MIGing stainless to mild ...

[Jan]

Or vice versa. For reasons that are far from clear all the exhaust systems available for one of my cars use stainless boxes joined by mild steel pipework. No idea of the specs on the stainless bits. How might I nail in new pipes when they finally give up the ghost? Fortunately I fitted a nearly new one about 18 months or so ago so it should be fine for a while, but as a full replacement comes in at £1000 + delivery + VAT I'm loath to part with that kind of cash if I can fix it.

 

[PhillipM]

That's probably all they've done anyway, MIG'd using normal wire, ideally you'd TIG them on with some 309L or similar, but then if you were doing that you may as well just put stainless tube in anyway...

 

[BrokenBiker]

i use mild wire if joining the 2 as the mild is going to rust anyway so i cant see any point in using stainless wire.

 

[Jan]

Good thought there. Unfortunately since it's an exhaust system there a lot of precise bends in the connecting pipework. In one place a pipe actually goes through a chassis rail so precision is vital!

 

[PhillipM]

Hah, you haven't seen my exhaust manifold

 

[dannyp]

you can mig stainless to mild with normal mild wire A18 iirc works just fine, in theory you'd probaly be best off with a dissimalar wire 312 ss but really on an exaust its not going to make any significant differance

 

[steviec_lj]

Worked for a Security Door manufacturer, and the lock covers were a mix of stainless and mild. Welded together with A18 0.8mm, had no problems. Didn't see the point in mixing mild and stainless on a lock cover, that in the end was powder coated. Either stainless or mild would have been better to be honest.

But yes, A18 will be fine.

 

[gaz1]

im sorry to enquire but in on this post, but could 304 stainless steel be welded the same way as well the item is being used for a rocket burner so no welds would be seen by anyone after the install inside the gas bottle

the ss being used is 5 x 5 3mm wall box section to 4" 2mm wall

 

[hotrodder]

A disimilar filler wire like 309 is about metallurgy not corrosion. Dilute stainless (lots of chromium etc, next to no carbon) with carbon steel (relatively high carbon but not much Cr etc) and you get something in between which can have a martensitic microstructure. Martensite is a 'kin hard and brittle phase and not something generally wanted in welds, at least in uncontrolled/random amounts. Disimilar filler wires are 'overalloyed' to take weld dilution into account and produce a weld deposit with a predictable microstructure that's not gonna be prone to solidification cracking or more brittle than it should be. Obviously application of the part plays a role in that cutting corners isn't likely to bite anyone with a car exhaust that's suspended on rubber hangers, especially when the mild steel bits will rust through in a few years anyway. Might get away with it on a rocket burner but for the sake of a few quid for the correct filler wire (and gas if talking MIG)...

http://www.gowelding.com/met/diss.html