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.

Abstract: Provided are a high-strength steel sheet having a specified chemical composition, in which a Mn-segregation degree in a region within 100 ?m from a surface thereof in a thickness direction is 1.5 or less, in a plane parallel to the surface of the steel sheet in a region within 100 ?m from the surface of the steel sheet in the thickness direction, the number of oxide-based inclusion grains having a grain long diameter of 5 ?m or more is 1000 or less/100 mm2, a proportion of the number of oxide-based inclusion grains having a chemical composition containing alumina of 50 mass % or more, silica of 20 mass % or less, and calcia of 40 mass % or less to the total number of oxide-based inclusions having a grain long diameter of 5 ?m or more is 80% or more, a specified metallographic structure, and a TS of 980 MPa or more, a high-strength galvanized steel sheet, and a manufacturing method thereof.

Abstract: A high-strength, cold-rolled steel sheet having a tensile strength of 980 MPa or more, the steel sheet having a chemical composition containing, by mass %, C: 0.070% to 0.100%, Si: 0.50% to 0.70%, Mn: 2.40% to 2.80%, P: 0.025% or less, S: 0.0020% or less, Al: 0.020% to 0.060%, N: 0.0050% or less, Nb: 0.010% to 0.060%, Ti: 0.010% to 0.030%, B: 0.0005% to 0.0030%, Sb: 0.005% to 0.015%, Ca: 0.0015% or less, Cr: 0.01% to 2.00%, Mo: 0.01% to 1.00%, Ni: 0.01% to 5.00%, Cu: 0.01% to 5.

Abstract: Provided are a steel sheet, having sufficient strength and formability regardless of reduction of thickness, for crown caps; a method for manufacturing the same; and a crown cap. The steel sheet for crown caps has a composition containing C: 0.0010% to less than 0.0050%, Si: 0.10% or less, Mn: 0.05% to less than 0.50%, P: 0.050% or less, S: 0.050% or less, Al: more than 0.002% to less than 0.070%, N: less than 0.0040%, and B: 0.0005% to 0.0020% on a mass basis, the balance being Fe and inevitable impurities, and also has a yield strength of 500 MPa or more in a rolling direction, an average Lankford value (r) of 1.1 or more, and an in-plane anisotropy (?r) of Lankford value of ?0.3 to 0.3.

Abstract: Provided are a high-strength steel sheet and a method for manufacturing the steel sheet. The high-strength steel sheet has a specified chemical composition with the balance being Fe and inevitable impurities, a microstructure including, in terms of area ratio, 30% or more of a ferrite phase, 40% to 65% of a bainite phase and/or a martensite phase, and 5% or less of cementite, in which, in a surface layer that is a region within 50 ?m from the surface in the thickness direction, the area ratio of a ferrite phase is 40% to 55% and the total area ratio of a bainite phase having a grain diameter of more than 5 ?m and/or a martensite phase having a grain diameter of more than 5 ?m is 20% or less, and a tensile strength is 980 MPa or more.

Abstract: Provided are a high-strength steel sheet and a method for manufacturing the steel sheet. The high-strength steel sheet has a specified chemical composition with the balance being Fe and inevitable impurities, a microstructure including, in terms of area ratio, 25% or less of a ferrite phase, 75% or more of a bainite phase and/or a martensite phase, and 5% or less of cementite, in which, in a surface layer that is a region within 50 ?m from the surface in the thickness direction, the area ratio of a ferrite phase is 5% to 20%, and a tensile strength is 1180 MPa or more.

Abstract: A steel sheet for a crown cap has sufficient strength and formability even when the thickness thereof is reduced for use, and has a composition containing, in percent by mass, C: 0.010% to 0.025%, Si: 0.10% or less, Mn: 0.05% to 0.50%, P: 0.050% or less, S: 0.005% to 0.050%, Al: 0.020% to 0.070%, N: less than 0.0040%, and the balance being Fe and inevitable impurities, wherein yield strength after heat treatment at 210° C. for 15 minutes is as follows: the yield strength is 550 MPa or more in a rolling direction, and the yield strength in a direction 45° from the rolling direction in a rolling plane is equal to or less than the average of the yield strength in the rolling direction and the yield strength in a direction 90° from the rolling direction in the rolling plane.

Abstract: A high strength galvanized steel sheet having tensile strength of 590MPa or more which is excellent in fatigue property in punching work, and a manufacturing method thereof are provided. The microstructure includes a ferrite phase having an average grain diameter of 15 ?m or less and an area fraction of 60% or more and a martensite phase having an area fraction of 5 to 40%, and an amount of one or more kinds of oxide selected from a group consisting of Fe, Si, Mn, Al, P, Nb, and Ti generated on a surface layer portion of the steel sheet within 100 ?m in a steel-sheet-side depth direction from a surface of a base steel sheet directly below a galvanized layer is less than 0.060 g/m2 per one-side surface of the steel sheet.

Abstract: A high-strength hot-dip galvanized steel sheet has excellent workability, namely, excellent ductility and hole expansion formability, and high yield ratio. The steel sheet has a chemical composition containing by mass %: C: 0.05-0.15%; Si: 0.10-0.90%; Mn: 1.0-1.9%; P: 0.005-0.10%; S: 0.0050% or less; Al: 0.01-0.10%; N: 0.0050% or less; Nb: 0.010-0.100%; and the balance being Fe and incidental impurities, in which: the steel sheet has a complex phase that includes: ferrite having an average crystal grain size of 15 ?m or less to at least 90% in volume fraction; martensite having an average crystal grain size of 3.0 ?m or less to 0.5% or more and less than 5.0% in volume fraction; pearlite to 5.0% or less in volume fraction; and the balance being a phase generated at low temperature.

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.

Abstract: A high strength galvanized steel sheet having tensile strength of 590 MPa or more which is excellent in fatigue property in punching work, and a manufacturing method thereof are provided. The microstructure includes a ferrite phase having an average grain diameter of 15 ?m or less and an area fraction of 60% or more and a martensite phase having an area fraction of 5 to 40%, and an amount of one or more kinds of oxide selected from a group consisting of Fe, Si, Mn, Al, P, Nb, and Ti generated on a surface layer portion of the steel sheet within 100 ?m in a steel-sheet-side depth direction from a surface of a base steel sheet directly below a galvanized layer is less than 0.060 g/m2 per one-side surface of the steel sheet.

Abstract: A galvanized steel sheet having excellent formability is provided including steel having a composition which contains, on a percent by mass basis, 0.03% to 0.15% of C, less than 0.5% of Si, 1.0% to 2.5% of Mn, 0.05% or less of P, 0.01% or less of S, 0.05% or less of Al, 0.0050% or less of N, 0.05% to 0.8% of Cr, 0.01% to 0.1% of V, and the balance being Fe and inevitable impurities; and a zinc plating film on a surface of a steel sheet, and wherein a microstructure of the steel contains ferrite having an average grain diameter of 15 ?m or less and 5% to 40% of martensite in an area ratio, and the ratio of martensite having an aspect ratio of less than 3.0 to all the martensite is more than 95% in area ratio.

Abstract: A high carbon hot-rolled steel sheet which is a hot-rolled spheroidizing annealed material, including 0.2 to 0.7% C, 2% or less Si, 2% or less Mn, 0.03% or less P, 0.03% or less S, 0.08% or less Sol.Al., and 0.01% or less N, by mass, which contains carbide having a particle size of smaller than 0.5 ?m in a content of 15% or less by volume to the total amount of carbide, and the difference between the maximum hardness Hv max and the minimum hardness Hv min, ?Hv (=Hv max?Hv min), in the sheet thickness direction being 10 or smaller.

Abstract: A high carbon cold-rolled steel sheet having both excellent stretch-flange formability and excellent homogeneity of hardness in the sheet thickness direction is provided by a manufacturing method having the steps of: hot-rolling a steel containing 0.2 to 0.7% C by mass at finishing temperatures of (Ar3 transformation point ?20° C.) or above to prepare a hot-rolled sheet; cooling the hot-rolled sheet to temperatures of 650° C. or below at cooling rates from 60° C./s or larger to smaller than 120° C./s; coiling the hot-rolled sheet after cooling at coiling temperatures of 600° C. or below; cold-rolling the coiled hot-rolled sheet at rolling reductions of 30% or more to prepare a cold-rolled sheet; and annealing the cold-rolled sheet at annealing temperatures from 600° C. or larger to Ac1 transformation point or lower.

Abstract: A high carbon hot-rolled steel sheet which is a hot-rolled spheroidizing annealed material, including 0.2 to 0.7% C, 2% or less Si, 2% or less Mn, 0.03% or less P, 0.035 or less S, 0.08% or less Sol.Al., and 0.01% or less N, by mass, which contains carbide having a particle size of smaller than 0.5 ?m in a content of 15% or less by volume to the total amount of carbide, and the difference between the maximum hardness Hv max and the minimum hardness Hv min, ?Hv (=Hv max?Hv min), in the sheet thickness direction being 10 or smaller.

Abstract: A steel sheet excellent in FB performance and also excellent in fabrication performance after FB working and a manufacturing method of the same are provided. The steel sheet is a steel sheet having a composition containing from 0.1 to 0.5% of C, not more than 0.5% of Si and from 0.2 to 1.5% of Mn in terms of % by mass, with P and S being adjusted at proper ranges and having a structure having a ferrite having an average grain size of more than 10 ?m and less than 20 ?m and a cementite present in the ferrite grain having an average particle size of from 0.3 to 1.5 ?m. In this way, the steel sheet becomes a steel sheet excellent in FB performance, mold life and performance (side bend elongation) after FB working.

Abstract: A steel sheet excellent in FB performance-and also excellent in fabrication performance after FB working and a manufacturing method of the same are provided. The steel sheet is a steel sheet having a composition containing from 0.1 to 0.5% of C, not more than 0.5% of Si and from 0.2 to 1.5% of Mn in terms of % by mass, with P and S being adjusted at proper ranges, and having a structure in which a ferrite has an average grain size of from 1 to 10 ?m, cementite has a spheroidization ratio of 80% or more, and of the cementite, an amount Sgb of ferrite intergranular cementite which is defined by the following expression (1): Sgb(%)={Son/(Son+Sin)}×100 (wherein Son represents a total occupied area of cementite present on the ferrite grain boundary of the cementite present per unit area; and Snin represents a total occupied area of cementite present in a ferrite grain of the cementite present per unit area) is 40% or more.

Abstract: A high carbon hot-rolled steel sheet, as a hot-rolled spheroidizing annealed material, having both excellent stretch-flange formability and excellent homogeneity of hardness in the sheet thickness direction is provided by a manufacturing method having the steps of: hot-rolling a steel containing 0.2 to 0.7% C by mass at finishing temperatures of (Ar3 transformation point?20° C.) or above to prepare a hot-rolled sheet; cooling the hot-rolled sheet to temperatures of 650° C. or below at cooling rates from 60° C./s or larger to smaller than 120° C./s; coiling the hot-rolled sheet after cooling at coiling temperatures of 600° C. or below; and annealing the coiled hot-rolled sheet at annealing temperatures from 640° C. or larger to Ac1 transformation point or lower.

Abstract: The present invention relates to a high strength hot rolled steel sheet consisting of 0.04 to 0.15% C, 1.5% or less Si, 0.5 to 1.6% Mn, 0.04% or less P, 0.005% or less S, 0.04% or less Al, 0.03 to 0.15% Ti, 0.03 to 0.5% Mo, by mass, and balance of Fe and inevitable impurities, and having a microstructure consisting of ferrite containing precipitates, second phase of bainite and/or martensite, and other phase, wherein the percentage of the ferrite containing precipitates is 40 to 95%, and the percentage of the other phase is 5% or less. For example, the high strength hot rolled steel sheet having a thickness of 1.4 mm shows a tensile strength of 780 MPa or higher, an elongation of 22% or higher elongation, and a hole expansion ratio of 60% or higher, thus the steel sheet is suitable for reinforcing members automobile cabin and crash worthiness members of automobile.

Abstract: A high carbon cold-rolled steel sheet having both excellent stretch-flange formability and excellent homogeneity of hardness in the sheet thickness direction is provided by a manufacturing method having the steps of: hot-rolling a steel containing 0.2 to 0.7% C by mass at finishing temperatures of (Ar3 transformation point ?20° C.) or above to prepare a hot-rolled sheet; cooling the hot-rolled sheet to temperatures of 650° C. or below at cooling rates from 60° C./s or larger to smaller than 120° C./s; coiling the hot-rolled sheet after cooling at coiling temperatures of 600° C. or below; cold-rolling the coiled hot-rolled sheet at rolling reductions of 30% or more to prepare a cold-rolled sheet; and annealing the cold-rolled sheet at annealing temperatures from 600° C. or larger to Ac1 transformation point or lower.