9TechNine9

Long story short, I bought a tank of 75/25, the guy at the welding shop is telling me it will work fine for the thin stainless I'm welding - 16g exhaust tubing (3" downpipe, dumppipe). However, my friend who has taken welding classes and works for a welding company welding mufflers says I need to use helium tri-mix. He says that 75/25 may introduce carbon into the weld and it could rust. They guy at the shop says that in essence helium is only used as a better conductor to get more heat for thicker stainless welds. Can anyone shed some light on this for me? I just want to make sure that I don't **** this up, I spent a lot of money on material. I am planning on having it ceramic coated right away if that helps any. The guy at the shop gave me some stainless coupons to try it out on. I'll post results of that today, just finishing setting up the welder.

9TechNine9

Wasn't able to get a weld in today.. Found out the mig gun I purchased was the correct specs, but didn't fit because of the bulky plastic guard that was on the end where it attaches to the welder. I took off the guard and it fit perfect, but it definitely seemed like not a good idea to have open wires and metal exposed. My local welding shop didn't have the mig gun I need in stock so I'm waiting on that. If you haven't figured it out by now, I have absolutely zero welding/fab experience. It took me an hour to figure out how to get the old flux core wire and gun out of my welder

seelback

75/25 will get the job done. The best thing you can do is go on youtube and find tons of videos on mig welding and get some scrap material to practice and dial your settings in before hitting your good stuff. I taught myself how to tig weld by watching weldingtipsandtricks on youtube and practicing. I dont have alot of experience on mig welding but i have seen stainless welded with 75/25 mig.

9TechNine9

I've done a lot of watching youtube vids especially weldingtipsandtricks. I couldn't find any good stainless mig videos though, especially any going into the metallurgy of it, which is my only concern.

I ordered the correct mig gun from my local welding shop today. I should be able to at least give it a shot by saturday. We'll see if I can lay a decent bead.

9TechNine9

I finally got all my equipment together and was able to try out the c25 gas with the stainless wire. These are the first welds I did and they did not turn out that bad. I used the settings that were on the guide on the welder. What I was most concerned about is the stainless losing its anti corrosive properties - which looks to still be present from these beads. I'm going to dial in my settings tomorrow when my friend comes over to help me.
To conclude this thread, 75/25 will work for stainless steel. Overall, I think that a helium tri mix would probably give me a smoother better looking weld but the c25 will work to fab a downpipe thats going to be ceramic coated anyway.

Caoboy

If you’re going to ceramic coat it, might as well build it out of mild steel.

tri Mix still has co2 in it. Just like .9%. With the right settings and gas you will still achieve that ‘colorful’ weld like you would with TIG welding.

I would forego trying to weld with just 75/25, your welds will still carbon precipitate and grey out, you might as well weld it together with er70...

9TechNine9

I'm already committed to the stainless. I can get the tri mix but its another $200+ out of my pocket. Are you saying that over time the welds with c25 will break down? It didn't look like I got any carbon precipitation on those welds..? Also, remember I'm extremely new to this - whats er70 (google search didn't do me any good)?

Caoboy

Er70s2 is mild steel wire...

Over time, yes the weld will break down sooner than if you were to weld it with tri mix or even argon with 2% co2.

You’re introducing too much carbon into the shielding and the molten metal will absorb it. Thats why your weld is grey.

The heat cycles is what will likely cause it to fail.


But again, if you’re going to ceramic coat it, why not just make it out of mild steel?