| 摘要 |
PROBLEM TO BE SOLVED: To improve toughness and ductility of a core and to improve strength of a tooth root of a gear tooth at a low cost by machining a low carbon steel material into a gear shape, after introducing carbon into a gear tooth surface and then slowly cooling, heat treating with induction heating and increasing a residual compression stress of a tooth root. SOLUTION: A low carbon steel material of about <=0.35% C is subjected to machining, forging, etc., to be worked into a shape approximate to a final gear having many gear teeth. Carbon of >=0.45 is introduced into a gear tooth surface by subjecting the gear to carburizing. By this method, a core of the gear is hardened to have a hardness of Rockwell C20-45 and the carbon is diffused into a depth of 0.045 inch of a gear tooth surface. The gear is slowly cooled after this heat treatment, if necessary to be annealed to prevent quenching. Successively, a surface of the gear tooth is reheated by induction heating so as to increase a residual compression stress, if necessary, further local heating treatment and machining are conducted. By this method, a gear tooth surface is made to have a hardness of >=Rockwell C60 and a residual compression stress of 100,000 psi.
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