For the first time the structural-phase changes in the stainless steel samples subjected to prolonged high-frequency (50 MHz) external hydrodynamic effects (EHDE) under high pressure (2-3 GPa) in the device of special design were comprehensively investigated. It was discovered that due to EHDE solid surface layer of steel of thickness up to 100 µm has a martensitic structure formed by deformation-induced twinning a and e phases. However, on the following intermediate layer located at a depth of 100-200 µm, the traces of fragmentation and twinning substructure inside the austenite grains were found, indicating phase hardening of reverted austenite in the process of direct and reverse martensitic transformations g-e-a. Based on the analysis of the obtained and known data for the first time concluded that when the multi-cycle high-frequency external impact are the place of thermo-, baro-, elastoplastic mechanisms of the realization of these martensitic transformations, which have to be accompanied by thermo-, baro - and magnetocaloric effects of heat by direct martensitic transformation and, consequently, the heat absorption during reverse transformation. The presence of their asymmetry can result, for example, to stable heat generation (heat-generating) or, on the contrary, the absorption of heat from the coolant.