Nhk Spring Co., Ltd.

Tadayoshi Akutsu

Akira Tange

Hiroshi Koyama

Yasuo Sato

Katsuyuki Nishioka

A spring steel containing 0.35 to 0.50% of carbon is refined to the hardness of .phi. 2.50 to 2.70 mm in Brinell indentation diameter (HBD) by rapid cooling for quenching and tempering. This spring steel is subjected to warm shot peening at a temperature of 150 to 300.degree. C. (423 to 573K) by using long-lived practical shots with the normal hardness of .phi. 2.65 to 2.80 mm in HBD, whereupon a high-strength spring is obtained having a compressive residual stress in its surface and enjoying the maximum shearing stress of 110 to 135 kgf/mm.sup.2 (1080 to 1325 MPa).

High strength spring

A spring steel containing 0.35 to 0.50% of carbon is refined to the hardness of .phi. 2.50 to 2.70 mm in Brinell indentation diameter (HBD) by rapid cooling for quenching and tempering. This spring steel is subjected to warm shot peening at a temperature of 150.degree. to 300.degree. C. (423 to 573 K.) by using long-lived practical shots with the normal hardness of .phi. 2.65 to 2.80 mm in HBD, whereupon a high-strength spring is obtained having a compressive residual stress in its surface and enjoying the maximum shearing stress of 110 to 135 kgf/mm.sup.2 (1080 to 1325 MPa).

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Yokohama, Japan

Tadayoshi Akutsu