О проявлении обратимой деформации при ударно-волновом нагружении азотистой Сr-Mn-Ni аустенитной стали

Abstract

The features of structural-phase transformations during cold rolling and shock-wave loading at (−129…20°C) in austenitic nitrogen-containing steel 0.4N-20Sg-6Ni-11Mn-2Mo-V-Nb are studied. The possibility of the formation of ε-martensite with a density lower than that of the initial γ-phase mainly at high shock loading rates (448 and 471 m / s) is shown. Cold rolling at 20°C does not cause a γ → ε martensitic transformation. A small amount of martensitic α and ε phases (less than 5 %) is formed during rolling only at a cryogenic temperature of 196°C. During the shock-wave impact at −129°C at a speed of 448 m / s, plates of ε-martensite are formed and preserved. The martensitic orientation relation (111)γ || (0001)ε, [101−]γ || [112−0]ε exists between the crystals of the γ and ε phases. The martensitic ε-phase formed under low-temperature (−129°C) explosive loading is preserved in the structure, since the observed deformation heating of the metal does not exceed the temperature range of the reverse martensitic transformation ε → γ (200 – 300°C). Shock-wave loading of steel at 20°C at a speed of 471 m / s leads not only to the formation of the ε-phase, but also causes the reverse ε → γ transformation in those areas that are heated to 250 – 300°C. Shock-wave loading at a speed of 471 m / s at 20°C contributes to the development of cyclic γ → ε → γ transformation, which may be the cause of the phase hardening of austenite and the manifestation of the shape memory effect. In place of the ε-martensite crystals, banded clusters of dislocations with a density of 8 ×1010 cm−2 are formed, corresponding in shape to the location of the transformed martensite plates. In this paper, the high density of dislocations in phase-hardened austenite is associated with the inheritance of the dislocation structure by austenite from the strongly deformed ε-phase.