Plastic Behavior of Ferrite–Pearlite, Ferrite–Bainite and Ferrite–Martensite Steels: Experiments and Micromechanical Modelling

In this work, low carbon low alloy steel specimens were subjected to suitable heat treatment schedules to develop ferrite–pearlite (FP), ferrite–bainite (FB) and ferrite–martensite (FM) microstructures with nearly equal volume fraction of hard second phase or phase mixture. The role of pearlite, bainite and martensite on mechanical properties and flow behaviour were investigated through experiments and finite element simulations considering representative volume elements (RVE) based on real microstructures. For micromechanical simulation, dislocation based model was implemented to formulate the flow behaviour of individual phases. The optimum RVE size was identified for accurate estimation of stress–strain characteristics of all three duplex microstructures. Both experimental and simulation results established that FM structure exhibited superior strength and FP structure demonstrated better elongation while FB structure yielded moderate strength and ductility. The von Mises stress and plastic strain distribution of the individual phase was predicted at different stages of deformation and subsequent statistical analyses indicated that hard phases experienced maximum stress whereas, maximum straining occurred in soft ferrite phase for all three structures. Micromechanical simulation further revealed that strain accumulation occurred at the F–P and F–B interfaces while the same was observed within the martensite particles apart from the F–M interfaces for FM. These observations were further substantiated through the identification of void and crack initiation sites via subsurface examinations of failed tensile specimens.