Super-carburization of low alloy steel in a vacuum furnace

The super-carburization process can provide outstanding performance in the surface hardening of high-alloyed steel. Because of the large amount of massive carbides accumulated in the steel surface caused by a repeated process of carburization and precipitation, the hardness and wear resistance of the work will be significantly improved. However, the fatigue strength of the high-alloyed steel is reduced due to the high core hardness after hardening. This article studies the super-carburizing treatment of low-alloyed steel, JIS SCM415, to obtain high surface hardness and to retain the core toughness. The experiment was conducted in a two-chamber vacuum furnace with 0.6-kPa acetylene gas at 950 °C, 30 min for each carburizing cycle. The carburized specimens were evaluated on their wear resistance by a Plint wear tester. The results show that the degree of spheroidization and the amount of massive carbides increase progressively as a function of the treating cycles. The formation of massive carbides saturated at the four-cycle of carburization and precipitation. The results of wear testing showed that the wear resistance of super-carburized specimens were affected by the degree of spheroidization of carbides, i.e. the higher the roundness of the carbides, the better the wear resistance it performed.