Effect of martensitic transformation on ratchetting in medium-manganese steel: Experiment and homogenized constitutive model

Abstract

Transformation-induced plasticity (TRIP) behavior and related cyclic plasticity model of medium-manganese steel subjected to uniaxial cyclic loading were studied. Cyclic loading tests were conducted at different mean stresses and stress amplitudes. The results show that medium-manganese steel exhibits two different ratchetting evolution characteristics. Moreover, microscopic characterizations reveal that martensitic transformation occurs in medium-manganese steel during asymmetrical cyclic stressing, and the higher the applied stress amplitude, the greater the ratchetting strain and the more likely the martensitic transformation will occur. The interaction between TRIP and ratchetting leads to accelerated accumulation of plastic strain. Based on the existing meso-mechanics cyclic elastoplastic constitutive model, a kinetic equation for the strain-induced martensitic transformation and a modified nonlinear kinematic hardening equation are introduced. Subsequently, the two-leveled homogenization method was used to construct a homogenized cyclic plasticity model containing a three-phase microstructure of austenite, martensite, and ferrite. By comparing the predicted results with the experimental results, the proposed model can reasonably describe the evolutionary features of each phase and the effect of the phase transformation on the ratchetting of medium-manganese steel. Finally, ratchetting is further predicted and discussed for different austenite contents and phase transformation rates using the proposed model.