DETERIORATION OF PITTING CORROSION OF 316 STAINLESS STEEL BY SENSITIZATION HEAT TREATlVIENT

In this research pitting corrosion of a sensitized 3j6 stainless steel was investigatedemploying potentiodynamic, potentiostatic techniques . sensitization process was carried out onas-received alloy by submitting the specimen in electric furnace set at 650°c for fiv e hours andthen the specimen was quenched 25°c water. potentiodynamic polarization of as received andsensitized specim ens in 1m h2s04 solution at room temperature and 70°c clearly revealed thatthe sensitization process has caused a magnificent change on electrochemical behavior of thespecimen by changing critical current density for passivation, passivation potential and passivecurrent density. optical microscopy examination of the specimen surface after oxalic acidelectrochemical etching also showed the deterioration of grain boundary of sensitized specimendue to chromium carbide precipitation in compared to as-received one. several anodicpotentiodynamic polarization on rode shaped working electrodes prepared from as-received andsensitized specim en in 3.5% nacl test solution proved an average ~220 mv drop in pittingpotential due to sensitization. anodic pot entiostatic polarization at 400 and 200 mv abovecorrosion pot ential also demonstrate the deterioration ofpitting resistance ofalloy as a result ofsensitization. scanning electron microscopy examination of anodically polarized of sensitizedspecimen at 700 mvprior and after oxalic acid etching revealed large stable pits with lacy coverand also open pits with deep crevice for etched specimens