Steel sheet having a 780~940N / mm2 tensile strength and yield strength 670~870N / mm2,

摘要

Chemical composition is within a predetermined range , 0.13 to 1.0 % by weight values , and the value is 8.45 to 15.2 , steel sheet according to the present invention , 670~870N the yield strength / mm ² , And tensile strength 780~940N / mm ² Is , the plate thickness is 25~200mm the average grain size in the center of plate thickness of the steel sheet , and is less than 35m . The steel sheet according to the present invention , when it is done with respect to the steel stress -relief annealing , of where the stress relief annealing is performed, the Charpy absorbed energy at -40 may be not more than 100J .