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AssigneeJfe Steel Corporation
InventorsMasao Yuga, Shigeki Kitsuya, Yusuke Terazawa, Minoru Suwa, Kenji Hayashi
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The present invention provides a high tensile strength steel plate having a chemical composition containing, in percent by mass, 0.03% to 0.12% of C, 0.01% to 0.30% of Si, 0.5% to 1.95% of Mn, 0.008% or less of P, 0.005% or less of S, 0.015% to 0.06% of Al, 0.011% to 0.05% of Nb, 0.005% to 0.02% of Ti, 0.001% to 0.006% of N, 0.0005% to 0.003% of Ca, optionally, one or two or more of Cr, Mo, V, Cu, and Ni, in which Ceq is 0.44 or less, Ti/N is 1.5 to 3.5, and parameter formulas composed of specific elements for controlling the sulfide morphology and the degree of center segregation in the steel are satisfied, and the balance being Fe and incidental impurities, in which the hardness of the center segregation area of the steel sheet is further specified.
A high tensile strength steel plate having a chemical composition comprising, in percent by mass, 0.03% to 0.12% of C, 0.01% to 0.30% of Si, 0.5% to 1.58% of Mn, 0.008% or less of P, 0.005% or less of S, 0.015% to 0.06% of Al, 0.011% to 0.05% of Nb, 0.005% to 0.02% of Ti, 0.001% to 0.0044% of N, 0.0005% to 0.003% of Ca, in which Ceq specified by formula (1) below is 0.44 or less, TI/N is 1.5 to 3.5, and formulas (2) and (3) below are satisfied, and the balance being Fe and incidental impurities, wherein the hardness of a center segregation area of the steel plate satisfies formula (4) below:
A method for producing a high tensile strength steel plate comprising heating a steel having the chemical composition according to claim 1 to 1,050° C. to 1,200° C., then subjecting the steel to hot rolling in such a manner that the cumulative rolling reduction in the temperature range of 950° C. or higher is 30% or more, and the cumulative rolling reduction in the temperature range of lower than 950° C. is 30% to 70%, and then performing accelerated cooling to 600° C. or lower at a cooling rate of 1.0° C./s or more.
A method for producing a high tensile strength steel plate comprising heating a steel having the chemical composition according to claim 5 to 1,050° C. to 1,200° C., then subjecting the steel to hot rolling in such a manner that the cumulative rolling reduction in the temperature range of 950° C. or higher is 30% or more, and the cumulative rolling reduction in the temperature range of lower than 950° C. is 30% to 70%, and then performing accelerated cooling to 600° C. or lower at a cooling rate of 1.0° C./s or more.
A method for producing a high tensile strength steel plate comprising heating a steel having the chemical composition according to claim 2 to 1,050° C. to 1,200° C., then subjecting the steel to hot rolling in such a manner that the cumulative rolling reduction in the temperature range of 950° C. or higher is 30% or more, and the cumulative rolling reduction in the temperature range of lower than 950° C. is 30% to 70%, and then performing accelerated cooling to 600° C. or lower at a cooling rate of 1.0° C./s or more.
Dependencies are inferred from the claim text.