Influence of plastic strain on mechanically induced martensitic transformations

The effects of plastic strain on mechanically induced martensitic transformations are investigated. An austenitic metastable stainless steel is plastically deformed to varying amounts in a tensile tester at 120 C. This temperature is enough to suppress transformation during the deformation up to 20% of plastic strain. The resulting pre-strained material is then cooled to a lower temperature and the tensile test is continued while the martensite amount is measured via a magnetic sensor. Results show that for this alloy plastic strain does not promote the transformation. On the contrary, an increase in the critical stress at which transformation starts is observed with increasing pre-strain. Therefore, to model the transformation instead of the strain-induced transformation theory, a stress-driven approach is followed. Utilizing the Patel-Cohen and Wechsler-Lieberman-Read theories, a transformation criterion is established which is verified by Biaxial tests. For the evolution of martensite fraction, a meso-scale simulation is performed in which a homogeneous stress is applied to random crystal orientations and the favored crystals are allowed to transform. A good correspondence with the experiments is obtained.