| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel sheet blank using, as a raw material, a high-strength steel sheet for laser processing which has excellent elongation and stretch-flanging properties while having a high strength of 780 MPa or higher.SOLUTION: A steel sheet blank has a laser-cut cut end surface and has a chemical composition comprising C of 0.07-0.25% inclusive, Si of 0.04-2% inclusive, Mn of 1.2-3% inclusive, P of 0.05% or less, S of 0.02% or less, sol. Al of 0.01-2% inclusive, with the balance being Fe and impurities. The steel sheet blank comprises a micro-structure having a total area ratio of martensite and bainite in the cut end surface part from the cut end surface with 40-μm inward width of 85% or higher, an area ratio of ferrite in the base metal part other than the cut end surface part of 10-80%, and an area ratio of retained austenite of 2% or higher, with the balance being martensite and bainite, and also has mechanical characteristics including a tensile strength of 780 MPa or higher. |
