help: mig welding westfield megablade stainless exhaust manifold

[bertsmini]

Hi there i am a newbee to the forum with over 20years mig welding experience(rusty mini's especially)
I am modifying a westfield megablade exhaust manifold to fit my "Raw striker" kitcar by way of shortening the primary pipes.
I have contacted westfield regarding the type & thickness of ss used and they are reluctant to give me the info. Any ideas?
Any suggestions regarding type of ss wire required and a recommended supplier for a small quantity (0.7kg) i am using argonshield light gas and 0.8mm wire.
This is a race car and i am obviously concerned about cracking issues after welding..Obviously a tig weld would be prefered but I have no access or the experience of using one but feel that a tig weld would be stronger.Any advice would be appreciated.
Thanks
Bert. (Hereford)

 

[pedrobedro]

Most exhaust work is done in 304 as it bends nicely for the pipe but the manifold flange could be anything even mild steel. I've welded stainless exhausts with mild steel wire and argoshield before and not had any problems but ideally you should use something like 308 wire which I think is available in small reels from Machine Mart and argon gas so you don't get carbon in the weld causing discolouration but in an exhaust situation I wouldn't worry too much as it going to go brown anyway.

 

[bertsmini]

thanks for your advise and quick reply.
I have today done a magnet test and there seems to be some magnetism existing in the manifold close to the flanges that i will be welding,this should mean that there is a low nickel content (am i right?) and it should be ok to weld with mild steel.
I have mig weld tacked with mild steel while awaiting a reply and it has tacked realy well.

 

[flak monkey]

IMHO for something like an exhaust you will be fine using the cheap reels of SS wire from machine mart et al.

The exhaust on my kit car is stainless with a mild steel flange and its been MIG'd with mild steel wire. No problems to report after 7000miles.

I have for other fabircations where there is a mix of stainless and mild (mainly as its what I had laying around) used both MS and stainless wire, and the welds always appear to be good.

 

[hotrodder]

You say there's some slight magnetism. Are we talking about just enough attraction to feel but not enough for the magnet to stick? The austenitic (non magnetic) grades do become very slightly magnetic when cold worked (like bending) and welds typically also show a slight magnetic response due to the filler metal composition (more ferrite)

If that's the case and magnetic attraction varies form none to a tiny bit then chances are it's 304 as said. Some OE exhausts are made from a 400 series stainless which has a strong magnetic attraction

There are specific gas mixes for welding stainless with MIG. Argoshield contains too much CO2 (dark welds with less corrosion resistance), pure argon doesn't work well either. The alternatives would be more expensive than paying someone to weld it for though

Should really use something like 309L for welding steel to stainless. It's possible to end up with a brittle weld without a dissimilar wire. Not much of an issue on a rubber mounted exhaust system, more of an issue with a manifold and more so if the engine is say turbocharged