Most Duplex Stainless Steels depend on nitrogen additions to promote rapid formation of austenite from the primary ferrite solidification phase. The addition of a small amount of nitrogen in the backing gas of single sided joints can be beneficial in preventing nitrogen loss in the CGHAZ (loss of austenite phase) and enhance austenite formation in the weld metal. In most cases such as with the use of ER2209 to weld Alloy 2205 (S031803) the weld metal chemistry is sufficiently adjusted to make the routine use of nitrogen in the shielding gas unnecessary. Of course one must be careful when welding to maintain a moderate heat input (neither too high or too low) to promote a proper ratio of ferrite:austenite.
The AWS Handbook, Volume 4, has a good brief discussion of welding duplex stainless steel.
John
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of rajagopal kannan
Sent: Tuesday, August 18, 2009 4:05 AM
To: materials-welding@googlegroups.com
Subject: [MW:2959] nitrogen
Hi,
I could see in a client spec. insisting the use of 98% Ar and 2% Nitrogen gas mixture for backing and shielding of duplex steel welding.
What could be the significance of using 2% Nitrogen?
How it is technically advantageous over use of single argon gas?
Thanks and Regards,
K.RAJAGOPAL
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