On 06/09/2020 08:00, Peter Hill wrote:
On 05/09/2020 21:45, newshound wrote:
On 05/09/2020 14:34, Cursitor Doom wrote:
On Sat, 5 Sep 2020 10:35:17 +0100, newshound
wrote:

On 04/09/2020 22:15, Peter Hill wrote:
On 04/09/2020 21:04, Cursitor Doom wrote:
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.
https://weldingpros.net/types-of-welding-gases/

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 isnt actually a pure gas, its 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.
https://www.wallworkht.co.uk/content/plasma_nitride/

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.