| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel sheet excellent in the delayed fracture resistance of the cut edge face, and a method useful for producing the high strength steel sheet.SOLUTION: Provided is a high strength steel sheet satisfying a prescribed chemical componential composition, and having a steel sheet structure being a mixed structure where a tempered martensitic phase is dispersed into the matrix of a ferritic phase, further, the ratio of the ferritic phase occupied in the whole body of the structure is 20 to 40 area%, also, in the observation of the steel sheet structure, when the size of one field is defined as 100 μm×100 μm and 10 lines are drawn at the equal intervals of 10 μm in an aspect ratio respectively in the field, in the crossed points at which the boundary of the ferritic phase and the tempered martensite and the above line are crossed, in the case where the segment with the crossed point adjacent on the line lies on the ferrite, the length of the segment is measured, the average value of the total in the 10 fields of the measured segment length is obtained as the average spacing of the tempered martensitic phase, and this average spacing is 6.5 μm or lower.SELECTED DRAWING: None |
