The formation of austenite from mixtures of ferrite and cementite as observed by HVEM

The detailed mechanism of the transformation of various mixtures of ferrite and austenite was studied byin situ experiments in a high voltage electron microscope. Various phenomena were observed which seemed to be controlled by the rate of carbon diffusion when the γ/α interface was curved. The effect of manganese was studied by using commercial steels. In agreement with theoretical predictions based upon the local equilibrium model, the dissolution of cementite in ferrite can be more or less prevented by manganese. The effect on the dissolution in austenite is smaller. The reaction from lamellar pearlite to austenite is more complex, the cementite lamellae providing carbon to the austenite but also acting as barriers. M. NEMOTO, formerly with Division of Physical Metallurgy, The Royal Institute of Technology, S-100 44 Stockholm 70, Sweden