Welding 304 SS to 409 SS

[snrusnak]

I'm a newbie welder, I have a lincoln MIG(I have only used it as flux core) I bought from home depot or lowes. It's pretty idiot proof, I've only used it to weld mild steel for household lawn equipment, etc.

I want to weld some exhaust pipe for my truck, I THINK the stock exhaust is 409 SS because I know it is stainless but it looks to have minor corrosion. The muffler I bought is 304 SS, can I weld these together using the flux core method? I assume I'll need a different spool of wire for the SS but I'm not really sure.

Any help from you guys that have more experience is appreciated.

[d_adams]

Most likely, use 309 ss filler or wire for dissimilar stainless types. Always go one grade higher for stainless for filler, so 304 needs 308, 316 should use 316L, etc. Welding mild steel to 304 stainless, use 309 filler. There's a lot to learn on welding and I know just enough to be somewhat dangerous.

Readily welded but a pre-heat of 150-260°C is recommended. Grade 409 or Grade 430 electrode or filler rods can be used, but AS 1554.6 pre-qualifies welding of 409 with Grade 309 rods or electrodes. These austenitic fillers result in a more ductile weld.

[snrusnak]

There's a lot to learn on welding

Yes I've certainly figured that out lol, and the fact that I know little about it and the materials.

I appreciate your help, I have one question I'm confused about. You say to use one grade higher but then say to use 309 ss wire for dissimilar ss types. Since one type will be 409 ss, should I use one grade higher(i.e. 410 or whatever it may be) or 309?

I'm not sure how the grade scale works but assume higher number = higher grade? I was under the impression 304 ss was better than 409 ss (for exhaust applications, anyway....as it is more corrosion resistant, it has more nickel and chromium I think).

Thanks again....I'll have to see if I can find a spool of flux core ss wire.

[snrusnak]

Found this:

UltraCore® FCP 309L

For welding dissimilar metals - stainless and mild or low alloy

Dissimilar Joints – Stainless types 410, 304L, 321, and 316L to mild and low alloy steels

Looks like what you recommended, 309 wire.

[d_adams]

304 won't really rust if it's polished, 409 is intended to get a surface rust or scale to preserve it. It will last forever, that's why magnaflow uses it. They build for the automotive market and the exhaust is typically hidden, so they win for longevity. I think 304 may be more prone to cracking over long term based on the material characteristics. It's got something to do with the crystaline structure.

[snrusnak]

The muffler I bought is like a knockoff magnaflow, but it is 304 IIRC. It is not polished. Do you think it will hold up ok? I'm not in a corrosive environment anyway, here in orlando.

So it pretty much won't matter much in my application if I weld the 409 to the 304, and I should try out the 309 wire?

Also, I found some T201 pipe cheaper and it seems to be a good corrosion resistant SS, just cheaper. Would this weld easily to the 304 and 409 with the 309 wire, in your opinion?

[d_adams]

The stock headers on xb's should be 304 as far as I know. If you're welding 409-304 then use 309 filler. I can't give an opinion on the 200 grade ss, but I wouldn't recommend it.

[Timeless]

You will be fine with the 304 muffler and it will definitely last assuming it is actually 304SS. If its an ebay can from China its hit or miss. Welding it in will be a whole other story.

If it were me...and I only had a flux core mig machine, I would go to an exhaust shop and have them weld the muffler in. I can't imagine it costing much and you wouldn't have to worry about your weld coming apart.

However, if you want to have some fun, d_adams is offering sound advice. Also, the 309L wire should work. However, from its spec. sheet, it seems to require a shielding gas.

[snrusnak]

I have a buddy that has a TIG, and he would do it for free. He is also fairly new to welding though, but knows more than I do and has better resources through people he knows through work.

I was looking to have some fun and practice/learn. It will probably take me more time than it's worth like you said but that's part of learning, and I'll be able to use these skills later on.

Does that mean that there is no such thing as a 309L flux core wire?

Thanks again guys.

Oh and the muffler is off ebay but not a china part. It is from an ebay company I think they are made in Hialeah Florida.

[Timeless]

The 309L wire that I found from Lincoln clearly says its flux core. However they seem to still be recommending shielding gas. Check it out here

I cannot comment on what would happen if you welded it with out shielding gas because I have no idea.