HOT-ROLLED STEEL SHEET FOR VARIABLE-THICKNESS ROLLED BLANK, VARIABLE-THICKNESS ROLLED BLANK, AND METHOD FOR PRODUCING SAME

摘要

FIELD: metallurgy.;SUBSTANCE: invention relates to metallurgy. To ensure a high tensile strength and excellent cold formability, the hot-rolled steel sheet has a chemical composition that contains C, Si, Mn, P, S, Al, N, Ti, Fe and impurities make up the balance and which satisfies the expression [Ti]-48/14×[N]-48/32×[S]≥0, as well as a microstructure containing, in terms of area ratio, 20 % or more of bainite, wherein 50 % or more of the remainder, in terms of area ratio, being ferrite. Inside the hot-rolled steel sheet, the average value of the pole densities of the orientation group {100}011 – {223}110 is 4 or less, and the pole density of a {332}113 crystal orientation is 4.8 or less. In the outer layer of the hot-rolled steel sheet, the pole density of the {110}001 crystal orientation is 2.5 or more. In addition, among the titanium carbonitrides in the hot-rolled steel sheet, the number density of fine titanium carbonitrides having a particle diameter of 10 nm or less is 1.0×10¹⁷ per cm³ or less, and the bake hardening amount (BH effect) is 15 MPa or more.;EFFECT: high tensile strength and excellent cold formability.;23 cl, 2 dwg, 4 tbl