Influence of filler variation on microstructural evolution, mechanical and corrosion performance of Ti-stabilized 439 ferritic stainless steel

In the present study, gas tungsten arc welding (GTAW) was used for the joining of Ti-stabilized 439 ferritic stainless steel (FSS) with different austenitic stainless steels (ASSs) filler electrodes i.e., 308 L, 309 L, and 316 L. The optical micrograph of the weld zone (WZ) revealed the formation of retained austenite (RA) at ferrite grain boundaries (GBs) in 308 L and 309 L filler electrodes weldment, while different forms of austenite such as widmanstatten austenite (WA), grain boundary austenite (GBA), and intra-granular austenite (IGA) were formed in the WZ of 316 L filler electrode weldment. No other intermetallic phases were observed in the WZ except austenite and ferrite in all the weldments. The heat-affected zone (HAZ) of all weldments revealed the formation of peppery structure of Cr-rich carbides. The presence of austenite and ferrite phases and their volumetric fractions in WZ of different weldments were examined via x-ray diffraction (XRD) and electron backscattered diffraction (EBSD) techniques. The 316 L filler electrode weldment showed the higher fraction of austenite as compared to its counterparts, whereas 309 L filler electrode weldment showed the higher fraction of RA than the 308 L filler electrode weldment. The 309 L filler electrode weldment depicted higher micro-hardness, higher ultimate tensile strength and lower intergranular corrosion resistance. Higher fraction GBs/interfaces was observed in WZ of 309 L filler electrode which shows the higher rate of sensitization as compared to 308 L condition.