| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel material having excellent balance of properties such as rolling and weldability, and roughness and fatigue crack propagation property and a manufacturing method therefor.SOLUTION: There is provided a high strength steel sheet excellent in strength, rolling property, roughness, weldable fatigue crack propagation property having an aggregate structure consisting of a martensite single phase or bainite and martensite and having X ray diffraction intensity ratio of 110and 110, and 110and 100and 111at a sheet thickness center position satisfying predetermined values by conducting heating at 900 to 1300°C, hot rolling with 50% or more of a cumulative draft in a temperature range of Arpoint or more and accelerate cooling from (Arpoint-80°C) or more to 600°C or less at a cooling speed of 3°C/s or more on a crude steel raw material containing, by mass%, C:0.02 to 0.25%, Si:0.01 to 0.60%, Mn:0.5 to 3.0% and Al:0.10% or less and further one or more kinds of Cu, Ni, Cr, Mo, Nb, V, Ti and B while satisfying Ceq of 0.45% or less and Pcm of 0.28% or less. |
