Abstract: When a zone surrounded by a grain boundary that is measured to be 5.0° or more by an EBSD analysis is assumed to be a grain, and when a K value is a value obtained by multiplying an average value of Image Qualities in a grain by 10?3, a Y value is an average crystal misorientation (°) in the grain, a metallic phase 1 is a metallic phase the K value of which is less than 4.000, a metallic phase 2 is a metallic phase the K value of which is 4.000 or more and the Y value of which is 0.5 to 1.0, a metallic phase 3 is a metallic phase the K value of which is 4.000 or more and the Y value of which is less than 0.5, and a metallic phase 4 is a metallic phase that falls under none of metallic phases 1 to 3, there is provided a steel sheet that has a predetermined chemical composition and includes a microstructure including, in area percent, a metallic phase 1: 1.0% or more and less than 35.0%, a metallic phase 2: 30.0% or more and 80.0% or less, a metallic phase 3: 5.0% or more and 50.

Abstract: A steel sheet according to an aspect of the present invention has predetermined chemical composition, in which a structure at a thickness ¼ portion includes, in terms of volume ratios, tempered martensite: 30% to 70% and one or both of ferrite and bainite: a total of 20% to 70%, in the structure at the thickness ¼ portion, a volume ratio of residual austenite is less than 10%, a volume ratio of fresh martensite is 10% or less, a volume ratio of pearlite is 10% or less, and a total volume ratio of the residual austenite, the fresh martensite, and the pearlite is 15% or less, a number density of iron-based carbides having a major axis of 5 nm or more in the tempered martensite at the thickness ¼ portion is 5×107 particles/mm2 or more, a ratio of the number of ?-type carbides in the number of the iron-based carbides having the major axis of 5 nm or more at the thickness ¼ portion is 20% or more, and a tensile strength is 780 MPa or higher.

Abstract: A steel sheet according to an aspect of the present invention has predetermined chemical composition, in which a structure at a thickness ¼ portion includes, in terms of volume ratios, tempered martensite: 70% or more and one or both of ferrite and bainite: a total of less than 20%, in the structure at the thickness ¼ portion, a volume ratio of residual austenite is less than 10%, a volume ratio of fresh martensite is 10% or less, a volume ratio of pearlite is 10% or less, and a total volume ratio of the residual austenite, the fresh martensite, and the pearlite is 15% or less, a number density of iron-based carbides having a major axis of 5 nm or more in the tempered martensite at the thickness ¼ portion is 5×107 particles/mm2 or more, a ratio of the number of ?-type carbides in the number of the iron-based carbides having the major axis of 5 nm or more at the thickness ¼ portion is 20% or more, and a tensile strength is 780 MPa or higher.

Abstract: When a zone surrounded by a grain boundary that is measured to be 5.0° or more by an EBSD analysis is assumed to be a grain, and when a K value is a value obtained by multiplying an average value of Image Qualities in a grain by 10?3, a Y value is an average crystal misorientation (°) in the grain, a metallic phase 1 is a metallic phase the K value of which is less than 4.000, a metallic phase 2 is a metallic phase the K value of which is 4.000 or more and the Y value of which is 0.5 to 1.0, a metallic phase 3 is a metallic phase the K value of which is 4.000 or more and the Y value of which is less than 0.5, and a metallic phase 4 is a metallic phase that falls under none of metallic phases 1 to 3, there is provided a steel sheet that has a predetermined chemical composition and includes a microstructure including, in area percent, a metallic phase 1: 1.0% or more and less than 35.0%, a metallic phase 2: 30.0% or more and 80.0% or less, a metallic phase 3: 5.0% or more and 50.

Abstract: A steel sheet according to an aspect of the present invention has predetermined chemical composition, in which a structure at a thickness ¼ portion includes, in terms of volume ratios, tempered martensite: 30% to 70% and one or both of ferrite and bainite: a total of 20% to 70%, in the structure at the thickness ¼ portion, a volume ratio of residual austenite is less than 10%, a volume ratio of fresh martensite is 10% or less, a volume ratio of pearlite is 10% or less, and a total volume ratio of the residual austenite, the fresh martensite, and the pearlite is 15% or less, a number density of iron-based carbides having a major axis of 5 nm or more in the tempered martensite at the thickness ¼ portion is 5×107 particles/mm2 or more, a ratio of the number of ?-type carbides in the number of the iron-based carbides having the major axis of 5 nm or more at the thickness ¼ portion is 20% or more, and a tensile strength is 780 MPa or higher.

Abstract: A steel sheet according to an aspect of the present invention has predetermined chemical composition, in which a structure at a thickness ¼ portion includes, in terms of volume ratios, tempered martensite: 70% or more and one or both of ferrite and bainite: a total of less than 20%, in the structure at the thickness ¼ portion, a volume ratio of residual austenite is less than 10%, a volume ratio of fresh martensite is 10% or less, a volume ratio of pearlite is 10% or less, and a total volume ratio of the residual austenite, the fresh martensite, and the pearlite is 15% or less, a number density of iron-based carbides having a major axis of 5 nm or more in the tempered martensite at the thickness ¼ portion is 5×107 particles/mm2 or more, a ratio of the number of ?-type carbides in the number of the iron-based carbides having the major axis of 5 nm or more at the thickness ¼ portion is 20% or more, and a tensile strength is 780 MPa or higher.

Abstract: A hot-rolled steel sheet includes a specified chemical composition and includes a steel structure represented by an area ratio of ferrite being 5% to 50%, an area ratio of bainite composed of an aggregate of bainitic ferrite whose grain average misorientation is 0.4° to 3° being 50% to 90%, and a total area ratio of martensite, pearlite, and retained austenite being 5% or less.

Abstract: A hot-rolled steel sheet includes a specified chemical composition and includes a steel structure represented by an area ratio of ferrite being 5% to 50%, an area ratio of bainite composed of an aggregate of bainitic ferrite whose grain average misorientation is 0.4° to 3° being 50% to 90%, and a total area ratio of martensite, pearlite, and retained austenite being 5% or less.

Abstract: A high-strength steel sheet includes, by mass %, C: 0.03% to 0.30%, Si: 0.08% to 2.1%, Mn: 0.5% to 4.0%, P: 0.05% or less, S: 0.0001% to 0.1%, N: 0.01% or less, acid-soluble Al: more than 0.004% and less than or equal to 2.0%, acid-soluble Ti: 0.0001% to 0.20%, at least one selected from Ce and La: 0.001% to 0.04% in total, and a balance of iron and inevitable impurities, in which [Ce], [La], [acid-soluble Al], and [S] satisfy 0.02?([Ce]+[La])/[acid-soluble Al]<0.25, and 0.4?([Ce]+[La])/[S]?50 in a case in which the mass percentages of Ce, La, acid-soluble Al, and S are defined to be [Ce], [La], [acid-soluble Al], and [S], respectively, and a microstructure includes 1% to 50% of martensite in terms of an area ratio.

Abstract: A high-strength steel sheet includes, by mass %, C: 0.03% to 0.30%, Si: 0.08% to 2.1%, Mn: 0.5% to 4.0%, P: 0.05% or less, S: 0.0001% to 0.1%, N: 0.01% or less, acid-soluble Al: more than 0.004% and less than or equal to 2.0%, acid-soluble Ti: 0.0001% to 0.20%, at least one selected from Ce and La: 0.001% to 0.04% in total, and a balance of iron and inevitable impurities, in which [Ce], [La], [acid-soluble Al], and [S] satisfy 0.02?([Ce]+[La])/[acid-soluble Al]<0.25, and 0.4?([Ce]+[La])/[S]?50 in a case in which the mass percentages of Ce, La, acid-soluble Al, and S are defined to be [Ce], [La], [acid-soluble Al], and [S], respectively, and a microstructure includes 1% to 50% of martensite in terms of an area ratio.

Abstract: The present invention provides a grain-oriented silicon steel sheet excellent in adhesiveness to tension-creating insulating coating films formed on the grain-oriented silicon steel sheet produced by removing inorganic mineral films composed of forsterite and so on with pickling or the like or by deliberately preventing the formation thereof, characterized by: having, at the interface between each of the tension-creating insulating coating films and the steel sheet, an external oxidation type membranous oxide film of 2 to 500 nm in average thickness mainly composed of amorphous silica and/or a mixed oxide film consisting of an external oxidation type membranous oxide film of 2 to 500 nm in average thickness mainly composed of amorphous silica and particulate oxides mainly composed of amorphous silica: and satisfying any one or more of the specified requirements.

Abstract: The present invention provides a grain-oriented silicon steel sheet excellent in adhesiveness to tension-creating insulating coating films formed on the grain-oriented silicon steel sheet produced by removing inorganic mineral films composed of forsterite and so on with pickling or the like or by deliberately preventing the formation thereof, characterized by: having, at the interface between each of the tension-creating insulating coating films and the steel sheet, an external oxidation type membranous oxide film of 2 to 500 nm in average thickness mainly composed of amorphous silica and/or a mixed oxide film consisting of an external oxidation type membranous oxide film of 2 to 500 nm in average thickness mainly composed of amorphous silica and particulate oxides mainly composed of amorphous silica: and satisfying any one or more of the specified requirements.