THE EFFECT OF THE CONCENTRATION-DEPENDENT DIFFUSIVITY OF CARBON IN AUSTENITE ON A MODEL OF REAUSTENITIZATION FROM FERRITE CEMENTITE MIXTURES IN FE-C STEELS/

Phase transformation theory applicable to reaustenitisation that takes place upon heating low-alloy steels is described. The assumption of l ocal equilibrium is made. Diffusivity of interstitial solute in austen ite is treated as concentration dependent and no diffusion is allowed in cementite and ferrite. Under these assumptions, the process is cont rolled by the diffusion of the interstitial solute in the growing phas e. A variational dual extremum principle is used to calculate the inte rstitial solute concentration profile for specified interface motions. These results are compared with those obtained for a constant diffusi vity equal to a weighted average of the concentration-dependent diffus ivity and to a variety of simple approximations to the full problem. C opyright (C) 1996 Acta Metallurgica Inc.