In this contribution strain induced precipitation of niobium carbides has been analyzed making use of different hot-rolling simulators and combining the advanced precipitation characterization methods of selective chemical extraction and transmission electron microscopy. A laboratory cast Fe-0.1C-0.07Nb alloy has been employed for the study. Thermomechanical simulations were carried out by torsion, plastodilatometry and plane strain compression techniques. The results have shown that, in spite of the different deformation modes a relatively good correlation is obtained between the measurements of the precipitate size and the amount of Nb precipitated in the different experiments.

The influence of initial grain size on the softening-precipitation interaction in a low niobium microalloyed steel has been investigated. The study has revealed that for the largest initial grain size (1000 μm), the recrystallised fraction remains lower than the softening fraction until relatively long times are reached. In contrast, for the smallest initial grain size (166 μm) both magnitudes are similar. As a result, precipitation interacts with recrystallisation in the case of the finest austenite grain size, whereas for the coarsest one, since recrystallisation is significantly retarded, interaction with recovery process is observed. Apparently, the initial austenite grain size does not affect precipitation kinetics.

The interaction between softening and precipitation mechanisms in hot worked Nb microalloyed austenite is analysed with the help of a physically based model. The model is able to calculate the evolution over time of the dislocation density (stress), stored energy and precipitate pinning force, the recrystallized fraction, the average precipitate diameter and precipitate number density, as well as the concentrations of the precipitating Nb over time. It is assumed that nucleation of precipitates occurs heterogeneously at dislocations with recovery producing a continuous decrease in dislocation density. This results in a reduction of the available nucleation sites for precipitation as well as a decrease in the driving force for recrystallization along time. By comparing the model predictions and the experimental results the values of several physical parameters involved in the model are discussed.