HIGH STRENGTH STEEL SHEET AND HIGH STRENGTH GALVANIZED STEEL SHEET EXCELLENT IN SHAPEABILITY AND METHODS OF PRODUCTION OF SAME

摘要

This high-strength steel sheet having superior moldability while securing the high strength of a maximum tensile strength of at least 900 MPa is characterized by having a predetermined component composition, the steel sheet structure containing a ferrite phase and an austenite phase, the ratio of bcc iron and unaligned Cu grains being at least 15% of the Cu grains overall, the Cu grain density in the ferrite phase being at least 1.0 × 1018 grains/m3, and the average grain size of the Cu grains in the ferrite phase being at least 2.0 nm.