Abstract: Provided are a high-yield-ratio high-strength galvanized steel sheet that includes a Mn-containing steel sheet serving as a base material, and a production method therefor. The high-yield-ratio high-strength galvanized steel sheet includes a steel sheet having a specific composition and a metallographic structure including, by area percentage, 20% or less ferrite, 40% or more in total of bainite and tempered martensite, and 60% or less as-quenched martensite, the bainite having an average grain size of 6.0 ?m or less, and a coated layer arranged on the steel sheet, the coated layer having a coating weight per side of 20 to 120 g/m2 and having a Mn content of 0.05 g/m2 or less, in which the high-yield-ratio high-strength galvanized steel sheet has a yield ratio of 65% or more and a tensile strength of 950 MPa or more.

Abstract: A method of manufacturing a galvanized steel sheet having a composition containing, by mass %, C: 0.05% or more and 0.5% or less, Si: 0.01% or more and 2.5% or less, Mn: 0.5% or more and 3.5% or less, P: 0.003% or more and 0.100% or less, S: 0.02% or less, Al: 0.010% or more and 0.5% or less, B: 0.0002% or more and 0.005% or less, Ti: 0.05% or less, a relationship of Ti>4N being satisfied, and the balance comprising Fe and inevitable impurities, and a microstructure containing 60% or more and 95% or less of tempered martensite in terms of area ratio and 5% or more and 20% or less of retained austenite in terms of area ratio.

Abstract: A method of manufacturing a hot press formed part by hot pressing a coated steel sheet that is obtained by forming a Zn-based coating layer on a surface of a steel sheet includes: heating the coated steel sheet to a temperature range of 750° C. or more and 1000° C. or less; cooling a surface of the coated steel sheet; and hot press forming the coated steel sheet under a condition that a surface temperature of the coated steel sheet is 400° C. or less and an average temperature of the coated steel sheet is 500° C. or more or a temperature of a center position of the coated steel sheet in a thickness direction is 530° C. or more.

Abstract: A method for manufacturing a hot press formed part, includes: preparing a hot press forming object comprising a single-ply portion and a two-ply portion; heating the hot press forming object to a temperature range from an Ac3 transformation temperature of a base steel sheet of the first coated steel sheet to 1000° C.; press forming the hot press forming object to obtain a formed body, the press forming being started upon temperatures of the single-ply portion and of the two-ply portion being no higher than solidification points of Zn—Ni coating layers of the first and second coated steel sheets and no lower than an Ar3 transformation temperature of the base steel sheet of the first coated steel sheet; and quenching the formed body to thereby obtain a hot press formed part, in which the hot press forming object has a thickness ratio from 1.4 to 5.0.

Abstract: A galvanized steel sheet has formability and crashworthiness, consists of 0.03% to 0.13% C, 1.0% to 2.0% Si, 2.4% to 3.5% Mn, 0.001% to 0.05% P, 0.0001% to 0.01% S, 0.001% to 0.1% Al, 0.0005% to 0.01% N, and 0.0003% to 0.01% B on a mass basis; and optionally contains at least one selected from the following A-C: A: at least one selected from the group consisting of 0.0005% to 0.1% Ti and 0.0005% to 0.05% Nb on a mass basis; B: at least one selected from the group consisting of 0.01% to 1.0% Mo, 0.01% to 2.0% Ni, and 0.01% to 2.0% Cu on a mass basis; and C: 0.001% to 0.

Abstract: A method of evaluating a hot stamped part manufactured by hot stamping a coated steel sheet having a Zn—Ni coating layer on a surface of a base steel sheet includes an analysis model setting step, a forming condition setting step, a forming analysis step, and an evaluation step which are performed using a computer, wherein in the evaluation step, a maximum micro-crack depth in the hot stamped part manufactured under a forming condition set in the forming condition setting step is evaluated using a correlation, obtained beforehand, between an equivalent plastic strain in a surface layer of the hot stamped part and the maximum micro-crack depth in the hot stamped part.

Abstract: A high-strength galvanized steel sheet with high yield ratio having excellent ductility and stretch flange formability, the steel sheet having a chemical composition containing, by mass %, C: 0.04% or more and 0.13% or less, Si: 0.9% or more and 2.3% or less, Mn: 0.8% or more and 2.4% or less, P: 0.1% or less, S: 0.01% or less, Al: 0.01% or more and 0.1% or less, N: 0.008% or less, and the balance being Fe and inevitable impurities and a microstructure including, in terms of area ratio, 94% or more of a ferrite phase and 2% or less of a martensite ferrite phase, wherein mean grain size of ferrite is 10 ?m or less, Vickers hardness of ferrite is 140 or more, mean grain size of carbide particles existing at grain boundaries of ferrite is 0.5 ?m or less, and aspect ratio of carbide particles existing at the grain boundaries of ferrite is 2.0 or less.

Abstract: A method of manufacturing a hot press-formed part by hot pressing a coated steel sheet formed with a Zn—Ni plating layer on a surface of a steel sheet includes: heating the coated steel sheet to a temperature range of Ac3 transformation temperature to 1000° C.; cooling the coated steel sheet to 550-410° C. at a cooling rate of 100° C./s or higher by squeezing the coated steel sheet with a press tool for cooling having flat surfaces configured to contact the coated steel sheet; press forming the coated steel sheet with a tool of press forming to obtain a formed body, the press forming being initiated within 5 seconds after the cooling while the temperature of the coated steel sheet is 550-400° C.; and quenching the formed body, while squeezing the formed body with the tool of press forming and holding at its press bottom dead center, to obtain a hot press-formed part.

Abstract: A high-strength hot-dip galvanized steel sheet excellent in formability includes, on the basis of mass percent, 0.05-0.3% C, 1.4% or less (including 0%) Si, 0.08%-3% Mn, 0.003-0.1% P, 0.07% or less S, 0.1-2.5% Al, 0.1-0.5% Cr, and 0.007% or less N, Si+Al?0.5%, and the balance being Fe and incidental impurities, wherein the steel sheet has a retained austenite content of 3% or more by volume fraction, a stretch-flange formability ?>50% and wherein the average aspect ratio (major axis/minor axis) of retained austenite grains is less than 2.5.

Abstract: A galvanized steel sheet has formability and crashworthiness, consists of 0.03% to 0.13% C, 1.0% to 2.0% Si, 2.4% to 3.5% Mn, 0.001% to 0.05% P, 0.0001% to 0.01% S, 0.001% to 0.1% Al, 0.0005% to 0.01% N, and 0.0003% to 0.01% B on a mass basis; and optionally contains at least one selected from the following A-C: A: at least one selected from the group consisting of 0.0005% to 0.1% Ti and 0.0005% to 0.05% Nb on a mass basis; B: at least one selected from the group consisting of 0.01% to 1.0% Mo, 0.01% to 2.0% Ni, and 0.01% to 2.0% Cu on a mass basis; and C: 0.001% to 0.

Abstract: A method of manufacturing a high strength steel sheet having excellent formability suitable for the material of an automotive part has a tensile strength (TS) of 980 MPa or more and total elongation (EL) is 25% or more. A steel slab has a chemical composition containing C: 0.03% to 0.35%, Si: 0.5% to 3.0%, Mn: 3.5% to 10.0%, P: 0.100% or less, S: 0.02% or less, and the remainder includes Fe and incidental impurities on a percent by mass basis is hot-rolled, a heat treatment is performed, in which an achieved temperature of Ac1 to Ac1+100° C. is held for 3 minutes or more, subsequently, cold rolling is performed at a rolling reduction of 20% or more and, annealing is performed, in which an achieved temperature of Ac1?30° C. to Ac1+100° C. is held for 1 minute or more.

Abstract: A high-strength galvanized steel sheet having excellent formability and crashworthiness, including a component composition containing 0.03% to 0.13% C, 1.0% to 2.0% Si, 2.4% to 3.5% Mn, 0.001% to 0.05% P, 0.0001% to 0.01% S, 0.001% to 0.1% Al, 0.0005% to 0.01% N, and 0.0003% to 0.01% B on a mass basis, the remainder being Fe and unavoidable impurities, and a microstructure containing a tempered martensitic phase and a bainitic phase such that the sum of an area fraction of the tempered martensitic phase and an area fraction of the bainitic phase is 30% or more (the area fraction of the martensitic phase is 30% or more in the absence of the bainitic phase), wherein a distance of closest approach of the tempered martensitic phase is 10 ?m or less and the contents of C, Mn, and B satisfy (1): (% Mn)+1000×(% B)?35×(% C)??(1).

Abstract: A method for manufacturing the high strength steel sheet having excellent formability includes hot-rolling a steel slab having a chemical composition containing, by mass %, C: 0.03% or more and 0.35% or less, Si: 0.5% or more and 3.0% or less, Mn: 3.5% or more and 10.0% or less, P: 0.1% or less, S: 0.01% or less, N: 0.008% or less and the balance comprising Fe and inevitable impurities, coiling the hot-rolled steel sheet at a temperature range of the Ar1 transformation point to the Ar1 transformation point+(the Ar3 transformation point?the Ar1 transformation point)/2, cooling the coiled steel sheet down to 200° C. or lower, heating and holding the cooled steel sheet at a temperature range of the Ac1 transformation point?200° C.

Abstract: The present invention provides a method for manufacturing a high-strength galvannealed steel sheet. The method includes hot-rolling a slab to produce a hot-rolled sheet having a microstructure in which a total area ratio of bainite and martensite is 80% or more, cold-rolling the hot-rolled sheet to produce a cold-rolled steel sheet, continuously annealing the cold-rolled steel sheet by heating to 750° C. to 900° C. at an average heating rate of 8° C./s or more from 500° C. to an A1 transformation point, holding the steel sheet for 10 seconds or more, and then cooling the steel sheet to a temperature region of 300° C. to 530° C. at an average cooling rate of 3° C./s or more from 750° C. to 530° C., galvanizing the steel sheet, and further coating-alloying the steel sheet in a temperature region of 540° C. to 600° C. for 5 to 60 seconds.

Abstract: In manufacturing a hot press forming part by hot pressing, using a tool of press forming, a coated steel sheet, the tool of press forming having a die, a blank holder, and a punch, edges of the coated steel sheet heated to a temperature range of Ac3 transformation temperature to 1000° C. are cooled with the edges squeezed between the die and the blank holder to a temperature of 550° C. or lower and 400° C. or higher at a cooling rate of 100° C./s or higher, press forming is performed so that the press forming is started when the edges reach a temperature of 550° C. or lower and 400° C. or higher, and after the press forming, a formed body is quenched with the formed body held at the press bottom dead center while being squeezed by the tool of press forming.

Abstract: A formable galvanized steel sheet includes, in terms of % by mass, 0.05 to 0.3% of C, 0.01 to 2.5% of Si, 0.5 to 3.5% of Mn, 0.003 to 0.100% of P, 0.02% or less of S, 0.010 to 1.5% of Al, and 0.01 to 0.2% in total of at least one element selected from Ti, Nb and V, the remainder being Fe and unavoidable impurities, having a microstructure composed of, in terms of area fraction, 20 to 87% of ferrite, 3 to 10% in total of martensite and residual austenite, and 10 to 60% of tempered martensite, and a second phase composed of the martensite, residual austenite, and tempered martensite having an average crystal grain diameter of 3 ?m or less, and having a ratio of absorption energy AE to tensile strength TS (AE/TS) not less than 0.063.

Abstract: A method of manufacturing a hot press formed part by hot pressing a coated steel sheet that is obtained by forming a Zn-based coating layer on a surface of a steel sheet includes: heating the coated steel sheet to a temperature range of 750° C. or more and 1000° C. or less; cooling a surface of the coated steel sheet; and hot press forming the coated steel sheet under a condition that a surface temperature of the coated steel sheet is 400° C. or less and an average temperature of the coated steel sheet is 500° C. or more or a temperature of a center position of the coated steel sheet in a thickness direction is 530° C. or more.

Abstract: A method of manufacturing a galvanized steel sheet having a composition containing, by mass %, C: 0.05% or more and 0.5% or less, Si: 0.01% or more and 2.5% or less, Mn: 0.5% or more and 3.5% or less, P: 0.003% or more and 0.100% or less, S: 0.02% or less, Al: 0.010% or more and 0.5% or less, B: 0.0002% or more and 0.005% or less, Ti: 0.

Abstract: A method of manufacturing a high strength galvanized steel sheet has a first heating step including heating to 400° C. to 750° C. in an atmosphere containing O2: 0.1 to 20 percent and H2O: 1 to 50 percent and heating to 600° C. to 850° C. in an atmosphere containing O2: 0.01 to less than 0.1 percent and H2O: 1 to 20 percent is applied to a steel sheet, a second heating step includes holding the steel sheet in an atmosphere containing H2: 1 to 50 percent and having a dew point of 0° C. or lower at 750° C. to 900° C. for 15 to 600 s, cooling to a temperature of 450° C. to 550° C., and holding is performed at that temperature for 10 to 200 s, and a galvanization treatment is applied.

Abstract: A galvanized steel sheet has a composition containing, by mass %, C: 0.05% or more and 0.5% or less, Si: 0.01% or more and 2.5% or less, Mn: 0.5% or more and 3.5% or less, P: 0.003% or more and 0.100% or less, S: 0.02% or less, Al: 0.010% or more and 0.5% or less, B: 0.0002% or more and 0.005% or less, Ti: 0.05% or less, a relationship of Ti>4N being satisfied, and the balance comprising Fe and inevitable impurities, and a microstructure containing 60% or more and 95% or less of tempered martensite in terms of area ratio and 5% or more and 20% or less of retained austenite in terms of area ratio.