To further improve toughness by changing the C and N component concentration continuously and/or gradually from the lower surface part composition to a layer thickness middle part composition, and from the layer thickness middle part composition to the upper surface part composition.
The x value in a composition formula Ti (CiNi) of a TiCN layer is so that the x values of the upper surface part and the lower surface part are 0.05 to 0.35, and the x value of the layer thickness part is 0.65 to 0.95. When the x values of the upper surface part and the lower surface part exceed 0.35 or the value of the layer thickness middle part is less than 0.65, the concentration change of C and N in the direction of layer thickness is decreased not to obtain an effect of further improving toughness, so that desired chipping resistance can not be secured in a hard coating layer. When the x values of the upper surface part and the lower surface part is less than 0.05 or the x value of the layer thickness middle part exceeds 0.95, conversely the concentration change of C and N is increased to excess not to avoid a remarkable lowering of toughness.
KUNUGI HITOSHI
MIICHI MASAYUKI
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