In-situ strain induced martensitic transformation measurement and consequences for the modeling of medium Mn stainless steels mechanical behavior

Abstract

This work aims at studying the control of medium manganese austenitic stainless steels’ mechanical behavior and austenite to martensite transformation via chemical composition. Six grades of austenitic stainless steel were cast with chemical compositions variations small enough able to keep relatively constant the stacking fault energy (SFE) value, but high enough to change the martensitic start temperature Ms. These experiments allow the effect of the martensite transformation on the mechanical behavior in tension to be compared while the austenitic mechanical behavior is almost unchanged. Tensile tests were performed at room temperature and at a low strain rate (10−4 s−1). In-situ magnetic measurement is implemented to quantify the martensite volume fraction evolution with strain. Strain heterogeneities are detected by digital image correlation (DIC) analysis. For all grades, stress–strain curves exhibit Portevin–le-Châtelier (PLC) phenomenon related to localized martensite transformation within the deformation bands. For the two most unstable alloys, a Lüders plateau is detected at the yield stress. The martensite evolution is modeled using the Olson–Cohen approach, which confirms slower kinetics for the most stable grades. Moreover, it is shown that the martensite fraction evolves linearly with stress after a stress threshold function of the austenite stability represented by Ms. The martensite volume fraction vs stress slope is constant whatever the composition. This result leads to the development of a coupled metallurgical/mechanical model which depends on a single parameter Ms related to the chemical composition.