THE BAINITIC MECHANISM OF AUSTENITE FORMATION DURING RAPID HEATING

Strips of a spheroidized 0.68% C, 0.67% Mn and 0.24% Si pearlitic stee l were submitted to rapid heat cycles. The samples were heated by dire ct electrical conduction up to a peak temperature and immediately wate r quenched. The morphological features of the alpha --> gamma transfor mation were studied by light and electron microscopy It was found that austenite at an early stage of the transformation has a specific lath -like morphology and that its growth always starts directly a grain bo undary of ferrite. Moreover, the presence of retained austenite allows the prediction of relatively high carbon content in the transformatio n product. The particular interaction of austenite laths with carbide particles gives an indication that the growth mechanism can be displac ive at its early stage. Comparing the morphological characteristics of austenite formation observed in this study with those reported for au stenite decomposition, a bainitic model of the early stage of alpha -- > gamma transformation is proposed. (C) 1998 Acta Metallurgica Inc. Pu blished by Elsevier Science Ltd All rights reserved.