HIGH STRENGTH STEEL SHEET HAVING EXCELLENT DELAYED FRACTURE RESISTANCE, AND ITS PRODUCTION METHOD

PROBLEM TO BE SOLVED : To provide a high strength steel sheet which has a tensile strength of ≥1, 180 MPa and has excellent delayed fracture resistance, and to provide its production method. SOLUTION : The high strength steel sheet having excellent delayed fracture resistance contains, by mass, 0.05 to 0.3% C, <3.0% Si, 0.5 to 3.0% Mn, ≤0.02% P and ≤0.02% S, and, if required, one or more kinds of metals selected from Mo, V, Cr, Ni, Cu, W, Al, Ti, Nb, B, N, Ca, Mg, Zr and rare earth metals, and the balance Fe with inevitable impurities, has a layered structure of tempered martensite and ferrite, and also has a tensile strength of ≥1, 180 MPa.