Laser surface melting of 17-4 PH precipitation-hardenable stainless steel

Preciptation-hardenable (PH) stainless steels are widely employed in industry for their high mechanical strength, reasonable toughness and moderate corrosion resistance. In the present study, laser surface melting of 17-4 PH precipitation-hardenable stainless steel (Fe-17%Cr-4%Ni-4%Cu-0.3%Nb) was attempted using a 2.5-kW continuous wave Nd:YAG laser for enhancing its corrosion resistance and hardness. The pitting corrosion behavior of laser surface-melted samples processed under different processing conditions in 3.5% NaCl solution at 25 °C was studied by open circuit potential measurement and potentiodynamic polarization technique. Compared with the annealed and aged 17-4 PH, the corrosion resistance of the laser surface-melted samples was significantly improved, as evidenced by a noble shift in open circuit potential, a higher pitting potential, a wider passive range and a lower passive current density. The enhanced corrosion resistance was attributed to the refinement of precipitation of copper particles in the ferrite matrix. In addition, the hardness of the laser surface-melted 17-4 PH was found to be higher than that of the aged and annealed ones by 14% and 27% respectively.