PURPOSE: To easily obtain an alloy high in bonding strength of the surface layer and excellent in surface hardness by forming an iron-based alloy layer on the surface of an alloy to be carbonitrided and specifying the carbon content and the ratio of the depth of specified hardness after treatment to the thickness of the iron-based alloy layer.
CONSTITUTION: The layer (F) of an iron-based alloy is formed on the surface of a Ti-based alloy, and the carbon content is controlled to ≤0.08wt.%. The ratio of the depth t2 of ≥513 Vickers hardness from the surface after carbonitriding to the thickness t1 of the layer F is controlled to ≤0.8. In this case, the iron-based alloy is a high temp. austenitic phase and has solubility for C and N. Therefore, the hardened surface layer is easily obtained by the carbonitriding treatment. In the case of containing ≥0.08% carbon content, a carbide is formed at the interface between the Ti-based alloy layer and the layer F during the treatment, and the bonding strength between both layers is lowered. In addition, when t2/t1≤0.8 is fulfilled, C and N do not reach the interface between the layer F and the Ti-based alloy layer by diffusion, and consequently, lowering of bonding strength due to the formation of Ti carbide and Ti nitride at the interface is prevented.
ISHIKAWA MISAO
MINAGAWA KUNINORI
