A recent trend in the development of tough steels has been to stimulate the heterogeneous nucleation of ferrite on nonmetallic particles, at the expense of that nucleated at the austenite grain surfaces. This leads to a refinement of the microstructure, which also becomes less organised, thus giving better mechanical properties. This article deals with a model for the competitive growth of ferrite nucleated both at austenite grain surfaces and intragranularly on inclusions. The classical Johnson-Mehl-Avrami theory for overall transformation kinetics has been adapted to deal with such simulatneous transformations. The theory is demonstrated to reproduce known trends in experimental observations and is shown to be of use in the design of steels.
Metallurgical and Materials Transactions A, 28A (1997) 2005-2013.
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