Effects of laser surface melting on the pitting resistance of sensitized nitrogen-bearing type 316L stainless steel

摘要

Laser surface melting of sensitized nitrogen-bearing type 316L austenitic stainless steel was carried out using a pulsed ruby laser. The sensitization heat treatment was carried out at 923K for 50,200,1000, and 2500 h, and the sensitizedmicrostructure was classified according to ASTM A 262 practice A. The degree of sensitization was assessed by the electrochemical potentiokinetic reactivation (EPR) test. The critical pitting potentials of as-sensitized as well as sensitized-laser meltedspecimens were determined by potentiodynamic anodic polarization method in a medium containing 0.5 M NaCl and 0.5 M H{sub}2SO{sub}4 at room temperature. Results indicated that upon laser melting the pitting resistance increased significantly. Thisincrease was attributed to the elimination of the sensitized heterogeneous microstructure by laser melting. The microscopic examination of the pitted specimens showed only micropits that developed at the interfaces of oxide/sulfide inclusions of titaniumand matrix.