Cold Metal Transfer Welding of Ferritic and Austenitic Stainless Steel: Microstructural, Mechanical, and Electrochemical Studies

In the present study, cold metal transfer arc welding was employed to weld the 304L austenitic stainless steel (ASS) and Ti-stabilized 439 ferritic stainless steel (FSS) using a 309L filler electrode. Dissimilar joints were prepared using low heat input (HI; W1 ~ 247 J/mm) and high HI (W2 ~ 282 J/mm). The solidification mode for both weldments were the ferritic-austenitic mode and the weld zone (WZ) regions of both the weldments consists of columnar austenites, lathy and skeletal ferrite phases. The interfaces between WZ and ASS base metal showed the unmixed zone, whereas a conventional heat-affected zone (HAZ) was formed between the WZ and FSS base metals. The formation of ferrite stringers were observed in the unmixed zone, whereas peppery features of chromium-rich carbides were observed in HAZ. Moreover, electron backscattered diffraction technique was used to distinguish the microstructural differences between W1 and W2 weldments. Increase in the HIs resulted in decreased ferrite fraction in WZ as well as decrease in the mechanical strength of the joints. The W1 weldment depicted higher values of average micro-hardness (WZ ≈ 334.32 HV) than W2 (WZ ≈ 310.92 HV)) weldment. The electrochemical behaviour of the weldments was analysed for both the base metals and WZ of weldments. The higher degree of sensitization (DOS ~ 9.24%) of W1-WZ showed lower intergranular corrosion resistance than W2-WZ (DOS ~ 7.77%), however, the opposite trend was observed for impedance and pitting resistance.