Surface Hardening of High-Nitrogen Austenitic Steel by Severe Deformation–Heat Treatment

The structure and mechanical properties of austenitic high-nitrogen steel (16.5 Cr, 18.8 Mn, 0.07 C, 0.53 N, 0.52 wt % Si, Fe for balance) have been investigated after severe deformation–heat treatment, which has involved shock surface forging at the ultrasonic frequency (USF) and electron-beam heat treatment (EBT). A subgrain structure hardened by CrN nanoparticles has been shown to form in the surface layer as a result of deformation–heat treatment. No discontinuous decomposition of austenite with the formation of Cr 2 N nitrides takes place. This structure modification in the surface layer enhances the strength properties of the steel, namely, σ 0.2 increases to 712 MPa and σ u to 923 MPa at a plasticity of 25%. The yield strength increases by 50% compared to the state after quenching.