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

This high-strength steel sheet includes: in 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; 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 sizes of 10 nm or smaller is in a range of 1010 precipitates/mm3 or more, and a ratio (Hvs/Hvc) of a hardness (Hvs) at a depth of 20 μm from a surface to a hardness (Hvc) at a center of a sheet thickness is in a range of 0.85 or more.

主权项

1. A high-strength steel sheet having excellent fatigue properties, elongation and collision properties, comprising: in 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; 0.01 to 1.2% of Al; 0.06 to 0.092% of Ti; 0.01% or less of N; and a balance of iron and inevitable impurities, wherein a tensile strength is in a range of 590 MPa or more, a ratio of a yield strength to the tensile strength is in a range of 0.80 or more, a microstructure comprises bainite at an area ratio of 40% or more and a balance of at least one of ferrite and martensite, a density of Ti(C,N) precipitates having sizes of 10 nm or smaller is in a range of 1010 precipitates/mm3 or more, and a ratio Hvs/Hvc of a hardness, Hvs, at a depth of 20 μm from a surface to a hardness, Hvc, at a center of a sheet thickness, of 0.92 or more.