The formation of austenite during the heating of high-silicon steels with a microstructure of bainitic ferrite plates separated by carbon-enriched regions of retained austenite has been studied. As the steel is heated, retained austenite decomposes into a mixture of ferrite and carbides before a temperature is reached where it becomes the more stable phase and hence can grow. The decomposition makes it necessary for the austenite to nucleate from the mixture of ferrite and carbides. In this work, dilatometric analysis, transmission electron microscopy and X-ray diffraction have helped to identify the processes that take place during the heating experiment.Spanish Ministerio de Ciencia y Tecnologia (MAT2001-167). F. G. Caballero would like to thank Spanish Ministerio de Ciencia y Tecnologia for the financial support in the form of a Ramon y Cajal contract (Programa RyC 2002)Peer reviewed