Effect of Austenitizing Treatment Followed by Slow Cooling on Graphitization in Hypo-Eutectoid Alloy Steels

An influence of the austenitizing treatment followed by slow cooling on the graphitization in hypo-eutectoid alloy steels has been studied. The number of graphite nodules and the rate of graphitization remarkably depend on the austenitizing conditions. The rate of graphitization increases with an increase in graphite nodule number. From both the above mentioned result and the fact that the growth rate of graphite is independent of the austenitizing conditions, it is suggested that the austenitizing conditions have a major influence on the nucleation of graphite.In the pre-treatment that a steel is held at the austenitizing temperatures, until traces of cementite disappear completely, and then slow-cooled to room temperature, the graphitization is most greatly stimulated. Cementite in pearlite formed after the above mentioned pre-treatment was found to be fine lamellae. It is concluded that fine cementite is unstable because of larger surface energy and may cause an easy nucleation of graphite thereby.