HIGH-STRENGTH COLD-ROLLED STEEL SHEET, HIGH-STRENGTH GALVANIZED STEEL SHEET AND HIGH-STRENGTH ALLOYED GALVANIZED STEEL SHEET HAVING MAXIMUM TENSILE STRENGTH OF 780 MPa AND EXCELLENT COLLISION CHARACTERISTIC AND THEIR PRODUCTION METHOD

摘要

PROBLEM TO BE SOLVED: To provide a high-strength cold-rolled steel sheet, a high-strength galvanized steel sheet and a high-strength alloyed galvanized steel sheet which have a maximum tensile strength(TS) of 780 MPa or higher and are applicable to impact absorption members on collision and their production method.;SOLUTION: A steel sheet has a micro-structure which contains, by volume fraction, 20% or more of ferrite as the main phase and a total of 5-80% of martensite and/or bentonite as the second phase and is restricted in volume fraction of retained austenite to smaller than 10%. The ratio of martensite and bentonite particles having one or more grains of penetrating ferrite is 20% or more of all the martensite and bentonite particles.;COPYRIGHT: (C)2015,JPO&INPIT