Abstract
In order to form thick and hard chromium carbide film on 2 1/4 Cr-1Mo alloy steel, (C, Cr) combined diffusion treatment which was composed of carburizing treatment and chromizing treatment was proposed. Thick chromium carbide film (>30 μm) could be obtained by selecting carburizing and chromizing conditions. The formed surface was composed of chromium carbide film on the substrate and precipitated chromium carbide particles below the film. Furthermore, the obtained film consisted of fine (about 0.5 μm) Cr23C6 and Cr7C3 particles. The precipitated chromium carbide particles below the film mainly consisted of Cr23C6. The distribution of these Cr23C6 particles gradually decreased in proportion to the distance from the boundary between the film and the substrate. The film showed excellent adhesion to the substrate under thermal cyclic condition from 400°C up to 700°C. It was thought that the chromium carbide film which partly penetrated into the grain boundary of the substrate acted as an anchoring effect and the precipitated chromium carbide particles below the film acted as a thermal expansion relief layer. The obtained film showed high hardness over Hv 1000.
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