| 摘要 |
PROBLEM TO BE SOLVED: To improve the wear resistance of the surface of a valve element without recourse to surface treatment, such as nitriding treatment and plating. SOLUTION: A carburized layer 4 is formed at least on the surface requiring wear resistance or fatigue strength of a valve element 3 which is made of titanium alloy and constituted in such a way that a valve head 2 is connected to one end of a valve stem 1. Simultaneously, oxide layers 9 are formed in the parts 5, 6, 7, 8 to be brought into contact with other valve gear mechanism parts, at the surface of the valve element 3 including the carburized layer 4, respectively, and the lower layers thereof are formed into acicular structure.
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