Welding of 2205 material.

Date 09-18-2015 13:52

Something like that usually means you are cooling too fast.
Remember, duplexes are not like other stainlesses where you concentrate on keeping heat inputs down.
You have to be cognizant of phase balance.
What's the process? GMAW?
And in my opinion you don't need N for 2205 unless the designer is really pushing the pitting envelope with the material service.

By mjgoessl Date 09-18-2015 14:47

Thank you for the fat response js55. We are using GTAW and from the different thinks I am reading all point to cooling too quick. We have a procedure that is qualified with 100% argon that we are going to try.

By Lawrence (*****)

Date 09-18-2015 15:15

Hey Js55

Your advice went right over my head... What mechanism would be involved particular to the duplex and cooling rates that would trigger porosity in a weld termination?

I'm just curious to know what your line of thinking is here, in hopes of learning something :)

By js55

Date 09-18-2015 15:31

Lawrence,
My experience has been that duplexes are a little more troublesome when it comes to gases escaping. And this thought was triggered by the location which will chill faster than the middle of the weld, and the fact that it is 1/2 material. Pretty heavy for duplex. You have a hell of a heat sink here.
But this is normally not an issue since you want to run them a little hotter anyway. If you run them like say a fully austenitic where you are trying to prevent hot cracking you will have trouble with phase balance.
And the problem seems to be aggravated by adding N into GTAW. I don't remember why. I'm too old.
If you feel you need N I'd run it in the purge. That way you get it on the interior surface of the weld deposit without all the problem of porosity with the shielding mix.

By Lawrence (*****)

Date 09-18-2015 16:10

Thanks,

The nitrogen in the shield gas is not something I've ever done... Certainly up to 100% on backing gas.. But only with austenitics..

Thanks for the primmer :)

By js55

Date 09-18-2015 16:40

N is part of the Pitting Equivalence Number calc. And the fear is if it is lost it will reduce pitting resistance, generally part of what duplex is intended for. Being a gas it is argued it is lost in the welding process. It is normally only an issue with super duplexes with stringent G48 requirments and such.
The idea is to add it back in through the gas either shielding or purge. Which one depends upon testing regime, process, etc.
It will also effect phase balance so one should be careful when using it. It is an extreme austenite stabilizer. And can also form detrimental nitrides.