HOT-ROLLED STEEL SHEET, COLD-ROLLED STEEL SHEET AND HOT-DIP GALVANIZED STEEL SHEET EXCELLENT IN STRAIN AGE HARDENING PROPERTY, AND MANUFACTURING METHOD THEREOF

摘要

A steel plate having a chemical composition in mass %, wherein contents of C , Si and Mn are 0.15 % or less, 2.0 % or less, and 3.0 % or less, respectively , wherein contents of P, S, Al and N are specified, and wherein Cu is containe d in an amount of 0.5 to 3.0 % ,or at least one of Cr, Mo and W is contained i n a total amount of 2.0 % or less, and having a composite structure comprising ferrite as a primary phase and a martensite phase in an area % of 2.0 or mor e; and a high tensile hot rolled steel plate, a high tensile cold rolled steel plate, and a hot dip galvanized steel plate comprising the steel plate. The steel plate is excellent in press formability, and also has excellent strain aging hardening characteristics wherein .DELTA.TS is 80 Mpa or more.