Ferrite Number Testing for Nickel alloys

[paavainathan]

One of our client specification says Ferrite number testing for Nickel alloys.In my knowledge Ferrite number testing is applicable for Stainless steel and Duplex stainless steel welding.
I feel the Nickel alloys (Alloy UNS N06625,N08825 &N08028 -Incoloy& Inconel)welding ferrite number testing is not applicable.

Any expert can advise me on this.

 

[rustbuster]

Mainly for austenetic materials see

http://www.nrc.gov/reading-rm/doc-collections/reg-guides/power-reactors/active/01-031/index.html

The client may have other reasons for measuring delta ferrite, nickel alloys can be carburized and a ferrite tester may indicate the amount of magnetism.

 

[EdStainless]

in clad or overlay FN will relate to excessive dilution.
It can also help identify if the wrong filler has been used.
You would be trying to measure small levels, say below 5%.

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[matkenmd]

I have my own question.....

We've been trying to put together a weld repair procedure for duplex for a while. Well, not trying, but just suffering without one.

A metallurgist consultant recommended that above other criteria, we must ensure that we have no more than 50% ferrite in the HAZ. (We have sealing surfaces exposed to sea water in these areas.) We've found through trial and error that we can't do it for some reason.

Can anyone provide some clues for me to bring up with manufacturing?

 

[metengr]

matkenmd;
What is the filler metal composition you are using for weld repair of duplex stainless steel? Normally, for weld metal microstructure for duplex stainless steel you want to achieve a 50/50 balance with ferrite and austenite.

 

[matkenmd]

I understand the 50/50 split. Our trouble as I understand it (I'm in my design silo, and mfg engr is in their silo), that if you start with 49% ferrite in base material, then weld it, you'll certainly increase the ferrite in the HAZ. It may still top out at 55% but we've bought into a hard 50% MAX tolerance.

I've been told that we've sought out material that is 40 or 45% ferrite to start, so the ferrite increase in the HAZ may still be at or below 50% but they've been unsuccessful up till now.

My application in this case is weld repair of completed parts, so full solution anneal is not acceptable as the parts would deform in the furnace under their own weight. We have get a solution to weld without PWHT. If we do it right, we'll keep the sigma problem at bay and will be able to move ahead. Possible with the right tuning?

 

[metengr]

matkenmd;
If you are in the range of 45 to 60% ferrite after welding duplex stainless steel, this is considered typical and should be acceptable.

 

[EdStainless]

You need to use an over alloyed filler, and accept a 60% upper limit. Run samples and have them tested for pitting resistance.

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