Welding 409 Stainless. Ferritic stainless steel AISI 409 and austenitic stainless steel AISI 316L by gas metal arc GMA welding process by using AISI 308L austenitic filler wire. This should give you some insight.
Stainless exhaust is sometimes made from 304 stainless but there are also quite a few exhaust components that use 400 series stainless like 409. Is it ok to weld stainless steel exhaust tubing with carbon steel mig wire. MIG is suggesting 308l 309 or 316.
Its definitely not a good idea.
We have heard about the possibility of in service cracking may be because of the low ductility of the heat affectd zone. This type of corrosion is minimized in 409 because of the addition of titanium. Stainless exhaust is sometimes made from 304 stainless but there are also quite a few exhaust components that use 400 series stainless like 409. Post weld heat treatment PWHT at around 620C is rarely carried out although a reduction in residual stress will give an improved fatigue performance.