The Role of Nitrogen Gas and PWHT on Pitting Corrosion Behavior of Duplex Stainless-Steel Joint Made by GTAW

The influence of nitrogen gas and post-weld heat treatment (PWHT) on microstructure and pitting corrosion behaviors of duplex stainless steel welds were investigated. After gas tungsten arc welding process, the microstructure of the weld zone included grain boundary austenite, Widmanstatten austenite which forms on the grain boundary austenite, and intergranular austenite. With application of PWHT process, intergranular austenite grew to reach a spheroidal shape which was uniformly distributed in the matrix. Precipitation of chromium nitride in the ferrite phase was observed in grain boundaries and inside the ferrite phase with addition of nitrogen. By application of PWHT, the value of pitting potential increased and additionally corrosion resistance improved as nitrogen gas was applied. Due to higher pitting resistance equivalent number (PREN value) of austenite in regard with ferrite, ferrite as a weaker phase plays a prominent role in predicting the pitting corrosion resistance.