Effects of strain state on the kinetics of strain-induced martensite in steels

This paper deals with the quantitative prediction of the volume fraction of strain-induced martensite produced in a steel that undergoes a thermomechanical loading. This issue is relevant for several steels with a low stacking fault energy, where a significant amount of transformed martensite drives many mechanical properties. Practical situations range from the optimization in the rolling process of a sheet to the improvement of the toughness of the final product. The model relies on the assumption that the martensite (alpha') is nucleated within a grain at the intersections of "shear bands" formed by the movement of partial dislocations on certain of the twelve {111}(gamma)[<(2)over bar 11>](gamma) systems (subscript gamma refers to the austenitic, or mother, phase). A modified Taylor-based numerical calculation is performed on a polycrystalline aggregate in order to obtain the intensity of the shear, and hence the volume fraction of martensite in each grain. Results are found to model and predict various experimental results obtained mainly on 304L stainless steel under different strain states. (C) 1998 Elsevier Science Ltd. All rights reserved.