The stress-strain response of monocrystals and polycrystals of Hadfield steel was modelled by using a self-consistent viscoplastic approach. A unique hardening formulation was proposed which incorporated the length scales which were associated with the spacings between twin lamellae and grain boundaries. Transmission electron microscopic observations further supported the use of the length-scales. Many of the experimental results were obtained from [¯111] and [¯144] crystal orientations which were deformed in tension. This revealed fine twin lamellae at small strains, in addition to slip in intra-twin regions. A natural feature of the model was a small deformation activity within twinned regions, and higher deformations between the twins. The model used the dislocation density as a state variable, and accurately predicted the stress-strain response and texture evolution in single crystals for a wide range of strains. The responses of polycrystals with various grain sizes (100, 300, 1000μm) were also accurately described by the model; as was the twin volume fraction change with increasing deformation. On the basis of the simulations, it was possible to explain the upward curvature of the stress-strain curves for monocrystals and coarse-grained polycrystals of Hadfield steel. It was concluded that combined experiment and modelling provided a reliable tool for characterizing slip-twin interaction in low stacking-fault energy face-centered cubic materials.

Modelling the Deformation Behavior of Hadfield Steel Single and Polycrystals due to Twinning and Slip. I.Karaman, H.Sehitoglu, A.J.Beaudoin, Y.I.Chumlyakov, H.J.Maier, C.N.Tomé: Acta Materialia, 2000, 48[9], 2031-47