THERMAL STABILIZATION OF AUSTENITE IN HIGH NICKEL-CARBON STEELS

Abstract
The thermal stabilization of austenite in high nickel-carbon steels was examined using a dilatometer, acoustic emission and a low temperature metallographic technique. M_s - temperatures depended on the austenitic grain size as the Hall-Petch relation. In the area of the retained austenite, where the martensite transformation occured, a complicated slip band system on the specimen surface was noted. This deformation also extended into the areas of the virgin martensite. Deeper in these specimens there were no microcracks. On the contrary, when the retained austenite was transformed to martensite in the aged specimens, there was no or little deformation in the martensite. Deeper in these specimens there were a lot of microcracks. Hence it seemed that the deformations created by the martensite transformation were in this way widely spread. On the basis of these observations it was proposed that the aging of martensite may be one of the reasons for the thermal stabilization of the retained austenite in carbon steels.