Carburization Ability of Novel Solid Carburizing Method Using a Mixture of Iron, Graphite and Alumina Powders

Abstract

When low-carbon steel is embedded in graphite powder containing iron powder and subsequently heat-treated at 1273 K, carbon is diffused into the steel and a pearlite area near the steel surface is increased as compared with that before heating. Such a carburizing method was named “iron-powder (IP) carburizing”. It can be carried out in both an air atmosphere and a nitrogen flow. In this work, IP carburizing method using a mixture of iron, graphite and alumina powders was applied to pure iron in a nitrogen flow, and the carburization ability was compared with conventional solid carburizing method using a mixture of activated carbon and sodium carbonate. The amount of carbon diffused into the specimen by IP carburizing was smaller than that by conventional method. In IP carburizing, it is thought that the direct diffusion of carbon from the powder mixture was dominant, rather than the carbon diffusion through a gas phase like carbon monoxide and carbon dioxide. On the other hand, instead of graphite, activated carbon was used as a carbon source of IP carburizing and there was little effect on the carburized structure. This was also one of the features of IP carburizing, since the microstructure obtained by conventional solid carburizing was affected by the replacement of activated carbon by graphite.

Fig. 7 Average carbon concentration profiles within a cross section of pure iron (approximately 750 µm × 1600 µm) after IP carburizing and conventional solid carburizing at 1273 K for 3.6 ks.