I'm no expert, but generally speaking, using ER70s wire can lead to cracking when used to weld mild steel to stainless so it really depends on the application.

The common advice is to use 309L filler/wire so that the weld bead is essentially a combination of mild steel and stainless steel that should hold.

 

I'm no expert, but generally speaking, using ER70s wire can lead to cracking when used on mild steel so it really depends on the application.

The common advice is to use 309L filler/wire so that the weld bead is essentially a combination of mild steel and stainless steel that should hold.

Er70S is the most common solid wire for use on mild steel.

I have a project I'm finishing up, which requires me to weld notched mild steel box tubing to a piece of stainless steel (unknown grade/alloy). The project doesn't require SS (corrosion is not a concern), its just I needed a short piece of 1" ID tubing and stainless was all I had on hand. Any reason I can't weld it to mild steel using .030 ER70s solid MIG wire?

I would just use the wire you have and you'll almost certainly be fine if the weld has enough meat to it. Maybe do a little test on scrap for your self and be sure it is going to meet your standards for the real part.

 

using ER70s wire can lead to cracking when used on mild steel

This is just not correct. ER70s wire is the preferred wire for mild steel. I would also advise on using stainless wire for welding mild to stainless, but you need a different gas than 75/25. But if you do use ER70s wire, understand there is a risk it will eventually rust, crack and fail.

https://weldingweb.com/showthread.php?12869-Newbie-with-a-question-about-MIG-and-stainless

 

This is just not correct. ER70s wire is the preferred wire for mild steel. I would also advise on using stainless wire for welding mild to stainless, but you need a different gas than 75/25. But if you do use ER70s wire, understand there is a risk it will eventually rust, crack and fail.

Sorry, I meant welding mild steel to stainless and worded it poorly. I fixed it.

 

https://www.bakersgas.com/weldmywor...myworld/2012/03/01/how-to-successfully-weld-steel-pipe-to-stainless-steel-pipe/

https://www.thefabricator.com/article/metalsmaterials/the-wide-world-of-welding-stainless-steel

https://www.hobartbrothers.com/news...news/175/523/Tips-for-Successfully-Welding-Stainless-Steel-to-Carbon-Steel.html

 

I actually have a bottle of tri-mix, and a couple of rolls of SS wire (not sure which grade), just didn't know if it was worth swapping everything over. The piece of stainless is only around 3" long, but is somewhat structural....its the "hinge" portion for a tire carrier, so there will be around 75lbs of weight when swung out (although it will be supported on both ends while latched in place).

Any tricks with MIG welding SS, or does it weld pretty much like mild steel? The machine is a Miller Multimatic 215...

 

Favor the heat toward the stainless piece. Stainless doesn't conduct heat as well as mild steel

 

Just use the steel wire and gas. It's done everyday in the real world. The ideal thing would probably be tig with 309 filler, but this sounds like a non critical situation , so almost any process or filler will work.

 

Just checked my SS wire, all I have is 308/308L...will it still be better than ER70s?

 

I think as I said before maybe try a little test if you can with some scrap. I think that is the surest way to see how it welds before you mess up your real piece. That way if you think it leaves a lot for improvement stop half way around the test tube weld and swap out wire and gas and give that a whirl for comparison.

 

May be better to simply go ahead and order a roll of 309, just for future projects.

I have several sticks of 309L TIG rod, but I've never TIG'd stainless steel, and certainly never TIG welded anything this thick.

 

What did you end up using? Any pix?

 

I ended up making a new collar out of mild steel, and used it instead.

 

Do you have any pictures of the full build? The tire carrier I mean.