Analysis of Martensitic Transformation Plasticity Under Various Loadings in a Low-Carbon Steel: An Elastoplastic Phase Field Study

An elastoplastic phase field model for the martensitic transformation of a Fe-0.22C-1.58Mn-0.81Si (wt pct) alloy was developed, to investigate transformation plasticity in response to uniaxial, biaxial, shear and axial-shear loadings below half the yield strength of austenite. The simulation results clearly demonstrate the preferential orientation of martensite variants as well as plastic behavior during transformation. The data also suggest that the transformation plasticity coefficient is independent of external stress. Preferential orientation can occur under both axial and shear loading conditions, and the equivalent values of transformation plastic strains are roughly the same regardless of the stress components in the combined axial and shear loadings. Similar microstructural evolution and deformation behaviors were identified in response to both uniaxial and biaxial loadings when the uniaxial stress was equal to the difference in applied stresses along both axes during biaxial loading. The Magee mechanism is considered to play a predominant role in martensitic transformation plasticity, although both the Magee and Greenwood-Johnson mechanisms can be identified through simulations. This work demonstrates that the accumulated plastic strain in martensite is primarily inherited from the parent austenite phase, with only a negligible portion due to the yielding of martensite.