Effect of oxygen on Impact toughness of Duplex Stainless-steel welds

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.



  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)

Solution is around you!!! Aid to solve the Technical problem…

Defect popping out of a weld is a common thing. A known defect is easy to handle, but sometimes if you unluckily have a date with unknown defect, it turns out to be nightmare.

I will be sharing you one of my such incident which occurred when I was starting my Career as welding engineer.

Welding process: Arc Spot Welding(GTAW). Three spot welds are carried out with 3 welding station. Individual weld head had individual power source.

One fine day, it was observed that shear values of arc spot welds were failing the minimum requirements. Investigation was initiated as till date we haven’t observed such case and everything was inline with approved welding procedure.

Investigation revealed that shear area of those failed sample were abrupt and less than minimum required area. We then carried out the mockup as to find the root cause analysis.

Looking at the visual pattern of the weld, arc blow might had happened during the welding and resulted in to less energy input to coupons to be welded. Now the question was why arc blow suddenly occurred and is now repeating for each welds we are welding.

As we were carrying out multiple validation trials in search of root cause, a helper deployed on the assignment was casually showing magic show to his fellow colleagues. He had gas cylinder opener made up of Carbon steel. As soon as we start welding, he silently place that cylinder key vertically up on table and ask his fellow colleagues to take this as challenge to repeat the same, i.e. to keep that cylinder opener vertical up on table without any external support.

They were unable to do that and he does that with very ease. I was observing this episode as well as was conducting my trials. It was known that table gets magnetized as the welding starts and when table is magnetized he use to place that cylinder key there. And this happened at very small area where the power cables carrying current were placed. As he was regularly deployed on that task he was aware of the area of table which got magnetized.

This reminded me all the principles of physics which we learnt in school and college days. That is magnetic field is getting generated when current is passed through a conducting medium. This is it, while conducting trials i saw that arc was getting blown only on the weld head which was nearer to the cable. Upon further investigation it revealed that cable was repositioned to get proper accessibility and strangely it was slightly close to the weld head. Had it been insulated properly this wouldn’t have occurred.

Power cable was repositioned and we conducted the trials and the case was resolved.

This was good technical problem and Solution was around us only which was a magic show to that helper.

Every time you face a problem, have a look at casual things around you.. as you say solution will be around us only!!!