| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide an oil tempered steel wire for a cold formed coil spring which has performance equal to or above that of a hot formed coil spring, and to provide a cold formed spring using the same wire. SOLUTION: Steel containing, by weight, 0.35 to 0.55% C, 1.8 to 3.0% Si, 0.5 to 1.5% Mn, 0.5 to 3.0% Ni and 0.1 to 1.5% Cr is used as the stock. The fraction of ferrite in the steel sheet of the stock is controlled to <=50%, and the hot rolled wire rod is subjected to cold wire drawing at a prescribed reduction of area. After that, heat treatment by high-frequency induction heating is performed thereto. Desirably, the maximum heating temperature is controlled to 900 to 1,020 deg.C (more desirably, to 950 deg.C), and the holding time is controlled to 5 to 20 sec. As the stock after oil tempering treatment, desirably, the crystal grain size number is controlled to >=9, and its tensile strength is controlled to 1,830 to 1,980 MPa.</p> |
