers in the event of a collision, the tensile strength for structural members such as the skeleton part of a vehicle body is extremely high at 1180 MPa or more. Application of high-strength cold-rolled thin steel sheets having strength has also been studied (for example, Patent Documents 1 to 3).
  • the ductility may be insufficient or the stretch flangeability may be insufficient.
  • an object of the present invention is to provide a high-strength cold-rolled thin steel sheet having a tensile strength of 980 MPa or more and having high ductility and high stretch flangeability, and a method for producing the same.
  • Thin steel plate refers to a steel plate having a thickness of 5 mm or less.
  • a cold-rolled thin steel sheet having a specific composition and structure has a high tensile strength of 980 MPa or more, and has ductility and stretch flangeability.
  • the present invention was completed.
  • the present invention provides the following [1] to [5].
  • the above composition is further mass%, Ti: 0.005% to 0.030%, Nb: 0.005% to 0.030%, B: 0.0001% to 0.0050%
  • Cr 0.05% to 0.20%
  • Cu 0.05% to 0.20%
  • Sb 0.002% to 0.050%
  • Sn 0.002% to 0.000%.
  • Ta 0.001% or more and 0.100% or less
  • Ca 0.0005% or more and 0.0050% or less
  • Mg 0.0005% or more and 0.0050% or less
  • REM 0.0005
  • the high-strength cold-rolled thin steel sheet according to [1] above which contains at least one element selected from the group consisting of% or more and 0.0050% or less.
  • [3] The high-strength cold-rolled thin steel sheet according to [1] or [2], which has a hot-dip galvanized layer, an alloyed hot-dip galvanized layer, or an electrogalvanized layer on the surface.
  • the first stage having a structure in which the sum of martensite and bainite is 80% or more by volume ratio by cooling to a cooling stop temperature T 2 of 500 ° C. or less at an average cooling rate of 5 ° C./s or more.
  • annealing temperature T 3 At annealing temperature T 3, and held 10s or 900s or less, from the annealing temperature T 3, at an average cooling rate of 50 ° C. / s or less 5 ° C. / s or higher, up to 200 ° C. or higher 500 ° C. or less of the cooling stop temperature T 4 cooling, in the cooling stop temperature T 4, by holding 10s or 1800s or less, the method of producing a high strength cold rolled steel sheets having a second-stage annealing process of obtaining a second Danhiyanobe annealed sheet, a.
  • the present invention it is possible to provide a high-strength cold-rolled thin steel sheet having a tensile strength of 980 MPa or more and having high ductility and high stretch flangeability, and a method for producing the same.
  • the high-strength cold-rolled thin steel sheet of the present invention to, for example, an automobile structural member, it is possible to greatly contribute to the weight reduction of the automobile body and to greatly contribute to the improvement of the fuel consumption of the automobile.
  • the high-strength cold-rolled thin steel sheet of the present invention has a composition and a volume ratio of 10% to 70% polygonal ferrite, 5% to 40% bainitic ferrite, 15% to 40% in terms of the composition described later. Residual austenite and a structure having martensite of greater than 0% and less than 30%, the average crystal grain size of the polygonal ferrite is 10.0 ⁇ m or less, and the aspect ratio of the polygonal ferrite is 1 A high-strength cold-rolled thin steel sheet having an average crystal grain size of 2.0 ⁇ m or less and an aspect ratio of the retained austenite of 2.0 or more.
  • composition of the high-strength cold-rolled steel sheet of the present invention will be described first, and then the structure of the high-strength cold-rolled steel sheet of the present invention will be described.
  • the high-strength cold-rolled thin steel sheet of the present invention is, in mass%, C: more than 0.15% and 0.45% or less, Si: 0.50% or more and 2.50% or less, Mn: 1.50% or more. 50% or less, P: 0.001% or more and 0.050% or less, S: 0.0100% or less, N: 0.0100% or less, and Al: 0.010% or more and 1.00%, the balance It has a composition consisting of Fe and inevitable impurities. First, the reason for composition limitation will be described. Hereinafter, unless otherwise specified, “mass%” is simply expressed as “%”.
  • C has a high solid solution strengthening ability, contributes to increase in strength, stabilizes retained austenite, secures retained austenite having a desired volume ratio, and contributes effectively to improving ductility.
  • C needs to contain more than 0.15%.
  • a large content exceeding 0.45% invites concern about deterioration of toughness and weldability and occurrence of delayed fracture.
  • ductility and stretch flangeability are reduced. Therefore, the C content is more than 0.15% and 0.45% or less, preferably 0.18% or more and 0.42% or less, and more preferably 0.20% or more and 0.40% or less.
  • Si is a useful element that has a high solid solution strengthening ability in ferrite, contributes to an increase in strength, suppresses the formation of carbide (cementite), and contributes to stabilization of retained austenite.
  • Si has the effect
  • Si dissolved in ferrite improves work hardening ability and contributes to improvement of ductility of ferrite itself. In order to acquire such an effect, Si needs to contain 0.50% or more.
  • the Si content is 0.50% or more and 2.50% or less, preferably 0.80% or more and 2.00% or less, and more preferably 1.00% or more and 1.80% or less.
  • Mn is an element that contributes effectively to an increase in strength through solid solution strengthening or improvement in hardenability and stabilizes austenite, and is an indispensable element for securing a desired amount of retained austenite. In order to acquire such an effect, Mn needs to contain 1.50% or more. On the other hand, when Mn exceeds 3.50%, it becomes difficult to obtain a desired amount of retained austenite, and martensite is excessively generated. For this reason, content of Mn is 1.50% or more and 3.50% or less, and 2.30% or more and 3.00% or less are preferable.
  • P is an element contributing to an increase in strength by solid solution strengthening, and can be contained in an appropriate amount according to a desired strength.
  • P is an element that has an action of promoting ferrite transformation and is effective in forming a composite structure. In order to acquire such an effect, P needs to contain 0.001% or more.
  • P exceeds 0.050%, weldability is deteriorated and grain boundary fracture due to grain boundary segregation is promoted. For this reason, content of P is 0.001% or more and 0.050% or less, and 0.005% or more and 0.030% or less are preferable.
  • S is an element that segregates at the grain boundaries and embrittles the steel during hot working, and is present in the steel as a sulfide to reduce local deformability, and is preferably reduced as much as possible. % Or less, the above-mentioned adverse effects are acceptable. For this reason, content of S is 0.0100% or less, and 0.0050% or less is preferable. Since excessively reducing S leads to restrictions on production technology or an increase in refining costs, the S content is preferably 0.0001% or more.
  • N is an element that lowers the aging resistance of steel and is preferably reduced as much as possible. However, if it is 0.0100% or less, the above-described adverse effects can be tolerated. For this reason, content of N is 0.0100% or less, and 0.0070% or less is preferable. Since excessively reducing N leads to restrictions on production technology or an increase in refining costs, the N content is preferably 0.0005% or more.
  • Al is a ferrite-forming element and is an element that improves the balance between strength and ductility (strength-ductility balance). In order to acquire such an effect, it is necessary to contain Al 0.010% or more. On the other hand, the content of Al exceeding 1.00% causes a decrease in surface properties. For this reason, content of Al is 0.010% or more and 1.00% or less, 0.030% or more and 0.500% or less are preferable, and 0.050% or more and 0.450% or less are more preferable.
  • the above composition is a basic composition, but the composition is further Ti: 0.005% to 0.030%, Nb: 0.005% to 0.030%, B: 0.0001% to 0 .0050% or less, Cr: 0.05% to 0.20%, Cu: 0.05% to 0.20%, Sb: 0.002% to 0.050%, Sn: 0.002% 0.050% or less, Ta: 0.001% or more and 0.100% or less, Ca: 0.0005% or more and 0.0050% or less, Mg: 0.0005% or more and 0.0050% or less, and REM: It may contain at least one element selected from the group consisting of 0.0005% or more and 0.0050% or less.
  • Ti and Nb are both effective elements that suppress the coarsening of crystal grains during heating in the annealing step or the like and contribute to the refinement and homogenization of the steel sheet structure after annealing. In order to obtain such effects, it is preferable to contain Ti: 0.005% or more and Nb: 0.005% or more, respectively. On the other hand, when the content exceeds Ti: 0.030% and Nb: 0.030%, respectively, Ti-based and Nb-based precipitates are excessively generated in the ferrite, so that the ductility may be lowered. For this reason, the content of Ti is preferably 0.005% or more and 0.030% or less, and more preferably 0.010% or more and 0.020% or less. The Nb content is preferably 0.005% or more and 0.030% or less, and more preferably 0.010% or more and 0.020% or less.
  • (B) B is an effective element that contributes to strengthening of the steel sheet through improvement of hardenability. In order to acquire such an effect, it is preferable to contain 0.0001% or more. On the other hand, if the content exceeds 0.0050%, the content of martensite is excessively increased, and the increase in strength is excessively increased, which may cause a decrease in ductility. For this reason, when B is contained, the content of B is preferably 0.0001% or more and 0.0050% or less, and more preferably 0.0005% or more and 0.0030% or less.
  • (Cr) Cr contributes to the strengthening of the steel sheet by solid solution strengthening, stabilizes austenite during cooling in the annealing process, and facilitates complexation of the structure.
  • the content is preferably 0.05% or more.
  • the content of Cr is preferably 0.05% or more and 0.20% or less.
  • (Cu) Cu contributes to the strengthening of the steel sheet by solid solution strengthening, stabilizes austenite during cooling in the annealing process, and facilitates complexation of the structure.
  • the content is preferably 0.05% or more.
  • the content of Cu is preferably 0.05% or more and 0.20% or less.
  • Sb and Sn have an effect of suppressing decarburization of the steel sheet surface layer (a region of several tens of ⁇ m) caused by nitriding and oxidation of the steel sheet surface.
  • By suppressing such nitriding and oxidation of the steel sheet surface layer it is possible to prevent a reduction in the amount of martensite produced on the steel sheet surface. As a result, it is effective to secure a desired strength.
  • variations in strength and elongation due to temperature fluctuations during annealing can be reduced, which is also effective in ensuring manufacturing stability.
  • the toughness may be lowered.
  • the content of Sb and Sn is preferably 0.002% or more and 0.050% or less, respectively.
  • Ta Ta generates carbides and carbonitrides and contributes to increasing the strength of the steel sheet.
  • the content is preferably 0.001% or more.
  • the content of Ta is preferably 0.001% or more and 0.100% or less.
  • Ca, Mg and REM are all elements used for deoxidation, and have an effect of improving the adverse effect on the local ductility and stretch flangeability of sulfides by making the shape of sulfides spherical. Yes, it can contain 1 type or 2 types or more as needed.
  • Ca, Mg, and REM are each preferably contained in a content of 0.0005% or more.
  • the content of Ca, Mg and REM is preferably 0.0005% or more and 0.0050% or less, respectively.
  • Remainder Fe and inevitable impurities In the above composition, the balance other than the above components consists of Fe (remainder Fe) and inevitable impurities.
  • the high-strength cold-rolled thin steel sheet of the present invention has a structure (composite structure) composed of polygonal ferrite, bainitic ferrite, retained austenite, and martensite.
  • the high-strength cold-rolled steel sheet of the present invention has a volume ratio of 10% or more and 70 at a position corresponding to 1 ⁇ 4 of the plate thickness in the plate thickness direction from the surface (plate thickness 1 ⁇ 4 position).
  • volume ratio of polygonal ferrite 10% to 70%
  • Polygonal ferrite contributes to improvement of ductility (elongation). For this reason, it is set as the structure
  • ⁇ Volume ratio of bainitic ferrite: 5% to 40% Bainitic ferrite has a high dislocation density and contributes not only to an increase in strength but also to an improvement in stretch flangeability (hole expansion ratio). Furthermore, in order to concentrate C in untransformed austenite, it is necessary to secure desired retained austenite. In order to acquire such an effect, bainitic ferrite is made into 5% or more by volume ratio. On the other hand, if the bainitic ferrite exceeds 40% by volume, the desired high strength cannot be ensured. For this reason, the volume ratio of bainitic ferrite is 5% or more and 40% or less.
  • the “bainitic ferrite” referred to here is a ferrite generated by the upper bainite transformation, and has a higher dislocation density than polygonal ferrite.
  • volume ratio of retained austenite more than 15% and 40% or less
  • Residual austenite itself is rich in ductility, but is a structure that contributes to further improving ductility by strain-induced transformation, and contributes to improving ductility and improving the strength-ductility balance.
  • the retained austenite needs to exceed 15% by volume.
  • the volume ratio of retained austenite is 15% to 40%, preferably 17% to 40%.
  • the “martensite” here includes fresh martensite and tempered martensite. When martensite exceeds 30% in volume ratio, desired ductility and stretch flangeability cannot be secured. On the other hand, in order to ensure a desired high strength, martensite is preferably in a volume ratio exceeding 0% (not including 0%) and 3% or more. For this reason, the volume ratio of martensite is more than 0% and 30% or less, and preferably 3% or more and 30% or less.
  • Average crystal grain size of polygonal ferrite 10.0 ⁇ m or less
  • the average crystal grain size of polygonal ferrite is preferably 8.0 ⁇ m or less.
  • the lower limit of the average grain size of polygonal ferrite is not particularly limited, but is, for example, 3.0 ⁇ m or more.
  • aspects ratio of polygonal ferrite 1.5 or more
  • the aspect ratio of polygonal ferrite is 1.5 or more, and preferably 2.0 or more.
  • the upper limit of the aspect ratio of polygonal ferrite is not particularly limited, but is, for example, 4.0 or less.
  • Average crystal grain size of retained austenite 2.0 ⁇ m or less
  • the average crystal grain size of retained austenite needs to be 2.0 ⁇ m or less.
  • the average crystal grain size of retained austenite is preferably 1.7 ⁇ m or less.
  • the lower limit of the average crystal grain size of retained austenite is not particularly limited, but is, for example, 0.3 ⁇ m or more.
  • aspects ratio of retained austenite 2.0 or more
  • the aspect ratio of retained austenite is 2.0 or more, and preferably 2.3 or more.
  • the upper limit of the aspect ratio of retained austenite is not particularly limited, but is, for example, 5.0 or less.
  • non-recrystallized ferrite, pearlite, cementite and the like may be further generated.
  • the volume ratio is preferably 10% or less for non-recrystallized ferrite, 5% or less for pearlite, and 5% or less for cementite.
  • the high-strength cold-rolled thin steel sheet of the present invention having the above composition and the above structure may further have a plating layer on its surface in order to improve corrosion resistance.
  • a hot dip galvanized layer, an alloyed hot dip galvanized layer, or an electrogalvanized layer is preferable.
  • the hot-dip galvanized layer, the alloyed hot-dip galvanized layer, and the electrogalvanized layer are not particularly limited, and are conventionally known hot-dip galvanized layer, conventionally known alloyed hot-dip galvanized layer, and conventionally known, respectively.
  • the electrogalvanized layer is preferably used.
  • the electrogalvanized layer may be a zinc alloy plated layer obtained by adding an appropriate amount of elements such as Fe, Cr, Ni, Mn, Co, Sn, Pb, or Mo to Zn according to the purpose. .
  • the manufacturing method of the present invention generally includes the above-described high-strength cold-rolled thin film of the present invention by sequentially performing hot rolling, pickling, cold rolling, and annealing on a steel material having the above composition. It is a method of obtaining a steel plate. And in the manufacturing method of this invention, the process of annealing is divided into two processes.
  • the steel material is not particularly limited as long as it is a steel material having the above composition.
  • the steel material having the above composition is melted by a conventional melting method using a converter or the like, and a continuous casting method is used.
  • the obtained slab having a predetermined dimension is preferably used.
  • a steel piece (steel material) may be manufactured by ingot-bundling rolling.
  • a hot rolling process is a process of obtaining a hot-rolled sheet by hot-rolling the steel raw material which has the said composition.
  • the hot rolling process is not particularly limited as long as it is a process in which a steel material having the above composition is heated and subjected to hot rolling to obtain a hot rolled sheet having a predetermined size, and a normal hot rolling process is applied. it can.
  • a normal hot rolling process for example, a steel material is heated to a heating temperature of 1100 ° C. or more and 1250 ° C. or less, and the heated steel material is hot rolled at a hot rolling outlet temperature of 850 ° C. or more and 950 ° C. or less.
  • an appropriate post-rolling cooling (specifically, for example, an average cooling rate of 40 ° C./s to 100 ° C./s in a temperature range of 450 ° C. to 950 ° C.)
  • the steel sheet is wound at a coiling temperature of 450 ° C. or higher and 650 ° C. or lower to obtain a hot-rolled sheet having a predetermined size and shape.
  • the pickling step is a step of pickling the hot-rolled sheet obtained through the hot rolling step.
  • the pickling step is not particularly limited as long as it can be pickled to such an extent that cold rolling can be performed on the hot-rolled sheet.
  • a conventional pickling step using hydrochloric acid or sulfuric acid can be applied.
  • the cold rolling process is a process of performing cold rolling on the hot-rolled sheet that has undergone the pickling process. More specifically, the cold rolling step is a step of obtaining a thin cold rolled plate having a predetermined thickness by subjecting the hot rolled plate subjected to pickling to cold rolling with a rolling reduction of 30% or more.
  • ⁇ Cold rolling reduction 30% or more>
  • the rolling reduction of cold rolling is 30% or more.
  • the processing amount is insufficient, and recrystallization of the processed ferrite cannot be sufficiently achieved in the subsequent annealing step.
  • the upper limit of the rolling reduction is determined by the capability of the cold rolling mill, but if the rolling reduction is too high, the rolling load increases and the productivity may decrease. For this reason, the rolling reduction is preferably 70% or less.
  • the number of rolling passes and the rolling reduction per pass are not particularly limited.
  • An annealing process is a process which anneals the thin cold-rolled sheet obtained through the cold rolling process, and is a process including the 1st stage annealing process and 2nd stage annealing process mentioned later in detail.
  • First stage annealing process a thin cold-rolled sheet is heated at an annealing temperature T 1 of the 800 ° C. or higher 950 ° C. or less, from the annealing temperatures T 1, at 5 ° C. / s or more average cooling rate, cooling below 500 °C by cooling to stop temperature T 2, which is a step of obtaining a first Danhiyanobe annealed sheets having tissue total of martensite and bainite is not less than 80% by volume.
  • annealing temperature T 1 800 ° C. or higher and 950 ° C. or lower
  • the annealing temperature T 1 is less than 800 ° C., too much amount of generated ferrite during annealing, it can not be secured on the total amount of the desired martensite and bainite.
  • it exceeds annealing temperature T 1 is 950 ° C., and the austenite grains are excessively coarsened, since the formation of ferrite is suppressed in the second stage annealing process, a second Danhiyanobe obtained through the second-stage annealing process Martensite is excessively generated in the annealed plate.
  • annealing temperatures T 1 is 800 ° C. or higher 950 ° C. or less.
  • Holding time at the annealing temperatures T 1 is not particularly limited, for example, is 10s or 900s or less.
  • the cooling is preferably gas cooling, but may be performed in combination with furnace cooling and mist cooling.
  • Cooling stop temperature T 2 500 ° C. or less
  • the cooling stop temperature T 2 In tissue after cooling, to 80% or more by volume of the total of martensite and bainite, the cooling stop temperature T 2 and the temperature of the temperature range below 500 °C. Cooling stop temperature T 2 is preferably 300 ° C. or higher 480 ° C. or less.
  • the second-stage annealing process may be continued. After cooling is stopped, it is allowed to cool, and after cooling to room temperature, it may be shifted to the second stage annealing step.
  • total volume ratio of martensite and bainite 80% or more
  • the second stage obtained through the second stage annealing step when the sum of martensite and bainite is less than 80% in volume ratio.
  • a cold-rolled annealed sheet it becomes difficult to secure desired retained austenite and it is difficult to secure polygonal ferrite having a desired shape (aspect ratio).
  • “bainite” includes upper bainite and lower bainite.
  • Second stage annealing process a first Danhiyanobe annealed sheets obtained through the first-stage annealing process, at 700 ° C. or higher 850 ° C. below the annealing temperature T 3, and held 10s or 900s or less, the annealing temperature T 3 from an average cooling rate of 50 ° C. / s or less 5 ° C. / s or more, cooled to 200 of the cooling stop ° C. or higher 500 ° C. or less temperature T 4, the cooling stop temperature T 4, by holding 10s or 1800s or less, This is a step of obtaining a second-stage cold-rolled annealed plate.
  • the annealing temperature T 3 700 °C more than 850 °C or less.
  • the annealing temperature T 3 is lower than 700 ° C., can not be secured a sufficient amount of austenite during annealing, final desired amount of retained austenite and bainitic ferrite can not be secured.
  • the annealing temperature T 3 is higher than 850 ° C., since the austenite single-phase region, and finally, after that can not be generated residual austenite desired amount, residual austenite with a desired aspect ratio, and a desired aspect ratio
  • the annealing temperature T 3 is at 700 ° C. or higher 850 ° C. or less, preferably 720 ° C. or higher 830 ° C. or less.
  • Holding time at the annealing temperature T 3 is less than 10s, can not be ensured a sufficient amount of austenite during annealing, final desired amount of retained austenite and bainitic ferrite can not be secured.
  • the holding time at the annealing temperature T 3 is when it comes to long beyond 900s, resulting grain coarsening, eventually no longer able to generate residual austenite desired amount. Therefore, the holding time at the annealing temperature T 3 is 10s or 900s or less.
  • the average cooling rate from the annealing temperature T 3 to a cooling stop temperature T 4 is lower than 5 ° C. / s, and generates a large amount of polygonal ferrite and pearlite during cooling, it can be ensured desired amount of bainitic ferrite Disappear.
  • the average cooling rate from the annealing temperature T 3 to a cooling stop temperature T 4 is greater than 50 ° C. / s, the low temperature transformation structure such as martensite is generated excessively. Therefore, the average cooling rate from the annealing temperature T 3 to a cooling stop temperature T 4 is 50 ° C. / s or less 5 ° C. / or.
  • the cooling is preferably gas cooling, but can be performed by combining furnace cooling and mist cooling.
  • the cooling stop temperature T 4 is 200 ° C. or more and 500 ° C. or less. If the cooling stop temperature T 4 is lower than 200 ° C., during retention after cooling down, a large amount of martensite is produced, it can not be ensured the desired tissue (volume ratio and aspect ratio of retained austenite). On the other hand, the cooling stop temperature T 4 is more than 500 ° C., during retention after cooling down, to generate a large amount of polygonal ferrite and pearlite, it can not be ensured the desired tissue. Specifically, for polygonal ferrite, the volume ratio is excessive, while the aspect ratio is excessive. Moreover, the volume fraction of bainitic ferrite becomes too small. Furthermore, the volume fraction and aspect ratio of retained austenite are too small. Therefore, the cooling stop temperature T 4 is 200 ° C. or higher 500 ° C. or less.
  • Second Danhiyanobe annealed sheet after holding in the cooling stop temperature T 4 cools.
  • This cooling is not particularly limited, and the cooling can be performed to a desired temperature such as room temperature by an arbitrary method such as cooling.
  • the second-stage cold-rolled annealed sheet obtained through the second-stage annealing process becomes the high-strength cold-rolled thin steel sheet of the present invention.
  • the second-stage cold-rolled annealed sheet may be referred to as “cold-rolled thin steel sheet”.
  • the second-stage cold-rolled annealed plate (cold-rolled thin steel plate) obtained through the second-stage annealing step may be further subjected to a plating treatment to form a plating layer on the surface thereof.
  • the second-stage cold-rolled annealed plate having a plating layer formed on the surface is the high-strength cold-rolled thin steel plate of the present invention.
  • hot dip galvanizing treatment hot dip galvanizing treatment and alloying treatment, or electrogalvanizing treatment is preferable.
  • the hot dip galvanizing treatment, the hot dip galvanizing treatment and the alloying treatment, and the electrogalvanizing treatment are not particularly limited, and are conventionally known hot dip galvanizing treatment, conventionally known hot dip galvanizing treatment and alloying treatment, respectively.
  • a conventionally known electrogalvanizing treatment is preferably used.
  • pretreatment such as degreasing and phosphate treatment may be performed prior to the plating treatment.
  • the hot dip galvanizing treatment for example, a conventional continuous hot dip galvanizing line is used to immerse the second stage cold-rolled annealing plate in a hot dip galvanizing bath and form a predetermined amount of hot dip galvanized layer on the surface. It is preferable that When immersed in a hot dip galvanizing bath, the temperature of the second-stage cold-rolled annealed plate is not less than the temperature of the hot dip galvanizing bath temperature ⁇ 50 ° C. and not more than the temperature of the hot dip galvanizing bath temperature + 80 ° C. by reheating or cooling. It is preferable to adjust within the range.
  • the temperature of the hot dip galvanizing bath is preferably 440 ° C or higher, and more preferably 500 ° C or lower.
  • the hot dip galvanizing bath may contain Al, Fe, Mg, Si or the like in addition to pure zinc.
  • the adhesion amount of the hot-dip galvanized layer can be adjusted to a desired adhesion amount by adjusting gas wiping or the like, and is preferably about 45 g / m 2 per side.
  • the plated layer (hot galvanized layer) formed by the hot dip galvanizing process may be an alloyed hot dip galvanized layer by performing a usual alloying process as necessary.
  • the temperature for the alloying treatment is preferably 460 ° C. or more and 600 ° C. or less.
  • adjusting the effective Al concentration in the hot dip galvanizing bath to a range of 0.10% by mass or more and 0.22% by mass or less from the viewpoint of securing a desired plating appearance. preferable.
  • the electrogalvanizing treatment is preferably, for example, a treatment of forming a predetermined amount of electrogalvanized layer on the surface of the second stage cold-rolled annealed plate using a conventional electrogalvanizing line.
  • the adhesion amount of the electrogalvanized layer can be adjusted to a predetermined adhesion amount by adjusting the sheet passing speed or the current value, and is preferably about 30 g / m 2 per side.
  • the annealing process was a two-stage process consisting of a first stage annealing process and a second stage annealing process. Holding time at the annealing temperature T 1 of the first stage annealing process was 100s. After the first stage annealing step, a specimen for observing the structure was collected from the first stage cold-rolled annealed sheet, and the structure was observed.
  • a hot-dip galvanized layer is formed on the surface of the hot-dip galvanized thin steel plate after the annealing has been completed. It was.
  • the hot dip galvanizing process using a continuous hot dip galvanizing line, the second-stage cold-rolled annealed plate (cold-rolled thin steel plate) is reheated to a temperature in the range of 430 ° C. or higher and 480 ° C. or lower as necessary. It was immersed in a hot dip galvanizing bath (bath temperature: 470 ° C.).
  • the bath composition was Zn-0.18 mass% Al. At this time, in some hot-dip galvanized steel sheets, the bath composition was Zn-0.14 mass% Al, and after the plating treatment, alloying treatment was performed at 520 ° C. to obtain an alloyed hot-dip galvanized thin steel sheet. .
  • the Fe concentration in the plating layer was 9% by mass or more and 12% by mass or less.
  • an electric galvanizing line is used after the annealing, so that the amount of plating is 30 g / m 2 per side. A galvanizing treatment was performed to obtain an electrogalvanized sheet steel.
  • the second-stage cold-rolled annealed sheet (cold-rolled sheet steel) that does not form a plating layer is “CR”
  • the hot-dip galvanized sheet steel is “GI”
  • the galvannealed sheet steel is “GA”.
  • the electrogalvanized sheet steel was denoted as “EG”.
  • tissue of the test piece was observed in the visual field of the range of 40 micrometers x 40 micrometers, respectively, and it imaged and obtained the SEM image.
  • the fraction (area ratio) of each tissue was determined by image analysis. The obtained value was treated as a volume fraction and used as a fraction of each tissue.
  • “Image-Pro” (trade name) manufactured by Media Cybernetics was used as analysis software.
  • polygonal ferrite is gray, martensite and retained austenite are white, so each structure was judged from the color tone.
  • a structure in which retained austenite and cementite are observed in fine lines or dots in ferrite is bainite.
  • the volume ratio of the retained austenite obtained separately was subtracted from the volume ratio of the structure exhibiting white to obtain the volume ratio of martensite.
  • the major axis and minor axis of each polygonal ferrite were determined by image analysis, the area was calculated from the determined major axis and minor axis, and the equivalent circle diameter was calculated from the calculated area. The values were arithmetically averaged to obtain the average crystal grain size of polygonal ferrite. From the obtained major axis and minor axis, the aspect ratio of each polygonal ferrite was calculated, and the obtained values were arithmetically averaged to obtain the polygonal ferrite aspect ratio (average).
  • Test specimens for observation with a transmission electron microscope were collected from the second-stage cold-rolled annealed plate (cold-rolled thin steel plate) or the second-stage cold-rolled annealed plate (cold-rolled thin steel plate) on which the plating layer was formed.
  • the collected specimen was ground and polished (mechanical polishing and electrolytic polishing) so that a position corresponding to 1/4 of the plate thickness was an observation position, and a thin film sample was obtained.
  • tissue was observed using the transmission electron microscope (TEM) (magnification: 15000 times), and 20 or more visual fields were imaged in the visual field of the range of 3 micrometers x 3 micrometers, and the TEM image was obtained.
  • TEM transmission electron microscope
  • the volume fraction of bainitic ferrite and the average crystal grain size and aspect ratio (average) of retained austenite were determined by image analysis.
  • the average crystal grain size of retained austenite was obtained by calculating the area of each retained austenite, calculating the equivalent circle diameter from the determined area, and arithmetically averaging the obtained values to obtain the average crystal grain size of retained austenite.
  • the major axis and the minor axis of each retained austenite are obtained by image analysis, the aspect ratio of each retained austenite is calculated, the obtained value is arithmetically averaged, and the aspect ratio of the retained austenite (average) ).
  • “Image-Pro” (trade name) of Media Cybernetics was used as the analysis software in the same manner as the image analysis of the SEM image.
  • Test specimens were collected. The collected specimen was ground and polished so that the position corresponding to 1/4 of the plate thickness was the measurement surface. About the test piece which grind
  • the volume fraction of retained austenite In calculating the volume fraction of retained austenite, the integrated intensity of the peaks of the ⁇ 111 ⁇ , ⁇ 200 ⁇ , ⁇ 220 ⁇ and ⁇ 311 ⁇ faces of austenite and the ⁇ 110 ⁇ , ⁇ 200 ⁇ and ⁇ 211 ⁇ faces of ferrite The intensity ratio was calculated for all the combinations. The average value thereof was obtained, and the volume fraction of retained austenite was calculated.
  • TS 980 MPa or more, it can be evaluated as high strength.
  • TS ⁇ El is 24500 MPa ⁇ % or more, and when TS is 1180 MPa or more, if TS ⁇ El is 23600 MPa ⁇ % or more, it can be evaluated that the strength-ductility balance is good.
  • each of the cold-rolled thin steel sheets (including the cold-rolled thin steel sheet on which the plating layer is formed) of the present invention has high strength, high ductility, excellent strength-ductility balance, and elongation. Flangeability was also good.
  • the cold-rolled thin steel sheet of the comparative example (including the cold-rolled thin steel sheet on which the plating layer is formed) has ductility and / or stretch flange even if the strength is insufficient or the strength is sufficient. Sex was insufficient.

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Abstract

Cette invention concerne : une tôle d'acier mince haute résistance laminée à froid qui présente une résistance à la traction de 980 MPa ou plus, tout en présentant une ductilité élevée et une haute capacité de formation de bords par étirage ; et un procédé de production de cette tôle d'acier mince haute résistance laminée à froid. Cette feuille d'acier mince haute résistance laminée à froid a une composition spécifique et une structure qui comprend, en pourcentage en volume, de 10 % à 70 % (inclus) de ferrite polygonale, de 5 % à 40 % (inclus) de ferrite bainitique, plus de 15 % et jusqu'à 40 % d'austénite résiduelle et de plus de 0 % et jusqu'à 30 % de martensite. La ferrite polygonale a une taille moyenne du grain cristallin de 10,0 µm ou moins ; et la ferrite polygonale a un rapport d'aspect de 1,5 ou plus. L'austénite résiduelle a une taille moyenne du grain cristallin de 2,0 µm ou moins ; et l'austénite résiduelle a un rapport d'aspect de 2,0 ou plus.
PCT/JP2017/040219 2016-11-10 2017-11-08 Tôle d'acier mince haute résistance laminée à froid et procédé de production de tôle d'acier mince haute résistance laminée à froid Ceased WO2018088421A1 (fr)

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CN110093491A (zh) * 2019-05-17 2019-08-06 中冶赛迪工程技术股份有限公司 一种冷轧热镀锌双相钢及其制造方法
WO2020174805A1 (fr) * 2019-02-25 2020-09-03 Ｊｆｅスチール株式会社 Tôle d'acier à haute résistance et procédé de fabrication de celle-ci
JPWO2022019209A1 (fr) * 2020-07-20 2022-01-27
CN114945694A (zh) * 2020-01-14 2022-08-26 日本制铁株式会社 钢板及其制造方法
CN115151673A (zh) * 2020-02-28 2022-10-04 杰富意钢铁株式会社 钢板、构件和它们的制造方法
CN115362275A (zh) * 2020-03-31 2022-11-18 杰富意钢铁株式会社 钢板、部件及其制造方法
CN115362279A (zh) * 2020-03-31 2022-11-18 杰富意钢铁株式会社 钢板、部件及其制造方法
EP4166685A4 (fr) * 2020-06-11 2023-11-22 Baoshan Iron & Steel Co., Ltd. Acier à ultra-haute résistance présentant une excellente plasticité et son procédé de fabrication
WO2024202804A1 (fr) * 2023-03-31 2024-10-03 Ｊｆｅスチール株式会社 Feuille d'acier, élément et leurs procédés de production
US12534784B2 (en) 2020-06-11 2026-01-27 Baoshan Iron & Steel Co., Ltd. Ultra-high-strength steel having excellent plasticity and method for manufacturing same

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WO2020174805A1 (fr) * 2019-02-25 2020-09-03 Ｊｆｅスチール株式会社 Tôle d'acier à haute résistance et procédé de fabrication de celle-ci
JP6809647B1 (ja) * 2019-02-25 2021-01-06 Ｊｆｅスチール株式会社 高強度鋼板およびその製造方法
US12365961B2 (en) 2019-02-25 2025-07-22 Jfe Steel Corporation High strength steel sheet and method for manufacturing the same
CN110093491A (zh) * 2019-05-17 2019-08-06 中冶赛迪工程技术股份有限公司 一种冷轧热镀锌双相钢及其制造方法
CN114945694A (zh) * 2020-01-14 2022-08-26 日本制铁株式会社 钢板及其制造方法
CN115151673B (zh) * 2020-02-28 2024-04-19 杰富意钢铁株式会社 钢板、构件和它们的制造方法
CN115151673A (zh) * 2020-02-28 2022-10-04 杰富意钢铁株式会社 钢板、构件和它们的制造方法
CN115362279B (zh) * 2020-03-31 2024-03-01 杰富意钢铁株式会社 钢板、部件及其制造方法
CN115362279A (zh) * 2020-03-31 2022-11-18 杰富意钢铁株式会社 钢板、部件及其制造方法
CN115362275B (zh) * 2020-03-31 2024-03-01 杰富意钢铁株式会社 钢板、部件及其制造方法
CN115362275A (zh) * 2020-03-31 2022-11-18 杰富意钢铁株式会社 钢板、部件及其制造方法
US12480175B2 (en) 2020-03-31 2025-11-25 Jfe Steel Corporation Steel sheet, member, and method for producing them
EP4166685A4 (fr) * 2020-06-11 2023-11-22 Baoshan Iron & Steel Co., Ltd. Acier à ultra-haute résistance présentant une excellente plasticité et son procédé de fabrication
US12534784B2 (en) 2020-06-11 2026-01-27 Baoshan Iron & Steel Co., Ltd. Ultra-high-strength steel having excellent plasticity and method for manufacturing same
JP7417165B2 (ja) 2020-07-20 2024-01-18 日本製鉄株式会社 鋼板及びその製造方法
WO2022019209A1 (fr) * 2020-07-20 2022-01-27 日本製鉄株式会社 Tôle d'acier et son procédé de production
JPWO2022019209A1 (fr) * 2020-07-20 2022-01-27
WO2024202804A1 (fr) * 2023-03-31 2024-10-03 Ｊｆｅスチール株式会社 Feuille d'acier, élément et leurs procédés de production
JP7616491B1 (ja) * 2023-03-31 2025-01-17 Ｊｆｅスチール株式会社 鋼板、部材およびそれらの製造方法

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