When choosing a laser machine for metal, customers often ask the question, which gas is CHEAPER to cut with?
Let’s face it - the question is incorrect. First, you need to understand WHAT YOU ARE CUTTING?
Stainless, aluminum or brass - choose AZOTH.
That doesn’t mean oxygen can’t cut stainless steel, for example. Yes, it can, but being a combustion catalyst (and combustion is an oxidation process at high temperature), oxygen will simply kill the stainless steel properties in the place of cutting.
Working with soft metals, in addition, we risk overheating them 
so we choose an inert non-flammable gas.
When working with black steel up to 3mm with a radiator up to 3000W, it is more practical to use AIR. Above 3mm it’s better to use OXYGEN - it’s a question of quality and speed.
Titanium - we cut it with ARGONOM.
Why not nitrogen? By reacting with nitrogen, titanium loses its properties and becomes LOCKED.