ULTRAHIGH STRENGTH STEEL SHEET HAVING EXCELLENT ELONGATION AND HYDROGEN EMBRITTLEMENT RESISTANCE, ITS PRODUCTION METHOD, AND METHOD OF MANUFACTURING ULTRAHIGH STRENGTH PRESS-FORMED COMPONENT USING THE ULTRAHIGH STRENGTH STEEL SHEET

摘要

PROBLEM TO BE SOLVED: To provide an ultrahigh strength steel sheet which is combinedly provided with excellent elongation and hydrogen embrittlement resistance in an ultrahigh strength region of a ≥1,180 MPa class, and to provide a method of efficiently manufacturing the ultrahigh strength steel sheet.;SOLUTION: The ultrahigh strength steel sheet contains, by mass, 0.06 to 0.6% C, 0.5 to 3% Si+Al, 0.5 to 3% Mn, ≤0.15% (exclusive of 0%) P and ≤0.02% (inclusive of 0%) S, and contains as a structure, by space factors to the whole structure, 15 to 60% tempered martensite, 5 to 50% ferrite, ≥5% retained austenite and 15 to 45% massive martensite having an aspect ratio of ≤3, and the space factor occupied by fine martensite having a mean particle diameter of ≤5 μm is ≥30% of the massive martensite.;COPYRIGHT: (C)2005,JPO&NCIPI