Abstract: A high strength hot rolled steel sheet with good formability, which has good magnetic properties, excellent punchability, and a tensile strength of 780 MPa or more. The high strength hot rolled steel sheet having a chemical composition containing C: 0.070% to 0.140%, Si: 0.10% to 1.00%, Mn: 1.00% to 1.80%, P: 0.050% or less, S: 0.0050% or less, N: 0.0080% or less, Al: 0.010% to 0.100%, Ti: 0.050% to 0.150%, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, and 95% or more of bainite microstructure on a volume fraction basis, wherein carbides constituting 80% or more of total precipitation carbides are dispersed at grain boundaries of bainitic ferrite constituting the bainite microstructure and 80% or more of total precipitation carbides have particle grain sizes of 20 to 300 nm.

Abstract: A hot-rolled steel sheet for a generator rim contains a structure containing a ferrite phase with an areal ratio of 95% or more in which precipitates containing Ti and V whose average grain diameter is less than 10 nm are precipitated in crystal grains of the ferrite phase. The ferrite phase has an average crystal grain diameter within the range of 2 ?m or more and less than 10 ?m. The hot-rolled steel sheet for a generator rim has strength with a yield strength YS in a rolling direction of 700 MPa or more and electromagnetic properties with a magnetic flux density B50 of 1.5 T or more and a magnetic flux density B100 of 1.6 T or more.

Abstract: A steel slab having a composition containing C: more than 0.07% and 0.2% or less, Si: 2.0% or less, Mn: 1.0% to 3.0%, Al: 0.1% or less, Ti: 0.05% to 0.3%, and V: 0.05% to 0.3% on a mass percent basis is heated to 1100° C. or more and is subjected to rough rolling and finish rolling. In the finish rolling, the total rolling reduction of two final passes is 30% or more, and the finish rolling temperature ranges from (Ar3 transformation temperature) to (Ar3 transformation temperature+120° C.). Cooling is started within 2 seconds after the finish rolling. Coiling is performed at an average cooling rate of 40° C./s or more at a coiling temperature in the range of 300° C. to 500° C. The resulting high-strength hot-rolled steel sheet has a microstructure in which a bainite phase constitutes more than 90% by volume, the average lath interval of bainite is 0.

Abstract: A high-strength hot-rolled steel sheet including a chemical composition containing, in percent by mass, 0.05% to 0.12% of C, 0.05% to 1.0% of Si, 0.5% to 1.8% of Mn, 0.04% or less of P, 0.0030% or less of S, 0.005% to 0.07% of Al, 0.006% or less of N, 0.05% to 0.15% of Ti, and the balance being Fe and incidental impurities, in which, in a region in the range of ? to ? of the sheet thickness, the content of Ti*, which is Ti existing as precipitates, is 0.3×[Ti] to 0.6×[Ti], where [Ti] is the Ti content, and the steel sheet has a microstructure in which the area fraction of the bainite phase in the entire structure is more than 95%.

Abstract: A steel slab having a composition containing C: more than 0.07% and 0.2% or less, Si: 2.0% or less, Mn: 1.0% to 3.0%, Al: 0.1% or less, Ti: 0.05% to 0.3%, and V: 0.05% to 0.3% on a mass percent basis is heated to 1100° C. or more and is subjected to rough rolling and finish rolling. In the finish rolling, the total rolling reduction of two final passes is 30% or more, and the finish rolling temperature ranges from (Ar3 transformation temperature) to (Ar3 transformation temperature+120° C.). Cooling is started within 2 seconds after the finish rolling. Coiling is performed at an average cooling rate of 40° C./s or more at a coiling temperature in the range of 300° C. to 500° C. The resulting high-strength hot-rolled steel sheet has a microstructure in which a bainite phase constitutes more than 90% by volume, the average lath interval of bainite is 0.

Abstract: A high strength hot rolled steel sheet with good formability, which has good magnetic properties, excellent punchability, and a tensile strength of 780 MPa or more. The high strength hot rolled steel sheet having a chemical composition containing C: 0.070% to 0.140%, Si: 0.10% to 1.00%, Mn: 1.00% to 1.80%, P: 0.050% or less, S: 0.0050% or less, N: 0.0080% or less, Al: 0.010% to 0.100%, Ti: 0.050% to 0.150%, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, and 95% or more of bainite microstructure on a volume fraction basis, wherein carbides constituting 80% or more of total precipitation carbides are dispersed at grain boundaries of bainitic ferrite constituting the bainite microstructure and 80% or more of total precipitation carbides have particle grain sizes of 20 to 300 nm.

Abstract: A high strength hot rolled steel sheet having a tensile strength TS of 980 MPa or more, has a composition containing, on a percent by mass basis, C: 0.05% or more and 0.18% or less, Si: 1.0% or less, Mn: 1.0% or more and 3.5% or less, P: 0.04% or less, S: 0.006% or less, Al: 0.10% or less, N: 0.008% or less, Ti: 0.05% or more and 0.20% or less, V: more than 0.1% and 0.3% or less, and the balance being Fe and incidental impurities, and has a microstructure including a primary phase and a secondary phase, the primary phase being a bainite phase having an area fraction of more than 85%, the secondary phase being at least one of ferrite phase, martensite phase, and retained austenite phase, the secondary phase having an area fraction of 0% or more and less than 15% in total, the bainite phase having an average lath interval of laths of 400 nm or less, and the laths having an average long axis length of 5.0 ?m or less.

Abstract: A steel slab having a composition containing C: more than 0.07% and 0.2% or less, Si: 2.0% or less, Mn: 1.0% to 3.0%, Al: 0.1% or less, Ti: 0.05% to 0.3%, and V: 0.05% to 0.3% on a mass percent basis is heated to 1100° C. or more and is subjected to rough rolling and finish rolling. In the finish rolling, the total rolling reduction of two final passes is 30% or more, and the finish rolling temperature ranges from (Ar3 transformation temperature) to (Ar3 transformation temperature+120° C.). Cooling is started within 2 seconds after the finish rolling. Coiling is performed at an average cooling rate of 40° C./s or more at a coiling temperature in the range of 300° C. to 500° C. The resulting high-strength hot-rolled steel sheet has a microstructure in which a bainite phase constitutes more than 90% by volume, the average lath interval of bainite is 0.

Abstract: A high-strength hot-rolled steel sheet has a tensile strength TS of 980 MPa or more and is manufactured by controlling the steel sheet to have a chemical composition containing C: more than 0.1% and 0.2% or less, Si: 0.5% or more and 3.0% or less, Mn: 1.0% or more and 3.5% or less, P: 0.05% or less, S: 0.004% or less, Al: 0.10% or less, N: 0.008% or less, Ti: 0.05% or more and 0.15% or less, V: more than 0.10% and 0.30% or less, and the balance being Fe and inevitable impurities. Surface regions have a microstructure including mainly a ferrite phase, and an inner region has a microstructure including mainly a bainite phase. The proportions of the surface regions in the thickness direction of the steel sheet are 1.0% or more and 5.0% or less of the whole thickness respectively from the upper and lower surfaces of the steel sheet.

Abstract: A high strength hot-rolled steel sheet has a tensile strength of not less than 780 MPa and exhibits excellent stretch flangeability and excellent fatigue resistance. A steel has a composition containing C at 0.05 to 0.15%, Si at 0.2 to 1.2%, Mn at 1.0 to 2.0%, P at not more than 0.04%, S at not more than 0.005%, Ti at 0.05 to 0.15%, Al at 0.005 to 0.10% and N at not more than 0.007%.

Abstract: There are provided a high-strength hot-rolled steel sheet having high burring formability and a method for manufacturing the high-strength hot-rolled steel sheet. A high-strength hot-rolled steel sheet having high burring formability contains, on a mass percent basis, C: 0.03% or more and 0.1% or less, Si: less than 0.5%, Mn: more than 0.7% and less than 1.2%, P: 0.05% or less, S: 0.005% or less, N: 0.01% or less, Al: 0.1% or less, and Ti: 0.1% or more and 0.25% or less such that C, S, N, and Ti satisfy Ti*?0.1 and C×(48/12)?0.14<Ti*<C×(48/12)+0.08 (wherein Ti*=Ti?N×(48/14)?S×(48/32), and C, S, N, and Ti denote the amounts (% by mass) of the corresponding elements), the remainder being Fe and incidental impurities, wherein the high-strength hot-rolled steel sheet has a microstructure in which a ferrite phase fraction is more than 90%, a carbide containing Ti is precipitated, and 70% or more of the carbide has a grain size of less than 9 nm.

Abstract: There are provided a high-strength hot-rolled steel sheet having high burring formability and a method for manufacturing the high-strength hot-rolled steel sheet. A high-strength hot-rolled steel sheet having high burring formability contains, on a mass percent basis, C: 0.06% or more and 0.13% or less, Si: less than 0.5%, Mn: more than 0.5% and 1.4% or less, P: 0.05% or less, S: 0.005% or less, N: 0.01% or less, Al: 0.1% or less, Ti: 0.05% or more and 0.25% or less, and V: more than 0.15% and 0.4% or less such that S, N, Ti, and V satisfy Ti.+V?0.35 (wherein Ti.?Ti—N×(48/14)?S×(48/32), and S, N, Ti, and V denote the amounts (% by mass) of the corresponding elements), the remainder being Fe and incidental impurities, wherein the high-strength hot-rolled steel sheet has a microstructure in which a ferrite phase fraction is more than 90%, a carbide containing Ti is precipitated, and 70% or more of the carbide has a grain size of less than 9 nm.

Abstract: There are provided a high-strength hot-rolled steel sheet having high burring formability and a method for manufacturing the high-strength hot-rolled steel sheet. The high-strength hot-rolled steel sheet having high burring formability contains, on a mass percent basis, C: 0.013% or more and less than 0.08%, Si: less than 0.5%, Mn: more than 0.8% and less than 1.2%, P: 0.05% or less, S: 0.005% or less, N: 0.01% or less, Al: 0.1% or less, and Ti: 0.03% or more and 0.15% or less such that C, S, N, and Ti satisfy 0.05?Ti*<0.1 and C×(48/12)?0.16<Ti* (wherein Ti*=Ti?N×(48/14)?S×(48/32), and C, S, N, and Ti denote the amounts (% by mass) of the corresponding elements), the remainder being Fe and incidental impurities, wherein the high-strength hot-rolled steel sheet has a microstructure in which a ferrite phase fraction is more than 90%, a carbide containing Ti is precipitated, and 70% or more of the carbide has a grain size of less than 9 nm.

Abstract: A high-strength steel sheet includes a composition containing, in mass percent, 0.08% to 0.20% of carbon, 0.2% to 1.0% of silicon, 0.5% to 2.5% of manganese, 0.04% or less of phosphorus, 0.005% or less of sulfur, 0.05% or less of aluminum, 0.07% to 0.20% of titanium, and 0.20% to 0.80% of vanadium, the balance being iron and incidental impurities.

Abstract: A steel sheet including C at 0.05 to 0.15%, Si at 0.2 to 1.2%, Mn at 1.0 to 2.0%, P at not more than 0.04%, S at not more than 0.0030%, Al at 0.005 to 0.10%, N at not more than 0.005% and Ti at 0.03 to 0.13%, the balance being Fe and inevitable impurities, includes surface regions having an area fraction of bainite of less than 80% and an area fraction of a ferrite phase with a grain diameter of 2 to 15 ?m of not less than 10%, the surface regions extending from both surfaces of the steel sheet each to a depth of 1.5 to 3.0% relative to a total sheet thickness, as well as an inner region other than the surface regions having an area fraction of a bainite phase of more than 95%, and has a tensile strength of not less than 780 MPa.

Abstract: Described is a high tensile strength hot rolled steel sheet having high strength and formability, and a manufacturing method. It has tensile strength ?980 MPa and excellent formability, and specifically identified ranges by mass % of C, Si, Mn, P, S, N, Al, Ti, V, Solute V, and Solute Ti; (ii) microstructure with fine carbides dispersion precipitated therein, the fine carbides containing Ti and V and having the average particle diameter <10 nm, as well as volume ratio with respect to the entire microstructure ?0.007; and matrix as ferrite phase having area ratio with respect to the entire microstructure ?97%. C, Ti, V, S and N satisfy (1) Ti?0.08 +(N/14×48+S/32×48) and (2) 0.8?(Ti/48+V/51)/(C/12)?1.2, where “C”, “Ti”, “V”, “S” and “N” represent contents (mass %) of corresponding elements, respectively.

Abstract: A high-strength hot-rolled steel sheet including a chemical composition containing, in percent by mass, 0.05% to 0.12% of C, 0.05% to 1.0% of Si, 0.5% to 1.8% of Mn, 0.04% or less of P, 0.0030% or less of S, 0.005% to 0.07% of Al, 0.006% or less of N, 0.05% to 0.15% of Ti, and the balance being Fe and incidental impurities, in which, in a region in the range of ? to ? of the sheet thickness, the content of Ti*, which is Ti existing as precipitates, is 0.3×[Ti] to 0.6×[Ti], where [Ti] is the Ti content, and the steel sheet has a microstructure in which the area fraction of the bainite phase in the entire structure is more than 95%.

Abstract: A high strength hot rolled steel sheet having excellent blanking workability is provided. The composition contains C: 0.050 to 0.15%, Si: 0.1 to 1.5%, Mn: 1.0 to 2.0%, P: 0.03% or less, S: 0.0030% or less, Al: 0.01 to 0.08%, Ti: 0.05 to 0.15%, N: 0.005% or less, and the balance being Fe and unavoidable impurities. More than 95% of the microstructure is formed of a bainite phase in terms of area fraction. Average grain diameters of the bainite phase in a region having a thickness equal to ¼ of the sheet thickness from the surface in the sheet thickness direction is 5 ?m or less in an L-direction cross section and 4 ?m or less in a C-direction cross section. The number of crystal grains extended in the rolling direction and having an aspect ratio of 5 or more is 7 or less in a sheet thickness center portion.

Abstract: A steel having a composition that includes C: 0.05 to 0.15%, Si: 0.2 to 1.2%, Mn: 1.0 to 2.0%, Al: 0.005 to 0.10%, N: 0.006% or less, and at least one selected from Ti: 0.03 to 0.13%, Nb: 0.02 to 0.10%, and V: 0.02 to 0.15% is subjected to rough rolling at a reduction of 80% or more and finish rolling at a finish rolling delivery temperature in the range of 800 to 950° C. The finish rolled sheet is subjected to cooling including cooling the finish rolled sheet from the finish rolling delivery temperature to a cooling end temperature in the range of 550 to 610° C. at an average cooling rate of 25° C./sec. or more and cooling the finish rolled sheet from the cooling end temperature of the previous process to a coiling temperature at an average cooling rate of 100° C./sec. or more.

Abstract: A high-strength hot-rolled steel sheet having excellent formability has a composition containing, by mass, 0.04% to 0.1% of C, 0.3% to 1.3% of Si, 0.8% to 1.8% of Mn, 0.03% or less of P, 0.005% or less of S, 0.005% or less of N, 0.005% to 0.1% of Al, and at least one element selected from 0.002% to less than 0.03% of Ti, 0.002% to less than 0.03% of V, and 0.002% to less than 0.02% of Nb, the balance being Fe and incidental impurities. The steel sheet has a microstructure in which the area fraction of ferrite phase in the entire structure is 85% or more, the area fraction of bainite phase in the entire structure is 10% or less, the area fraction of phases other than the ferrite and bainite phases in the entire structure is 5% or less, and the area fraction of acicular ferrite phase in the entire ferrite phase is 30% to less than 80%.