High-strength steel sheet and manufacturing method thereof

A high-strength steel sheet which satisfies a composition containing, in terms of mass%, 0.12-0.40% C, 0-0.6% Si, 0-1.5% (excluding 0%) Mn, 0-0.15% (excluding 0%) Al, 0-0.01% (excluding 0%) N, 0-0.02%(excluding 0%) P, and 0-0.01% (excluding 0%) S and which has a martensite single-phase structure. Of the steel sheet, the regions having a Kernel average misorientation value (KAM value) of 1 DEG orgreater account for 50% or more. In the steel sheet, a surface layer region extending from the surface to a depth corresponding to 1/4 the sheet thickness has a maximum residual tensile stress of 80 MPa or less. Due to this configuration, the high-strength steel sheet is excellent in terms of the delayed-fracture resistance of the cut end surfaces and the steel sheet base material. 种高强度钢板，以质量％计满足C：0.12～0.40％、Si：0％以上且0.6％以下、Mn：超过0％且1.5％以下、Al：超过0％且0.15％以下、N：超过0％且0.01％以下、P：超过0％且0.02％以下、S：超过0％且0.01％以下，并且具有马氏体单相组织，其中，KAM值亦即Kernel Average Misorientation值为1°以上的区域占50％以上，从表面到板厚1/4深度位置的表层区域的最大拉伸残余应力为80MPa以下。由此，能够实现切割端面和钢板母材的耐延迟断