An EM study of carbides in double austenitized AISI M2 high-speed steel

Abstract

Multiple austenitization is not a conventional heat treatment process in tool steel industry and has only recently attracted some attention. Several workers who studied multiple austenitized high speed steels reported a fine carbide precipitation in the matrix of double austenitized specimens. However, the metallography of this precipitation is not well documented and needs further investigation. In this study, the microstructure of AISI M2 high speed steel and the effect of double austenitization on carbide distribution is investigated using SEM.The heat treated specimens were prepared by conventional metallographic methods for SEM examination. Polishing with diamond paste gave better results as much less carbides were extracted from their sites. Picral was used as an etchant.It is known that in M2 steels, undissolved carbides are either M6C or MC type. However, in the present investigation some of the massive undissolved M6C carbides contained small dark regions within them (Fig.l). X-ray mapping for W, Mo and V of such a carbide has shown that it is mainly a M6C carbide,whereas the dark regions on it is rich in vanadium implying that these regions represent V4C3(Fig.2).