| 摘要 |
PROBLEM TO BE SOLVED: To provide a manufacturing method of a non-heat-treating type electric resistance welded pipe whose strain is small and which has excellent delayed fructure resisting characteristic and collapsing property under various corrosive environments. SOLUTION: A steel sheet containing, by weight, 0.08-0.25% C, 1.0-3.0% Mn and martensite or bainite of >=50% independently and compositiely and whose teisile strength is >=980N/mm<2> is made into a pipe by roll forming, electric resistance welding is executed, the total amount of strain is taken as 5-30% as the average strain in the interior of thickness and the residual stress in the outer surface part of pipe which is determined by a method of section using a strain gage method isσR<=(0.0369σB<2> -122σB+102405)×(HVM/HVO). (σR is the max. residual stress (N/mm<2> ) in a direction in which the stress of the surface of the pipe is max.,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 and HVO is the average hardness in the interior at 0.1-0.2mm from the outside surface of the pipe).
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