Question... welding stainless to carbon steel?

Date 04-09-2009 11:48

The joining of stainless steel to carbon steel or mild steel has long represented a major problem in industry. Every electrode tested invariably picked up so much carbon from the carbon steel by dilution that cracking and accelerated corrosion resulted. I tried MAGNA 303 which exhibits a high resistance to carbon pick-up and dilution and has repeately been proven to be an outstanding material for welding any type of stainless steel to any type of mild or carbon steel.

By js55

Date 04-09-2009 12:33

Not sure what filler metals you've used in the past but the primary problem with SS to CS welds is not enough alloying to prevent large scale martensite formation. Thats why 309 as opposed to 308 is the common choice. As for the implication of inevitable cracking and accelerated corrosion, this is patently false. Even a 308 that is 75% sensitized will have greater alloying for corrosion resistance (~say nominally 4.5% Cr) than the CS it is welded to. Certainly C will diffuse to the higher alloy microstrucure but failures associated with this would be an extreme exception. Not the rule. And if C diffusion is a concern you can go with a Ni based alloy (which has been common in the power industry with boiler tubes) which will prevent to a great extent the diffusion of C across the fusion line, though there will still be a build up of C on the fusion line against the Ni generated austenitic microstructure.
There are primarily two problems involved in the cracking tendency of these types of dissimilars. High temp cyclical loading that stresses the difference in thermal expansion of the austenitic and ferritc microstructure (this is why Ni is recommended as an alternative for SS fillers at higher temps or cyclic loading applications)and of course the recently often discussed Type II grain boundary cracking, wherein a grain boundary parallel to the fusion line has greater crack sensitivity than equiaxed grain boundaries.
In the end however, these types of welds have been performed by the tens of thousands over the decades with great success, but like any alloying combination as service expectations become more severe problems will eventually be revealed.

By Metarinka (****)

Date 04-09-2009 16:28

js55 and fredspoppy nailed it

for reference generally dilution can always be reduced by running short circuit GMAW, TIG or other low penetration processes. We successfully bonded large volumes of stainless steel to carbon steels generally using 309. (which if I remember correctly was originally developed for this express purpose)

By Fredspoppy (**)

Date 04-09-2009 14:03

The basic answer to your question is another question. What fabrication code/specification and you working to? If you are fabricating components for a client, there must be some document that they have issued to you that provides guidance. If you are working to virtually any fabrication code, e.g., AWS D1.1, ASME/ANSI B31.3, etc. you will be requried to qualify a WPS and your welders will need to be qualified on that WPS.

js55 is correct, in that welding carbon/mild steel to stainless steel is done everyday, normally with success, if those doing the welding know what they are doing. The use of a "specialty electrode" like the Magna 303 is a waste of money, in that it has no benefit over a normal AWS classification electrode, such as E309-16 or E312-16. Standard practice for the maintance welding companies is to "take it from the big box, print your special name on it, put it in the little box and sell it for 2-5 times the normal price". Good business if you can find someone to fall for it.

A good quality electrode from a quality supplier (Sandvik, Esab, Avesta or others) will do everything you need in welding stainless to carbon/mild/low alloy steels.

By js55

Date 04-09-2009 17:28

"take it from the big box, print your special name on it, put it in the little box and sell it for 2-5 times the normal price".

Thats funny!