| 摘要 |
PROBLEM TO BE SOLVED: To provide a non-heat-treating type electric resistance welded pipe which is a pipe consisting of an ultra high strength steel sheet having the tensile strength of >=980N/mm<2> , whose strain is small and which has delayed fracture resisting characteristic excellent under various corrosive environment. SOLUTION: The pipe made of the ultra high strength steel sheet excellent in delayed fructure resisting characteristic consists of the steel sheet containing, by weight, 0.08-0.25%C, 1.0-3.0% Mn and martensite or bainite of >=50% independently and compositely and having the tensile strength of 980N/mm<2> , and the residual stress in the outside surface part of the pipe determind by a method of section using the strain gage method is expressed by the equation ofσR<=(0.0369σB<2> -122σB+102405)×(HVM/HVO). (In the equationσR is the max. residual stress (N/mm<2> ) on the surface of the pipe,σB is the tensile strength (N/mm<2> ) of the pipe, HVM is the average hardness in the center part of thickness of the pipe, HVO is the average hardness in the interior at 0.1-0.2mm from the outside surface of the pipe).
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