THIN STEEL SHEET AND PLATED STEEL SHEET, METHOD FOR PRODUCING HOT-ROLLED STEEL SHEET, METHOD FOR PRODUCING COLD-ROLLED FULL HARD STEEL SHEET, METHOD FOR PRODUCING HEAT-TREATED SHEET, METHOD FOR PRODUCING THIN STEEL SHEET AND METHOD FOR PRODUCING PLATED STEEL SHEET

摘要

Provided herein is a steel sheet of a specific composition that has a micro structure containing, by volume, 75 to 95% of ferrite, 3 to 15% of martensite, 0.5 to 10% of perlite, 10% or less of unrecrystallized ferrite, and 21.5% or less of a low-temperature occurring phase representing the remainder, and in which the ferrite has an average crystal grain diameter of 6 μm or less, and the martensite has an average crystal grain diameter of 3 μm or less, and an average aspect ratio of 4.0 or less, and in which a Nb base precipitate having an average grain diameter of 0.10 μm or less is contained. The steel sheet has a tensile strength of 590 MPa or more.