304 ss to a36 mild

Date 03-06-2008 12:17

307, 308, or even 309 will all do the job. The service temp, and environment conditions will help determine which one is the best fit.

By Fredspoppy (**)

Date 03-06-2008 13:27

307 is not a common filler metal and 308 would not be recommended for SS to mild steel. The 309 type or 312 type wire/electrode grades would be the preferred.

By Kix

Date 03-06-2008 13:39

310 is even more suitable for disimilar metals then the 309, but 309 is more readily available.

By MDG Custom Weld (***)

Date 03-06-2008 15:57

Why would you not consider 307? I agree that 307 is not common on the shelf, but we use ~1,000# of 307 tig rod per year and it's easy to get. We also use ~30,000# of 307 GAMW and don't have to wait for delivery. It's made in Scranton, PA.

I agree with 310 or 312, but if the service temp is elevated I don't think it's a good idea.

The only real differences between 307 and the others is that it has fully austenitic microstructure, more Mn%, and a few % less of Cr and Ni.
We went to 307 a few years ago as a cost save for all 304 and 304L welding, this includes 304 to mild steel. Most of these parts see service temps of 800-1300F without issue. These components don't see a heavy chemical attack thus the mild steel is good for some flanges, the thickness is just increased. 307 has a higher yield strength than that of 308, 309, or 310 (excluding 301H). The high carbon and Cr in 310H brings the yield strength up to within 2000psi of 307. And the even higher Cr in 312 takes its yield above 307.

For a single part or short run, 309 would be easy to get and cost effective, but for higher volume or large wire consumption, 307 is much more cost effective and suitable for the application.

By js55

Date 03-06-2008 17:20

The deciding factor would be to run a WRC diagram to see if you're in the martensitic range for the dilution involved. Thats the primary issue for dissimilars with CS. As for service temps I'm not sure the choice of SS fillers is that critical when its a dissimilar with CS, so price would most likely be the primary factor.

By MDG Custom Weld (***)

Date 03-06-2008 17:43

Yeah, I agree thanks for pointing that out. We use the the Delong and or the Schaeffler diagram to map out the perfomance of the finished weld metal deposit with Ar/O2 gas.

By aevald

Date 03-08-2008 20:47

Hello gmabon, This may not be totally relevant to your question but I would like to include one additional consideration, the welding process might have a small bit of impact into making a choice here. It was pointed out to me in a post on another topic quite some time ago that the GTAW process allows for greater dilution between the base metals and filler metal for the initial pass on multi-pass welds or single pass welds than the other welding processes. In some cases this could be an issue when considering the resulting weld deposit and it's intended purpose. This same post described certain bead-cracking issues related to GTAW when other processes didn't exhibit the same result. Thus in certain cases GMAW, FCAW, SMAW being used with a like alloy worked better than GTAW. The "why for this" was explained something along these lines: GTAW melts the two materials being joined and forms a fluid pool, then the filler is introduced and mixed with the puddle to form the weld deposit, hence a fairly high rate of dilution. In most all other processes the filler is transferred across the arc by various modes of transfer and much less dilution takes place. Generally this should be a consideration when any dissimilar materials are being joined as in many cases the amount of dilution can have a great effect on the finished weldment and it's as welded characteristics. Just a bit of additional information for consideration. Best regards, aevald