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

I I 75 ABSTRACT This high-strength steel sheet includes: iij terms of percent by mass, 0.03 to 0.10% of C; 0.01 to 1.5% of Si; 1.0 to 2.5% of Mn; 0.1% or less of P; 0.02% or less of S; 5 0.01 to 1.2% of Al; 0.06 to 0.15% of Ti; and 0.01% or less of N; and contains as the balance, iron and inevitable impurities, wherein a tensile strength is in a range of 590 MPa or more, and a ratio between the tensile strength and a yield strength is in a range of 0.80 or more, a microstructure includes bainite at an area ratio of 40% or more and the balance being either one or both of ferrite and martensite, a density of Ti(C,N) precipitates having 10 sizes of 10 imi or smaller is in a range of 10 precipitates/mm or more, and a ratio (Hvs/Hvc) of a hardness (Hvs) at a depth of 20 j^m from a surface to a hardness (Hvc) at a center of a sheet thickness is in a range of 0.85 or more.