2004 年 2004 巻 49 号 p. 21-26
The recent development of lightweight yet high output automotive engines has increased demand for valve springs with high fatigue resistance. This has led to the development of valve spring wire with high fatigue strength. The Cr-Si steel oil tempered wire (SAE 9254) has been commercially used for the valve spring wire, and our company developed C and Si-enriched oil tempered wire that has both high-heat resistance and high fatigue strength. In this research, the authors focused on evaluating the effect of prior γ grain sizes on fatigue strength. It was found that finer structure is effective in improving fatigue strength.