329 Duplex Temper Embrittlement 2

[LanaCarrie]

I have a 1.5" thick piece of equipment made of 329 Duplex (old duplex grade, approximately 70% ferrite). We experience metal loss in isolated areas (cutting due to slurry) and weld repair these areas. The manufacturer does not recommend weld repairing the material more than 3 times, as they believe more than 3 repairs will cause temper embrittlement. I have not been able to find any literature relating the number of welds to probability of temper embrittlement. Does anyone have any advice they could offer on this matter?

Thank you.

 

[mcguire]

That's an old enough grade that data is hard to find for it, but the danger of embrittlement is from sigma formation which happens to duplex grades in the 800C range. This brittle sigma phase takes time at temperature to form and this is why he's saying limit the number of welds, because each weld will contribute to the time required to precipitate sigma in the heat affected zone.
If I can find the TTT curve for 329 I'll add it later.

 

[LanaCarrie]

That makes sense. I've been trying to find a TTT curve but haven't come up with one yet. You're right - it's hard to find any info on this material except for references to the general tune of "new duplex materials are far superior to the original duplex alloys like 329". Thanks for your help.

 

[mcguire]

The new grades have more nitrogen which delays sigma formation and also helps pitting corrosion resistance.

 

[CalvinKelly]

For duplex 2205 (nominal 22.1Cr 3.1Mo 5.6Ni 0.16N, UNS S32205) I believe AvestaPolarit literature suggests limiting total time spent at temperatures of around 700-980C. Under 5 minutes would be preferred, and at 15 minutes loss of notch impact strength may become significant. One question might be how important is resistance to brittle failure in your particular equipment?

James Kelly

http://www.rolledalloys.com

 

[Carburize]

The reduction of Charpy Impact properties is usually accompanied by a reduction in corrosion resistance. The sigma phase formation causes both effects.