| 摘要 |
When the carbon content, silicon content and manganese content of this cold-rolled steel sheet are expressed as [C], [Si] and [Mn], respectively, in terms of unit mass%, a relationship of (5 × [Si] + [Mn])/[C] > 11 holds; and the metal structure after hot stamping contains ferrite at 40% to 90% and martensite at 10% to 60% by area ratio, and the sum of the area ratio of ferrite and the area ratio of martensite is at least 60%. Furthermore, the hardness of the martensite, as measured by a nanoindenter, satisfies H2/H1 < 1.10 and σHM < 20 before hot stamping, and TS × λ, which is the product of the tensile strength (TS) and hole expansion rate (λ), is at least 50000 MPa∙%. |
