HIGH STRENGTH HOT ROLLED SHEET STEEL AND ITS PRODUCTION METHOD

摘要

PROBLEM TO BE SOLVED: To provide an inexpensive hot rolled steel sheet which has tensile strength of ≥590MPa and excellent ductility, and stretch-flanging properties, is free of island-shaped scale flaws and red scale on a steel sheet surface, and a production method therefor.;SOLUTION: The hot rolled steel sheet is composed of 0.02 to 0.18% C, 0.01 to 1.5% Si, 0.2 to 2.0% Mn, ≤0.10 P, ≤0.07% S, 0.02 to 2.0% Al, ≤0.01% N, 0.01 to 0.3% Ti, and 0.01 to 0.1% Nb, and if necessary, further 0.0010 to 0.0070% Ca and/or 0.0010 to 0.0070% Mg and the balance Fe and impurities, and the ferrite has an area rate of ≥90%, tensile strength of ≥590 MPa, and the product of the tensile strength (MPa) and a pore expanding rate (%)is ≥650,000 MPax%. At the time of production, the steel is subjected to crude hot rolling after turning to a specified temperature T_SRT. The obtained crude bar is subjected to descaling at the specified temperature T_SRT.;COPYRIGHT: (C)2006,JPO&NCIPI