In this study, large-scale molecular dynamic simulations were performed to analyze the dislocation substructure interaction with various types of obstacles present in microalloyed steels during severe plastic deformation. Specifically, fully functional numerical models of the atomic upsetting test were developed, with particular emphasis on the presence of precipitates inside the microstructure grains. The obtained results compared with the microstructural tests, performed using Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscope (TEM) techniques, allowed for a more accurate assessment of the microstructure refinement mechanisms by means of the in-situ recrystallization effect in the deformed samples subjected to the multi-axis compression using the MaxStrain system (Dynamic Systems Inc., New York, NY, USA).

The mechanical behaviours of microalloyed and low-carbon steels under strain reversal were modelled based on the average dislocation density taking into account its allocation between the cell walls and cell interiors. The proposed model reflects the effects of the dislocations displacement, generation of new dislocations and their annihilation during the metal-forming processes. The back stress is assumed as one of the internal variables. The value of the initial dislocation density was calculated using two different computational methods, i.e. the first one based on the dislocation density tensor and the second one based on the strain gradient model. The proposed methods of calculating the dislocation density were subjected to a comparative analysis. For the microstructural analysis, the high-resolution electron backscatter diffraction (EBSD) microscopy was utilized. The calculation results were compared with the results of forward/reverse torsion tests. As a result, good effectiveness of the applied computational methodology was demonstrated. Finally, the analysis of dislocation distributions as an effect of the strain path change was performed.

Bimetals produced by explosive welding and subjected to surface mechanical attrition treatment (SMAT) were investigated. It is expected that the way of manufacturing and the morphology of nano- crystalline and multilayered materials obtained by the "top down" group of methods such as severe plastic deformation (SPD) has significant influence on the deformation mechanisms. The basic materials investigated in the paper were microalloyed steel and Nickel super-alloy. Bimetals were subsequently subjected to the deformation by compression test under dynamic and quasi-static conditions. Microstructural study based on light microscopy and scanning electron microscopy was performed focused presumably on the plastic flow of the deformed metallic laminate.