HIGH-STRENGTH STEEL SHEET, IMPACT ABSORPTION ELEMENT AND METHOD FOR MANUFACTURING THE HIGH-STRENGTH STEEL SHEET

Abstract

The objectives are to provide a high-strength steel sheet and a shock energy absorption element that have an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or greater, and that also have excellent uniform ductility, pliability, and compression performance, and to provide a method for manufacturing the high-strength steel sheet. A high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or greater. The high-strength steel sheet has a specific chemical composition. The high-strength steel sheet has a microstructure in which ferrite is present in an area fraction of 30.0% or more and less than 80.0%, martensite is present in an area fraction of 3.0% or more and less than 30.0%, and retained austenite is present in a volume fraction of 12%.0% or more, the ferrite has an average grain size of 5.0 µm or less, the retained austenite has an average grain size of 2.0 µm or less, a value obtained by dividing a Mn content (% by mass) of the retained austenite by a Mn content (% by mass) of steel is 1.50 or higher, 15% or more of all austenite grains retained in the retained austenite have an aspect ratio of 3.0 or higher, and 15% or more of all austenite grains retained in the retained austenite have an aspect ratio less than 2.0, wherein a value obtained by dividing a volume fraction V?a by a volume fraction V?b is 0.40 or greater, where the volume fraction V?a is a volume fraction of austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C, and the volume fraction V?b is a volume fraction of austenite retained before the hot tensile test at 150°C.

Description

High-strength steel sheet, shock-absorbing element, and method for manufacturing high-strength steel sheet FIELD OF INVENTION The present invention relates to a high-strength steel sheet suitable for use in impact energy absorbing elements used in the automotive field and also relates to a collision energy absorbing element. In particular, the present invention relates to a high-strength steel sheet and a crash energy absorbing element having an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or higher and also having excellent uniform ductility, foldability, compression performance, and the present invention also relates to a method for manufacturing the high-strength steel sheet. BACKGROUND OF THE INVENTION In recent years, improving the fuel efficiency of motor vehicles has been an important issue in terms of global environmental protection. Consequently, efforts are being made to reduce the weight of the vehicle body itself by increasing the strength of a vehicle body material, thereby reducing the thickness of the material. Furthermore, the social demand for improving the collision safety of motor vehicles is further increasing, and there is a need not only to increase the strength of a steel sheet but also to develop a steel sheet with excellent collision resistance (compressive performance) that can be exhibited in the event of a collision during vehicle use, and to develop components based on it. However, the steel sheets used in the impact energy absorbing elements, which are the front side members and the rear side members, have a tensile strength (TS) of less than 850 MPa. This is because steel sheets with higher strength have reduced formability, e.g., reduced local ductility, bendability, and the like, and therefore crack in a flexural compression test or an axial compression test simulating a crash test, indicating an inability to sufficiently absorb impact energy. A proposed steel sheet with both high strength and high ductility is a high-strength steel sheet that utilizes the stress-induced transformation of retained austenite. The high-strength steel sheet has a microstructure that includes retained austenite. During forming, the retained austenite facilitates forming, and after forming, the retained austenite transforms into martensite; as a result, high strength is achieved. For example, Patent Literature 1 describes a high-strength steel sheet with a tensile strength of 1,000 MPa or higher and a total elongation (EL) of 30% or more. The high-strength steel sheet utilizes the stress-induced transformation of retained austenite and has very high ductility.Furthermore, Patent Literature 2 describes an invention that realizes a high strength-ductility balance, which is achieved by using a high Mn steel and performing a heat treatment in a ferrite-austenite two-phase temperature region. Furthermore, Patent Literature 3 describes an invention that improves local ductility, noefrnn / zznz / e / YiAi which is achieved by using a high Mn steel to obtain a hot-rolled microstructure including bainite and martensite; and performing annealing and tempering to form retained fine austenite and obtain a microstructure including tempered bainite or tempered martensite.In addition, Patent Literature 4 describes a high-strength steel sheet, a high-strength hot-dip galvanized steel sheet, and a high-strength hot-dip galvanized steel sheet that have an ultimate tensile strength (TS) of 780 MPa or higher and can be used in impact absorption elements in collision events. List of appointments Patent literature PTL 1: Japanese Unexamined Patent Application Publication No. 61-157625 PTL 2: Japanese Unexamined Patent Application Publication No. 1-259120 PTL 3: Japanese Unexamined Patent Application Publication No. 2003-138345 PTL 4: Japanese Unexamined Patent Application Publication No. 2015-78394 BRIEF DESCRIPTION OF THE INVENTION Technical problem The high-strength steel sheet described in Patent Literature 1 is manufactured by performing a process called bainitic quenching, in which a steel sheet comprising C, Si, and Mn as basic components is bainitically quenched, and subsequently, the resulting steel sheet is cooled to a temperature within a bainite transformation temperature range and maintained at an isothermal temperature. The bainitic quenching process causes austenite to be enriched with C, and consequently, retained austenite is formed. In order to obtain a large amount of retained austenite, it is necessary to add a large amount of C, that is, a C content greater than 0.3% is required. However, when the amount of C in the steel is high, the spot weldability is reduced, and the reduction is significant when the amount of C, in terms of content, is greater than 0.3%.Consequently, it is difficult to use the high-strength steel sheet described in Patent Literature 1 as a steel sheet for automobiles in practice. Furthermore, in the invention described in Patent Literature 1, a primary objective is to improve the ductility of a high-strength steel sheet, and therefore, bendability and compression performance are not considered. Furthermore, in the invention described in Patent Literature 2, improving ductility, particularly uniform ductility, by enriching untransformed austenite with Mn is not described, and therefore, there is room for improving formability.Furthermore, in the steel sheet described in Patent Literature 3, a microstructure includes a large amount of bainite or martensite that has been tempered at a high temperature, and therefore, it is difficult to ensure strength; furthermore, an amount of retained austenite to improve local ductility is limited, and consequently, an overall elongation is insufficient. Furthermore, in the high-strength steel sheet, the high-strength hot-dip galvanized steel sheet, and the high-strength post-zinc-plated heat-treated steel sheet described in Patent Literature 4, an amount of retained austenite is about 2%, and therefore, ductility, in particular, uniform ductility, is low and insufficient. The present invention has been made in view of the above-described problems, and the objects of the present invention are to provide a high-strength steel sheet and a norfrnn / zznz / e / YiAi crash energy absorbing member having an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or greater and also having excellent uniform ductility, foldability, and compression performance, and to provide a method for manufacturing the high-strength steel sheet. Solution In order to obtain a high-strength steel sheet and a crash energy absorbing member having an ultimate elongation (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or more and also having excellent uniform ductility, foldability, and compression performance, the present inventors diligently conducted studies from the viewpoint of a chemical composition of a steel sheet and control of a microstructure thereof and consequently made the following discoveries. Specifically, it was found that it is possible to obtain a high-strength steel sheet and crash energy absorbing member with a yield strength (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or greater and also featuring excellent uniform ductility, foldability, and compression performance as follows. A chemical composition should be a specific chemical composition, in which, in particular, an Mn content equal to or greater than 3.10% by mass and equal to or less than 6.00% by mass is controlled. A microstructure shall be controlled to be one in which ferrite is present in an area fraction of 30.0% or more and less than 80.0%, martensite is present in an area fraction of 3.0% or more and 30.0% or less, retained austenite is present in a volume fraction of 12.0% or more, ferrite has an average grain size of 5.0 μm or less, the retained austenite has an average grain size of 2.0 gm or less, a value obtained by dividing a Mn content (mass %) of the retained austenite by a Mn content (mass %) of the steel is 1.50 or more, 15% or more of all austenite grains retained in the retained austenite have an aspect ratio of 3.0 or more, and 15% or more of all austenite grains retained in the retained austenite have an aspect ratio of less than 2.0, wherein a value obtained by dividing a volume fraction Vya by a volume fraction Vyb is 0.40 or more, where the volume fraction Vya is a volume fraction of austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C, and the volume fraction of volume Vyb is a volume fraction of retained austenite before the hot tensile test at 150°C. The present invention has been made based on the discoveries described above, and a summary of the present invention is as follows. [1] A high-strength steel sheet, the high-strength steel sheet having an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or more, the high-strength steel sheet has a chemical composition containing, % by mass norfrnn / zznz / e / YiAi, C: 0.030% or more and 0.250% or less, Yes: 2.00% or less, Mn: 3.10% or more and 6.00% or less, P: 0.100% or less, S: 0.0200% or less, N: 0.0100% or less, and Al: 1,200% or less, the remainder being Fe and incidental impurities, and high-strength steel sheet having a microstructure in which ferrite is present at an area fraction of 30.0% or more and less than 80.0%, martensite is present at an area fraction of 3.0% or more and 30.0% or less, retained austenite is present at a volume fraction of 12.0% or more, ferrite has an average grain size of 5.0 pm or less, retained austenite has an average grain size of 2.0 pm or less, a value obtained by dividing an Mn content (mass %) of the retained austenite by an Mn content (mass %) of steel is 1.50 or more, 15% or more of all retained austenite grains in the retained austenite have an aspect ratio of 3.0 or greater, and 15% or more of all retained austenite grains in the retained austenite have an aspect ratio less than 2.0, wherein a value obtained by dividing a volume fraction Vya by a volume fraction Vyb is 0.40 or greater, where the volume fraction Vya is a volume fraction of austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C, and the volume fraction Vyb is a volume fraction of austenite retained before the hot tensile test at 150°C. [2] High strength steel sheet according to [1], the high strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or more, the high strength steel sheet has a chemical composition containing, mass%, C: 0.030% or more and 0.250% or less, If: 0.01% or more and 2.00% or less, Mn: 3.10% or more and 6.00% or less, P: 0.001% or more and 0.100% or less, S: 0.0001% or more and 0.0200% or less, N: 0.0005% or more and 0.0100% or less, and Al: 0.001% or more and 1.200% or less, the remainder being Fe and incidental impurities, and high-strength steel sheet having a microstructure in which ferrite is present at an area fraction of 30.0% or more and less than 80.0%, martensite is present at an area fraction of 3.0% or more and 30.0% or less, retained austenite is present at a volume fraction of 12.0% or more, ferrite has an average grain size of 5.0 pm or less, retained austenite has an average grain size of 2.0 pm or less, a value obtained by dividing a Mn content (mass %) of the retained austenite by a Mn content (mass %) of steel is 1.50 or more, 15% or more of all austenite grains retained in the retained austenite have an aspect ratio of 3.0 or greater, and 15% or more of all retained austenite grains in the retained austenite have an aspect ratio less than 2.0, wherein a value obtained by dividing a volume fraction Vya by a volume fraction Vyb is 0.40 or greater, where the volume fraction Vya is a volume fraction of noefrnn / zznz / e / YiAi austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C, and the volume fraction Vyb is a volume fraction of austenite retained before the hot tensile test at 150°C. [3] The high-strength steel sheet according to [1] or [2], the high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or more, wherein the chemical composition further contains, % by mass, at least one element selected from Ti: 0.200% or less, Nb: 0.200% or less, V: 0.500% or less, W: 0.500% or less, B: 0.0050% or less, Ni: 1.000% or less, Cr: 1.000% or less, Mo: 1.000% or less, Cu: 1.000% or less, Sn: 0.200% or less, Sb: 0.200% or less, Ta: 0.100% or less, Zr: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0050% or less, and REM: 0.0050% or less. [4] The high-strength steel sheet according to [3], the high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or more, wherein the chemical composition contains, % by mass, at least one element selected from Ti: 0.002% or more and 0.200% or less, Nb: 0.005% or more and 0.200% or less, V: 0.005% or more and 0.500% or less, W: 0.0005% or more and 0.500% or less, B: 0.0003% or more and 0.0050% or less, Ni: 0.005% or more and 1.000% or less, Cr: 0.005% or more and 1.000% or less, Mo: 0.005% or more and 1.000% or less, Cu: 0.005% or more and 1.000% or less, Sn: 0.002% or more and 0.200% or less, Sb: 0.002% or more and 0.200% or less, Ta: 0.001% or more and 0.100% or less, Zr: 0.0005% or more and 0.0050% or less, Ca: 0.0005% or more and 0.0050% or less, Mg: 0.0005% or more and 0.0050% or less, and norfrnn / zznz / e / YiAi REM: 0.0005% or more and 0.0050% or less. [5] The high-strength steel sheet according to any one of [1] to [4], the high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or more, wherein the amount of diffusible hydrogen in the steel of 0.50 ppm by mass or less. [6] The high-strength steel sheet according to any one of [1] to [5], the high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or more, wherein the high-strength steel sheet has a zinc-coated layer on a surface of the steel sheet. [7] The high-strength steel sheet according to any one of [1] to [5], the high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or more, wherein the high-strength steel sheet has an aluminum coated layer on a surface of the steel sheet. [8] A shock absorption member, the shock absorption member including a shock absorption portion that absorbs impact energy by compression and bending deformation, the shock absorption portion including the high-strength steel sheet according to any one of [1] to [7]. [9] A shock absorption member, the shock absorption member including a shock absorption portion that absorbs impact energy by axial compression and bellows-shaped deformation, the shock absorption portion including the high-strength steel sheet according to any one of [1] to [7].

[10] A method for manufacturing the high-strength steel sheet according to any one of [1] to [4], the method including performing a pickling process on a hot-rolled steel sheet; maintaining a resulting steel sheet within a temperature range of a transformation temperature Am or higher and the transformation temperature Aci +150°C or lower for a period of more than 21,600 seconds and 259,200 seconds or less; subsequently cooling the resulting steel sheet at an average cooling rate of 5°C / hour or higher and 200°C / hour or lower through a temperature range of 550°C to 400°C; subsequently cold-rolling the resulting steel sheet; heating a resulting cold-rolled steel sheet at an average heating rate of 8°C / second or higher and 50°C / second or lower through a temperature range of 400°C to the transformation temperature Am;and keeping the resulting cold-rolled steel sheet within a temperature range of the Aci transformation temperature or higher and “the Aci transformation temperature+150°C” or lower for a period of 20 seconds or more and 3,600 seconds or less.;

[11] A method for manufacturing the high-strength steel sheet according to [6], the method including performing a pickling process on a hot-rolled steel sheet; maintaining a resulting steel sheet within a temperature range of a transformation temperature Am or higher and the transformation temperature Aci +150°C or lower for a period of more than 21,600 seconds and 259,200 seconds or less; subsequently cooling the resulting steel sheet at an average cooling rate of 5°C / hour or higher and 200°C / hour or lower through a temperature range of 550°C to 400°C; noefrnn / zznz / e / YiAi subsequently cold-rolling the resulting steel sheet; heating a resulting cold-rolled steel sheet at an average heating rate of 8°C / second or higher and 50°C / second or lower through a temperature range of 400°C to the transformation temperature Aci; keeping the resulting cold-rolled steel sheet within a temperature range of the transformation temperature Am or higher and “the transformation temperature Aci + 150°C” or lower for a period of 20 seconds or more and 3,600 seconds or less; and subsequently performing a hot-dip galvanizing process or an electrogalvanizing process on the resulting cold-rolled steel sheet

[12] A method for manufacturing the high-strength steel sheet according to [7], the method including performing a pickling process on a hot-rolled steel sheet; maintaining a resulting steel sheet within a temperature range of a transformation temperature Am or higher and the transformation temperature Am +150°C or lower for a period of more than 21,600 seconds and 259,200 seconds or lower; subsequently cooling the resulting steel sheet at an average cooling rate of 5°C / hour or higher and 200°C / hour or lower through a temperature range of 550°C to 400°C; subsequently, cold-rolling the resulting steel sheet; heating a resulting cold-rolled steel sheet at an average heating rate of 8°C / second or higher and 50°C / second or lower through a temperature range of 400°C to the transformation temperature Aci;Maintaining the resulting cold-rolled steel sheet within a temperature range of the transformation temperature Am or higher and “the transformation temperature Aci+150°C” or lower for a period of 20 seconds or more and 3,600 seconds or less; and subsequently performing a hot-dip aluminum coating process on the resulting cold-rolled steel sheet;

[13] The method for manufacturing the high strength steel sheet according to item

[10] , wherein, after the resulting cold rolled steel sheet is maintained within the temperature range of the transformation temperature Aci or higher and the transformation temperature Aci +150°C or less for a period of 20 seconds or more and 3,600 seconds or less, the resulting cold rolled steel sheet is maintained within a temperature range of 50°C or higher and 300°C or lower for a period of 1,800 seconds or more and 259,200 seconds or less.

[14] The method for manufacturing the high-strength steel sheet according to item

[11] or

[12] , wherein, after the coating process, the resulting cold-rolled steel sheet is maintained within a temperature range of 50°C or more and 300°C or less for a period of 1,800 seconds or more and 259,200 seconds or less. Advantageous effects of the invention With the present invention, it is possible to obtain a high-strength steel sheet and crash energy absorbing member with a yield strength (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or more and excellent uniform ductility, foldability, and compression performance. DETAILED DESCRIPTION OF THE INVENTION Now, a high-strength steel sheet and a crash energy absorbing member of the present invention will be described. norfrnn / zznz / e / YiAi First, the reasons for the limitations imposed on a chemical composition of the steel of the high-strength steel sheet of the present invention will be described. C: 0.030% or more and 0.250% or less C is a necessary element for the formation of a low-temperature transformed phase, such as martensite, thereby increasing the tensile strength of the steel sheet. Furthermore, C is an effective element for improving the stability of retained austenite, thereby improving the ductility, particularly uniform ductility, of the steel sheet. If the C content is less than 0.030%, it is difficult to ensure a desired area fraction of martensite, and consequently, the desired tensile strength cannot be achieved. Furthermore, it is difficult to ensure a sufficient volume fraction of retained austenite, and consequently, good ductility, particularly uniform ductility, cannot be achieved. On the other hand, if there is an excessive amount of C, i.e., if the content is greater than 0.250%, the area fraction of the hard martensite becomes excessively high; consequently, the ductility, particularly the uniform ductility, of the steel sheet is reduced, and furthermore, during various types of bending deformation, an increased number of microvoids are formed at the grain boundaries of the martensite. Furthermore, crack propagation advances, that is, the bendability of the steel sheet is reduced. Furthermore, a weld zone and a heat-affected zone are significantly hardened, which reduces the mechanical properties of the weld zone, and therefore, spot weldability, arc weldability, and the like are degraded. From these standpoints, it is specified that the C content should be equal to or more than 0.030% and equal to or less than 0.250%. Preferably, the C content is 0.080% or more and 0.200% or less. Yes: 2.00% or less Si is a necessary element for increasing the tensile strength of steel sheets through solid solution hardening of ferrite. Furthermore, Si improves the work hardenability of ferrite and is therefore effective in ensuring good ductility, particularly good uniform ductility. If the Si content is less than 0.01%, the effect is not sufficient. Therefore, a lower limit of Si content of 0.01% is preferable. On the other hand, if there is an excessive amount of Si, i.e., if the content is greater than 2.00%, surface quality degradation occurs, and furthermore, a value obtained by dividing a volume fraction Vya by a volume fraction Vyb cannot be a desirable value, where the volume fraction Vya is a volume fraction of austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C, and the volume fraction Vyb is a volume fraction of austenite retained before the hot tensile test at 150°C; that is, good foldability and compression performance cannot be achieved. Accordingly, the Si content is specified to be less than or equal to 2.00%. The Si content is preferably greater than or equal to 0.01%, and more preferably greater than or equal to 0.10%. Preferably, the Si content is less than or equal to 1.60%. Mn: 3.10% or more and 6.00% or less In the present invention, Mn is a very important additive element. Mn stabilizes retained austenite and is therefore effective in ensuring good ductility, particularly good uniform ductility. Furthermore, Mn is an element that increases the tensile strength of steel sheets through solid solution hardening. These functions are manifested when the Mn content is equal to or greater than 3.10%. On the other hand, if there is an excessive amount of Mn, i.e., if the content is greater than 6.00%, surface quality degradation occurs, and furthermore, a value obtained by dividing a volume fraction Vya by a volume fraction Vyb cannot be a desirable value, where the volume fraction Vya is a volume fraction of austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C, and the volume fraction Vyb is a volume fraction of austenite retained before the hot tensile test at 150°C; that is, good foldability and compression performance cannot be achieved. From these standpoints, the Mn content is specified to be equal to or more than 3.10% and equal to or less than 6.00%. Preferably, the Mn content is 3.40% or more and 5.20% or less. P: 0.100% or less P is an element that has the function of achieving solid solution hardening and can be included in correspondence with a desired tensile strength. In addition, P is also an effective element for forming a multiphase structure because P promotes the transformation of ferrite. It is preferable for the P content to be greater than or equal to 0.001% to produce these effects. On the other hand, if the P content is greater than 0.100%, weldability is degraded, and in a case where a hot-dip zinc coating is subjected to an alloying process, the alloying rate is reduced, which lowers the quality of the hot-dip zinc coating. Accordingly, the P content is specified to be less than or equal to 0.100%. The P content is preferably greater than or equal to 0.001% and more preferably greater than or equal to 0.005%. Preferably, the P content is less than or equal to 0.050%. S: 0.0200% or less S weakens the steel sheet during hot working by segregating at grain boundaries and, in addition, reduces the sheet's pliability by existing as sulfide. Therefore, the S content should be less than or equal to 0.0200%. Preferably, the S content is less than or equal to 0.0100%, and more preferably, less than or equal to 0.0050%. Given the limitations associated with industrial technologies, it is preferable for the S content to be greater than or equal to 0.0001%. N: 0.0100% or less N is an element that degrades the aging resistance of steel sheets. In particular, if the N content exceeds 0.0100%, the aging resistance is significantly degraded. It is preferable for the N content to be as low as possible; however, since there are limitations associated with industrial technologies, it is preferable for the N content to be greater than or equal to 0.0005%. Accordingly, the N content is specified to be less than or equal to 0.0100%. Preferably, the N content is greater than or equal to 0.0005%, and more preferably, greater than or equal to 0.0010%. Preferably, the N content is less than or equal to 0.0070%. noefrnn / zznz / e / YiAi To: 1,200% or less Al broadens the temperature range of ferrite-austenite, thereby reducing the dependence of mechanical properties on the annealing temperature. In other words, Al is an effective element for achieving stable mechanical properties. If the Al content is less than 0.001%, the effect of Al addition is not sufficient. Therefore, it is preferable to specify the lower limit at 0.001%. Furthermore, Al acts as a deoxidizing agent and is therefore effective in achieving cleanliness of the steel sheet. It is preferable to include Al in a deoxidation process. However, if there is a large amount of Al, that is, if the Al content is greater than 1,200%, the risk of strand cracking during continuous casting increases, which reduces manufacturability. From this perspective, the Al content is specified to be less than or equal to 1,200%.The Al content is preferably greater than or equal to 0.001%, more preferably greater than or equal to 0.020%, and even more preferably greater than or equal to 0.030%. The Al content is preferably less than or equal to 1.000% and more preferably less than or equal to 0.800%. In addition to the components described above, at least one element selected from the following elements may be further included: % by mass, Ti: 0.200% or less, Nb: 0.200% or less, V: 0.500% or less, W: 0.500% or less, B: 0.0050% or less, Ni: 1.000% or less, Cr: 1.000% or less, Mo: 1.000% or less, Cu: 1.000% or less, Sn: 0.200% or less, Sb: 0.200% or less, Ta: 0.100% or less, Zr: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0050% or less, and one or more of REM: 0.0050% or less. Ti: 0.200% or less Ti is effective for precipitation hardening of steel sheets. Ti improves the strength of ferrite, thereby reducing the hardness difference between ferrite and a second hard phase (retained martensite or austenite), and therefore Ti can ensure good bendability. In addition, Ti refines the grains of martensite and retained austenite, resulting in good bendability. It is preferable for the Ti content to be greater than or equal to 0.002% for this effect to occur. However, if the content exceeds 0.200%, the areal fraction of hard martensite becomes excessively high; consequently, during various types of bending tests, an increased number of microvoids form at the grain boundaries of martensite, and crack propagation progresses, that is, the bendability of the steel sheet is reduced.Therefore, in cases where Ti must be included, the Ti content must be less than or equal to 0.200%. The Ti content is preferably greater than or equal to 0.002% and more preferably greater than or equal to 0.005%. The Ti content is preferably less than or equal to 0.100%. Nb: 0.200% or less, V: 0.500% or less, and W: 0.500% or less Nb, V, and W are effective in strengthening precipitation hardening. In addition, Nb, V, and W improve the strength of ferrite, thereby reducing the hardness difference between ferrite and a second hard phase (retained martensite or austenite), and therefore, Nb, V, and W can ensure good bendability. In addition, Nb, V, and W refine the grains of martensite and retained austenite, resulting in good bendability. It is preferable that the Nb content, W content, and V content be greater than or equal to 0.005% to produce the effects. However, when the Nb content is greater than 0.200%, the noefrnn / zznz / e / YiAi Cu: 1.000% or less Cu is an effective element for hardening steel sheets and can be included as needed. It is preferable for the Cu content to be greater than or equal to 0.005% to achieve this effect. On the other hand, if the content exceeds 1,000%, the area fraction of hard martensite becomes excessively high; consequently, during a bending test, a greater number of microvoids form at the grain boundaries of the martensite, and crack propagation is accelerated; that is, the bendability of the steel sheet is reduced. Therefore, in cases where Cu must be included, the Cu content is specified to be less than or equal to 1,000%. Sn: 0.200% or less and Sb: 0.200% or less Sn and Sb may be included as needed to inhibit decarburization that may occur when a steel sheet surface is nitrided and / or oxidized, in a region of approximately several tens of micrometers in a surface layer of the steel sheet. The inhibition of nitriding and oxidation results in the inhibition of the reduction of the area fraction of martensite on a steel sheet surface. Accordingly, Sn and Sb are effective in ensuring the strength and stability of the mechanical properties of the steel sheet. It is preferable that an Sn content and an Sb content each be greater than or equal to 0.002% to produce the effect. On the other hand, with respect to each of these elements, if an excessive amount of the element is added, i.e., the content is greater than 0.200%, the hardness of the steel sheet is reduced.Therefore, in cases where these elements are included, it is specified that the content of each of them must be less than or equal to 0.200%. Ta: 0.100% or less Like Ti and Nb, Ta contributes to increasing the strength of steel by forming an alloy carbide and / or an alloy carbonitride. In addition, Ta partially dissolves in a Nb carbide and / or a Nb carbonitride to form a complex precipitate, such as (Nb, Ta)(C, N), thereby significantly inhibiting the fatliquoring of the precipitates, which is believed to produce a stabilizing effect on the contribution to the strength of the steel sheet due to precipitation hardening. It is preferable for the Ta content to be greater than or equal to 0.001% to produce the aforementioned effect of stabilizing the precipitates. On the other hand, even if an excessive amount of Ta is included, the stabilizing effect of the precipitates no longer increases while the cost of the alloy increases. Therefore, in cases where Ta must be included, the Ta content is specified to be less than or equal to 0.100%. Zr: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0050% or less, and REM: 0.0050% or less Zr, Ca, Mg, and REM are effective elements for spheroidizing the shape of sulfides in order to mitigate the adverse effects of sulfides on the bendability of steel sheets. It is preferable for each of these elements to have a content of 0.0005% or greater to achieve this effect. However, if the content of any of these elements is excessively high, that is, if the content exceeds 0.0050%, an increased number of inclusions and the like will form, resulting in surface, internal, and similar defects. Therefore, in cases where Zr, Ca, Mg, and one or more REM are included, it is specified that each of the contents be less than or equal to 0.0050%. It should be noted that the remainder is Fe and incidental impurities. Now, a microstructure of the high-strength steel sheet of the present invention will be described. Ferrite area fraction: 30.0% or more and less than 80.0% Ferrite must be present in an area fraction greater than or equal to 30.0% to ensure good ductility, particularly good uniform ductility, and to ensure good bendability. Furthermore, ferrite, which is soft, must be present in an area fraction less than 80.0% to ensure a tensile strength of 980 MPa or higher. The area fraction of ferrite is preferably 35.0% or more, or 75.0% or less. Area fraction of martensite: 3.0% or more and 30.0% or less Martensite, which is hard, must be present in an area fraction greater than or equal to 3.0% to ensure a tensile strength of 980 MPa or higher. Furthermore, martensite, which is hard, must be present in an area fraction less than or equal to 30.0% to ensure good ductility, particularly good uniform ductility, and to ensure good bendability. The area fraction of martensite is preferably 5.0% or more and 25.0% or less. It should be noted that the ferrite and martensite fractions can be determined by the following procedure. A cross-section (cross-section L) is polished along a sheet thickness and parallel to a rolling direction of the steel sheet. Subsequently, the cross-section is etched with 3% vol. Nital. A position 1 / 4 of the sheet thickness (a position corresponding to 1 / 4 of the sheet thickness in a depth direction, with respect to a surface of the steel sheet) is observed with a SEM (scanning electron microscope) at a magnification of 2000*, through 10 fields of view in a 60 μm χ 45 μm region. From the obtained images of the microstructures, the area fractions of each of the constituents (ferrite and martensite) are calculated for the 10 fields of view using Image-Pro (Media Cybernetics, Inc.). Area fractions are determined as an average of the calculated values.In the microstructure images, ferrite is observed as a gray constituent (matrix constituent), and martensite as a white constituent. Volume fraction of retained austenite: 12.0% or more A volume fraction of retained austenite is a very important constituent element of the present invention. In particular, the volume fraction of retained austenite must be present at 12.0% to ensure good uniform ductility and bendability. The volume fraction of retained austenite is preferably greater than or equal to 14.0%. It should be noted that the volume fraction of retained austenite can be determined by the following procedure. The steel sheet is polished until a surface 1 / 4 of the sheet thickness is exposed (a surface corresponding to 1 / 4 of the sheet thickness in a depth direction, relative to one surface of the steel sheet). The volume fraction is determined by measuring the X-ray diffraction intensity of the 1 / 4-sheet thickness surface. Mo-Kα radiation is used as the incident X-ray. An intensity ratio of an integrated peak from the {111}, {200}, {220}, or {311} plane of the retained austenite noefrnn / zznz / e / YiAi to an integrated peak from the {110}, {200}, or {211} plane of the ferrite is calculated for the twelve combinations. The volume fraction can be determined as an average of the calculated values. Average ferrite grain size: 5.0 pm or less The average grain size of ferrite is a very important constituent element of the present invention. In cases where ferrite grains are refined, a maximum elongation limit (YP-EL) can be exhibited, and the bendability of the steel sheet is improved. Accordingly, the average grain size of ferrite should be less than or equal to 5.0 pm to ensure a maximum elongation limit (YP-EL) of 1.0% or more and good bendability. Preferably, the average grain size of ferrite is less than or equal to 4.0 pm. Average grain size of retained austenite: 2.0 pm or less In cases where the retained austenite grains are refined, the stability of the retained austenite itself improves, which in turn improves the ductility, particularly the uniform ductility, of the steel sheet. Furthermore, during a bendability test, the stress-induced martensite, which results from the transformation of retained austenite due to bending deformation, does not experience grain boundary crack propagation, i.e., the steel sheet consequently has better bendability and improved flexural and axial compression performance. Consequently, the average grain size of the retained austenite should be less than or equal to 2.0 pm to ensure good ductility, particularly good uniform ductility, good bendability, good flexural compression performance, and good axial compression performance.Preferably, the average grain size of the retained austenite is less than or equal to 1.5 pm. It should be noted that the average grain size of ferrite and retained austenite can be determined as follows. Using Image-Pro, mentioned above, the areas of the ferrite grains and the areas of the retained austenite grains are determined, their equivalent circular diameters are calculated, and the calculated values ​​are averaged. To distinguish between retained austenite and martensite, EBSD (electron backscattered diffraction) phase maps were used. Value obtained by dividing the Mn content (% by mass) of the retained austenite by the Mn content (% by mass) of the steel: 1.50 or higher The value obtained by dividing a Mn content (% by mass) of the retained austenite by a Mn content (% by mass) of the steel must be greater than or equal to 1.50. This is a very important constituent element of the present invention. To ensure good ductility, in particular, good uniform ductility, a large volume fraction of stable, Mn-enriched retained austenite is required. Furthermore, in a flexural compression test or an axial compression test at room temperature, heat is generated due to a high strain rate, and, in part, phase transformation heat is generated due to the stress-induced transformation of the retained austenite into martensite; consequently, a temperature of 150°C or higher is reached as a result of self-heating alone. At 150°C, austenite does not readily transform into stress-induced martensite.As a result, in flexural or axial compression, the steel sheet does not crack, but collapses, before norfrnn / zznz / e / YiAi a further stage of deformation, and, in particular, in axial compression, the steel sheet collapses in a bellows-like manner without cracking. Consequently, a high impact energy absorption is achieved. In addition, a value obtained by dividing a volume fraction Vya by a volume fraction Vyb becomes larger. The volume fraction Vya is a volume fraction of austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C. The volume fraction Vyb is a volume fraction of austenite retained before the hot tensile test at 150°C. Preferably, the value obtained by dividing a Mn content (% by mass) of the retained austenite by a Mn content (% by mass) of the steel is greater than or equal to 1.70.The Mn content of the retained austenite can be determined as follows. In a cross-section along the rolling direction at a position 1 / 4 of the sheet thickness, a distribution state of Mn in each of the phases is quantitatively determined using a FE-EPMA (field emission electron probe microanalyzer). The amount of Mn is analyzed for 30 grains of retained austenite and 30 grains of ferrite, and the results are averaged. 15% or more of all austenite grains retained in the retained austenite have an aspect ratio of 3.0 or more, and 15% or more of all austenite grains retained in the retained austenite have an aspect ratio of less than 2.0 In the present invention, 15% or more of all the austenite grains retained in the retained austenite have an aspect ratio of 3.0 or greater (the retained austenite is referred to as lath-retained austenite). This improves ductility, in particular, uniform ductility, various types of bendability, flexural compression performance, and axial compression performance. 15% or more of all the austenite grains retained in the retained austenite have an aspect ratio of less than 2.0 (the retained austenite is referred to as block-retained austenite).Furthermore, in a flexural compression test or an axial compression test at room temperature, heat is generated due to a high strain rate, and, in part, phase transformation heat is generated due to the stress-induced transformation of retained austenite into martensite; consequently, a temperature of 150°C or higher is reached as a result of self-heating alone. At 150°C, austenite does not readily transform into stress-induced martensite. As a result, in flexural compression or axial compression, the steel sheet does not crack but collapses, prior to a further stage of deformation. In particular, in axial compression, the steel sheet collapses in a bellows-like manner without cracking. Consequently, a high impact energy absorption is achieved. The value obtained by dividing the volume fraction Vya by the volume fraction Vyb is equal to or greater than 0.40, where the volume fraction Vya is the volume fraction of austenite retained in the fractured portion of the tensile test specimen after the hot tensile test at 150°C, and the volume fraction Vyb is the volume fraction of austenite retained before the hot tensile test at 150°C. A value obtained by dividing a volume fraction Vya by a volume fraction Vyb must be greater than or equal to 0.40, where the volume fraction Vya is a volume fraction of austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C, and the volume fraction Vyb is a volume fraction of noefrnn / zznz / e / YiAi austenite retained before the hot tensile test at 150°C. This is a very important constituent element of the present invention. When the value obtained by dividing a volume fraction Vya by a volume fraction Vyb is greater than or equal to 0.40, where the volume fraction Vya is a volume fraction of austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C, and the volume fraction Vyb is a volume fraction of austenite retained before the hot tensile test at 150°C, austenite is not easily transformed into stress-induced martensite in a case where a hot tensile test is performed at 150°C. Consequently, in bending compression or axial compression, the steel sheet does not crack but collapses, before a subsequent stage of deformation, and, in particular, in axial compression, the steel sheet collapses in a bellows-like manner without cracking. Consequently, a high impact absorbed energy is achieved. Accordingly, it is specified that the value obtained by dividing a volume fraction Vya by a volume fraction Vyb is greater than or equal to 0.40, where the volume fraction Vya is a volume fraction of austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C, and the volume fraction Vyb is a volume fraction of austenite retained before the hot tensile test at 150°C. Preferably, the value is greater than or equal to 0.50. It should be noted that the “fractured portion of a tensile test specimen after a hot tensile test at 150°C” refers to a transverse position of 1 / 4 of sheet thickness along a longitudinal direction (direction parallel to the rolling direction of the steel sheet) of the tensile test specimen 0.1 mm inward from the fractured portion. Amount of diffusible hydrogen in steel: 0.50 ppm by mass or less It is preferable that the amount of diffusible hydrogen in the steel be less than or equal to 0.50 ppm by mass to ensure good bendability. It is more preferable that the amount of diffusible hydrogen in the steel be within a range of less than or equal to 0.30 ppm by mass. The amount of diffusible hydrogen in the steel was calculated as follows. A test sample 30 mm long and 5 mm wide was cut from an annealed steel sheet, a coated layer was removed by grinding, and subsequently, the amount of diffusible hydrogen in the steel and an emission peak of the diffusible hydrogen were measured. The emission peak was measured by thermal desorption spectrometry (TDS), and the heating rate was 200 °C / h. It is worth noting that the amount of diffusible hydrogen in the steel was an amount of hydrogen detected at temperatures less than or equal to 300 °C.Furthermore, the test sample used to calculate the amount of diffusible hydrogen in steel is not limited to a test sample cut from an annealed steel sheet. The test sample can be cut, for example, from a formed product, such as an automobile part or an assembled motor vehicle body. In the microstructure of the high-strength steel sheet of the present invention, tempered martensite, bainite, and carbides such as cementite may be present in an area fraction of less than or equal to 8%, in addition to ferrite, martensite, and retained austenite. Even in such a case, the advantageous effects of the present invention are not compromised. norfrnn / zznz / e / YiAi The high-strength steel sheet of the present invention may have a zinc-coated layer or an aluminum-coated layer on a surface of the steel sheet. Now, the manufacturing conditions for the high-strength steel sheet of the present invention will be described. Heating temperature of a steel slab The heating temperature of a steel slab is not particularly limited and is preferably within a temperature range of 1100°C or more and 1300°C or less. The precipitates that exist at the time of heating the steel slab exist as coarse precipitates in the final steel sheet obtained and do not contribute to the strength of the steel. Consequently, it is necessary to redissolve the Ti and / or Nb precipitates that have precipitated during casting. If the heating temperature of the steel slab is lower than 1100°C, it is difficult to sufficiently dissolve the carbides, which can cause a problem. The problem is, for example, an increased risk of malfunction during hot rolling due to an increase in the rolling load. Therefore, it is preferable for the heating temperature of the steel slab to be greater than or equal to 1100°C.Furthermore, from the viewpoint of scale loss defects present in a surface layer of the slab, such as bubbles and segregation, thereby reducing cracks and irregularities on a surface of the steel sheet to achieve a smooth surface of the steel sheet, it is preferable that the heating temperature for the steel slab be greater than or equal to 1100°C. On the other hand, if the heating temperature of the steel slab is higher than 1300°C, scale loss increases as a result of the increase in the amount of oxidation. Therefore, it is preferable that the heating temperature of the steel slab be less than or equal to 1300°C. More preferably, the heating temperature for the steel slab is greater than or equal to 1150°C and less than or equal to 1250°C. It is preferable for the steel slab to be manufactured by a continuous casting process so that macrosegregation can be avoided. Alternatively, the steel slab can be manufactured using an ingot casting process, a thin slab casting process, or the like. In addition, after the steel slab is manufactured, a conventional process can be carried out, in which the slab is cooled to room temperature and subsequently reheated; or an energy-saving process can be suitably used. Examples of the energy-saving process include hot rolling and direct hot rolling, in which the hot slab is directly charged into a heating furnace without cooling to room temperature, or the slab is kept heated for a short time and then immediately hot-rolled.The steel slab is rough rolled under typical conditions to form a transfer bar. When the heating temperature is low, it is preferable to heat the transfer bar before final rolling using a bar heater or similar, to prevent malfunctions during hot rolling. Delivery temperature of the finishing roll in hot rolling The heated steel slab is hot-rolled through rough rolling and finish rolling to form a hot-rolled steel sheet. In this case, if the finish rolling delivery temperature exceeds 1,000°C, the amount of scale formation increases rapidly, which roughens the interface between the base metal and the oxide. Consequently, the surface quality after pickling and cold rolling may deteriorate. Furthermore, if a hot-rolling scale residue or similar remains on a part after pickling, the ductility and bendability of the steel sheet may be adversely affected.On the other hand, if the finished rolling delivery temperature is lower than 750°C, the reduction ratio of the rolled material in the non-recrystallized state of austenite is high; consequently, an abnormal texture develops, resulting in significant in-plane anisotropy in a final product, and as a result, the uniformity of material quality (stability of mechanical properties) may be compromised. Accordingly, it is preferable for the finished rolling delivery temperature in hot rolling to be within a temperature range of 750°C or more and 1,000°C or less. More preferably, the finished rolling delivery temperature is 800°C or more and 950°C or less. Winding temperature for winding after hot rolling If the winding temperature for post-hot rolling coiling is higher than 750°C, the grain size of ferrite in the microstructure of the hot-rolled steel sheet increases, and as a result, it may be difficult to ensure good bendability of the final annealed steel sheet. Furthermore, the surface quality of the final material may deteriorate. Furthermore, if the winding temperature for post-hot rolling coiling is lower than 300°C, the strength of the hot-rolled steel sheet increases; consequently, the cold-rolling load increases, resulting in a shape defect in the steel sheet, and thus, productivity may be reduced. Therefore, it is preferable for the winding temperature for post-hot rolling coiling to be within a temperature range of 300°C or higher and 750°C or lower.More preferably, the winding temperature for winding after hot rolling is 400°C or more and 650°C or less. It should be noted that in hot rolling, finish rolling can be performed continuously by joining raw-rolled steel sheets. Furthermore, raw-rolled steel sheets can be temporarily coiled. Furthermore, finish rolling can be carried out, partially or completely, by oil rolling, thereby reducing the rolling load in hot rolling. Oil rolling is effective in achieving uniform shape and material quality of the steel sheet. It should be noted that the coefficient of friction for oil rolling is preferably within a range of 0.10 or more and 0.25 or less. The hot-rolled steel sheet produced in the manner described above is then pickled.Pickling can remove rust from the surface of steel sheets and is therefore important to ensure good chemical convertibility and coating quality on the final high-strength steel sheet product. Pickling can be performed in a single step or in multiple steps. After pickling, the hot-rolled steel sheet is heat treated under the following conditions. Heat treatment of hot-rolled steel sheet: The hot-rolled steel sheet is kept within a transformation temperature range of Am or higher and noefrnn / zznz / e / YiAi “transformation temperature Aci +150°C” or lower for a period of more than 21,600 seconds and 259,200 seconds or less. If the hot-rolled steel sheet is kept within a temperature range lower than the Aci transformation temperature, within a temperature range higher than “the Aci transformation temperature +150°C”, and / or for a period of 21,600 seconds or less, the enrichment of austenite with Mn does not progress sufficiently. Consequently, it is difficult to ensure that, after final annealing, there is a sufficient volume fraction of retained austenite, that the average grain size of the retained austenite is less than or equal to 2.0 pm, and that the value obtained by dividing a Mn content (mass %) of the retained austenite by a Mn content (mass %) of the steel is greater than or equal to 1.50. Consequently, the ductility, in particular, uniform ductility, and the bendability of the steel sheet may be reduced.Furthermore, it may be difficult to ensure that the value obtained by dividing a volume fraction Vya by a volume fraction Vyb is greater than or equal to 0.40, where the volume fraction Vya is a volume fraction of austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C, and the volume fraction Vyb is a volume fraction of austenite retained before the hot tensile test at 150°C. Preferably, the temperature range is a temperature range of “the transformation temperature Am +30°C” or greater and “the transformation temperature Aci +130°C” or less. In addition, it is preferable that the holding time be less than or equal to 259,200 seconds.If the holding time exceeds 259,200 seconds, the progress of Mn enrichment of austenite is halted; consequently, the effectiveness of ensuring ductility after final annealing, particularly uniform ductility after final annealing, is reduced, and furthermore, the cost may increase. Average cooling rate in the temperature range of 550°C to 400°C for cooling after annealing of hot-rolled steel sheet: 5°C / hour or more and 200°C / hour or less Even in the case of Mn-enriched austenite during an annealing process for hot-rolled steel sheet, the austenite becomes coarse when the steel sheet is held for a long time, and the austenite inhibits the transformation to pearlite if an average cooling rate over a temperature range of 550°C to 400°C is above 200°C / h. The use of an appropriate amount of pearlite allows the formation of fine ferrite and retained fine austenite during an annealing process after cold rolling and is therefore effective in ensuring the ultimate elongation (YP-EL) of 1.0% or more and guaranteeing various types of foldability, flexural compression performance, and axial compression performance.Moreover, if an appropriate amount of pearlite is used, it is easy to ensure that 15% or more of all austenite grains retained in the retained austenite of the final microstructure have an aspect ratio of 3.0 or higher (the retained austenite is called lath-shaped retained austenite), and as a result, the ductility, in particular, uniform ductility, various types of bendability, flexural compression performance, and axial compression performance, is improved. Accordingly, the average cooling rate in a temperature range of 550°C to 400°C for post-annealing cooling of hot-rolled norfrnn / zznz / e / YiAi steel sheet is specified to be less than or equal to 200°C / hour.On the other hand, if the average cooling rate in a temperature range of 550°C to 400°C is less than 5°C / h, it is difficult to ensure that there is a sufficient volume fraction of retained austenite after final annealing, and in addition, the grain sizes of ferrite and retained austenite become large; consequently, it is difficult to guarantee the elongation limit (YP-EL) of 1.0% or more. Consequently, it may be difficult to ensure good ductility, in particular, good uniform ductility, various types of bendability, flexural compression performance, and axial compression performance. Preferably, the average cooling rate is 10°C / h or more and 170°C / h or less.It should be noted that the average cooling rate in the temperature range of 550°C to 400°C for cooling after the annealing process of hot-rolled steel sheet was determined as the result of (550°C–400°C) / (the time required to reduce the temperature from 550°C to 400°C). The steel sheet that has undergone heat treatment after hot rolling is pickled as required, which is performed according to a common method. The resulting steel sheet is then cold-rolled to form a cold-rolled steel sheet. The reduction ratio of cold rolling is not particularly limited and is preferably within a range of 20% or more and 85% or less. If the reduction ratio of cold rolling is less than 20%, uncrystallized ferrite may remain, which can reduce the ductility of the steel sheet. On the other hand, if the reduction ratio of cold rolling is greater than 85%, the load on cold rolling increases, and consequently, a coupling problem may arise. The resulting cold-rolled steel sheet is then subjected to heat treatment, which is described below. Heat the cold-rolled steel sheet at an average heating rate of 8°C / second or higher and 50°C / second or lower through the temperature range from 400°C to the transformation temperature Am If cold-rolled steel sheet is heated at an average heating rate of less than 8°C / second through a temperature range of 400°C up to the transformation temperature Aci, recovery and recrystallization progress excessively, and consequently, the microstructure becomes coarse. As a result, the ferrite in the final microstructure has a large grain size, making it difficult to exhibit a yield strength (YP-EL) and ensure good bendability. If cold-rolled steel sheet is heated at an average heating rate of more than 50°C / second through a temperature range of 400°C up to the transformation temperature Am, a large amount of undissolved pearlite remains, and consequently, there is an excessively high volume fraction of martensite after a second annealing process of the cold-rolled steel sheet.Consequently, it is difficult to ensure good ductility, in particular, good uniform ductility, and it is difficult to ensure various types of foldability, flexural compression performance and axial compression performance. First heat treatment of cold-rolled steel sheet: The cold-rolled steel sheet is kept within a temperature range of the transformation temperature Am or higher and “the transformation temperature Am +150°C” or lower for a period of 20 seconds or more and 3,600 seconds or less. If the cold-rolled steel sheet is kept within a temperature range below the transformation temperature Aci and / or for a period of less than 20 seconds, a carbide formed during heating may remain undissolved. As a result, it is difficult to ensure sufficient volume fractions of retained martensite and austenite, and the tensile strength of the steel sheet may be reduced. Furthermore, if the cold-rolled steel sheet is kept within a temperature range below the transformation temperature Am, it is difficult to ensure that 15% or more of all austenite grains retained in the retained austenite have an aspect ratio less than 2.0 (the retained austenite is called blocky retained austenite).Furthermore, if the cold-rolled steel sheet is maintained within a temperature range higher than the Aci transformation temperature +150°C, an excessively high volume fraction of martensite is formed. Furthermore, the average grain sizes of the ferrite and retained austenite become large. As a result, the yield strength (YP-EL) of 1.0% or more may not be achieved, and consequently, it may be difficult to ensure good ductility, particularly good uniform ductility, various types of bendability, flexural compression performance, and axial compression performance. The temperature range within which the cold-rolled steel sheet should be maintained is preferably the transformation temperature Am or higher and the Aci transformation temperature +130°C or lower.Furthermore, if the cold-rolled steel sheet is held for a period of more than 3,600 seconds, the average grain sizes of the retained ferrite and austenite become large. As a result, the elongation limit (YP-EL) of 1.0% or more may not be achieved, and consequently, it may be difficult to ensure good ductility, in particular, good uniform ductility, various types of bendability, flexural compression performance, and axial compression performance. More preferably, the holding time is 50 seconds or more and 1,800 seconds or less. After the first heat treatment of the cold-rolled steel sheet, the cold-rolled steel sheet is cooled to room temperature. After cooling to room temperature, the cold-rolled steel sheet, if necessary, may undergo a pickling process, which is carried out according to a common method. In addition, after the first heat treatment of the cold-rolled steel sheet, the cold-rolled steel sheet is cooled to room temperature and, if necessary, may undergo a second heat treatment, which is carried out under the following conditions. Second heat treatment of cold-rolled steel sheet: The cold-rolled steel sheet is kept within a temperature range of 50°C or more and 300°C or less for a period of 1,800 seconds or more and 259,200 seconds or less. If the cold-rolled steel sheet is kept within a temperature range below 50°C or for a period of less than 1,800 seconds, the diffusible hydrogen in the steel is not released from the steel sheet, and as a result, various types of bendability of the steel sheet may be reduced. On the other hand, if the cold-rolled steel sheet is kept within a temperature range above 300°C or for a period of more than 259,200 seconds, the retained austenite decomposes, and consequently, a sufficient volume fraction of retained austenite cannot be obtained. As a result, the ductility, particularly the uniform ductility, of the steel sheet may be reduced. It should be noted that after the second heat treatment of the cold-rolled steel sheet, the cold-rolled steel sheet can be cooled to room temperature.Furthermore, in cases where a coating process is carried out, the second heat treatment of the cold-rolled steel sheet must be performed after the coating process, which will be described later. More preferably, the temperature range is 70°C or more and 200°C or less. Furthermore, more preferably, the holding time is 3,600 seconds or more and 216,000 seconds or less. Carrying out the coating process A coating process can be performed on the cold-rolled steel sheet produced in the manner described above. Examples of coating processes include hot-dip galvanizing processes, electrogalvanizing processes, and hot-dip aluminum coating processes. Consequently, a high-strength steel sheet can be obtained that has a galvanized layer or an aluminum coating layer on one surface of the steel sheet. It should be noted that “hot-dip galvanizing” should be interpreted as including annealing after hot-dip galvanizing. Furthermore, as described above, in cases where a coating process is performed, the second heat treatment of the cold-rolled steel sheet can be performed after the coating process, as needed. In cases where a hot-dip galvanizing process is to be performed, the hot-dip galvanizing process is performed, for example, by immersing the steel sheet, which has undergone the annealing process, in a hot-dip galvanizing bath having a temperature range of 440°C or higher and 500°C or lower, and then adjusting a coating weight by using gas cleaning or the like. It should be noted that the hot-dip galvanizing bath to be used is preferably a hot-dip galvanizing bath having an Al content of 0.08% or higher and 0.18% or lower. In cases where an alloying process is to be performed in the hot-dip zinc coating, the alloying process is performed in the hot-dip zinc coating within a temperature range of 450°C or higher and 600°C or lower after the hot-dip galvanizing process.If the alloying process is carried out at temperatures above 600°C, the untransformed austenite converts to pearlite, and the desired volume fraction of retained austenite cannot be guaranteed. As a result, the ductility, particularly uniform ductility, of the steel sheet may be reduced. Therefore, in cases where an alloying process is to be carried out in hot-dip zinc coating, it is preferable to carry out the alloying process in hot-dip zinc coating within a temperature range of 450°C or higher and 600°C or lower. Furthermore, in cases where an electrogalvanizing process is to be performed, the thickness of the coating is not particularly limited and is preferably within a range of 5 μΐη to 15 μΐη. Furthermore, in cases where a hot-dip aluminum coating process is to be performed, the hot-dip aluminum coating process is performed by immersing the cold-rolled steel sheet, which was produced by the cold-rolled sheet annealing process, into an aluminum coating bath having a temperature of 660°C to 730°C and subsequently adjusting a coating weight by using gas cleaning or the like.In cases where the steel is compatible with an aluminum plating bath temperature that is within a temperature range of the Aci transformation temperature or higher and the Am transformation temperature +100°C or lower, the hot-dip aluminum plating process allows the formation of more refined and stable retained austenite; consequently, ductility, in particular uniform ductility, can be further improved. It should be noted that in cases where a high-strength hot-dip galvanized steel sheet, a high-strength post-hot-dip galvanized heat-treated steel sheet, a high-strength hot-dip aluminum-coated steel sheet, or a high-strength electro-galvanized steel sheet is to be manufactured, a good coating quality can ultimately be obtained by performing a pickling process before a heat treatment that is performed immediately before coating (for example, between the completion of hot coiling and the first heat treatment, or between a heat treatment that is performed immediately before coating (a third heat treatment) and a heat treatment that is performed immediately before the third heat treatment (the second heat treatment)).This is because, in this case, the presence of oxides on a surface is inhibited immediately before the coating process, and therefore, coating defects due to oxides are inhibited. More specifically, during heat treatments, oxidizable elements (e.g., Mn, Cr, and Si) form oxides and concentrate on the surface of the steel sheet. Consequently, after heat treatments, there is a depletion layer of oxidizable elements on the surface of the steel sheet (immediately below the oxides). In the subsequent pickling process, the oxides of the oxidizable elements are removed, and consequently, the depletion layer of oxidizable elements appears on the surface of the steel sheet. Consequently, during the third postheat treatment, surface oxidation due to oxidizable elements is inhibited. Other conditions for the manufacturing method are not particularly limited. From a productivity standpoint, it is preferable for the annealing described above to be performed on a continuous annealing line. Furthermore, it is preferable for the series of processes, including annealing, hot-dip galvanizing, and an alloying process for hot-dip zinc coating, to be performed on a CGL (continuous galvanizing line), which is a hot-dip galvanizing line. It should be noted that high-strength hot-dip galvanized steel sheet can be surface rolled to achieve shape correction, surface roughness adjustment, and the like. Preferably, a rolling reduction ratio for stand rolling is greater than or equal to 0.1% and less than or equal to 2.0%. If the rolling reduction ratio is less than 0.1%, the effects are small and control is complicated.If the rolling reduction ratio exceeds 2.0%, productivity is significantly reduced. It should be noted that stand rolling can be performed in-line or offline. Furthermore, stand rolling can be performed in a single step with a desired rolling reduction ratio or in multiple steps. In addition, any of the various coating processes, such as resin coating and grease coating, can be performed. noefrnn / zznz / e / YiAi The high-strength steel sheet of the present invention can be used in an impact absorption portion of an impact absorption member in motor vehicles. Specifically, the high-strength steel sheet of the present invention can be used in an impact absorption portion of impact absorption members that are provided with an impact absorption portion that absorbs impact energy by undergoing bending compression and deformation, and in an impact absorption portion of impact absorption members that are provided with an impact absorption portion that absorbs impact energy by undergoing axial compression and bellows-shaped deformation. Impact absorbing members having an impact absorption portion formed from the high-strength steel sheet of the present invention have an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or greater, and also have excellent uniform ductility, foldability, and compression performance. Consequently, shock-absorbing elements excel at absorbing impacts. EXAMPLES Steels with the chemical composition shown in Table 1, with the remainder being Fe and incidental impurities, were produced in a converter using a steelmaking process. The steels were melted by a continuous casting process to form steel slabs. The obtained steel slabs were hot-rolled and subsequently pickled. The resulting steel sheets were then subjected to heat treatment of hot-rolled steel sheets, quenching, cold rolling, and a heat treatment of cold-rolled steel sheets, which were carried out under the conditions indicated in Tables 2-1 and 2-2. Consequently, high-strength (HR) cold-rolled steel sheets were obtained.Some of the steel sheets were further subjected to a hot-dip galvanizing process (including a process in which an alloying process was performed after the hot-dip galvanizing process), a hot-dip aluminum coating process, or an electrogalvanizing process to form hot-dip galvanized (GL) steel sheets, heat-treated steel sheets after hot-dip zinc coating (GA), hot-dip aluminum-coated (AI) steel sheets, and electrogalvanized (EG) steel sheets. As for the hot-dip galvanizing baths, a zinc bath with an Al content of 0.19 mass% was used in the hot-dip galvanized (GL) steel sheets. A zinc bath with an Al content of 0.14 mass% was used in the hot-dip galvanized (GA) steel sheets, and the bath temperature was 465°C.The coating weight per side was 45 g / m2 (two-sided coating), and for GA, the Fe concentration in the coated layer was adjusted to be within a range of 9 mass % or more and 12 mass % or less. Furthermore, the temperature of a hot-dip aluminum coating bath for the hot-dip aluminum-coated steel sheets was 680°C. The resulting steel sheets were evaluated for microstructure, tensile properties, bendability, bending compression performance, and axial compression performance. The transformation temperature Am was determined using the following equation. Transformation temperature Am (°C) = 751 - 16 x (%C) + 11 x (%S¡) - 28 x (%Mn) - 5.5 x (%Cu) - 16 x (%N¡) + 13 x (%Cr) + 3.4 x (%Mo) norfrnn / zznz / e / YiAi The microstructures of the steel sheets were determined by observation according to the method described above. Tensile properties were determined by the following method. A room temperature tensile test was performed in accordance with JIS Z 2241 (2011) using a JIS No. 5 test specimen, which was obtained by cutting a sample so that one tensile direction was perpendicular to the rolling direction of the steel sheet. Consequently, TS (tensile strength), EL (total elongation), YP-EL (elongation limit), and U.EL (uniform elongation) were measured at room temperature. In cases where the following conditions were met, the corresponding tensile property was determined to be good. <TS es de 980 MPa o más y menos de 1,180 MPa> YP-EL > 1.0%, EL > 22%, and U.EL > 18%<TS es 1,180 MPa o más> YP-EL > 1.0%, EL> 18%, and U.EL > 14% In addition, a hot tensile test was performed at 150°C in accordance with JIS G 0567 (2012) using a JIS No. 5 test specimen, which was obtained by cutting a specimen so that a tensile direction was perpendicular to the rolling direction of the steel sheet. Both the volume fraction Vya of retained austenite in a fractured portion of the tensile test specimen after the hot tensile test at 150°C and the volume fraction Vyb of retained austenite before the hot tensile test at 150°C were calculated using X-ray diffraction. A material test was carried out to evaluate the flexural cracking of the vertical portion of the wall by performing a bending test after the U-bending test. The test specimen used had a size of 60 mm (C) χ 30 mm (L) (C: a C direction, which is a direction along a direction perpendicular to the rolling direction of the steel sheet, L: an L direction, which is a direction along the rolling direction), with both widthwise edge surfaces ground. U-bending was performed in the longitudinal direction C (length of a bending vertex line: 30 mm (L)) using a hydraulic bending testing machine, such that the bending radius (R) of the punch was 4 mm, which was a bending radius at which no cracking occurred in any of the specimens, and a travel speed of 1,500 mm / minute (high speed).Subsequently, contact bending was performed on the U-bent specimen. Contact bending was carried out using a hydraulic bending testing machine, such that the thickness of a spacer, which was held between the testing machine and the steel sheet, was varied, the travel speed was 20 mm / min (low speed) and 1,500 mm / min (high speed), a pressing load was 10 tons, a pressing time was 3 seconds, and a bending vertex line of the U-bend test specimen and a pressing direction were perpendicular to each other. It should be noted that the spacer thickness was varied in 0.5 mm increments, and a cracking threshold spacer thickness was determined as a minimum spacer thickness at which no crack measuring 0.5 mm or more was formed along the bend vertex line. In cases where the crack threshold spacer thickness was 5.0 mm or less, a rating of “good” was given. norfrnn / zznz / e / YiAi A material test was performed to evaluate quadruple bending cracking by performing a handkerchief bend. The test specimen used had a size of 60 mm (C) χ 100 mm (L), with all edge surfaces ground. U-bending was performed in the longitudinal direction L (length of a bending vertex line: 60 mm (C)) using a hydraulic bending testing machine such that the bending radius R of the punch was 4 mm, which was a bending radius at which no cracking occurred in any of the specimens, and the travel speed was 1,500 mm / min (high speed). Subsequently, contact bending was performed on the U-bent specimen.Contact bending was carried out using a hydraulic bending testing machine, such that the thickness of a spacer was 5 mm, which was a thickness at which cracking did not occur in any of the samples; the travel speed was 1,500 mm / minute, which is relatively high; the pressing load was 10 tons; the pressing time was 3 seconds; and a bending vertex line of the U-bent test specimen and a pressing direction were perpendicular to each other. Subsequently, the resulting contact-bent specimen, which was bent in two places, was rotated 90° and subjected to U-bending to bend the specimen in four places.U-bending was performed in the longitudinal direction C (length of a bending vertex line: 50 mm (L)) using a hydraulic bending testing machine, such that the bending radius R of the punch was varied, the travel speed was 1,500 mm / min, which is relatively high, and a bending vertex line of the contact bending test specimen and the vertex line of the U-bending for bending the specimen at four locations were perpendicular to each other. In the U-bending for bending the specimen at four locations, a cracking threshold R / t (t: sheet thickness) was determined as a minimum R / t at which no crack of 0.5 mm or more was formed inside and outside the bending vertex. In cases where R / t < 5.0, a grade of “good” was given. A material test was performed to evaluate flexural cracking of the vertex line portion as follows. A test specimen was rotated 90° after being subjected to V-bending, and then the test specimen was subjected to U-bending. The test specimen used was a test specimen having a size of 75 mm (C) χ 55 mm (L), with all edge surfaces ground. V bending was performed in the longitudinal direction L (length of a bending vertex line: 75 mm (C)) using an Autograph, which is a product of Shimadzu Corporation, so that the bending radius R of the punch was 5 mm, which was a bending radius at which no cracking occurred in any of the samples, the punch was pushed with a punch bending angle of 90° and a punch stroke speed of 20 mm / minute, the pressing load was 10 tons, and the pressing time was 3 seconds.Subsequently, the V-bent sample was reverse bent to flatten it. Next, U-bending was performed so that the V-bending vertex line and the U-bending vertex line were perpendicular to each other. U-bending with a 90° rotation was performed in the longitudinal direction C (length of one bending vertex line: 55 mm (L)) using a hydraulic bending testing machine, such that the bending radius of the punch was varied, and the travel speed was 1,500 mm / minute, which is relatively high. The vertex line flexural cracking was evaluated by performing two types of flexural tests: an outward bending test and an inward bending test. In the outward bending test, the V-shaped bending vertex side, which was performed first, was the same as the 90°-rotated U-shaped bending vertex side, which was performed later, and therefore the flexural vertex line positions were located outside the 90°-rotated U-shaped bending test specimen. In the inward bending test, the V-bend apex side, which was performed first, was different from the 90°-rotated U-bend apex side, which was performed later, and therefore, the bending apex line positions were located inside and outside the 90°-rotated U-bend test specimen.In the 90°-rotated U-shaped bending test specimen, the presence or absence of a crack at the bending end was determined at a position on the bending vertex line that was bent twice. Specifically, the cracking threshold R / t was determined for each of the two types of bending tests with the specimen bent outward and with the specimen bent inward. When the R / t values ​​were the same, the R / t value was used as the evaluation result of the bending cracking of the vertex line portion, and when the R / t values ​​were different, the larger R / t value was used as the evaluation result of the bending cracking of the vertex line portion. The cracking threshold R / t was evaluated, which was a minimum R / t at which no crack of 0.5 mm or more formed. In cases where R / t < 5.0, a rating of “good” was given. Regarding the compression performance, a flexural compression test was performed as described below, and determinations were made based on the deformation state. Bending was performed to form a member with a hat-shaped cross-section. A steel sheet of the same type was joined to the member by spot welding so that the steel sheet could serve as a support. The member was then struck with a weight of 100 kgf in a widthwise direction at a speed corresponding to 36 km / h, thus crushing it. The deformation state of the member was then visually examined. In cases where the member collapsed without cracking, a rating of “O” was given, and in cases where cracking occurred, a rating of “x” was given.Regarding the compression performance, an axial compression test was performed as described below, and determinations were made based on the deformation pattern. Bending was performed to form a hat-shaped element. A steel sheet of the same type was attached to the element by spot welding, so that the steel sheet could serve as a support. The element was then struck with a weight of 300 kgf in an axial direction at a speed corresponding to 36 km / h, thus crushing it. The deformation state of the element was then visually examined. In cases where the element collapsed without cracking, a grade of "O" was given, and in cases where cracking occurred, a grade of "x" was given. The evaluation results are shown in Tables 3-1 and 3-2. noefrnn / zznz / e / YiAi & hc O 01 O 01 O 01 O hcc & Board 1 c Type of steel Chemical composition (% by mass) Transformation temperature Aci Notes C Si Mn PSN Al Ti Nb VWB Ni Cr Mo Cu Su Sb Ta Ca Mg Zr REM °C) A 0.134 042 4.08 0.008 0.0010 0.0031 0.032 • 639 Steel of the mention B 0.144 0.15 5.08 0.011 0.0009 0.0022 0.023 608 Steel of the invention C 0.133 0.38 3.73 0.034 0.0014 0.0033 0.039 • 649 Steel of the invention D 0.127 0.14 4.32 0.011 0.0044 0.0038 0.033 • 630 Invention Steel E 0.045 0.88 5.59 0.014 0.0010 0.0042 0.040 - 603 Invention Steel F 0.175 1.70 4.82 0.008 0.0015 0.0045 0.036 - 632 Invention Steel G 0.129 0.04 5.24 0.015 0.0012 0.0032 0.034 • 603 Invention Steel H 0.012 0.68 4.82 0.013 0.0020 0.0042 0.031 623 Comparative Steel 1 0.129 352 3.69 0.015 0.0016 0.0033 0.035 684 Comparative Sidewalk J 0.136 0.35 242 0.019 0.0019 0.0032 0.038 • 693 Comparative Sidewalk K 0.142 0.38 4.12 0.010 0.0006 0.0024 0.003 • 638 Invention Sidewalk L 0.152 0.13 4.64 0.012 0.0007 0.0040 1.100 620 Invention Sidewalk M 0.154 0.52 5.09 0.008 0.0007 0.0033 0.036 0.042 • 612 Sidewalk of the invention N 0.163 0.28 2.94 0.018 0.0012 0.0032 0.042 0.038 - 669 Sidewalk of the invention 0 0.134 1.28 3.67 0.012 0.0024 0.0034 0.041 W) 660 Sidewalk of the invention P 0.179 0.78 5.03 0.013 0.0014 0.0038 0.045 0.019 • 616 Sidewalk of the invention Q 0.102 1.05 4.03 0.031 0.0018 0.0049 0.032 0.052 0.0015 648 Invention side R 0.108 1.22 3.69 0.022 0.0025 0.0035 0.031 MSP - 651 Invention side S 0.135 0.46 4.45 0.016 0.0017 0.0021 0.045 0.236 • 632 Invention side T 0.156 0.48 5.23 0.014 0.0021 0.0052 0.033 М48 • 608 Invention side U 0.207 0.07 3.45 0.012 0.0030 0.0025 0.027 651 About the invention V 0.089 0.66 5.58 0.009 0.0021 0.0043 0.035 • W41 601 About the invention W 0.133 0.29 4.59 0.018 0.0015 0.0065 0.044 • M 624 About the invention. a ω o Ül ω μ μ O Ü1 ο -1σι σι ο X 0.161 0.38 5.13 0.015 0.0012 0.0042 0.036 609 Steel of the invention Y 0.141 0.29 4.73 0.015 0.0014 0.0028 0.033 0042 0.009 619 Sidewalk of the invention z 0.120 0.59 5.39 0.021 0.0012 0.0048 0.050 0.038 0.008 605 Sidewalk of the invention AA 0.114 0.34 4.19 0.010 0.0015 0.0041 0.038 0.0026 636 Sidewalk of the invention AB 0.146 0.71 5.31 0.032 0.0032 0.0041 0.035 • 0.0025 608 Invention Steel AC 0.168 0.52 4.35 0.012 0.0022 0.0034 0.031 0.0024 632 Invention Steel AD 0.182 0.15 5.56 0.013 0.0015 0.0032 0.052 0.0024 594 Invention Steel AE 0.105 0.15 £15 0.015 0.0015 0.0025 0.035 579 Comparative Steel Underlined values ​​indicate that the value or type of steel is outside the scope of the present invention. The symbol indicates that the content is at a similar level to incidental impurities. > & hchhcc 4 & C c (O ω CJ1 ω μ μ ο υι ο Table 2-1 No. Steel Type As-rolled Delivery Temperature Coiling Temperature (°C) Annealing Process for Hot Rolled Steel Sheet Average Cooling Rate in the Range of 550°C to 400°C after Heat Treatment of Hot Rolled Steel Sheet (°C / h) Reduction Ratio where Cold Rolled (%) Average Heating Rate in the Temperature Range of 400°C to Transformation Temperature Aci W First Heat Treatment of Hot Rolled Steel Sheet Alloying Temperature (°C) Second Heat Treatment of Hot Rolled Steel Sheet Type* Notes Annealing Temperature (°C) Holding Time (s) Heat Treatment Temperature (°C) Heat Treatment Time (s) Heat Treatment Temperature (°C) Heat Treatment Time |s| 1 A 920 490 690 80000 100 60.0 15 700 200 CR Example of invention 2 A 850 600 700 60000 70 56.3 14 690 180 CR Invention example 3 A 830 620 720 50000 110 55.6 13 730 200 Gl Invention example 4 A 880 570 690 80000 60 60.0 17 720 280 Gl Invention example 5 A 900 510 690 190000 40 66.7 19 710 160 110 40000 Gl Invention example 6 A 900 550 710 90000 110 61.1 22 690 170 140 50000 Gl Invention example 7 A 870 590 690 120000 140 55.6 13 700 250 500 GA Invention example 8 A 900 530 730 90000 80 66.7 20 690 210 490 GA Invention example 9 A 850 610 690 150000 70 55.6 14 720 160 510 100 80000 GA Invention example 10 A 900 540 700 70000 70 61.1 12 700 220 500 120 50000 GA Invention example 11 A 880 500 710 60000 60 64.7 13 690 190 Al Invention example 12 A 940 570 680 70000 80 61.1 15 720 250 To Invention Example 13 A 910 600 690 100000 100 66.7 14 710 240 90 100000 To Invention Example 14 A 910 460 720 80000 70 70.6 13 690 220 120 60000 To Invention Example 15 A 920 530 730 140000 50 64.7 17 700 120 EG Invention example 16 A 870 580 700 80000 40 66.7 19 700 150 EG Invention example 17 A 860 550 670 120000 70 61.1 16 700 180 110 80000 EG Invention example 18 A 920 600 690 80000 90 61.1 21 690 150 80 120000 EG Invention example 19 A 900 500 550 60000 110 56.3 15 700 180 CR Comparative example. & hchhcc & C c ω ω μ σι ο σι Μ ο σι ο σι 20 A 850 550 800 50000 130 556 16 730 200 510 GA Comparative example 21 A 930 480 690 15000 70 60.0 17 690 250 Gl Comparative example 22 A 870 510 690 120000 2 66.7 19 710 150 490 GA Comparative example 23 A 830 490 720 80000 400 61.1 14 720 300 90 80000 CR Comparative example 24 A 910 550 700 100000 60 55.6 3 690 500 EG Example Comparative 25 A 890 580 690 180000 100 64.7 13 530 200 500 110 60000 GA Comparative example 26 A 860 600 710 150000 80 66.7 17 920 100 CR Comparative example 27 A 840 520 730 90000 90 56.3 19 710 5 530 GA Comparative example 28 B 900 550 660 150000 110 58.8 22 670 160 CR Inventive example 29 B 860 620 650 80000 40 56.3 13 690 180 510 90 70000 GA Example of invention 30 C 900 520 700 90000 30 60.0 20 720 160 CR Example of invention 31 D 910 540 650 100000 50 58.8 14 690 220 520 100 60000 GA Example of invention Underlined values ​​indicate that the value or type of sidewalk is outside the scope of the present invention. 'CR: Cold-rolled sidewalk sheet, Gl: Hot-dip galvanized sidewalk sheet (without alloying process for zinc coating), GA: Heat-treated sidewalk sheet after hot-dip galvanizing, Al: Hot-dip aluminum-coated steel sheet, EG: Electro-galvanized steel sheet U1 ω n ro Or Ü1 or Table 2-2 No. Steel Type Finish Rolling Delivery Temperature ('C) Coiling Temperature ('C) Annealing Process for Hot Rolled Steel Sheet Average Cooling Rate in the Range of 550'0 to 400'0 after Heat Treatment of Hot Rolled Steel Sheet ('C / h) Cold Rolled Reduction Ratio (%) Average Heating Rate in the Temperature Range of 400'C Transformation Temperature Aci ('C / s) First Heat Treatment of Hot Rolled Steel Sheet Alloying Temperature ('C) Second Heat Treatment of Hot Rolled Steel Sheet Type* Notes Annealing Temperature ('C) Slow Holding Time ww Heat Treatment Temperature ('C) Heat Treatment Time (s) Heat Treatment Temperature ('C) Heat Treatment Time 32 E 920 530 630 50000 20 58.8 12 670 210 500 GA Example of invention 33 F 900 570 660 60000 90 57.1 13 700 300 130 70000 Gl Invention example 34 G 880 580 640 80000 30 50.0 15 660 180 CR Invention example 35 H 870 600 670 130000 60 46.2 14 690 280 CR Comparative example 36 I 860 530 710 190000 100 62.5 13 740 220 140 50000 CR Comparative example 37 J 900 500 730 110000 110 58.8 17 750 180 510 GA Comparative example 38 K 910 520 680 90000 130 61.1 19 710 150 CR Invention example 39 L 890 500 650 140000 90 58.8 22 690 280 500 120 90000 GA Invention example 40 M 880 530 640 80000 40 56.3 13 670 200 CR Invention example 41 M 870 580 630 110000 80 57.1 20 680 170 100 70000 Gl Invention example 42 M 850 600 650 80000 120 50.0 14 690 210 510 130 50000 GA Invention example 43 M 900 610 640 140000 150 46.2 12 670 230 110 80000 Al Invention example 44 M 920 630 650 150000 80 64.7 13 680 230 90 100000 EG Invention example 45 N 860 620 700 90000 120 62.5 15 720 360 500 180 110000 GA Invention example 46 0 870 560 690 60000 60 64.7 14 720 270 CR Invention example 47 P 830 570 650 80000 60 50.0 13 690 250 CR Invention example 48 Q 850 530 680 140000 50 53.8 17 700 180 540 180 50000 GA Invention example 49 R 930 540 690 200000 50 52.9 19 710 200 550 GA Invention example 50 S 900 550 680 90000 40 47.1 19 680 170 520 GA Invention example 51 T 920 560 640 90000 20 55.6 15 670 140 510 210 30000 GA Example of invention 52 U 890 520 690 50000 40 56.3 16 710 150 Al Example of invention. > & h C hh C c 4 & cca ω ω μ ο οι ο υι M o in ο σι 53 V 880 500 650 80000 60 70.6 13 670 80 520 GA Invention example 54 W 870 590 700 110000 50 64.7 16 690 110 90 120000 GI Invention example 55 X 880 610 630 70000 60 50.0 15 690 140 EG Invention example 56 Y 890 620 670 80000 30 56.3 13 680 200 CR Invention example 57 z 900 580 640 90000 70 52.6 15 660 180 490 GA Example of invention 58 AA 920 620 690 130000 50 28.1 16 700 200 230 30000 Al Example of invention 59 AB 860 560 650 180000 60 50.0 17 660 450 510 150 50000 GA Example of invention 60 AC 850 570 680 50000 30 56.3 19 690 150 CR Example of invention 61 AD 810 530 630 80000 120 57.1 17 650 180 500 110 70000 GA Example of invention 62 AE 860 480 650 140000 60 58.8 15 700 200 180 70000 CR Comparative example Underlined values ​​indicate that the value or type of steel is outside the scope of the present invention. 'CR: tri-rolled steel sheet, GI: hot-dip galvanized steel sheet (without alloying process for zinc coating), GA: steel sheet subjected to heat treatment after hot-dip stamping, Al: hot-dip aluminum-coated steel sheet, EG: electro-galvanized steel sheet l ω ω ο σι o Μ Μ σι ο σι Table 3-1 > & hchhcci & cc No. Sidewalk Type Sheet Thickness (mm) Area Fraction of F(%) Area Fraction of M(%) Area Fraction of RA(%) Average Grain Size of F(pm) Average Grain Size of RAW RA Content (% by mass) Ra Content Mn / Mn Content of Steel Ratio of Retained Austenite Grains with An Aspect Ratio of 3.0 or Greater (%) Ratio of Retained Austenite Grains with An Interior Aspect Ratioa ≥ 2.0(¾) Amount of Diffusible Hydrogen in Steel (mass / pm) Vya / Vyb Remaining Constituents TS (MPa) EL (¾) YP EL w U.EL (%) Thickness of Threshold Crack Spacing in Contact Bending Test after U-Bending (mm) Handkerchief Fold Test (HFR) R / t V-bend with 90' rotation Bending test in UR / t Strain shape in flexural compression. Strain shape in axial compression. Type* Notes 1 A 1.2 72.7 8.9 17.2 3.1 0.6 8.02 1.97 49 38 0.06 0.65 0 1012 28.9 4.1 23.9 3.5 3.0 3.5 0 0 CR Invention Example 2 A 1.4 77.3 9.2 12.8 3.3 0.5 8.37 2.05 38 48 0.05 0.64 0 997 32.7 3.2 27.7 3.0 2.5 3.0 0 0 CR Invention Example 3 A 1.6 74.1 11.2 13.2 3.2 0.5 8.08 1.98 52 35 0.56 0.61 0 1009 29.8 4.8 24.8 5.0 4.0 4.5 0 0 Gl Invention Example 4 A 1.6 76.4 8.5 13.7 2.2 0.7 8.45 2.07 28 68 0.58 0.65 0 1020 33.8 3.1 28.8 5.0 4.0 4.0 0 0 Gl Invention example 5 A 1.2 74.3 6.2 16.3 2.9 0.8 8.01 1.96 72 25 0.02 0.66 TM,TB, 0 989 30.9 4.5 25.9 3.5 3.5 4.0 0 0 Gl Invention example 6 A 1.4 74.9 5.3 16.1 3.2 0.5 8.24 2.02 47 42 0.01 0.62 TM,TB, 0 996 35.1 2.8 30.1 3.0 3.5 3.0 0 0 Gl Invention example 7 A 1.6 74.6 11.8 13.1 2.8 0.7 8.05 1.97 39 53 0.57 0.61 0 989 30.4 4.0 25.4 5.0 4.5 5.0 0 0 GA Invention example. hc AUU M MA OUIOUIOWOUI hcc 8 A 1.2 77.5 6.4 15.7 3.7 0.8 8.12 1.99 22 69 0.57 0.61 0 1001 339 3.1 28.9 5.0 4.0 4.0 0 0 GA Invention example 9 A 1.6 72.2 6.7 16.4 2.8 0.5 8.02 197 36 56 0.02 0.64 TM,TB, 0 994 30.8 4.3 25.8 3.5 3.5 3.5 0 0 GA Invention example 10 A 1.0 74.4 5.1 16.5 2.2 0.6 8.68 2.13 43 41 0.01 0.67 TM,TB, 0 1006 35.1 2.8 30.1 3.0 3.0 4.5 0 0 GA Invention example 11 A 1.2 69.3 10.1 18.9 2.0 0.4 8.97 2.20 58 36 0.52 0.70 0 1002 29.8 4.5 24.8 4.5 4.0 4.0 0 0 AI Invention example 12 A 1.4 71.5 9.4 17.8 2.2 0.7 912 2.24 63 24 0.53 0.71 0 996 339 2.8 28.9 4.5 4.0 4.5 0 0 AI Invention example 13 A 1.6 70.3 10.3 15.1 2.3 0.8 9.02 2.21 71 25 021 0.70 TM,TB, 0 1018 28.5 4.8 23.5 3.5 3.5 3.0 0 0 AI Invention example 14 A 1.2 73.9 9.2 15.8 2.1 0.5 8.85 2.17 23 67 0.25 0.69 TM,TB, 0 1012 32.8 3.1 27.8 4.0 2.5 4.0 0 0 AI Invention example 15 A 1.4 72.8 5.4 20.4 2.2 0.7 916 2.25 40 51 0.53 0.72 0 998 29.5 4.3 24.5 4.5 4.0 4.0 0 0 EG Invention example 16 A 1.4 75.6 4.8 19.2 2.0 0.6 8.74 2.14 51 43 0.52 0.67 0 992 32.0 2.8 27.0 4.5 4.0 4.5 0 0 EG Invention example 17 A 1.4 69.8 10.5 15.9 2.2 0.4 9.22 2.26 62 34 0.31 0.72 TM,TB, 0 988 29.5 4.1 24.5 3.5 4.0 3.0 0 0 EG Invention example 18 A 1.4 73.1 7.6 16.5 2.8 0.3 8.91 2.18 47 42 0.22 0.69 0 1002 32.1 3.2 27.1 3.0 2.5 4.0 0 0 EG Invention Example 19 A 1.4 72.3 12.1 4.4 34 5.32 130 17 80 0.06 026 6 1024 16.3 2.5 12.3 7.5 6.5 6.5 XX CR Comparative Example 20 A 1.6 73.1 14.2 92 3.3 27 5.06 124 72 18 0.59 032 0 1085 15.5 2.1 119 6.0 6.5 7.0 XX GA Comparative Example 21 A 1.6 75.9 8.6 105 2.6 39 5.42 U3 23 72 0.61 023 0 994 19.2 2.8 14.2 6.5 6.0 6.0 XX GI Comparative example 22 A 1.2 77.2 9.6 84 63 42 6.70 1.64 39 51 0.64 0.45 0 1008 12.2 05 10.1 7.0 7.5 7.5 XX GA Comparative example 23 A 1.4 74.5 6.9 14.0 59 22 6.98 1.71 4 78 0.02 0.52 TM,TB, 0 1010 14.7 02 13.2 6.0 6.5 6.5 XX CR Comparative example. a ω ω μ ο σι ο σι M ο σι ο 24 A 1.6 78.4 4.7 12.8 72 1.6 7.04 1.73 20 75 0.56 0.80 0 1021 26.2 05 21.3 6.0 6.5 6.5 XX EG Comparative example 25 A 1.2 85.6 28 33 4.8 0.4 9.12 2.24 78 11 0.07 617 TM,TB, 0 687 26.1 2.4 20.2 4.5 4.0 4.5 XX GA Comparative example 26 A 1.2 41.9 302 45 68 34 9.11 2.23 38 47 0.05 0.82 0 1289 11.1 02 9.3 7.0 7.5 7.0 XX CR Comparative Example 27 A 1.4 869 25 36 49 0.3 9.08 2.23 42 44 0.54 0.74 0 708 23.9 2.4 19.1 5.0 5.0 4.5 0 0 GA Comparative Example 28 B 1.4 70.7 6.2 20.7 2.1 0.7 892 1.76 39 52 0.06 0.69 0 1018 29.5 2.8 24.5 3.5 3.0 3.5 0 0 CR Invention Example 29 B 1.4 71.8 5.1 18.9 2.8 0.6 9.20 1.81 65 31 0.01 0.72 TM,TB, 0 1012 32.0 4.0 27.0 4.0 2.5 3.0 0 0 GA Invention example 30 C 1.2 64.8 13.4 20.8 2.6 0.6 9.30 2.49 43 41 0.06 0.73 0 998 29.5 2.8 24.5 3.5 3.0 3.0 0 0 CR Invention example 31 D 1.4 65.8 10.2 19.1 2.5 0.4 9.28 2.15 29 67 0.04 0.73 TM,TB, θ 996 35.1 4.3 30.1 4.0 4.0 4.5 0 0 GA Invention example Underlined values ​​indicate that the value or type of steel is outside the scope of the present invention. > & hchhcc 4 & C c F: ferrite, M: martensite, RA: retained austenite, TM: tempered martensite, TB: tempered bainite, θ: carbides such as cementite ω 0) 'CR: cold-rolled steel sheet, Gl: hot-dip galvanized steel sheet (without alloying process for zinc coating), GA: steel sheet subjected to heat treatment after hot-dip galvanizing, Al: hot-dip aluminum-coated steel sheet, EG: electro-galvanized steel sheet ω ω ο σι ο μ μ σι ο σι Table 3-2 No. Steel type Sheet thickness (mm) Volume fraction of F W Volume fraction of M W Volume fraction of RA Average grain size of F Average grain size of RA (µPΊ) Mn content of RA (% by mass) Mn content of Ra / M content of steel Ratio of retained austenite grains with an aspect ratio of 3.0 or greater W Ratio of retained austenite grains with an aspect ratio less than 2.0 (%) Amount of diffusible hydrogen in steel (mass / ppm) Vya / V Remaining constituents TS (MPa) EL (%) YPEL (%) U.EL (%) Thickness of crack threshold spacer in contact bending test after U-bending (mm) Handkerchief bend test RA 90° rotation V-bend test URA bend test Shape of deformation in flexural compression. Form of deformation in axial compression. Tpo* Notes 32 E 1.6 63.3 13.6 21.2 2.8 0.5 9.30 1.66 64 30 0.53 0.73 θ 989 30.4 4.5 25.4 4.5 4.0 4.0 0 0 GA Example of invention 33 F 1.6 64.2 11.8 18.9 2.9 0.4 9.28 1.92 54 34 0.04 0.73 ΤΜ,ΤΒ, θ 989 30.9 3.1 25.9 4.0 4.0 4.5 0 0 Gl Example of invention 34 G 1.2 64.5 10.2 21.5 2.6 0.6 9.10 1.74 32 59 0.05 0.71 θ 996 35.1 4.5 30.1 3.5 3.0 3.5 0 0 CR Example of invention 35 H 1.4 78.9 23 2J 4.5 1.2 9.23 1.91 72 12 0.05 o θ Μ4 20.4 2.2 15.4 7.5 6.5 7.0 XX CR Comparative example 36 1 1.6 65.2 12.5 18.7 2.9 1.0 9.08 2.46 38 54 0.01 822 ΤΜ,ΤΒ, θ 993 21.7 1.8 16.7 7.0 6.0 6.5 XX CR Comparative example 3? J 1.2 66.0 24.8 82 4.6 0.7 9.22 4.35 32 58 0.57 0.55 θ 995 186 2.0 13.6 7.5 7.0 7.0 XX GA Comparative example 38 K 1.6 69.1 11.1 17.9 1.5 0.4 9.14 2.22 31 53 0.06 0.71 θ 1002 29.8 4.5 24.8 3.0 3.0 3.0 0 0 CR Example of invention 39 L 1.0 67.4 9.2 19.6 1.9 0.8 9.09 1.96 49 36 0.01 0.71 ΤΜ,ΤΒ, θ 996 33.9 2.8 28.9 3.0 3.5 3.0 0 0 GA Example of invention 40 M 1.4 72.7 8.9 17.2 2.4 0.7 8.89 1.75 41 52 0.05 0.69 θ 996 35.1 2.8 30.1 3.0 3.5 3.5 0 0 CR Example of invention. > & h c h h c c 4 & C c A 0 ω ΟΙ ω 0 M υι M 0 _ι σ —k 0 σ > & h C hhcc 41 M 1.4 67.5 10.2 18.6 2.5 0.8 8.94 1.76 28 70 0.31 0.69 TM,TB, θ 989 30.4 4.0 25.4 3.0 2.5 3.0 0 0 GI Example of invention 4 & C c 42 M 1.2 68.7 8.9 17.2 2.2 0.6 7.80 1.53 34 55 0.02 0.55 TM,TB, θ 1001 33.9 3.1 28.9 4.0 2.5 2.5 0 0 GA Example of invention 43 M 1.4 70.9 10.7 13.2 2.7 0.8 7.97 1.57 52 38 0.04 0.60 TM,TB, θ 994 30.8 4.3 25.8 3.5 3.0 2.5 0 0 AI Example of invention 44 M 1.6 71.7 10.8 13.9 2.6 0.7 8.27 1.62 24 68 0.21 0.63 TM,TB, θ 989 30.9 4.5 25.9 3.5 2.5 3.0 0 0 EG Example of invention 45 N 1.8 69.7 6.7 19.7 2.5 0.5 8.36 2.84 49 I 989 30.4 4.0 25.4 3.0 2.5 3.0 0 0 CR Ejemplo de invención 47 P 1.2 71.8 7.4 19.2 2.8 0.8 8.01 1.59 62 35 0.05 0.60 θ 1001 33.9 3.1 28.9 3.5 2.5 3.5 0 0 CR Ejemplo de invención 48 Q 1.4 68.2 10.2 17.6 2.9 1.0 6.29 1.56 28 68 0.29 0.64 TM,TB, θ 994 30.8 4.3 25.8 4.0 3.0 3.0 0 0 GA Invention example ω 49 R 1.4 70.6 8.7 18.9 2.8 0.8 7.91 2.14 22 71 0.51 0.59 θ 1006 35.1 2.8 30.1 4.5 4.0 4.5 0 0 GA Invention example co 50 S 1.2 71.2 7.3 19.7 1.9 0.7 9.16 2.06 25 59 0.52 0.72 θ 1002 29.8 4.5 24.8 4.5 4.0 5.0 0 0 GA Invention example 51 I 1.2 71.2 10.2 17.6 2.2 0.7 8.04 1.54 34 59 0.04 0.60 ΤΜ,ΤΒ, θ 996 33.9 2.8 28.9 3.0 3.0 3.0 0 0 GA Example of invention 52 U 1.4 70.7 10.5 18.2 2.5 0.4 8.58 2.49 42 50 0.55 0.66 θ 1018 28.5 4.8 23.5 5.0 4.0 4.5 0 0 ΑΙ Example of invention 53 V 1.2 71.1 6.2 21.5 2.8 0.6 8.73 1.56 32 55 0.53 0.60 θ 1012 32.8 3.1 27.8 4.5 4.0 4.0 0 0 GA Invention example 54 W 1.6 70.2 9.8 15.8 2.3 0.8 8.47 1.85 22 69 0.06 0.65 TM,TB, θ 998 29.5 4.3 24.5 3.5 2.5 3.0 0 0 GI Invention example 55 X 1.8 69.1 10.6 19.2 2.2 0.9 8.57 1.67 28 70 0.56 0.66 θ 1019 28.5 4.8 23.5 5.0 4.5 4.5 0 0 EG Invention example 56 Υ 1.6 71.4 8.9 19.5 2.9 0.7 8.38 1.77 34 53 0.05 0.64 θ 1012 32.8 3.1 27.8 4.0 3.0 3.0 0 0 CR Example of invention. £ ω ω μ μ ο σι ο σι ο σι ο σι 57 Z 14 72.2 10.1 164 2.2 0.6 842 1.56 54 41 0.56 0.64 θ 998 29.5 4.3 24.5 5.0 4.0 4.5 0 0 GA Invention example 58 AA 1.0 73.1 7.7 149 2.6 0.5 8.66 2.07 36 56 0.25 0.67 TM,TB, θ 1002 29.8 4.5 24.8 4.0 3.0 3.0 0 0 AI Invention example 59 AB 1.2 70.2 5.7 212 2.9 04 8.81 1.66 30 64 0.02 0.68 ΤΜ,ΤΒ, θ 996 33.9 2.8 28.9 3.5 2.5 3.5 0 0 GA Invention example 60 AC 1.6 70.6 10.3 17.8 3.1 0.7 8.71 2.00 27 69 0.05 0.67 θ 1018 28.5 4.8 23.5 4.0 2.5 3.0 0 0 CR Example of invention 61 AD 14 714 6.7 18.1 3.2 04 8.53 1.53 42 49 0.05 0.65 ΤΜ,ΤΒ, θ 1012 32.8 3.1 27.8 3.0 2.5 3.0 0 0 GA Example of invention 62 AE 1.6 55.2 22.5 18.7 2.2 0.7 9.58 1.56 35 50 0.02 ΤΜ,ΤΒ, θ 1025 18.5 2.2 13.5 6.5 6.5 6.5 XX CR Comparative example Underlined values ​​indicate that the value or type of sidewalk is outside the scope of the present invention. F: ferrite, M: martensite, RA: retained austenite, TM: tempered martensite, TB: tempered bainite, θ: carbides such as cementite CR: trio-rolled sidewalk sheet, Gl: hot-dip galvanized steel sheet (without alloying process for zinc coating), GA: heat-treated steel sheet after hot-dip galvanizing, Al: hot-dip aluminum-coated steel sheet, EG: electro-galvanized steel sheet ω The steel sheets of the present invention had a TS of 980 MPa or higher and also had excellent uniform ductility, bendability, and compression performance. In contrast, in Comparative Examples, one of the properties, particularly, TS, EL, YP-EL, 5 U.EL, various types of bendability and compression shapes, was deficient.

Claims

1. A high-strength steel sheet, characterized in that the high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or higher, the high-strength steel sheet has a chemical composition containing, by mass %, C: 0.030% or more and 0.250% or less, Si: 2.00% or less, Mn: 3.10% or more and 6.00% or less, P: 0.100% or less, S: 0.0200% or less, N: 0.0100% or less, and Al: 1.200% or less, with some Fe and incidental impurities, and the high-strength steel sheet having a microstructure in which ferrite is present in an area fraction of 30.0% or more and less than 80.0%, and martensite is present in an area fraction of 3.0% or more and 30.0% or less, the retained austenite is present in a volume fraction of 12.0% or more, the ferrite has an average grain size of 5.0 μm or less, the retained austenite has an average grain size of 2.0 gm or less, a value obtained by dividing a Mn content (% by mass) of the retained austenite by a Mn content (% by mass) of steel is 1.50 or higher, 15% or more of all austenite grains retained in the retained austenite have an aspect ratio of 3.0 or higher, and 15% or more of all austenite grains retained in the retained austenite have an aspect ratio lower than 2.0, wherein a value obtained by dividing a volume fraction Vya by a volume fraction Vyb is 0.40 or higher, wherein the volume fraction Vya is a volume fraction of austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C, and the volume fraction Vyb is a volume fraction of austenite retained before the hot tensile test at 150°C.

2. The high-strength steel sheet according to claim 1, further characterized in that the high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or higher, the high-strength steel sheet having a chemical composition containing, by mass %, C: 0.030% or more and 0.250% or less, Si: 0.01% or more and 2.00% or less, Mn: 3.10% or more and 6.00% or less, P: 0.001% or more and 0.100% or less, S: 0.0001% or more and 0.0200% or less, N: 0.0005% or more and 0.0100% or less, and Al: 0.001% or more and 1.200% or less, with a remainder of Fe and incidental impurities, and the high-strength steel sheet having a microstructure in which ferrite is present in an area fraction of 30.0% or more and less than 80.0%, martensite is present in an area fraction of 3.0% or more and 30.0% or less, retained austenite is present in a volume fraction of 12.0% or more, the ferrite has an average grain size of 5.0 μm or less, the retained austenite has an average grain size of 2.0 pm or less, a value obtained by dividing a Mn content (% by mass) of the retained austenite by a Mn content (% by mass) of steel is 1.50 or higher, 15% or more of all austenite grains retained in the retained austenite have an aspect ratio of 3.0 or higher, and 15% or more of all austenite grains retained in the retained austenite have an aspect ratio less than 2.0, wherein a value obtained by dividing a volume fraction Vya by a volume fraction Vyb is 0.40 or higher, where the volume fraction Vya is a volume fraction of austenite retained in a fractured portion of a tensile test specimen after a hot tensile test at 150°C, and the volume fraction Vyb is a volume fraction of austenite retained before the hot tensile test at 150°C.

3. The high-strength steel sheet according to claim 1 or 2, further characterized in that the high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or higher, wherein the chemical composition further contains, by mass %, at least one element selected from: Ti: 0.200% or less, Nb: 0.200% or less, V: 0.500% or less, W: 0.500% or less, B: 0.0050% or less, Ni: 1.000% or less, Cr: 1.000% or less, Mo: 1.000% or less, Cu: 1.000% or less, Sn: 0.200% or less, Sb: 0.200% or less, Ta: 0.100% or less, Zr: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0050% or less, and REM: 0.0050% or less.

4. The high-strength steel sheet according to claim 3, further characterized in that the high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or higher, wherein the chemical composition contains, % by mass, at least one element selected from Ti: 0.002% or more and 0.200% or less, Nb: 0.005% or more and 0.200% or less, V: 0.005% or more and 0.500% or less, W: 0.0005% or more and 0.500% or less, B: 0.0003% or more and 0.0050% or less, Ni: 0.005% or more and 1.000% or less, Cr: 0.005% or more and 1.000% or less, Mo: 0.005% or more and 1.000% or less, Cu: 0.005% or more and 1.000% or less, Sn: 0.002% or more and 0.200% or less, Sb: 0.002% or more and 0.200% or less, Ta: 0.001% or more and 0.100% or less, Zr: 0.0005% or more and 0.0050% or less, Ca: 0.0005% or more and 0.0050% or less, Mg: 0.0005% or more and 0.0050% or less, and REM: 0.0005% or more and 0.0050% or less.

5. The high-strength steel sheet according to any of claims 1 to 4, further characterized in that the high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or higher, wherein the amount of diffusible hydrogen in the steel is 0.50 ppm by mass or less.

6. The high-strength steel sheet according to any of claims 1 to 5, further characterized in that the high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or higher, wherein the high-strength steel sheet has a zinc-coated layer on a surface of the steel sheet.

7. The high-strength steel sheet according to any of claims 1 to 5, further characterized in that the high-strength steel sheet has an elongation limit (YP-EL) of 1.0% or more and a tensile strength (TS) of 980 MPa or higher, wherein the high-strength steel sheet has an aluminum-coated layer over a surface of the steel sheet.

8. An impact absorption element, characterized in that the impact absorption element comprises an impact absorption portion that absorbs impact energy by compression and bending deformation, the impact absorption portion comprising the high-strength steel sheet according to any one of claims 1 to 7.

9. An impact absorption element, characterized in that the impact absorption element comprises an impact absorption portion that absorbs impact energy by axial compression and bellows-like deformation, the impact absorption portion comprising the high-strength steel sheet according to any one of claims 1 to 7.

10. A method for manufacturing high-strength steel sheet according to any one of claims 1 to 4, characterized in that the method comprises: performing a pickling process on a hot-rolled steel sheet; holding the resulting steel sheet within a temperature range of a transformation temperature Aci or higher and “the transformation temperature Am +150°C” or lower for a period of more than 21,600 seconds and 259,200 seconds or less; subsequently cooling the resulting steel sheet at an average cooling rate of 5°C / hour or higher and 200°C / hour or lower through a temperature range of 550°C to 400°C; and subsequently cold-rolling the resulting steel sheet.heating a resulting cold-rolled steel sheet at an average heating rate of 8°C / hour or higher and 50°C / hour or lower through a temperature range from 400°C to the transformation temperature Am, and maintaining the resulting cold-rolled steel sheet within a temperature range of the transformation temperature Aci or higher and “the transformation temperature Aci +150°C” or lower for a period of 20 seconds or more and 3,600 seconds or less.

11. A method for manufacturing the high-strength steel sheet according to claim 6, characterized in that the method comprises: performing a pickling process on a hot-rolled steel sheet; holding the resulting steel sheet within a temperature range of a transformation temperature Aci or higher and “transformation temperature Aci + 150°C” or lower for a period of more than 21,600 seconds and 259,200 seconds or less; subsequently cooling the resulting steel sheet at an average cooling rate of 5°C / hour or higher and 200°C / hour or lower through a temperature range of 550°C to 400°C; subsequently cold-rolling the resulting steel sheet; heating a resulting cold-rolled steel sheet at an average heating rate of 8°C / second or higher and 50°C / second or lower through a temperature range of 400°C to the transformation temperature Am,Maintain the resulting cold-rolled steel sheet within a temperature range of the Aci transformation temperature or higher and “the Aci transformation temperature +150°C” or lower for a period of 20 seconds or more and 3,600 seconds or less; and subsequently perform a hot-dip galvanizing process or an electrogalvanizing process on the resulting cold-rolled steel sheet.

12. A method for manufacturing the high-strength steel sheet according to claim 7, characterized in that the method comprises: performing a pickling process on a hot-rolled steel sheet; holding the resulting steel sheet within a temperature range of a transformation temperature Aci or higher and “transformation temperature Aci + 150°C” or lower for a period of more than 21,600 seconds and 259,200 seconds or less; subsequently cooling the resulting steel sheet at an average cooling rate of 5°C / hour or higher and 200°C / hour or lower through a temperature range of 550°C to 400°C; subsequently cold-rolling the resulting steel sheet; heating a resulting cold-rolled steel sheet at an average heating rate of 8°C / second or higher and 50°C / second or lower through a temperature range of 400°C to the transformation temperature Am,Maintaining the resulting cold-rolled steel sheet within a temperature range of the transformation temperature Aci or higher and “the transformation temperature norfrnn / zznz / e / YiAi Am +150°C” or lower for a period of 20 seconds or more and 3,600 seconds or less; and subsequently performing a hot aluminum coating process on the resulting cold-rolled steel sheet.

13. The method for manufacturing the high-strength steel sheet according to claim 10, further characterized in that, after the resulting cold-rolled steel sheet is held within the temperature range of the transformation temperature Am or higher and the transformation temperature Am +150°C or less for a period of 20 seconds or more and 3,600 seconds or less, the resulting cold-rolled steel sheet is held within a temperature range of 50°C or higher and 300°C or less for a period of 1,800 seconds or more and 259,200 seconds or less.

14. The method for manufacturing the high-strength steel sheet according to claim 11 or 12, further characterized in that, after the coating process, the resulting cold-rolled steel sheet is maintained within a temperature range of 50°C or more and 300°C or less for a period of 1,800 seconds or more and 259,200 seconds or less.