The toughness of weld deposits varies by the welding process due to the differences in the amount of oxygen in the weld typical for each process. Figure 1 shows that higher toughness is generally achieved with GTAW, PAW and GMAW than with SMAW, SAW and FCAW.

As the oxygen content increases, the content of non- metallic inclusions. This increase means that non- metallic inclusions in the welded part are mainly composed of oxides. When compared by welding process, GTAW has the lowest oxygen content, while FCAW has the highest oxygen content. the oxide inclusions were mainly Mn- Si TYPE and Mn- Si- Ti TYPE and the oxygen in the clumping portion exists in the form of inclusions by reacting with the deoxidizer (Mn. Si. Ti…) that has a high affinity for oxygen.

When oxidized inclusions exist in the welded area, the bonding force between metals adjacent to the oxidized inclusions is weakened, so it is thought that the generation of micro- voids is facilitated, and the impact value is lowered. This is supported by the discontinuous appearance of dimples near the oxidized inclusions in the SEM fracture image of the welded part in Figure 2.

Reference:

1. API 938-C, Use of Duplex Stainless Steels in the Oil Refining Industry.
2. Effect of Oxygen Content on Impact toughness of Austenitic and Duplex Stainless steel weld metal, Journal of the Korean Welding society-1987, Y.H. Moon, H.T. Kim, S.D. Hur

Keep Reading, happy Welding

Nikhil (Team Weldknowledge)