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Up Topic Welding Industry / Technical Discussions / MIG Welding 4340 to 304L
- - By RMD Date 09-08-2005 14:41
We are trying to weld some 4340 to 304L, but we are experiencing problems with porosity in the weld. The porosity is occurring at the edges of the weld, moreso at the stainless steel side than the 4340 side. Does anyone have some advice on how to eliminate this?
Parent - - By - Date 09-08-2005 15:04
What filler metal are you using, and what shielding gas are you using?

Chuck
Parent - - By RMD Date 09-08-2005 15:19
For wire are using a 309 at the root, and 316L at the cap. The gas is a Praxair supplied C2 mix, just something they recommended for this application. The porosity problem is occurring at the 316L cap. The welding parameters that were used is 20 cfh of gas, 336 ipm wire speed, 25.4 volts, with .045 wire. Preheat temperature 450 degrees.
Parent - - By - Date 09-08-2005 16:18
Sounds like you are in the spray mode of transfer. I'm not sure what the Praxair C2 mixture is, but for this combination of steels, I would recommend a 98%Argon-2%oxygen mixture. It is quite possible that you are experiencing a hydrogen gas release propogating to the weld surface. With the porosity being on the surface of the cap, that is usually related to the shielding gas, but not always. I assume you are brushing each pass before welding over it. The oxide layer can cause porosity if the oxide layer is prominent enough. As you already know, both base metals MUST be perfectly clean to insure no porosity.

Chuck
Parent - - By RMD Date 09-08-2005 18:43
Thanks for the help. Another thing we may look at trying is "buttering" the weld, where we put a surface weld on each of the two pieces of material individually first, machine it down and make sure there is no porosity at that point, then weld them together after that. This would mean we are just welding together the 309 surfaces after the buttering is done, which sounds like it would help a lot.
Parent - - By - Date 09-08-2005 19:08
That might not be a bad idea, since the HTLA and the SS are of quite different chemistries. But, the things I mentioned above would still apply. To be honest, you should be able to weld the 4340 to the 304L without any problems with porosity. I mean, low alloyed steels are welded to SS every day without problems. If you do decide to butter both edges with 309, do not use that preheat when you start welding the 309 to 309. Again, I would recommend the 98/2 as your gas shielding.

Chuck
Parent - By turbo38t (*) Date 01-27-2006 00:07
Praxair C2 is 98%/2%. Dave
Up Topic Welding Industry / Technical Discussions / MIG Welding 4340 to 304L

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