Effects of Temperature and Atmosphere for Dissolution of Cr Carbide Precipitate near the Surface on Fe-Cr-C alloy

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The dissolution behavior and mechanism of chromium carbide precipitation near the surface of Fe-Cr-C alloy were investigated by electron probe microanalysis. There was a 100μm of chromium carbide dissolution layer near the surface of SCH2 heat resistant steel exposed at 1273K for 345.6ks in air. The chromium carbide dissolution layer was also identified on the specimen exposed at 1473K for 345.6ks in air and at 1273K for 14.4ks in H2. The result of EPMA analysis showed that not only chromium but also carbon were depleted on chromium carbide dissolution layer. The chromium content that was detected at the chromium carbide dissolution layer/chromium carbide layer interface was higher than the critical chromium content to form chromium carbide on Fe-Cr-C phase diagram. The Fe-Cr-C phase diagram shows that critical chromium content to form the Cr carbide increases with the reduction of carbon. This shows that the chromium content that was detected at the chromium carbide dissolution layer/chromium carbide layer interface was increased by decarburization from the surface during the exposure.It was concluded that the chromium carbide dissolution layer formed at 1273K was formed both in air and H2 by the same mechanism as that at higher temperature up to 1473K.
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