ROOM-TEMPERATURE STRESS-CORROSION CRACKING RESISTANCE OF POST-WELD HEAT-TREATED AUSTENITIC WELD METALS

Room-temperature stress corrosion cracking (SCC) of austenitic clad metals (with different contents) deposited by submerged arc welding (SAW) was studied. Clads were remelted using gas tungsten arc welding (GTAW) in order to study the effect of weld heat input. They were post-weld heat-treated (PWHT) at 600, 800, and 1000-degrees-C for 1, 10, and 100 h. Secondary phases that precipitated were extracted electrolytically and identified by x-ray diffraction (XRD). Stress corrosion cracking (SCC) tests were conducted on notched tensile samples in 5 N H2SO4 + 0.5 N NaCl solution at room temperature. A net-section stress that was needed to break the sample in 100 h was taken as the criterion to assess the relative SCC susceptibilities. The results showed that PWHT at 600 and 800-degrees-C decreased the SCC resistance of both high- and low-ferrite samples, the decrease being more for the high-ferrite samples. The PWHT at 1000-degrees-C improved the SCC resistance much above that of the asweld values. Welds deposited by GTAW showed better SCC resistance after PWHT than their SAW counterparts. Fracture was found to be mainly due to stress-assisted dissolution of prior ferrite network and SCC in austenite. Stress corrosion cracking in austenite is found to take place by tunneling mechanism.