High Ferrite Reading for 316 SS Weld 2

[iam42]

Hi,

I have an issue with a 316 GTAW weld where the ferrite is reading as high as 12%.

We have a customer imposed ferrite range of 3-8%.

Base material 1 chemistry is:
A479-316/316L
C .014, Co .047, Cr 16.69, Cu .28, Mn 1.34, Mo 2.119, N .040, Ni 10.55, P .029, S .0220, Si .27 (Calculated F% 6%)

Base material 2 chemistry is:
A182-316/316L
C .016, Mn 1.56, P .029, S .023, Si .49, Ni 10.01, Cr 16.69, Mo 2.03, N .058 (Calculated F% 8%)

Weld Wire Chemistry is:
ER316/316L
C.02, Mn 1.8, P .02, S <.01, Si .38, Cr 18.5, Ni 12.2, Mo 2.2, Cu .03, N .03 (Calculated F% 6%)

I have tried change weld wire with no change to F%.

I have also increased the heat input in the hope that this would reduce F%.

I have never came across this before with high ferrite, i am usually trying to keep the ferrite at a minimum value!

Am I missing something obvious or is there anything else I can try to reduce the ferrite?

Thanks in advance for your help.

 

[EdStainless]

What is your gas?
You can always cheat and use N2 as a backing gas.
This is likely tied to your heat input.
You didn't give us any dimensions, but these welds are solidifying and cooling too fast.
Some pre-heat may be the easiest way around this.
Though with your FNs where they are I am not surprised.
The FN is the equilibrium FN, not a max.

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P.E. Metallurgy, consulting work welcomed

 

[DVWE]

How are you measuring? Fischer Ferritescope? Severn Gauge?

The devil is in the details; she also wears prada.

 

[iam42]

Hi Ed, thanks for the input.

We are using 100% argon. I did try a 2.5% Nitrogen mix for the shielding gas but we started to get porosity so I rejected that idea.

We are welding a 1/2"-300# Sch 40S Branchette to the OD of a 1/2" thick round bar (see attached sketch).

I have also just spoken with the welder and he is allowing the weld/base material to cool back to ambient before starting the next weld. Could this have an impact on the increased F%?

 

[iam42]

Hi DVWE,

We are using a Fischer Ferritescope

 

[EdStainless]

If your N2 mix had issues then it is related to either your N2 source or your mixer.
I have welded in a lot higher N2 than that, but 2% is a nice value.
A bit of preheat and less cooling between passes would both help.
Look at your shield gas (lens, flow, weld speed), that is more oxidation than I like.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[DVWE]

I agree with Ed that the weldment is cooling too fast. This is typically an issue in the colder winter months (not sure what your shop temp is).

A little preheat might be in order if things are cold in your shop. But, try completing the weld fully rather than let it cool to ambient between passes. Welders are notorious for hitting weldments with a blast of air to get it to cool quicker when cooling between passes. Remind the welder(s) to mind the interpass temperature between passes.

If you need to slow the cooling rate more, wrap with an insulating blanket after welding. Both of those parts look like relatively large heat sinks compared to the size of the weld.

If none of that works, make sure the weld rod is correct to the MTR. Weld up a weld button and verify the FN reading that way.

Lastly, I’m sure you’ve done this part, but it begs mentioning, ensure your scope is reading FN, and not % ferrite. The scope should have standards to verify the scope’s accuracy.

The devil is in the details; she also wears prada.

 

[iam42]

Thanks Guys.

We are in the North East and it is pretty cold.

I will follow your advice and see where we go from there.

Thanks again.

 

[DVWE]

Just my opinion here, but you should be able to hit 3-8 FN relatively easily with 100% Ar. The 2% N mix is typically used only as a backing gas, which looks like you are not using.

The devil is in the details; she also wears prada.

 

[iam42]

DVWE,

I am using 100% Argon for the backing.

So far, we have never had a problem achieving the correct Ferrite content and we have welded this same job quite a few times.

The only time I have used the 2.5% N mix for a backing gas is when welding super duplex and it helped a lot, especially with the corrosion testing.

 

[EdStainless]

When welding duplex or 6%Mo grades you must use N2 added weld and backing gases.
We sometimes used to back with 100%N2 in a pinch.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[r6155]

Why this design?: Fillet welding is excessive as show the picture
Why not use a simple 1/2" sch 40S pipe without an extended section?.

Regards

 

[iam42]

r6155,

This is what the customer specified.

 

[iam42]

Ed,

An update on my Ferrite problem!

I followed your advice and maintained a pre-heat of 200F until the joint was complete and we now have ferrite reading in he range of 5.5 to 7.5

Thanks for your help, i was starting to pull my hair out, not that there is much left!!!

 

[0707]

You also have to be careful when welding this materials with the cleaning devices you are using on the bevel such as brushies and cleanig discs.

regards