| 摘要 |
A spring with superior fatigue resistance and a production method therefor are provided by decreasing the material cost and simplifying the production process. The spring consists of, by mass %, 0.5 to 0.7 % of C, 1.0 to 2.0 % of Si, 0.1 to 1.0 % of Mn, 0.1 to 1.0 % of Cr, not more than 0.035 % of P, not more than 0.035 % of S, and the balance of Fe and inevitable impurities. The spring has a structure including not less than 65 % of bainite and 4 to 13 % of residual austenite by area ratio in a cross section, and the residual austenite contains carbon at an average concentration of 0.65 to 1.7 %. The spring has a compressive residual stress layer in a cross section from a surface to a depth of 0.35 mm to D/4, in which D (mm) in a circle-equivalent diameter of the cross section. The compressive residual stress layer has maximum compressive residual stress of 800 to 2000 MPa. The spring has a center portion with hardness of 550 to 650 HV in a cross section and has a high hardness layer with greater hardness than the center portion by 50 to 500 HV from a surface to a depth of 0.05 to 0.3 mm. |
