Abstract: A hot-rolled steel sheet includes, by mass %, C: 0.030% or more and less than 0.075%, Si+Al: 0.08% to 0.40%, Mn: 0.5% to 2.0%, and Ti: 0.020% to 0.150%, and includes a microstructure having a ferrite and a martensite. The hot-rolled steel sheet includes a microstructure having, by area %, 90% to 98% of the ferrite, 2% to 10% of the martensite, 0% to 3% of a bainite, and 0% to 3% of a pearlite. In the martensite, the number proportion of martensite grains having a hardness of 10.0 GPa or more is 10% or less, and a ratio N1/N2 of the number N1 of martensite grains having a hardness of 8.0 GPa or more and less than 10.0 GPa to the number N2 of martensite grains having a hardness of less than 8.0 GPa is 0.8 to 1.2.

Abstract: A hot rolled steel sheet having a chemical composition consisting of, in mass %, C: 0.020-0.070%, Si: 0.05-1.70%, Mn: 0.60-2.50%, Al: 0.010-1.000%, N: >0-0.0030%, P?0.050%, S?0.005%, Ti: 0.015-0.170%, Nb: 0-0.100%, V: 0-0.300%, Cu: 0-2.00%, Ni: 0-2.00%, Cr: 0-2.00%, Mo: 0-1.00%, B: 0-0.0100%, Mg: 0-0.0100%, Ca: 0-0.0100%, REM: 0-0.1000%, Zr: 0-1.000%, Co: 0-1.000%, Zn: 0-1.000%, W: 0-1.000%, Sn: 0-0.050%, the balance: Fe and impurities, a metal microstructure includes, in area %, ferrite: 5-70%, bainite: 30-95%, retained ??2%, martensite?2%, pearlite?1%, ferrite+bainite?95%, a number density of the precipitates in ferrite grains is 1.0×1016?50.0×1016/cm3, an average circle-equivalent diameter of the TiN precipitates in the steel sheet is 1.0-10.0 ?m, an average of minimum distances between adjacent TiN precipitates is 10.0 ?m or more, and a standard deviation of nano hardness is 1.00 GPa or less.

Abstract: A hot rolled steel sheet having a chemical composition consisting of, in mass %, C: 0.020-0.180%, Si: 0.05-1.70%, Mn: 0.50-2.50%, Al: 0.010-1.000%, N: 0.0060%, P?0.050%, S?0.005%, Ti: 0-0.150%, Nb: 0-0.100%, V: 0-0.300%, Cu: 0-2.00%, Ni: 0-2.00%, Cr: 0-2.00%, Mo: 0-1.00%, B: 0-0.0100%, Mg: 0-0.0100%, Ca: 0-0.0100%, REM: 0-0.1000%, Zr: 0-1.000%, Co: 0-1.000%, Zn: 0-1.000%, W: 0-1.000%, the balance: Fe and impurities, wherein a metal microstructure includes, in area %, at a position ¼ W or ¾ W from an end face of the steel sheet and ¼ t or ¾ t from a surface, martensite: more than 2%-10%, retained austenite <2%, bainite 40%, pearlite 2%, the balance: ferrite, an average circle-equivalent diameter of a metallic phase constituted of martensite/retained austenite is 1.0-5.0 ?m, an average of minimum distances between adjacent metallic phases is 3 ?m or more, and a standard deviation of nano hardness is 2.0 GPa or less.

Abstract: A hot rolled steel sheet including a chemical composition consisting of, in mass %, C: 0.07-0.22%, Si: 1.00-3.20%, Mn: 0.80-2.20%, Al: 0.010-1.000%, N?0.0060%, P?0.050%, S?0.005%, Ti: 0-0.150%, Nb: 0-0.100%, V: 0-0.300%, Cu: 0-2.00%, Ni: 0-2.00%, Cr: 0-2.00%, Mo: 0-1.00%, B: 0-0.0100%, Mg: 0-0.0100%, Ca: 0-0.0100%, REM: 0-0.1000%, Zr: 0-1.000%, Co: 0-1.000%, Zn: 0-1.000%, W: 0-1.000%, Sn: 0-0.050%, the balance: Fe and impurities, wherein a metal microstructure includes, in area %, at a position ¼ W or ¾ W from an end face of the steel sheet and ¼ t or ¾ t from a surface, retained austenite: more than 2%-10%, martensite ?2%, bainite: 10-70%, pearlite ?2%, the balance: ferrite, an average circle-equivalent diameter of a metallic phase constituted of retained austenite/martensite is 1.0 to 5.0 ?m, an average of minimum distances between adjacent metallic phases is 3 ?m or more, and a standard deviation of nano hardness is 2.5 GPa or less.

Abstract: The present invention provides a hot-rolled steel sheet capable of preventing softening of the strength of a sheet-thickness central portion of the steel sheet in thermal treatment, even in the case where an amount of working performed on the steel sheet is small and a work hardening rate is low. A hot-rolled steel sheet of the present invention consists of chemical components of, in mass %, C: 0.040 to 0.150%, Si: 0 to 0.500%, Mn: 0.10 to 1.50%, P: 0 to 0.050%, S: 0 to 0.020%, Al: 0.010 to 0.050%, N: 0.0010 to 0.0060%, Nb: 0.008 to 0.035%, Cu: 0 to 0.10%, Ni: 0 to 0.10%, Cr: 0 to 0.02%, Mo: 0 to 0.020%, V: 0 to 0.020%, Ca: 0 to 0.0100%, B: 0 to 0.0050%, and the balance: Fe and impurities. The hot-rolled steel sheet contains 0.005 to 0.030% dissolved Nb. An area fraction of ferrite structure is 85% or more, the balance is cementite and/or pearlite structure, and an average crystal grain size of ferrite is equal to or more than 5 ?m and equal to or less than 20 ?m.

Abstract: A hot-rolled steel sheet including predetermined components, in which the amounts of Cr and Al added satisfy Expression (1) below, a metallographic structure has, by % by volume, a ferrite fraction of more than 90% and 98% or less, a martensite fraction of 2% to less than 10%, and, a fraction of a residual structure made of one or more of pearlite, bainite, and residual austenite being less than 1%, the ferrite has an average circle-equivalent diameter of 4 ?m or more and a maximum circle-equivalent diameter of 30 ?m or less, and the martensite has an average circle-equivalent diameter of 10 ?m or less and a maximum circle-equivalent diameter of 20 ?m or less. [Cr]×5+[Al]?0.50??Expression (1) Here, in Expression (1), [Cr] represents an amount of Cr (mass %), and [Al] represents an amount of Al (mass %).

Abstract: A hot rolled steel sheet having a chemical composition consisting of, in mass %, C: 0.020-0.180%, Si: 0.05-1.70%, Mn: 0.50-2.50%, Al: 0.010-1.000%, N: 0.0060%, P?0.050%, S?0.005%, Ti: 0-0.150%, Nb: 0-0.100%, V: 0-0.300%, Cu: 0-2.00%, Ni: 0-2.00%, Cr: 0-2.00%, Mo: 0-1.00%, B: 0-0.0100%, Mg: 0-0.0100%, Ca: 0-0.0100%, REM: 0-0.1000%, Zr: 0-1.000%, Co: 0-1.000%, Zn: 0-1.000%, W: 0-1.000%, the balance: Fe and impurities, wherein a metal microstructure includes, in area %, at a position ¼ W or ¾ W from an end face of the steel sheet and ¼ t or ¾ t from a surface, martensite: more than 2%-10%, retained austenite <2%, bainite 40%, pearlite 2%, the balance: ferrite, an average circle-equivalent diameter of a metallic phase constituted of martensite/retained austenite is 1.0-5.0 ?m, an average of minimum distances between adjacent metallic phases is 3 ?m or more, and a standard deviation of nano hardness is 2.0 GPa or less.

Abstract: A hot rolled steel sheet having a chemical composition consisting of, in mass %, C: 0.020-0.070%, Si: 0.05-1.70%, Mn: 0.60-2.50%, Al: 0.005-0.020%, N: >0.0030-0.0060%, P?0.050%, S?0.005%, Ti: 0.015-0.170%, Nb: 0-0.100%, V: 0-0.300%, Cu: 0-2.00%, Ni: 0-2.00%, Cr: 0-2.00%, Mo: 0-1.00%, B: 0-0.0100%, Ca: 0-0.0100%, Mg: 0-0.0100%, REM: 0-0.1000%, Zr: 0-1.000%, Co: 0-1.000%, Zn: 0-1.000%, W: 0-1.000%, Sn: 0-0.050%, the balance: Fe and impurities, wherein Ca+Mg+REM?0.0005, a metal microstructure includes, in area %, ferrite: 5-70%, bainite: 30-95%, retained ??2%, martensite ?2%, pearlite ?1%, ferrite+bainite?95%, a number density of the precipitates in ferrite grains is 1.0×1016-50.0×1016/cm3, an average circle-equivalent diameter of the TiN precipitates in the steel sheet is 1.0-10.0 ?m, an average of minimum distances between adjacent TiN precipitates is 10.0 ?m or more, and a standard deviation of nano hardness is 1.00 GPa or less.

Abstract: A hot rolled steel sheet including a chemical composition consisting of, in mass %, C: 0.07-0.22%, Si: 1.00-3.20%, Mn: 0.80-2.20%, Al: 0.010-1.000%, N?0.0060%, P?0.050%, S?0.005%, Ti: 0-0.150%, Nb: 0-0.100%, V: 0-0.300%, Cu: 0-2.00%, Ni: 0-2.00%, Cr: 0-2.00%, Mo: 0-1.00%, B: 0-0.0100%, Mg: 0-0.0100%, Ca: 0-0.0100%, REM: 0-0.1000%, Zr: 0-1.000%, Co: 0-1.000%, Zn: 0-1.000%, W: 0-1.000%, Sn: 0-0.050%, the balance: Fe and impurities, wherein a metal microstructure includes, in area %, at a position ¼ W or ¾ W from an end face of the steel sheet and ¼ t or ¾ t from a surface, retained austenite: more than 2%-10%, martensite ?2%, bainite: 10-70%, pearlite ?2%, the balance: ferrite, an average circle-equivalent diameter of a metallic phase constituted of retained austenite/martensite is 1.0 to 5.0 ?m, an average of minimum distances between adjacent metallic phases is 3 ?m or more, and a standard deviation of nano hardness is 2.5 GPa or less.

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, by mass %, C: 0.030% or more and less than 0.075%, Si+Al: 0.08% to 0.40%, Mn: 0.5% to 2.0%, and Ti: 0.020% to 0.150%, and includes a microstructure having a ferrite and a martensite. The hot-rolled steel sheet includes a microstructure having, by area %, 90% to 98% of the ferrite, 2% to 10% of the martensite. 0% to 3% of a bainite, and 0% to 3% of a pearlite. In the martensite, the number proportion of martensite grains having a hardness of 10.0 GPa or more is 10% or less, and a ratio N1/N2 of the number N1 of martensite grains having a hardness of 8.0 GPa or more and less than 10.0 GPa to the number N2 of martensite grains having a hardness of less than 8.0 GPa is 0.8 to 1.2.

Abstract: The present invention provides a hot-rolled steel sheet capable of preventing softening of the strength of a sheet-thickness central portion of the steel sheet in thermal treatment, even in the case where an amount of working performed on the steel sheet is small and a work hardening rate is low. A hot-rolled steel sheet of the present invention consists of chemical components of, in mass %, C: 0.040 to 0.150%, Si: 0 to 0.500%, Mn: 0.10 to 1.50%, P: 0 to 0.050%, S: 0 to 0.020%, Al: 0.010 to 0.050%, N: 0.0010 to 0.0060%, Nb: 0.008 to 0.035%, Cu: 0 to 0.10%, Ni: 0 to 0.10%, Cr: 0 to 0.02%, Mo: 0 to 0.020%, V: 0 to 0.020%, Ca: 0 to 0.0100%, B: 0 to 0.0050%, and the balance: Fe and impurities. The hot-rolled steel sheet contains 0.005 to 0.030% dissolved Nb. An area fraction of ferrite structure is 85% or more, the balance is cementite and/or pearlite structure, and an average crystal grain size of ferrite is equal to or more than 5 ?m and equal to or less than 20 ?m.

Abstract: A hot-rolled steel sheet including predetermined components, in which the amounts of Cr and Al added satisfy Expression (1) below, a metallographic structure has, by % by volume, a ferrite fraction of more than 90% and 98% or less, a martensite fraction of 2% to less than 10%, and, a fraction of a residual structure made of one or more of pearlite, bainite, and residual austenite being less than 1%, the ferrite has an average circle-equivalent diameter of 4 ?m or more and a maximum circle-equivalent diameter of 30 ?m or less, and the martensite has an average circle-equivalent diameter of 10 ?m or less and a maximum circle-equivalent diameter of 20 ?m or less. [Cr]×5+[Al]?0.50??Expression (1) Here, in Expression (1), [Cr] represents an amount of Cr (mass %), and [Al] represents an amount of Al (mass %).

Abstract: This hot rolled steel contains, in terms of mass %, C: 0.01 to 0.1%, Si: 0.01 to 0.1%, Mn: 0.1 to 3%, P: not more than 0.1%, S: not more than 0.03%, Al: 0.001 to 1%, N: not more than 0.01%, Nb: 0.005 to 0.08%, and Ti: 0.001 to 0.2%, with a remainder being iron and unavoidable impurities, wherein a formula: [Nb]×[C]?4.34×10?3 is satisfied, a grain boundary density of solid solution C is not less than 1 atom/nm2 and not more than 4.5 atoms/nm2, and a grain size of cementite grains precipitated at grain boundaries within the steel sheet is not more than 1 ?m.

Abstract: This hot rolled steel contains, in terms of mass %, C: 0.01 to 0.1%, Si: 0.01 to 0.1%, Mn: 0.1 to 3%, P: not more than 0.1%, S: not more than 0.03%, Al: 0.001 to 1%, N: not more than 0.01%, Nb: 0.005 to 0.08%, and Ti: 0.001 to 0.2%, with a remainder being iron and unavoidable impurities, wherein a formula: [Nb]×[C]?4.34×10?3 is satisfied, a grain boundary density of solid solution C is not less than 1 atom/nm2 and not more than 4.5 atoms/nm2, and a grain size of cementite grains precipitated at grain boundaries within the steel sheet is not more than 1 um. This method for manufacturing a hot rolled steel sheet includes: heating a steel slab having the same composition as the above hot rolled steel sheet at a temperature that is not less than a temperature of SRTmin (° C.) and not more than 1,170° C.; performing rough rolling at a finishing temperature of not less than 1,080° C. and not more than 1,150° C.