Sensitivity to Intergranular Corrosion According to Heat Treatment of 304L Stainless Steel

Even though 304 low-carbon (304L) stainless steel was developed to enhance the resistance to intergranular corrosion and stress corrosion cracking, it is occasionally subject to degradation in harsh environments. The degree of sensitization (DOS) of 304L stainless steel was studied as a function of sensitization using a double-loop electrochemical potentiokinetic reactivation (DL-EPR) method. Sensitizing heat treatment was performed in an Ar atmosphere at 500 degrees C, 600 degrees C, and 700 degrees C, with heat treatment times varying from 0 to 96 h. DOS was measured by the ratio of the peak current density value of the forward scan to that of the reverse scan. After the EPR experiment, the specimen surface was observed by scanning electron microscopy and energy dispersive spectroscopy. The DOS of the specimens heat-treated at 600 degrees C increased with heat treatment times up to 48 h and then decreased due to a self healing effect. The DOS was higher in specimens heat-treated at 600 degrees C than those at 500 degrees C or 700 degrees C. Corrosion of the sensitized specimens occurred mainly at the delta-gamma phase boundary. The corrosion morphology at the delta-gamma phase boundary changed with sensitizing heat-treatment conditions due to differences in chromium activity in gamma austenite and delta ferrite.