Carburizing and quenching are one of the surface modification treatments to impart mechanical properties to materials. Carburizing is a lengthy process, generally performed at approximately 1203 K. Conventional carburizing (gas carburizing or low pressure carburizing) is processed in batches. Consequently, this creates many in-process inventories, which negatively affects the production efficiency. To devise an efficient production process, it is necessary to reduce the carburizing duration. Carburizing is a carbon-diffusion phenomenon, and increasing the temperature accelerates the process. In this study, we investigated the carbon penetrating behavior of a steel specimen by carburization it at temperatures 1473 K to 1573 K, which are above the eutectic temperature of the specimen. A ring specimen- Cr-Mo steel (JIS SCM420) was used in this investigation. Methane and nitrogen gases were used for carburizing. The specimen was rapidly heated by induction heating in a carburized atmosphere and kept for processing at each temperature, followed by quenching. It was observed that the time required to reach the same total carburizing depth was 1/20 times of the treatment at 1203 K compared to that of the treatment at 1523 K. Moreover, the total carburizing depth variations followed the parabolic law, the Harris’s empirical formula. It was evident that carbon penetration is proportional to the duration of the carburizing process. The rate of carbon penetration per unit time varied exponentially with the carburizing temperature. The activation energy was calculated from the Arrhenius plot of carbon penetration rate, which was close to that in the decomposition reaction of methane. Thereby, it was verified that the carburizing reaction is rate-controlled by the decomposition reaction of methane.
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