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Electron microscopy and X ray diffraction have been used to investigate a nitrogen 07Kh17AG18 steel with an austenitic structure after the surface deformation treatment-ultrasonic forging. During ultra sonic forging, an austenitic structure transforms into a new structure with an elevated concentration of defor mation induced stacking faults, a lot of deformation microtwins, ε martensite crystals. The austenite lattice parameter is found to be decreased in the surface layer. After ultrasonic forging, nitrided steel exhibits enhanced strength properties with retained high plasticity.

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The deformation behavior, mechanical properties, and microstructure of Fe-Cr-Mn-0.53%N austenitic stainless steel were studied at a temperature range of 77 up to 293 K. The dynamics of the steel elongation were non-monotonic with a maximum at 240–273 K, when peaks of both static atom displacements from their equilibrium positions in austenite and residual stresses in the tensile load direction were observed. The results of X-ray diffraction analysis confirmed that the only stress-induced γ→ε-martensite transformation occurred upon deformation (no traces of the γ→α′ one was found). In this case, the volume fraction of ε-martensite was about 2–3%. These transformation-induced plasticity (TRIP) patterns were discussed in terms of changes in the phase composition of steel as the root cause.

The computational approach for modeling the deformation behavior and fracture of materials with stress concentrators is proposed on the basis of the cellular automata technique. Numerical simulations performed on miniaturized specimens under dynamic loading are accompanied by laboratory tensile testing under quasi-static conditions applied to the specimens of a ductile structural steel with three typical notch shapes. Using in situ acoustic emission paired with digital image correlation techniques, it is shown that the notch shape exerts a very strong influence on the development of localized plastic flow and crack initiation ahead of the notch tip. It is concluded that the stress release occurs most effectively when the modulation of various components of the force moment takes place on mesoscopic scale.