MIG welding with Nitrogen?

Gentlemen,

I've run out of the ideal 90:10 mix of argon and CO2 for mild steel and was wondering if Nitrogen could be pressed into service as an expedient, given how long it takes for gas to be delivered currently. I have a nearly full half-size cylinder of pure nitrogen and it would be handy to say the least if it would make a workable substitute as an inert gas. Any thoughts?

CD

Nitrogen is used as a blanketing gas on back of stainless steel welds. This site says it won't work on mild steel.

Nitrogen, if I remember my science is not inert in the same way as argon. After all you get nitrides and nitrates and plants also use it, so I guess something given off by steel might combine with it and screw things up. Brian

As Brian implies, nitrides in steels change the mechanical properties. I'm not surprised that professionals don't recommend it on mild steel, but surely you have nothing to lose by doing some trials on dummy specimens. It all depends on how critical your welds are.

Problem is, the welds might *look* totally fine but be compromised strength-wise, as implied by the remarks on the site Peter pointed to. Since some of the stuff I'm doing is structural, I'm not convinced it's worth taking any chances with. Be interesting to experiment with, nevertheless.

I was quite impressed by that site until I came to this:

"Propylene isn?t actually a pure gas, it?s a blend with Oxygen"

Otherwise a fair point. But remember we usually assume that structures contain defects. So, where possible go for redundancy, or proof loading.

But yes, it does very much depend on the application. My welding is such rubbish that I wouldn't do it on anything important. I still remember Florian Camathias killing himself because of a bad weld (although I thought it was reported as a braze).

I suspect welding steel with N2 as the shield gas would be like an uncontrolled plasma nitriding process. The weld could very easily be more hard and brittle than desired.

EN8 and some cast irons can be plasma nitrided and welding steel is basically a plasma process to deposit cast steel.

Sounds pretty cool!

That was my concern also.

Anyway, I suspect using N2 as a shield on structural areas of a vehicle could seriously come back and bite me on the arse, so I'll hang back until some more argon turns up.

Just use straight CO2

Ain't got nun. All I have here currently is a full sized cylinder of UHP Hydrogen and a half-sized N2; both full.

Yes, you would certainly get significant nitride formation. Some brittleness might be tolerable in a compression structure. But I still think it would be interesting to try on a test piece, followed by a standard extreme bend test. I'd have some confidence if it survived that.

Get a reel of cored wire?

Not me. What if the brittleness only develops over a period of weeks or months later? This would really need a long-term test under carefully controlled conditions before we could place any faith in its application in structural work. And I'm assuming that's already been done at some time and the results found wanting.

Well I was wondering about that stuff, Newsy. I know it creates extra splatter compared to shielded, but that wouldn't matter in this case. But isn't it a bit too much like normal arc/stick welding? And if so, it's going to blow holes in the typically 0.7-0.8mm mild steel used for car sills and other structural areas like outriggers, surely?

Maybe if you kept it at high temperatures, but that's just not the way nitrogen behaves in steel at ambient temperature.

Case hardening and gas nitriding have been around for a long time.

I gave away an inherited transformer stick welder before I bought the MIG, I couldn't do a thing with it which is doubtless down to my lack of technique.

I did manage to fix a (non structural) hole in a Diahatsu panel once with gasless MIG. Not terribly neatly. I've done better on more favourable materials though.

TBH I have not had the MIG out since I bought a little Lidl inverter welder for stick, I've been surprised how well I can re-fill the holes I sometimes make with it. As the You-tube videos for the generic ones confirm, the displayed amps are a bit optimistic but it's fine for one stick size down from the claimed maximum. Definitely a nice toy to have.

But these days the cars go to a mate who owns a garage.

It's still very handy to have a heafty arc welder, though. I keep a trolley-mounted 320 Amp Olympic oil cooled job made in England in 1973 (and still going strong) in the workshop for the big stuff. You can't beat it for heavy structural work like RSJs. I know you can do thick plate with MIG, but to match the penetrating power of a stick welder at that end of the scale you'd have to spend a small fortune on a MIG big enough to cut the mustard.

Yup, but it can be unreliable at times so I have a gennie which does single and 3 phase.