A new approach for modelling strain induced precipitation of niobium carbonitrides in austenite during multipass hot rolling

Strain induced precipitation of microalloy elements during hot deformation of steels has been an area of Interest for several decades. Several researchers have produced models for strain induced precipitation phenomena that gave reasonably good predictions of precipitate evolution during hot deformation. These models were however, applicable only for single pass deformation. The present work aims to develop a new model that could be extended to prediction of precipitate evolution during multi-pass hot deformation during rolling. In this work, a new approach has been adopted in modelling strain induced precipitation of niobium carbonitrides during hot deformation. A dislocation geometry is proposed for a typical microband, which is considered as a key factor In the model. This microband geometry enables one to obtain the local solute concentration gradients in the regions between the microbands. Diffusion of solute atoms towards the microbands is considered to govern the growth rate of the precipitates on the dislocation nodes in the microbands; i.e., the solute atoms reaching the microbands are immediately consumed in either nucleating a new precipitate or growing an existing precipitate. Depending on the considerations of how precipitates nucleate on the microbands, different models have been proposed and their results analysed. Extending this model to a multipass model depends on the location of the next generation microbands after a second/subsequent deformation. The local solute concentration, already obtained after the first pass, will govern the precipitation potential of the nodes on the second generation microband. Plane strain compression tests were conducted on Fe-30wt.%Ni-Nb alloys at different temperatures and deformation conditions. The test samples were subjected to thin foil transmission electron microscopy to obtain the particle size distribution of the niobium carbonitride particles. The experimental results were then correlated with the model results and found to be in reasonably good agreement.EThOS - Electronic Theses Online ServiceGBUnited Kingdo