METHOD FOR PRODUCING HIGH TENSILE STRENGTH COLD ROLLED DEEP-DRAWING STEEL SHEET EXCELLENT IN SURFACE PROPERTY

摘要

PROBLEM TO BE SOLVED: To provide a method for producing a high tensile strength cold rolled deep-drawing steel sheet excellent in surface properties.;SOLUTION: A steel having a composition containing, by mass, 0.0040 to 0.02% C, ≤1.5% Si, 0.5 to 3.0% Mn, 0.01 to 0.1% P, ≤0.02% S, ≤1.0% sol.Al, ≤0.005% N and 0.02 to 0.2% Nb, and the balance Fe with inevitable impurities, and in which (12/93)×(Nb/C) prescribed by the Nb content and the C content satisfies 1.0 to 3.0 is melted, is thereafter subjected to continuous casting while being cooled at the average casting velocity Vc satisfying 1≤Vc≤4.5-0.5×(12/93)×(Nb/C) prescribed by the Nb content and the C content {wherein, Vc is the average casting velocity (m/min), and the atomic symbols satisfy the respective contents (mass%)} at a cooling water content of 0.5 to 4.0 l/kg (the water content used per kg of the steel ingot), is next subjected to hot rolling, pickling and cold rolling, and is then annealed at a recrystallization temperature or above.;COPYRIGHT: (C)2007,JPO&INPIT