Laser Surface Treatment for Enhancing Intergranular Corrosion Resistance of AISI Type 304 Stainless Steel

A novel laser surface modification approach to suppress sensitization in AISI 304 (UNS S30400) austenitic stainless steel is described. Surface modification of austenitic stainless steel was carried out with a 10-kW carbon dioxide (CO2) laser in both continuous wave and pulse-modulated modes. After laser surface modification, the material was subjected to a sensitization heat treatment at 923 K for 9 h. The degree of sensitization was determined by electrochemical potentiokinetic reactivation test while the susceptibility to intergranular corrosion was determined using the ASTM A262, practice B test. The results of the study demonstrated that the laser-melted surface exhibited significantly higher resistance against sensitization and intergranular corrosion than the base metal. The laser-melted surface, even after being subjected to severe sensitization heat treatment, developed comparable or even a lower degree of sensitization than the base metal in the as-received condition. Enhanced immunity against sensitization of the laser-treated surface is attributed to its duplex micro-structure and higher fraction of low-angle grain boundaries. The highlight of the investigation was that a laser surface melting treatment of unstabilized austenitic stainless steel brings about significant reduction in its susceptibility to sensitization during subsequent exposure to a susceptible temperature region and to intergranular corrosion during service.