HIGH-STRENGTH COLD-ROLLED STEEL SHEET, HIGH-STRENGTH GALVANIZED STEEL SHEET AND HIGH-STRENGTH GALVANNEALED STEEL SHEET, HAVING EXCELLENT FORMABILITY AND SHAPE FIXABILITY, AND PROCESSES FOR MANUFACTURING SAME.

摘要

This high-strength cold-rolled steel sheet has both a prescribed composition and a prescribed structure and exhibits a tensile strength of 980MPa or higher, said structure satisfying the requirements: the total content of bainitic ferrite (BF) and tempered martensite (TM) is 65% or more (in % by area relative to the structure, the same applies hereinbelow); the content of fresh martensite (M) is 3 to 18%; the content of retained austenite (retained γ) is 5% or more; the content of polygonal ferrite (F) is 5% or less; and the prescribed average KAM < 1.00° is 0.50° or more. The high-strength cold-rolled steel sheet exhibits excellent formability and shape fixability.