Formation Mechanism of Austenite

Taking T 8 steel and other steels as an example,the process and mechanism of reverse eutectoid transformation of pearlite into austenite were comprehensively investigated.It was pointed out that the austenite is a solid solution formed by dessolving carbon or other chemical elements inγ-Fe.The austenite will nucleate in the ferrite/ cementite interface or either in the junction of pearlite fields or in the prior austenite grain boundary.Besides,the austenite will grow up in the form of bulk diffusion.In the course of nucleation and growth of austenite the ferrite and cementite will be simultaneously swallowed,or only the ferrite be swallowed,or ferrite be swallowed more quickly than the cementite.Consenquently,the reverse eutectoid transformation of pearlite will be performed,finally leaving a part of the cementite behind.In order to reduce accumulated distortion and strain energy resulting from the phase transformation,the growth direction of austenite will be adjusted,thus forming a twin.The undisolved carbides present in austenite are to be further dissolved and the austenite compostion is to be homogenized.