I cut stainless reasonably often but so far, I’ve only ever cut very thin stainless. 22Ga, 20Ga and 16Ga stainless steel and also perforated sheet.
I recently lucked into some 10"x12" drops of both 1/4" and 3/16" at an incredible price. Once of my neighbor’s suggested that I cut it with Nitrogen gas and a pressure regulator hooked up between the bottle and the plasma cutter power head, similar to the way I did the plasma marking with Argon.
I know Hypertherm recommends Nitrogen cutting of stainless in some of their very high end machines, but I also notice down at the lower levels (PowerMax-45) where I am, they don’t even mention it in the cutting recommendations. The problem is further complicated by a few forum posts that discuss no benefit.
Does anyone out there have any experience? I’m definitly going to give it a try since the same neighbor has a few very large bottle’s he is willing to donate to the investigation.
F5 (aka 5% hydrogen 95% nitrogen) actually. Expensive stuff.
You can use compressed air but the cut isn’t pretty;
If you are cutting austenitic stainless steels you can try flooding it so that you don’t get as bad of chromium precipitation oxidation. Flooding with F5 of course is probably the best.
But take what I say with a grain of salt. Try it for yourself and see. As always, try it on scrap first.
One thing of note is you can install the modbus adapter to your 45xp and adjust the flow and current better with a bit of Lua. Then the F5 or even nitrogen won’t be so darn expensive. I am working on getting my store online so I am buried right now. I can’t be the only one doing cool projects 
This is the manual on using F5;
https://www.hypertherm.com/Download?fileId=HYP157301&zip=False
OK, scratch all of that;
Do not use this process with the Powermax45 and T45m machine torch or with the
Duramax Hyamp torches and consumables. It is designed for Duramax machine torches
and consumables.
Stick with the compressed air , I forget the little 45’s aren’t 100% duty cycle machines. Try to flood instead.
With that interlude out of that way, … Back to the question that was posed. Does anyone have any experience cutting stainless with pure nitrogen like a lot of the old school plasma shops used to do, but with smaller lower powered machines like HyperTherm’s 45XP. The argument seems to be the minimal quality improvement vs price but the ultimate inquiry is about characterizing the quality improvement, where a hobbies might take on something to make a few parts at a higher cost where a mass manufacturer would not.
Jim Colt is Hypertherm’s main evangelist, find his response to your question here; Plasma cutting with nitrogen
That last one had some useful info on it. That and it makes sense. The water isn’t about the cut quality as much as it is the heat affected zone and the boundary of crystal growth + interaction with the atmosphere because the torch is (for 1/4in material) moving so darn fast that the area of the cut is moving well beyond the area of gas coverage. So, yes, just like welding stainless except here the torch w/gas coverage is just moving WAY to fast. The data point that I had observed (without submersion) is that the wander of the cut is significantly reduced. The draft angle is less, and the surface finish is much smoother. Of course this is useless because once the HAZ becomes exposed to air (due to travel speed) you’re going to have to grind it off which means the higher quality cut is moot at that point. Water submersion (in place of a back up gas) just makes so much sense in that context.
Thanks for the link @subnoize
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One tid-bit learned along the way on this one: When cutting mild steel and punching holes where I care about the diameter and draft the idea of running 30% slower that the slower/high-quality ratings in the cut charts comes into play. In mild steel this doesn’t seem to cause problems. With the THC the system and the speed set slower the plasma cutter chews through material in this manner just about every weekend here.
With stainless steel however, this isn’t the case. Of course I am talking stainless thick enough that the travel speed comes down into a range that the THC can turn on before the feature is completed. The recommended slow travel speed in the cut charts is pretty much the bottom end of the range the THC can deal with, without diving into the workpiece. That 30% speed reduction (rule of thumb) for better quality small diameter holes is ‘right-out’ when it comes to stainless steel. Of course one can disable the THC in G-Code before that feature/geometry and re-enable it again upon completion of the feature.
Just a tid-bit there I found experimentally that I thought to share given the difference between that operation in 1/4 & 3/8 A35 & 1018 vs the same thicknesses in 304.
