| 摘要 |
Provided are a high-strength steel sheet, which is suitable as a material of automotive parts, and a method for producing the high-strength steel sheet. In the high-strength steel sheet, the C content is 0.15% or less, the area ratio of ferrite is 8% to 45%, the area ratio of martensite is 55% to 85%, the proportion of martensite grains adjacent to only ferrite grains in the entire microstructure is 15% or less, the average crystal grain sizes of ferrite and martensite are each 10 μm or less, and the area ratio of ferrite grains having a size of 10 μm or more to all the ferrite grains included in a portion of the steel sheet which extends from 20 to 100 μm below the surface thereof is less than 5%. |
| 主权项 |
1. A high-strength steel sheet comprising a composition containing, by mass, C: 0.05% to 0.15%, Si: 0.01% to 1.00%, Mn: 1.5% to 4.0%, P: 0.100% or less, S: 0.02% or less, Al: 0.01% to 0.50%, Cr: 0.010% to 2.000%, Nb: 0.005% to 0.100%, Ti: 0.005% to 0.100%, B: 0.0005% to 0.0050%, and the balance being Fe and inevitable impurities, wherein K represented by Formula (I) below is 3.0 or more; and a microstructure in which, when the microstructure is observed in a cross section of the steel sheet which is perpendicular to the surface of the steel sheet at a depth of ¼ thickness below the surface of the steel sheet, the area ratio of ferrite is 8% to 45%, the area ratio of martensite is 55% to 85%, the proportion of martensite grains adjacent to only ferrite grains in the entire microstructure is 15% or less, the average crystal grain sizes of ferrite and martensite are each 10 μm or less, and the area ratio of ferrite grains having a size of 10 μm or more to all ferrite grains included in a portion of the steel sheet which extends from 20 to 100 μm below the surface of the steel sheet is less than 5%,
K=−0.4×[Si]+1.0×[Mn]+1.3×[Cr]+200×[B] Formula (I), where [Si] represents the Si content [mass %], [Mn] represents the Mn content [mass %], [Cr] represents the Cr content [mass %], and [B] represents the B content [mass %]. |
