HIGH TENSILE STRENGTH HOT ROLLED STEEL PLATE AND HIGH TENSILE STRENGTH COLD ROLLED STEEL SHEET FOR AUTOMOBILE USE, EXCELLENT IN IMPACT RESISTANCE, AND THEIR PRODUCTION

摘要

PROBLEM TO BE SOLVED: To obtain a hot rolled steel plate and a cold rolled steel plate for automobile use, excellent in impact strength under high strain rate and easy of press forming, and their production. ;SOLUTION: A hot rolled steel plate or cold rolled steel plate, having a composition consisting of, by weight, 0.05-0.20% C, 0.01-1.50% Si, 0.5-3.0% Mn, ≤0.010% S, one or ≥2 kinds selected from 0.03-0.15% P, 0.5-2.0% Cr, and 0.1-1.0% Mo, further either or both of 0.03-1.0% Ti and 0.01-0.2% Nb, and the balance Fe with inevitable impurities, is produced. This steel plate or steel sheet has a structure which is composed of a dual phase structure of martensite of ≤3μm average grain size and ferrite of ≤5μm average grain size and in which the volume percentage of the martensite is regulated to 5-30%.;COPYRIGHT: (C)1997,JPO