HIGH STRENGTH STEEL SHEET HAVING EXCELLENT DELAYED FRACTURE RESISTANCE AND METHOD FOR PRODUCING THE SAME

PROBLEM TO BE SOLVED: To provide a high strength steel sheet having delayed fracture resistance more excellent than that of the conventional steel sheet.SOLUTION: Regarding the high strength steel sheet having excellent delayed fracture resistance, in a chemical componential composition, C, Si, Mn, Al, P, S and N satisfy prescribed ranges, and the balance iron with inevitable impurities, and, the total of martensite and carbides occupied in the total structure is 95 area% or higher, also, in a structure to the position of the depth of 1/4 of the sheet thickness from the position of the depth of 10 μm to the sheet thickness direction from the surface of the steel sheet, old austenite grain diameter (Dγ) is 20 μm or lower and the area ratio occupied by carbides (Q value) satisfies 3.0% or lower (wherein, Q value=0% is not included), and, further, its tensile strength is 1,180 MPa or higher to 1,370 MPa or lower.