HIGH-STRENGTH STEEL SHEET, HOT-DIPPED STEEL SHEET, AND ALLOY HOT-DIPPED STEEL SHEET THAT HAVE EXCELLENT FATIGUE, ELONGATION, AND COLLISION CHARACTERISTICS, AND MANUFACTURING METHOD FOR SAID STEEL SHEETS

摘要

Provided is a high-strength steel sheet that contains, by mass, 0.03-0.10% carbon, 0.01-1.5% silicon, 1.0-2.5% manganese, no more than 0.1% phosphorus, no more than 0.02% sulfur, 0.01-1.2% aluminum, 0.06-0.15% titanium, and no more than 0.01% nitrogen, with the remainder comprising iron and unavoidable impurities. The steel sheet has a tensile strength of at least 590 MPa and a tensile strength/yield strength ratio of at least 0.80. The microstructure of the steel sheet comprises bainite with an area ratio of at least 40%, with the remainder comprising ferrite and/or martensite. The density of Ti(C, N) deposits no larger than 10 nm is at least 1010 deposits per mm3, and the ratio (Hvs/Hvc) between the hardness at a depth of 20 µm from the surface (Hvs) and the hardness at the center of the thickness of the sheet (Hvc) is at least 0.85.