Abstract: The issue of the present invention is to provide a hot-rolled steel sheet with excellent press formability and method for producing the steel sheet, wherein the steel sheet has not only hole expandability but also stretch flanging workability by not assessing hole expandability for stretch flanging as conventional but an actual phenomena of side-bend elongation.

Abstract: Tooling used in a punching process which uses a die and projecting punch to form a worked material of steel sheet into a predetermined outer shape, in which tooling for punching, a radius of curvature Rd of a die cutting edge is from 0.03 mm to 0.2 mm and an angle (?) formed by a tangent drawn from a punch cutting edge to a projection shoulder and a direction perpendicular to a direction of movement of the punch is from 12° to 72°, and a punching method and shaping method using the same, are provided. Further, when making the die cutting edge (shoulder R part) a two-stage R of radii of curvature R1 and R2 and making a slant of a line passing through the centers of R1 and R2 ?, by making 0.03 mm?R1?0.2 mm, 1?R2/R1?5, 0?R2(1?sin ?1)?0.3t, and 30°???90°, punching hole expandability can be improved.

Abstract: A hot-rolled steel sheet includes, as a chemical composition, by mass %, C: 0.030% to 0.10%, Mn: 0.5% to 2.5%, and Si+Al: 0.100% to 2.5%, in which the steel sheet has a microstructure including, by area fraction, ferrite: 80% or more, martensite: 3% to 15.0%, and pearlite: less than 3.0%, in which a number density of martensite having an equivalent circle diameter of 3 ?m or more at a position which is at a depth of ¼ of the steel sheet thickness from the surface of the steel sheet, is 5.0 pieces/10000 ?m2 or less, and the following Expression (1) is satisfied. R/DM2?1.00??Expression (1) Here, R is an average martensite interval (?m) defined by the following Expression (2), and DM is a martensite average diameter (?m). R={12.5×(?/6VM)0.5?(?)0.5}×DM??Expression (2) Here, VM is a martensite area fraction (%) and DM is the martensite average diameter (?m).

Abstract: A hot rolled steel sheet includes, as a chemical composition, at least one selected from Ti, REM, and Ca, and includes, as a metallographic structure, a ferrite as a primary phase, at least one of a martensite and a residual austenite as a secondary phase, and plural inclusions, wherein a total length in the rolling direction of both inclusion-cluster whose length in the rolling direction is 30 ?m or more and independent-inclusion whose length in the rolling direction is 30 ?m or more is 0 mm to 0.25 mm per 1 mm2.

Abstract: The present invention provides a high-strength steel sheet including: C: 0.03 to 0.25 mass %, Si: 0.1 to 2.0 mass %, Mn: 0.5 to 3.0 mass %, P: not more than 0.05 mass %, T.O: not more than 0.0050 mass %, S: 0.0001 to 0.01 mass %, N: 0.0005 to 0.01 mass %, acid-soluble Al: more than 0.01 mass %, Ca: 0.0005 to 0.0050 mass %, and a total of at least one element of Ce, La, Nd, and Pr: 0.001 to 0.01 mass %, with a balance including iron and inevitable impurities, in which the steel sheet contains a chemical component on a basis of mass that satisfies 0.7<100×([Ce]+[La]+[Nd]+[Pr])/[acid-soluble Al]?70 and 0.

Abstract: Punching hole expandability of high strength thin-gauge steel sheet is improved for the purpose of application of high strength thin-gauge steel sheet to auto parts so as to lighten the weight of automobiles. Tooling used in a punching process which uses a die and projecting punch to form a worked material of steel sheet into a predetermined outer shape, in which tooling for punching, a radius of curvature Rd of a die cutting edge is from 0.03 mm to 0.2 mm and an angle (?) formed by a tangent drawn from a punch cutting edge to a projection shoulder and a direction perpendicular to a direction of movement of the punch is from 12° to 72°, and a punching method and shaping method using the same, are provided. Further, when making the die cutting edge (shoulder R part) a two-stage R of radii of curvature R1 and R2 and making a slant of a line passing through the centers of R1 and R2 ?, by making 0.03 mm?R1?0.2 mm, 1?R2/R1?5, 0?R2(1?sin ?1)?0.3t, and 30°???90°, punching hole expandability can be improved.

Abstract: A hot-rolled steel sheet according to the present invention is a steel sheet containing a predetermined components, and satisfying O<S/Ca<0.8, N?14/48×Ti?“0” (zero) %. It is a high-strength hot-rolled steel sheet for a spiral pipe excellent in low-temperature toughness in which a pro-eutectoid ferrite fraction is 3% or more and 20% or less, and the other is a low-temperature transformation phase in a microstructure at a depth of a half thickness of a sheet thickness from a steel sheet surface, a number average crystal grain size of a whole of the microstructure is 2.5 ?m or less, an area average grain size is 9 ?m or less, a standard deviation of the area average grain size is 2.3 ?m or less, and a reflected X-ray intensity ratio {211}/{111} in a direction and in a {111} direction relative to a plane in parallel to the steel sheet surface at the depth of the half thickness of the sheet thickness from the steel sheet surface is 1.1 or more.

Abstract: A hot-rolled steel sheet includes, as a chemical composition, by mass %, C: 0.030% to 0.10%, Mn: 0.5% to 2.5%, and Si+Al: 0.100% to 2.5%, in which the steel sheet has a microstructure including, by area fraction, ferrite: 80% or more, martensite: 3% to 15.0%, and pearlite: less than 3.0%, in which a number density of martensite having an equivalent circle diameter of 3 ?m or more at a position which is at a depth of ¼ of the steel sheet thickness from the surface of the steel sheet, is 5.0 pieces/10000 ?m2 or less, and the following Expression (I) is satisfied. R/DM2?1.00??Expression (1) Here, R is an average martensite interval (?m) defined by the following Expression (2), and DM is a martensite average diameter (?m). R={12.5×(?/6VM)0.5?(?)0.5}×DM??Expression (2) Here, VM is a martensite area fraction (%) and DM is the martensite average diameter (?m).

Abstract: On a cross section with a sheet width direction of a high-strength hot-rolled steel sheet set as a normal line, with regard to an inclusion having a major diameter of 3.0 ?m or more, a maximum of a major diameter/minor diameter ratio expressed by (a major diameter of the inclusion)/(a minor diameter of the inclusion) is 8.0 or less, and a sum total of a rolling direction length per 1 mm2 cross section of a predetermined inclusion group composed of plural inclusions each having a major diameter of 3.0 ?m or more and a predetermined extended inclusion having a length in a rolling direction of 30 ?m or more is 0.25 mm or less. The plural inclusions composing the predetermined inclusion group congregate in both the rolling direction and a direction perpendicular to the rolling direction 50 ?m or less apart from each other. The predetermined extended inclusion is spaced over 50 ?m apart from all the inclusions each having a major diameter of 3.

Abstract: The issue of the present invention is to provide a hot-rolled steel sheet with excellent press formability and method for producing the steel sheet, wherein the steel sheet has not only hole expandability but also stretch flanging workability by not assessing hole expandability for stretch flanging as conventional but an actual phenomena of side-bend elongation.

Abstract: A hot rolled steel sheet includes, as a chemical composition, at least one selected from Ti, REM, and Ca, and includes, as a metallographic structure, a ferrite as a primary phase, at least one of a martensite and a residual austenite as a secondary phase, and plural inclusions, wherein a total length in the rolling direction of both inclusion-cluster whose length in the rolling direction is 30 ?m or more and independent-inclusion whose length in the rolling direction is 30 ?m or more is 0 mm to 0.25 mm per 1 mm2.

Abstract: The present invention provides a high-strength steel sheet including: C: 0.03 to 0.25 mass %, Si: 0.1 to 2.0 mass %, Mn: 0.5 to 3.0 mass %, P: not more than 0.05 mass %, T.O: not more than 0.0050 mass %, S: 0.0001 to 0.01 mass %, N: 0.0005 to 0.01 mass %, acid-soluble Al: more than 0.01 mass %, Ca: 0.0005 to 0.0050 mass %, and a total of at least one element of Ce, La, Nd, and Pr: 0.001 to 0.01 mass %, with a balance including iron and inevitable impurities, in which the steel sheet contains a chemical component on a basis of mass that satisfies 0.7<100×([Ce]+[La]+[Nd]+[Pr])/[acid-soluble Al]?70 and 0.

Abstract: A hot-rolled steel sheet according to the present invention is a steel sheet containing a predetermined components, and satisfying O<S/Ca<0.8, N?14/48×Ti?“0” (zero) %. It is a high-strength hot-rolled steel sheet for a spiral pipe excellent in low-temperature toughness in which a pro-eutectoid ferrite fraction is 3% or more and 20% or less, and the other is a low-temperature transformation phase in a microstructure at a depth of a half thickness of a sheet thickness from a steel sheet surface, a number average crystal grain size of a whole of the microstructure is 2.5 ?m or less, an area average grain size is 9 ?m or less, a standard deviation of the area average grain size is 2.3 ?m or less, and a reflected X-ray intensity ratio {211}/{111} in a {211} direction and in a {111} direction relative to a plane in parallel to the steel sheet surface at the depth of the half thickness of the sheet thickness from the steel sheet surface is 1.1 or more.

Abstract: On a cross section with a sheet width direction of a high-strength hot-rolled steel sheet set as a normal line, with regard to an inclusion having a major diameter of 3.0 ?m or more, a maximum of a major diameter/minor diameter ratio expressed by (a major diameter of the inclusion)/(a minor diameter of the inclusion) is 8.0 or less, and a sum total of a rolling direction length per 1 mm2 cross section of a predetermined inclusion group composed of plural inclusions each having a major diameter of 3.0 ?m or more and a predetermined extended inclusion having a length in a rolling direction of 30 ?m or more is 0.25 mm or less. The plural inclusions composing the predetermined inclusion group congregate in both the rolling direction and a direction perpendicular to the rolling direction 50 ?m or less apart from each other. The predetermined extended inclusion is spaced over 50 ?m apart from all the inclusions each having a major diameter of 3.

Abstract: The present invention provides a steel sheet excellent in both a balance between strength and elongation and a balance between strength and hole expandability, in other words, a multi-phase steel sheet having an excellent balance between strength and hole expandability. The present invention is a multi-phase steel sheet excellent in hole expandability characterized in that: the steel sheet contains, as chemical components in mass, C: 0.03 to 0.15%, P: not more than 0.010%, S: not more than 0.003%, and either one or both of Si and Al in a total amount of 0.5 to 4%, and one or more of Mn, Ni, Cr, Mo and Cu in a total amount of 0.

Abstract: An exemplary hot rolled steel sheet can included, in terms of percent by mass, C of 0.01 to 0.2%; Si of 0.01 to 2%; Mn of 0.1 to 2%; P of ?0.1%; S of ?0.03%; Al of 0.001 to 0.1%; N of ? 0.01%; and as a remainder, Fe and unavoidable impurities. For example, a microstructure can be substantially a homogeneous continuous-cooled microstructure, and an average grain size of the microstructure may be more than 8 ?m and 30 ?m or less. An exemplary method for manufacturing a hot rolled steel sheet can include subjecting a slab having the above composition to a rough rolling so as to obtain a rough rolled bar, subjecting the rough rolled bar to a finish rolling so as to obtain a rolled steel under conditions in which a finishing temperature is (Ar3 transformation point +50° C.) or more; and starting cooling the rolled steel after 0.5 seconds or more pass from the end of the finish rolling at a temperature of the Ar3 transformation point or more.

Abstract: The present invention provides a steel sheet excellent in both a balance between strength and elongation and a balance between strength and hole expandability, in other words, a multi-phase steel sheet having an excellent balance between strength and hole expandability. The present invention is a multi-phase steel sheet excellent in hole expandability characterized in that: the steel sheet contains, as chemical components in mass, C: 0.03 to 0.15%, P: not more than 0.010%, S: not more than 0.003%, and either one or both of Si and Al in a total amount of 0.5 to 4%, and one or more of Mn, Ni, Cr, Mo and Cu in a total amount of 0.

Abstract: An exemplary hot rolled steel sheet for processing can include, in terms of percent by mass, C of 0.01 to 0.2%; Si of 0.01 to 0.3%; Mn of 0.1 to 1.5%; P of ?0.1%; S of ?0.03%; Al of 0.001 to 0.1%; N of ?0.006%; and as a remainder, Fe and unavoidable impurities. The microstructure may include a main phase in the form of polygonal ferrite and a hard second phase, a volume fraction of the hard second phase is 3 to 20%, a hardness ratio (hardness of the hard second phase/hardness of the polygonal ferrite) is 1.5 to 6, and a grain size ratio (e.g., grain size of the polygonal ferrite/grain size of the hard second phase) is 1.5 or more.

Abstract: An exemplary hot rolled steel sheet for processing can include, in terms of percent by mass, C of 0.01 to 0.2%; Si of 0.01 to 0.3%; Mn of 0.1 to 1.5%; P of ?0.1%; S of ?0.03%; Al of 0.001 to 0.1%; N of ?0.006%; and as a remainder, Fe and unavoidable impurities. The microstructure may include a main phase in the form of polygonal ferrite and a hard second phase, a volume fraction of the hard second phase is 3 to 20%, a hardness ratio (hardness of the hard second phase/hardness of the polygonal ferrite) is 1.5 to 6, and a grain size ratio (e.g., grain size of the polygonal ferrite/grain size of the hard second phase) is 1.5 or more.

Abstract: An exemplary hot rolled steel sheet can included, in terms of percent by mass, C of 0.01 to 0.2%; Si of 0.01 to 2%; Mn of 0.1 to 2%; P of ?0.1%; S of ?0.03%; Al of 0.001 to 0.1%; N of ?0.01%; and as a remainder, Fe and unavoidable impurities. For example, a microstructure can be substantially a homogeneous continuous-cooled microstructure, and an average grain size of the microstructure may be more than 8 mm and 30 mm or less. An exemplary method for manufacturing a hot rolled steel sheet can include subjecting a slab having the above composition to a rough rolling so as to obtain a rough rolled bar, subjecting the rough rolled bar to a finish rolling so as to obtain a rolled steel under conditions in which a finishing temperature is (Ar3 transformation point +50° C.) or more; and starting cooling the rolled steel after 0.5 seconds or more pass from the end of the finish rolling at a temperature of the Ar3 transformation point or more.