To provide a spring that has a high compression residual stress layer having improved fatigue resistance and that has increased simplicity of the production process and reduced materials cost, and to provide a method for producing the spring.
A steel material contains 0.5-0.7 mass% C, 1.0-2.0 mass% Si, 0.1-1.0 mass% Mn, 0.1-1.0 mass% Cr, ≤0.035 mass% P, ≤0.035 mass% S, and the remainder comprising iron and inevitable impurities. The steel material is processed by the following steps in sequence: a forming step of forming the steel material into spring shape; a heat treatment step of austenitizing it at a temperature in a range of (a temperature of Ac3 point) to (the temperature of Ac3 point +250°C), cooling it at a speed of ≥20°C/sec, isothermally holding it for 400 seconds or more at a temperature in a range of (Ms point -20°C) to (Ms point +60°C), and cooling it to a room temperature at cooling speed of ≥20°C/sec; a setting step of giving a permanent strain to it; and a shot peening step of impacting it with shot.
YAMAMOTO FUMIO
ONO YOSHIKI
SUZUKI TAKESHI
KUROKAWA SHINPEI
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