In industry, both oxygen and nitrogen are used as cutting gases for stainless steel and other high-alloy steels.

High cutting speeds are possible when using oxygen, due to the exothermic energy contribution. The maximum thickness today is 16 – 18mm (3/4 in). The optimal focal position situats at or just below the upper surface of the sheet. By contrast, with mild steels, relatively high oxygen pressure – approx. 5 bar (75 psi) – is also advantageous when cutting thicker sheets. Greater oxygen purity (99.9%–99.95%) than standard oxygen purity (approx. 99.5%) we can use it to increase the cutting speed.

The disadvantage of oxygen cutting is that burrs will always appear at the cut. And the cut surface will be discolored due to chromium and iron oxide. These oxides obstruct the subsequent welding procedure. TIG welds, for example, have black oxide spots on the root side, which sometimes cause incomplete penetration. Beyond that, the oxidised cut surface facilitates corrosion of the cut edges. These drawbacks in oxygen-cutting are serious, as they often require expensive fi nishing operations.

High-pressure nitrogen cutting can obtain oxide-free and burr-free incisions, although the cutting speed must greatly reduce compared with oxygen cutting. We can use higher cutting speeds with higher power lasers. We commonly use CO2 lasers with a power of at least 2.5kW for this application. Today, the maximum sheet thickness range where burr-free cuts are possible is about 12–16mm (0.50–0.64 in).

The focal point should be close to the back surface of the sheet during high-pressure nitrogen-cutting in order to assure burr-free cuts.

The kerf then becomes wider so that a larger part of the nitrogen flow can penetrate into the kerf and fl ush out the molten material. The lower focal position results in a larger cross-section of the laser beam inside the gas nozzle than in oxygen-cutting . The diameter of the nozzle must also increase to allow the laser beam to pass through the nozzle without restriction. A nozzle diameter of at least 1.5mm (0.05 in) is usually require for high-pressure nitrogen-cutting.

The purity of the cutting nitrogen has little effect on the cutting speed. At least as long as nitrogen purity is better than 99.5%. Even small amounts of oxygen impurity, though, have an oxidising effect. In stainless steel this means a discolouration of the cut surface. Corrosion resistance of the workpiece may also be impaired. The oxygen impurity level would have to be below 20 PPM (0.002%) in order to avoid all traces of oxidation. This specification, however, is desirable when laser cutting stainless steel, but is normally not require in other industrial applications.

The oxygen impurity level is important when using gaseous nitrogen in cylinders or bundles as there are various purity grades available. On the other hand, the use of liquid nitrogen in tanks, which generally has a very low impurity level, does not lead to discolouration of cut surfaces.