Nitronic 50 (austenitic stainless steel) welding 1

[warrior1987]

Hello everybody, I have some questions regarding Nitronic 50 welding. I conducted some tests using the GMAW and SMAW process with ER209 as the recommended filler metal for welding Nitronic 50 to achieve similar mechanical properties. However, the impact properties of the weld metal are low, approximately 55 J or less. I have two questions:

1) Does anyone have experience welding Nitronic 50? Have you used ER209 or other filler metals to weld Nitronic 50? Have you experienced any problems with impact toughness?

2) Have you had experience with austenitic stainless steel weld metals, other than ER209, that have low impact toughness? This is uncommon because, in general, austenitic stainless steels have great impact toughness. Do you happen to know why the impact toughness is low in some austenitic weld metals? My only answer for that is that the grains are big, which can lead to lower impact toughness.

Thank you for reading this topic. Best regards.

 

[EdStainless]

How thick?
Are you welding annealed material?
How clean are your welds? Hint - there should be zero discoloration on both sides of the weld.
We did a lot of N40 and N50.
All TIG and all autogenous. But our material was all 0.120" and thinner.
We would run a little (2-4%) N2 in both the weld and the shield gas to keep the N2 levels up.
I honestly don't know how you would get low impact toughness unless you have excessive N2, and/or O2, and/or C in the welds.
What are the tensile elongations?

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P.E. Metallurgy, consulting work welcomed

 

[warrior1987]

Hi Ed,

Thank you for your response. Yes, this is annealed material with a thickness of 20 mm. The welds are clean with some minor discolorations. Could you please explain why discolorations are important?

"Based on my experience, surface discolorations should not be a major issue and can be removed with proper cleaning. However, it is important to consider the potential impact of the discolorations on corrosion, but they are less likely to affect mechanical properties".

Regarding the gases used, we have tried using Ar-2% O2 but have not yet tried a nitrogen mixture. Additionally, we do not know the chemical analysis of the weld metal, but we will conduct further research on this topic.

Regarding the impact properties of ER209, the typical impact strength of 54.2 Ftlb (73 J) at -20ºC according to some datasheets, I think it is low for austenitic stainless steels. What are your thoughts on this?

Thank you for your response once again.

Best regards,

 

[EdStainless]

O2 in SS is a no-no under any conditions. Either go to pure Ar or a little N2 in the mix.
You are forming Cr carbides and reducing both corrosion resistance and toughness.
What are you getting for residual delta ferrite?
Does your filler closely match your base metal chemistry?
Considering that your base metal toughness is likely >130J getting 50 in welds does not sound right.

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P.E. Metallurgy, consulting work welcomed

 

[warrior1987]

Hi Ed, thanks for your response once again.
We will try to use a different gas mixture, either Ar or Ar-N2.

We opted for a gas mixture that contained oxygen to achieve a GMAW spray transfer.

The weld metal has a ferrite content ranging between 5-10%.

The chemical composition of the weld metal is the same as that of the base metal. We used ER209 as the filler metal, except that it lacks Niobium which is present in the base metal. We have not yet conducted a chemical analysis of the weld metal.

I am aware that these values of impact toughness are low, which is unusual.

Regards,