Modeling the deformation behavior of Hadfield steel single and polycrystals due to twinning and slip

Stress-strain responses of single and polycrystals of Hadfield steel were modeled using a viscoplastic self-consistent approach. A unique hardening formulation was proposed in the constitutive model incorporating length scales associated with spacing between twin lamellae and grain boundaries. TEM observations lend further support to the length scales incorporated into the constitutive model. Many of the experimental findings were made on [(1) over bar 11] and [(1) over bar 44] crystal orientations deformed in tension, displaying fine twin lamellae at small strains in addition to slip in intra-twin regions. A natural outcome of the model was the small deformation activity inside the twinned regions and higher deformations between the twins. The model utilized dislocation density as a state variable and predicted the stress-strain responses and texture evolution in single crystals accurately over a broad range of strains. The responses of polycrystals with three grain sizes (100, 300, and 1000 mu m) were also captured closely with the model in addition to the twin volume fraction evolution with increasing deformation. Based on the simulations, it was possible to explain unequivocally the upward curvature in stress-strain curves in the single crystals and in coarse grained polycrystals of Hadfield steel. Overall, the combined experimental and modeling efforts provide a reliable tool to characterize slip-twin interaction in low stacking fault energy f.c.c. materials. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.