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|1. (WO2017168991) THIN STEEL SHEET, PLATED STEEL SHEET, HOT-ROLLED STEEL SHEET MANUFACTURING METHOD, COLD-ROLLED FULL HARD STEEL SHEET MANUFACTURING METHOD, THIN STEEL SHEET MANUFACTURING METHOD, AND PLATED STEEL SHEET MANUFACTURING METHOD|
|Applicants:||JFE STEEL CORPORATION
|Title:||THIN STEEL SHEET, PLATED STEEL SHEET, HOT-ROLLED STEEL SHEET MANUFACTURING METHOD, COLD-ROLLED FULL HARD STEEL SHEET MANUFACTURING METHOD, THIN STEEL SHEET MANUFACTURING METHOD, AND PLATED STEEL SHEET MANUFACTURING METHOD|
The purpose of the present invention is to provide: a 340 MPa grade thin steel sheet, which in addition to excellent bake hardenability and aging resistance combines excellent ductility and excellent surface quality; a plated steel sheet in which a thin steel sheet has been plated; methods for manufacturing a hot-rolled steel sheet and a cold-rolled full hard steel sheet that are necessary for obtaining a thin steel sheet; a thin steel sheet manufacturing method; and a plated steel sheet manufacturing method. Provided is a thin steel sheet characterized in: having a component composition that contains, in mass%, C: 0.0008-0.0024%, Si: less than 0.15%, Mn: greater than 0.55% and less than 0.90%, P: greater than 0.025% and less than 0.050%, S: 0.015% or less, sol. Al: 0.01%-0.1%, N: 0.01% or less, B: greater than 0.0003% and less than 0.0035%, Nb: greater than 0.005% and less than 0.016%, Ti: 0.009% or less, and Sb: 0.002-0.030%, wherein C and Nb satisfy expression (1) and the balance is made of Fe and unavoidable impurities, and having a steel structure in which the average crystal grain diameter d of ferrite at the ¼ sheet thickness position is 8-18 µm and the ratio ds/d of the average crystal grain diameter ds of ferrite in the steel sheet surface layer to d is 0.40-1.20; tensile strength being 340-380 MPa; bake hardening amount BH being 20-60 MPa; and r value being at least 1.4. −10≤([%C]−([%Nb]/93)×12)×10000≤14 (1) [%C] and [%Nb] represent the C and Nb contents, respectively.