The purpose of the work reported was an investigation of the influence of the phase composition and also of the possibility of occurrence of a γ → α transformation during dynamic action of the medium on the character, corrosion rate, and in general the cavitation-corrosion failure of steel. The working media were .5M sulfuric and 5 m phosphoric acids. The corrosion resistance was evaluated from the current density in the passive area of the polarization curves. It was determined that corrosion in both cases occurs with active solution of the martensite. In the passive area under static conditions strong passivation of the steel is observed and in cavitation a less resistant passive condition indicating dynamic equilibrium of the activation and passivation processes.