Stainless to carbon steel

Okay, welding gurus: I've got some 5" pipe to weld, schedule 40, one is 316L stainless, one side is standard 5" Sch. 40 carbon steel pipe. Process will be MIG. My supplies rep told me to go with 309 stainless w/ tri-mix gas: anybody here concur with that? Any other suggestions?
Thanks!

Yup thats right...Bob
ER 309 Used for welding stainless to carbon steel.

309 yes, tri-mix ? not so sure you'd need that, sounds fancy and all but we've ran most of our stainless on normal C-25, same as for carbon steel and it did just fine.

C25 can add carbon to the weld. You want something around 98 to 95 percent argon and the remainder CO2.

Should be 309L for steel to SS. Depending on the application the 309L may only be a butter application to the steel. C25 will work...the tri-mix is not off base.

Now that I think of it, it was 308L fluxcore dual shield, maybe thats why it ran fine on C25, I know we tried argon/helium mix and it didn't go as nice.

I'm doing some side work in a asme code shop and they use 309 with tri-mix for carbon to stainless

On stainless to stainless with the pulse mig they use 95-5 or 90-10.

jamscal said:

I'm doing some side work in a asme code shop and they use 309 with tri-mix for carbon to stainless

On stainless to stainless with the pulse mig they use 95-5 or 90-10.

Click to expand...

I'm afraid I'm beating a dead horse here (thread, anyways) but I'm curious, everyone always specs "Tri-Mix" but there are so many different blends. Which blend would you be referring to? 66/33/.25 (HeliStar SS)?

I'm welding some 304L stainless and the only mix I could even get in my "Q" tank was 98/2 Ar/CO2. Tri-mixes here in Canada are strictly for the big boys, not availible in less than 250-something CF tanks. There is the slightly ridiculous possibility of shipping my tank off and if the guys in another province were having a good day it might get filled... for only an extra $90 to ship the tank. The 98/2 mix I ended up with is used for making foodservice equipment (ie kitchen fixtures).

jamscal said:

I'm doing some side work in a asme code shop and they use 309 with tri-mix for carbon to stainless

On stainless to stainless with the pulse mig they use 95-5 or 90-10.

Click to expand...

I'm afraid I'm beating a dead horse here (thread, anyways) but I'm curious, everyone always specs "Tri-Mix" but there are so many different blends. Which blend would you be referring to? 66/33/.25 (HeliStar SS)? Or another of the many blends, or just any tri-mix for stainless?

I'm welding some 304L stainless and the only mix I could even get in my "Q" tank was 98/2 Ar/CO2. Tri-mixes here in Canada are strictly for the big boys, not availible in less than 250-something CF tanks. There is the slightly ridiculous possibility of shipping my tank off and if the guys in another province were having a good day it might get filled... for only an extra $90 to ship the tank. The 98/2 mix I ended up with is used for making foodservice equipment (ie kitchen fixtures).

98/2 is spray arc transfer mig gas. I'm not thinking anything good would happen adding oxygen to a tig arc, but I could be wrong.

Jim Shaper said:

98/2 is spray arc transfer mig gas. I'm not thinking anything good would happen adding oxygen to a tig arc, but I could be wrong.

Click to expand...

there are two variants of 98/2 one with 2% co2 one with 2%Oxygen. Oxygen improves puddle fluidity and wetting at the toes. However oxygen is also about 30 times more oxidizing than CO2. You can get away with 2% oxygen in stainless steel welds no problem and 98/2O runs very smooth and has a good bead appearance. However when you start running mutliple passes you can get things like oxide inclusions. I always spec 98/2 CO2 it's my prefered stainless steel Mig gas. I haven't heard of using 2% o2 on TIG i'm not aware how that would effect the arc, but often 2% nitrogen is added to influence the ferrite content of stainless steels.

as far as tri-mix. It's all marketing hype really, tri-mix gases run much hotter than binary argon-co2 mixes. The O2 gives you slightly better wetting action so theoretically at identical settings the toes will smooth in a little better and the bead will be a little smoother, but the exact same results can be done by optimizing your welding paramters and running a tiny bit hotter. There are 2 main variants argon right and helium rich. there's an industrial shortage of helium right now and the scracity of helium is shooting up. Helium is by far the hottest shieldig gas and I don't reccommend it for stainless steel. especially if it's thin gauage work. The argon rich tri-mixes really don't offer any benefit over good ol argon CO2. I personally run 85-15 for carbon steels and 98-2 for stainless steels. c-25 is a little more all around but it can't produce spray transfer at reasonable parameters. Not important to all but you can run faster and cleaner under spray transfer.

http://www.weldreality.com/MIG_welding_gases.htm Ed Craig's site has some very good information on mig welding gas.

Here is Praxairs version..Bob
http://www.praxair.com/praxair.nsf/...f4dff08b7edc06e285256e75006577f5?OpenDocument