In a given work, we are studied the metastable two-phase (gamma + epsilon) high-manganese steel 05 Gamma 20C2 with about 55% epsilon-phase in the initial state. It is shown that the preliminary deformation by hydro-pressing with 10-30% reduction amplifies the delayed-fracture susceptibility of steel at issue that is displayed as decreasing of limiting strength. Above 30% reduction, a certain increasing of limiting strength is observed.