| 摘要 |
PROBLEM TO BE SOLVED: To provide a non-heat treated bolt which has excellent fatigue properties, and to provide production method thereof. SOLUTION: The non-heat treated bolt has a ferrite single phase structure after rolling, and in which fine precipitates with a particle diameter of <10 nm are finely dispersed after precipitation treatment. The bolt has a steel composition containing, by mass,≤0.10% C,≤0.3% Si,≤2% Mn, 0.03 to 0.20% Ti and 0.05 to 0.6% Mo, if required, containing one or more kinds of metals selected from≤0.08% Nb,≤0.15% V,≤1.5% W, 0.03 to 0.1% S,≤0.2% Pb,≤50 ppm Ca and≤200 ppm B, and satisfying 0.5≤(C/12)/ä(Ti/48)+(Mo/96)+(Nb/93)+(V/51)+(W/192)}≤1.5, and the balance Fe with inevitable impurities. Steel having the above composition is heated at≥1,100°C, and is rolled at a finishing temperature of 800°C. The steel is cooled in a range of 700 to 550°C at >0.5°C/sec. Subsequently, the steel is subjected to cold working so as to be a bolt shape, and is thereafter held at 550 to 700°C for≥10 min. COPYRIGHT: (C)2004,JPO
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