J. Phys. IV France 112 (2003) 305
DOI: 10.1051/jp4:2003889

On the influence of aluminium and silicon contents on the kinetics of bainite transformation of intercritical austenite

A. Mertens^{1, 2}, P.J. Jacques¹, L. Zhao³, S.O. Kruijver³, J. Sietsma² and F. Delannay<sup>1

1</sup>  Université Catholique de Louvain, Département des Sciences des Matériaux et des Procédés, PCIM, 2 place Sainte Barbe, 1348 Louvain-la-Neuve, Belgium
²  Delft University of Technology, Laboratory for Materials Science, Rotterdamseweg 37, 2628 Delft, The Netherlands
³  Netherlands Institute for Metals Research, Rotterdamseweg 137, 2628 Delft, The Netherlands

Abstract
TRIP-assisted steels show enhanced mechanical properties thanks to the strain-induced transformation of retained austenite to martensite (TRIP effect). Stabilisation of austenite is made possible by the combination of appropriate chemical composition (containing classically high levels of silicon, or, as developed more recently, aluminium) and of a two-step heat treatment comprising an intercritical annealing followed by an isothermal holding in the bainite formation range. A detailed understanding of the effects of Si and Al on the bainite transformation kinetics is thus of primary importance for the optimisation of austenite retention. The present study aims at a better knowledge of the influence of aluminium on the kinetics of the bainite transformation of intercritical austenite, as compared to the effect of silicon. The bainite transformation kinetics was followed by dilatometry in a set of 6 steel grades with varying aluminium and silicon contents. These dilatometry experiments were coupled with a characterisation of the microstructures by X-ray diffraction, SEM and image analysis. Il was shown that aluminium has a less pronounced effect than silicon in retarding the bainite transformation.

© EDP Sciences 2003