There was much interest recently in the possibility of combining two strengthening effects, namely the reduction of grain size (Hall–Petch effect) and the transformation-induced plasticity effect (strengthening due to a martensitic transformation). The present work was concerned with the analysis of the combination of these two effects using a discrete dislocation–transformation model. The transformation-induced plasticity mechanism was studied for aggregates of grains of ferrite and austenite of different sizes. The discrete model allowed the simulation of behaviour at sub-grain length scales, capturing the complex interaction between pile-ups at grain boundaries and the evolution of the microstructure due to transformation. The simulations indicated that, as the average grain size decreased, the relative strengthening due to the formation of martensite was significantly reduced and that the overall strengthening was mostly due to a Hall-Petch effect. This finding suggested that strengthening by the transformation-induced plasticity mechanism was ineffective in the presence of fine-grained microstructures.

Analysis of Grain Size Effects on Transformation-Induced Plasticity Based on a Discrete Dislocation–Transformation Model. J.Shi, S.Turteltaub, E.Van der Giessen: Journal of the Mechanics and Physics of Solids, 2010, 58[11], 1863-78