Simplified Carburizing Process for Stainless Steel

A ferritic stainless steel was embedded in mixtures of steel and activated carbon powders, and heated at 1273 K for 3.6 ks in flowing N-2. The specimen was quenched into the water after heating. This simplified treatment enabled the diffusion of carbon into the stainless steel, which is known to have difficulty in carburizing. The microstructural change was not recognized in the vicinity of the surface in the specimen heated in only activated carbon. However, the carburized layer was found in the stainless steel when the steel powder was added to activated carbon. The thickness of the carburized layer was more than 200 mu m in the case of the mixed powder consisting of 10 vol% steel powder and 90 vol% activated carbon, and increased with increasing steel powder. The surface hardness of the carburized steel also increased with increasing steel powder in the mixed powder. In addition, the carburized layer was observed in the stainless steel heated in mixtures of steel and graphite powders. The details of the carburization phenomenon are discussed on the basis of the measurement of carbon monoxide gas during heating and of the heat treatment without directly contacting with the mixed powder.