Patent ID: 6123785
Filing Date: 2000-09-26
Classification: C21D,C22C,Y02P,Y10S

Abstract:
A process for producing a constant velocity joint having improved cold workability, rolling fatigue life, and torsional strength, comprising the steps of:rolling or forging an alloy as a starting material at a heating temperature of Ac.sub.3 to 1000.degree. C. with a reduction in area of not less than 30%, said alloy comprising by weight carbon: 0.52 to 0.60%, silicon: 0.03 to 0.15%, manganese: 0.10 to 0.40%, chromium: 0.05 to 0.30%, molybdenum: 0.10 to 0.30%, sulfur: 0.003 to 0.020%, boron: 0.0005 to 0.005%, titanium: 0.02 to 0.05%, nitrogen: not more than 0.01%, aluminum: 0.005 to 0.05%, and manganese+chromium+molybdenum: 0.35 to 0.80% with the balance consisting of iron and unavoidable impurities;spheroidizing the rolled or forged alloy in such a manner that, after heating to Ac.sub.1 to 770.degree. C., slow cooling is performed from 730.degree. C. to 700.degree. C. at a rate of not more than 15.degree. C./hr, thereby producing a steel product having a hardness of 68 to 78 HRB after the spheroidizing; andinduction hardening the steel product to obtain a constant velocity joint having a surface hardness of not less than 60 HRC.