| 摘要 |
PROBLEM TO BE SOLVED: To improve the roll-over and the circularity of a cut piece, to reduce the roll-over quantity at the end face of a product, and to improve the yield of the material by setting the maximum hardness position in the section of the steel wire to be in the prescribed position, reducing the hardness from this position toward the center of the steel wire, and specifying the surface hardness increase ratio. SOLUTION: The maximum hardness area V in the section is set at the position within 1/10 of the radius (r) of the steel wire from the surface of a steel wire 11, and the area toward the center side from this area is set to be the area W where the hardness is dropped. The surface hardness increase ratio ((H-Q)/Q)×100% is set to be 15-30%, where H is the maximum hardness, and Q is the hardness at the position of r/2 from the surface. Only the hardness of the surface of the steel wire is increased, the circularity and the roll-over of the cut piece is improved, the roll-over quantity at the end face of a product after the cold forging can be sufficiently reduced, the cutting cost of the roll- over is reduced, and the yield of the material is improved.
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