The evaluation of microstructure and mechanical properties of API 5L X80/DSS 2205 weld metals produced by PCGTAW

Dissimilar welding of API 5L X80/DSS 2250 steels was carried out using PCGTAW process. The welds were produced using three types of filler metals (ER2209, ER309L and KJS-124). The microstructural investigations showed that the microstructure of ER2209 weld metal is duplex (ferrite and austenite) and ferrite content changes from root pass (35%) to cap pass (41%). It was revealed that the solidification mode of ER309L weld metal was ferritic-austenitic mode and its microstructure has an austenitic matrix with skeletal ferrites and smaller amount of vermicular ferrites along the grain boundaries. Ferrite scope results revealed that ferrite content of root pass (6%) is less than the final pass (10%). Microscopic results showed that the microstructure of KJS-124 weld metal consists of grain-boundary, Widmanstätten and acicular ferrites with martensite-austenite islands. Epitaxial growth was detected in the interfaces of ER309L/DSS 2209 ، ER2209/DSS 2205 and KJS-124/API 5L X80 and unmixed zones and type II boundaries were detected in the ER2209/API 5L X80- ER309L/API 5L X80 and KJS-124/DSS 2205 interfaces. The results of impact and hardness tests revealed that ER2209, ER309L and KJS-124 weld metals have the best toughness and the KJS-124, ER2209 and ER309L filler metals got the highest hardness, respectively.