| 摘要 |
PROBLEM TO BE SOLVED: To improve the spring formability of high strength oil tempered steel wire by comprising it of low alloy steel for a spring, applying it with a decarburizing layer in which hardness is reduced from the surface of the wire to a specified depth, regulating the hardness of the surface of the wire to a specified rang and regulating the hardness on the inside of the wire exceeding the depth of the decarburizing layer to specified vale or above. SOLUTION: The low alloy steel for spring has a compsn. contg., by weight, 0.45 to 0.80% C, 1.2 to 2.5% Si, 0.5 to 1.5% Mn, 0.5 to 2.0% Cr, and the balance Fe with inevitable impurities. The oil tempered steel wire produced from this has a decarburizing layer in which hardness is reduced from the surface of the wire to a depth of <=200μm. Then, the hardness of the surface of the wire is regulated to the range lower than the on the inside of the wire by 50HV from 420HV. Furthermore, than hardness on the inside of the wire exceeding the depth of the decarburizing layer is regulated to >=550HV. In this way, stable spring working can be executed without breaking in the process of spring forming even in the case fine surface defects are present in the process of operating the spring. |
