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.

Abstract: A high-strength galvanized steel sheet whose base steel is a high-strength steel sheet contains Si, Mn, and B and has good coating adhesiveness. A base steel sheet containing Si, Mn, and B is oxidized at a heating temperature of steel sheet T that satisfies the formula, and then subjected to reduction-annealing and galvanizing T?58.65×[Si]+29440×[B]?13.59×[O2]+548.1 [Si]: amount of Si in the steel on a mass percent basis [B]: amount of B in the steel on a mass percent basis [O2]: O2 concentration on a volume percent basis in an atmosphere at oxidizing treatment.

Abstract: Provided is a high-strength steel sheet that has good chemical convertibility and good corrosion resistance after electro deposition painting despite high Si and Mn contents. Also provided are a method for producing the high-strength steel sheet, a high-strength galvanized steel sheet formed by using the high-strength steel sheet, and a method for producing the high-strength galvanized steel sheet. A steel sheet containing, in terms of % by mass, C: 0.03 to 0.35%, Si: 0.01 to 0.50%, Mn: 3.6 to 8.0%, Al: 0.001 to 1.00%, P?0.10%, S?0.010%, and the balance being Fe and unavoidable impurities is annealed under condition under which a dew point of an atmosphere in a temperature zone of 550° C. or higher and A° C. or lower (A is a particular value that satisfies 600?A?750) inside an annealing furnace is controlled to ?40° C. or lower.

Abstract: A hot dip galvanized steel sheet includes a steel sheet, a hot dip galvanizing layer, and an intermetallic compound, in which the steel sheet has a chemical composition containing, by mass %, C: 0.03% or more and 0.70% or less, Si: 0.10% or less, Mn: 0.5% or more and 0.9% or less, P: 0.020% or more and 0.050% or less, S: 0.010% or less, Nb: 0.010% or more and 0.035% or less, N: 0.005% or less, Al: 0.10% or less, and the balance being Fe and inevitable impurities, in which the hot dip galvanizing layer contains 0.3% or more and 0.6% or less of Al, and in which the intermetallic compound contains 0.12 gm?2 or more and 0.22 gm?2 or less of Al and Fe2Al5 having an average grain diameter of 1 ?m or less.

Abstract: A method for manufacturing a galvanized steel sheet includes heating a base steel sheet in a heating zone such that the surface of the base steel sheet is heated at a temperature of 600° C. or higher and 790° C. or lower while a furnace temperature T° C. in the heating zone of an annealing furnace is controlled based on the water vapor partial pressure PH2Oin Air of air fed into the heating zone, the base steel sheet having a chemical composition consisting of, by mass %, C: 0.05% or more and 0.25% or less, Si: 0.1% or more and 3.0% or less, Mn: 0.5% or more and 3.0% or less, P: 0.001% or more and 0.10% or less, Al: 0.01% or more and 3.00% or less, S: 0.200% or less, and the balance being Fe and inevitable impurities, heating the base steel sheet in the heating zone such that the surface of the base steel sheet is heated at a temperature of 630° C. or higher and 850° C.

Abstract: A high strength hot-dip galvanized steel sheet has TS of 440 MPa or more and an average r value of 1.30 or more, where the absolute value of the planar anisotropy of the r value (?r) is 0.20 or less. A chemical composition contains C: 0.010% or more and 0.04% or less, Si: more than 1.0% and 1.5% or less, Mn: 1.0% or more and 3.0% or less, P: 0.005% or more and 0.1% or less, S: 0.01% or less, sol. Al: 0.005% or more and 0.5% or less, N: 0.01% or less, Nb: 0.010% or more and less than 0.05%, Ti: 0.015% or more and 0.120% or less, and the remainder composed of Fe and incidental impurities, wherein (Nb/93)/(C/12) 0.20 and 0.005<C*?0.020 are satisfied.

Abstract: A high-strength galvanized steel sheet with excellent formability and shape fixability and a method for manufacturing the high-strength galvanized steel sheet.

Abstract: Provided is a galvannealed steel sheet with excellent anti-powdering property when press forming is performed, without controlling the contents of chemical elements in steel which are effective for strengthening a steel sheet, such as Si and P, to be low in order to achieve required material properties and without increasing cost due to, for example, processes being complicated. A galvannealed steel sheet with excellent anti-powdering property has a coated layer taking in grains of a base steel sheet such that the grains constitute 2.0% or more and 15.0% or less of the coated layer in terms of cross section area ratio.

Abstract: A galvannealed steel sheet includes a zinc coating layer containing 7 to 15% Fe on the surface of steel sheet including, C: 0.02% to 0.30%, Si: 0.01% to 2.5%, Mn: 0.1% to 3.0%, P: 0.003% to 0.08%, S: not more than 0.01%, Al: 0.001% to 0.20%, one or more selected from Ti: 0.03% to 0.40%, Nb: 0.001% to 0.2%, V: 0.001% to 0.2%, Mo: 0.01% to 0.5% and W: 0.001% to 0.2%. In the zinc coating layer, carbides with average particle size of 1 nm to 20 nm including one or more selected from titanium, niobium, vanadium, molybdenum and tungsten are present with a density of five or more particles per segment that is defined by the thickness of the coating layer and also by dividing a cross section of the coating layer at intervals of 1 ?m in a direction perpendicular to the thickness of the coating layer.

Abstract: A method for manufacturing a high strength galvanized steel sheet and a high strength galvanized steel sheet are provided. A base steel sheet having a chemical composition comprising C: 0.03% to 0.35%, Si: 0.01% to 0.50%, Mn: 3.6% to 8.0%, Al: 0.001% to 1.000%, P?0.10%, S?0.010%, and the balance comprising Fe and incidental impurities, on a percent by mass basis, is subjected to annealing and galvanization treatment, wherein the maximum steel sheet temperature in an annealing furnace is 600° C. or higher and 700° C. or lower, the steel sheet transit time in a temperature region of the maximum steel sheet temperature of 600° C. or higher and 700° C. or lower is specified to be 30 seconds or more and 10 minutes or less, and the dew point in an atmosphere is specified to be ?45° C. or lower.

Abstract: A method for manufacturing a high strength galvanized steel sheet and a high strength galvanized steel sheet are provided. A high strength galvanized steel sheet having a zinc coating layer with an amount of deposition of coating of 20 to 120 g/m2 per one surface on the surface of a base steel sheet having a chemical composition comprising C: 0.03% to 0.35%, Si: 0.01% to 0.50%, Mn: 3.6% to 8.0%, Al: 0.001% to 1.000%, P?0.10%, S?0.010%, and the balance comprising Fe and incidental impurities, on a percent by mass basis, is produced. At this time, in annealing and galvanization treatment of the base steel sheet in a continuous galvanizing line, the maximum steel sheet temperature in an annealing furnace is 600° C. or higher and 750° C. or lower, the steel sheet transit time in a temperature region of the maximum steel sheet temperature of 600° C. or higher and 750° C. or lower is specified to be 30 seconds or more and 10 minutes or less, and the dew point in an atmosphere is specified to be ?10° C. or higher.

Abstract: A high strength galvanized steel sheet has a composition including, C: 0.02% or more and 0.30% or less, Si: 0.01% or more and 2.5% or less, Mn: 0.1% or more and 3.0% or less, P: 0.003% or more and 0.08% or less, S: 0.01% or less, Al: 0.001% or more and 0.20% or less, Ti: 0.03% or more and 0.40% or less and the balance being Fe and inevitable impurities, and a zinc-coated layer having a coating weight per surface of 20 g/m2 or more and 120 g/m2 or less. The concentration ratio of C to Ti (C/Ti) in a portion within 10 ?m from the surface of the base steel sheet is 0.8 or more and 1.5 or less, and the total amount of oxides of one or more selected from Fe, Si, Mn, P, Al and Ti formed in a surface portion within 100 ?m from the surface of the base steel sheet is 0.05 g/m2 or less.

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, or further containing 10% or less (including 0%) of ferrite in terms of area ratio and/or 10% or less (including 0%) of martensite in terms of area ratio, the tempered martensite having an average grain diameter of 5 ?m or less.

Abstract: A hot rolled steel sheet having a chemical composition containing, by mass %, C: 0.04% or more and 0.20% or less, Si: 0.7% or more and 2.3% or less, Mn: 0.8% or more and 2.8% or less, P: 0.1% or less, S: 0.01% or less, Al: 0.1% or less, N: 0.008% or less, and the balance being Fe and inevitable impurities. The microstructure of the hot rolled steel sheet includes ferrite and pearlites, in which the area ratio of the ferrite is 75% or more and less than 95%, the mean grain size of the ferrite is 5 ?m or more and 25 ?m or less, the area ratio of pearlite is 5% or more and less than 25%, the mean grain size of pearlite is 2.0 ?m or more, and the mean free path of pearlite is 5 ?m or more.

Abstract: A high strength hot-dip galvanized steel sheet has TS of 440 MPa or more and an average r value of 1.30 or more, where the absolute value of the planar anisotropy of the r value (?r) is 0.20 or less. A chemical composition contains C: 0.010% or more and 0.04% or less, Si: more than 1.0% and 1.5% or less, Mn: 1.0% or more and 3.0% or less, P: 0.005% or more and 0.1% or less, S: 0.01% or less, sol. Al: 0.005% or more and 0.5% or less, N: 0.01% or less, Nb: 0.010% or more and less than 0.05%, Ti: 0.015% or more and 0.120% or less, and the remainder composed of Fe and incidental impurities, wherein (Nb/93)/(C/12)<0.20 and 0.005<C*?0.020 are satisfied, a steel sheet microstructure includes 80% or more of ferrite and 3% or more of martensite on an area ratio basis, and C*=C-(12/93)Nb-(12/48){Ti-(48/14)N-(48/32)S}.

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: Provided is a hot-rolled steel sheet having a composition containing 0.04 mass percent to 0.20 mass percent C, 0.7 mass percent to 2.3 mass percent Si, 0.8 mass percent to 2.8 mass percent Mn, 0.1 mass percent or less P, 0.01 mass percent or less S, 0.1 mass percent or less Al, and 0.008 mass percent or less N, the remainder being Fe and inevitable impurities. Internal oxides containing one or more selected from the group consisting of Si, Mn, and Fe are present at grain boundaries and in grains in a base metal. The internal oxides present at the grain boundaries in the base metal are located within 5 ?m from the surface of the base metal. The difference between the depths at which the internal oxides are formed in the cross direction of the steel sheet is 2 ?m or less.

Abstract: A high strength cold rolled steel sheet includes a chemical composition containing, by mass %, C: 0.010% or more and 0.060% or less, Si: more than 0.5% and 1.5% or less, Mn: 1.0% or more and 3.0% or less, P: 0.005% or more and 0.100% or less, S: 0.010% or less, sol.Al: 0.005% or more and 0.500% or less, N: 0.0100% or less, Nb: 0.010% or more and 0.100% or less, Ti: 0.015% or more and 0.150% or less and the balance comprising Fe and inevitable impurities. The microstructure includes, in area fraction, 70% or more of a ferrite phase and 3% or more of a martensite phase. The tensile strength is 440 MPa or more and an average r value is 1.20 or more.

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: Provided are a high-strength hot-dip galvanized steel sheet having excellent formability and a tensile strength of 440 MPa or more and a method for manufacturing the same. A steel sheet has a microstructure containing a ferrite phase having an area fraction of 60% or more, a pearlite phase having an area fraction of 20% to 30%, and a bainite phase having an area fraction of 1% to 5%, the area fraction of a cementite phase present in a grain of the ferrite phase being 5% or less. Upon manufacture, a hot-rolled sheet or a cold-rolled sheet is heated to a temperature of 650° C. or higher at an average heating rate of 10° C./s or more, is held at a temperature of 700° C. to (Ac3-5)° C. for ten seconds or more, is cooled to a temperature of 300° C. to 500° C. at an average cooling rate of 10° C./s to 200° C./s, is held at a temperature of 300° C. to 500° C. for 30 seconds to 300 seconds, and is then hot-dip galvanized.