Novel Solid Carburizing Method for Steel Using a Mixture of Iron and Graphite Powders

Abstract

A low-carbon steel plate embedded in graphite powder was heat-treated at 1273 K for 3.6 ks in the atmosphere. The steel plate was oxidized and carburization due to carbon in the powder did not occur. On the other hand, when the steel plate was embedded in a 1:1 (volume ratio) mixture of iron and graphite powders and held at 1273 K for 3.6 ks in the atmosphere, an increase in area fraction of pearlite emerging in the plate was observed. In other words, the steel plate was carburized by the diffusion of carbon from the mixture. Furthermore, an XRD pattern of the surface of the carburized plate did not have peaks for iron oxides. Since iron powder located inside the mixture was also not oxidized after heating, it is thought that a non-oxidizing atmosphere formed around the plate during heat treatment. A pearlite structure formed by the diffusion of carbon began to be observed at a heating temperature of 1073 K, and carburized steel with a distinguishing microstructure consisting of cementite grains and a ferrite matrix was obtained in the case of 1273 and 1373 K. The carburizing method using a mixture of iron and graphite powders is named “iron-powder carburizing”, and the details are discussed.