| 摘要 |
PROBLEM TO BE SOLVED: To obtain a member which is equal to a high carbon steel kind in strength, low in carbon equivalence and superior in weldability by cutting a steel material which has a specific carbon equivalence and is heat-treated to heighten the tensile strength, into a given dimension, forming cut pieces into a given shape with cold plastic deformation processing, and providing a specific tensile strength. SOLUTION: A steel material of 0.2-0.4 carbon equivalence is processed into a wire rod through many rolling steps, and the wire rod of high temperature being pulled out from a finish rolling mill is heat-treated by warm water immersion, wind-cooling or salt bath immersion so as to heighten the tensile strength. Then, the wire rod is drawn through dies to be process-hardened, and is wound up at a given diameter. The wire rod 4 pulled out from an uncoil part 6a is supplied to a pressure forging device 6, and cut into a given dimension. Thereafter, the cut piece 7 is continuously pressure forged to a welding member A such as a welding nut and a stud bolt with cold plastic deformation processing, and the tensile strength of 70-100 kgf/mm2 is provided to a final product.
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