On the morphology of pearlite - Bainite isothermal transformation in the austenite bay region

Hillert has suggested before that at the austenite bay region intermediate pearlite between ordinary pearlite at high transformation temperature and inverse bainite at low temperatures, with cementite is the leading phase. Ridley reported that partitioning at these region shows a substantial partitioning at the tip indicates the operation of a short circuit diffusion path provided by austenite-pearlite interface, and does not support the idea of a leading phase. From studying the Microstructure at the austeinte bay region for different eutectoid steels containing chromium, molybdenum, and nickel to follow up the change in the microstructures and if it supports the idea of a leading phase or not. The results gave a similar microstructure which starts with wavy austenite/pearlite interface and with further lower temperature shows a spiky interface. It is concluded that at lower transformation temperatures the sequence of the microstructures was jagged front wavy front is dominant with a central cementite lamellae longer than the adjacent ones as shown for the present two eutectoid steels. Also, these microstructures support the idea that cementite is a leading phase in the nucleation process of the pearlite.