Nitrogen ions (N+) with five different energies (100-600 keV) were implanted on the 13Cr4Ni steel (base) samples under high vacuum at temperature <100 degrees C. The base and implanted samples were also annealed at 600 degrees C for 6 h at high vacuum (similar to 10(-9) bar). Energy dependent change in structure and mechanical properties of implanted samples were observed after annealing process. Structural study suggested formation of nitrides and implantation induced surface segregation of nitrogen. The nano-indentation hardness and elastic modulus were increased from 5 to 13 and 183 to 314 GPa respectively with increasing N+ energy. The N+ implantation process had significantly enhanced the cavitation erosion resistance of the base steel. The minimum cumulative weight loss and maximum erosion resistance were obtained for the sample implanted at 600 keV energy. The roughness values of surfaces at various erosion periods were correlated with erosion process to understand erosion mechanism. The lowest roughness values (R-a = 164.42 nm, R-q = 214.75 nm) after 12 h of cavitation erosion test were obtained for the sample implanted at 600 keV energy.