| 摘要 |
PROBLEM TO BE SOLVED: To produce an oil tempered steel wire for a spring excellent in fatigue strength and settling resistance in the use by specifying the content of carbon and ratio of residual phases in the whole body and in the surface layer part at a specified depth. SOLUTION: This oil tempered steel wire for a spring is the one contg., by weight, 0.5 to 0.8% carbon, and in which, the ratio of residualγphases, by volume, is regulated to 1 to 5% in the whole body and to >5 to 14% in the surface layer part in which the depth is regulated to 1/10 of the wire diameter. For producing the wire rod, a steel contg. 0.5 to 0.8% carbon is subjected to quenching for two times and is thereafter tempered. At this time, preferably, the secondary quenching is applied only to the surface layer part at a depth of 1/10 of the wier diameter. As a means of executing quenching only to the surface layer part, high-frequency heating is given. Moreover, the cooling rate at the time of the secondary quenching is preferably slowed down more than that of the cooling rate at the time of the primary quenching.
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