COOL SPRING EXCELLENT IN DELAYED FRACTURE RESISTANCE AND PRODUCTION THEREOF

摘要

PROBLEM TO BE SOLVED: To obtain a coil spring which can prevent the development of delayer fracture after cold-coiling by using a wire rod which is the oil tempered wire, which has hardness of ≥ the specific value of the inner part of the cross sectional surface after applying oil-tempering treatment, and of which surface hardness after the treatment is adjusted whitin a specific range, and forming the coiling. ;SOLUTION: The hardness in the inner part of the cross sectional surface of the wire rod after applying the oil-tempering treatment, is supporsed to be ≥Hv 550. Then, the hardness of the surface is adjusted within are range of the HV value from Hv 420 at the min. value to HV value deducted by at least 50 from the hardness in the inner part of the cross sectional surface of the oil tempered wire at the max. value. This adjustment is executed by decarburizing a stock surface at the time of heating the stock of the oil-tempered wire for quenching. The material composed of 0.45-0.8% C, 1.2-2.5% Si, 0.5-0.1% Mn, 0.5-2.0% Cr by wt. and prescribed contents of at least one element selected from among Mo, V, N and Nb and the balance Fe with impurity elements is used for the stock.;COPYRIGHT: (C)1998,JPO