Welding Stainless

[Tom K]

I'm building an exhaust header for a race car with a 600cc honda engine and want to weld 304 stainless to 321 stainless. Does anyone know of any problems that I might see doing this? I plan on using a Tig welder and shielding the inside and outside of the tubes with Argon. Any recommended filler rod?

BTW, I was planning on building the exhaust out of Titanium, and got a lot of good advice from this board. I actually made some successfull trial welds, but the cost of bending the tubes ended up putting the idea on the shelf for this years exhaust system. But thanks for all the help!

Tom K

[Dan]

Tom

308 is the recommended filler rod.

[Guest]

Tom, 321 has a higher nickel and chrome content than 304. While 308 is a recommended for 304, the 321 is welded with 347, since there isn't a 321 rod. In the aircraft industry in which I work, and have certifications in 304 and 321, and a bunch of others, as a rule of thumb in the industry, when welding dissimilar metals, choose a rod that comes close to the higher nickel and chrome content. All that being said, 300 series stainless is very forgiving, and 308 would probably work just fine.

[Dan]

Originally posted by Rocky D
Tom, 321 has a higher nickel and chrome content than 304. While 308 is a recommended for 304, the 321 is welded with 347, since there isn't a 321 rod. In the aircraft industry in which I work, and have certifications in 304 and 321, and a bunch of others, as a rule of thumb in the industry, when welding dissimilar metals, choose a rod that comes close to the higher nickel and chrome content. All that being said, 300 series stainless is very forgiving, and 308 would probably work just fine.

Rocky and Tom

The 308 recommendation is from the Lincoln Electric Handbook. Also, it states that this recommendation comes from NASA.

[Tom K]

thanks

Once again, I got all the information I needed from you guys in the same day. Thanks a lot for your help.

Tom K

[Mike Sherman]

Tom, it is going to depend on the sevice temperature. E308L can be used if it is under 700 degrees F. If not, use the E308. Sorry Rocky, these two metals are both austenitic, share the same P number and are best welded together with E308.

[Guest]

Thanks Mike and Dan, .... I stand corrected. Now that I think about it, it wasn't 300 series stainless that I got tha info, it was Inconel 625 to 718...sorry for the confusion...I don't want to be giving any mis-information.

[Mowjunk]

A related question - Could Tom have used an 75/25 argon/co2 mix for the purging on the inside of the tube and pure argon at the torch? I have both gasses but no manifold or adapter to run to two places with one tank. I was thinking if I ever needed to do something similar to Tom, I could back purge with the 75/25 and weld with the 100% argon without too much added expense.

Would this be practical or would it compromise the weld?

Could nitrogen be used instead?

I'm just curious and looking to learn........Thanks.

[Roger]

With flow gages you can plug 2 flow gage regulators into one bottle using adapter between bottle and regulators. With flow meter and regulator you can tee in another flowmeter rated for same supply pressure into regulator output.

Some flowmeters are built into regulator body so another flowmeter can't be added to regulator's output.

[Tom K]

shielding questions

Now that someone has asked about shielding gas, I have another question. Why do people use CO2? Is it only for cost? At school I have Argon connected to my mig and tig welders. At work we run Argon in the tig and CO2 in the mig. At work they tell me there is nothing wrong with running Argon in the mig welder, they just run Co2 for cost. I have heard from other people that there are performance reasons for running CO2 in a mig. Can someone explain this to me?

Thanks,
Tom K

[CPB]

Tom K, I have not yet used co2 by itself as a shielding gas so I can only tell you what I have heard from others. Along with the fact that it costs less than argon it also produces good penetration with a lower current. You can make nice looking welds with co2 if you don't mind the extra spatter. I hope this helps, I'm sure some of the other welders with more experience at co2 than me can tell you a lot more.
CPB

[Guest]

Re: shielding questions

Originally posted by Tom K
Now that someone has asked about shielding gas, I have another question. Why do people use CO2? Is it only for cost? At school I have Argon connected to my mig and tig welders. At work we run Argon in the tig and CO2 in the mig. At work they tell me there is nothing wrong with running Argon in the mig welder, they just run Co2 for cost. I have heard from other people that there are performance reasons for running CO2 in a mig. Can someone explain this to me?

Thanks,
Tom K

CPB is right as to the reasons for using CO2 in MIG. It can be set to run like an argon mix gas with some difficulty, but it can be done. Most folks like the appearance of an argon / CO2 mixed gas, but as stated before, it is almost 3 times as expensive. There are several types of gasses used with MIG...argon, helium, CO2 and oxygen. The latter 3 are used with argon, in part or all three.
In Tig only two gasses are used...argon and helium, hence the name 'heliarc'. Argon is mainly used, now....helium will give you good results on heavy aluminum, on straight, DCEN, polarity. Now there are other gasses I could mention, but for the purpose and scope of this forum, I'll leave them out.

[Roger]

Mojunk
If you want to maintain the Stainless Steel properties both inside and outside of the tube it needs back purging with proper shielding gas or shielded some other way. Shielding paste applied on back side of joint might work or even aluminum foil might help. Test welds will indicate if alternate shielding methods are good enough.