Nitrogen and oxygen: What should you use to cut steel?

Preface:
Nitrogen is usually used in cutting stainless steel or aluminium to obtain excellent quality. Unlike oxygen, nitrogen is used as a protective gas in light materials to prevent combustion and to evaporate the laser material. This means that power is the determinant of cutting speed; more power equals faster speed.

Laser cutting is a hot working process in which laser beams are used as tools. Specific parameters used in this process, such as laser power and auxiliary gas type, will significantly affect the overall quality and processing time during operation. The most commonly used auxiliary gases are oxygen and nitrogen. Their selection depends on the type of material being cut, thickness and required edge quality.
Traditionally, oxygen is most often used in cutting steel. Because of the combustion process, thin steel does not need a lot of power, which involves exothermic reaction - oxygen combustion of iron chemical reaction, through heat and light release excess energy. Oxygen will do about 60% of the work. This, in turn, is a limiting factor in the rate of reduction. Before excessive combustion occurs, only such a large amount of power can be applied to the material, resulting in poor cutting. This means that the cutting speed using oxygen as an auxiliary gas in thin steel will be the same for lasers ranging from 1500 to 6000 watts.
Nitrogen is usually used in cutting stainless steel or aluminium to obtain excellent quality. Unlike oxygen, nitrogen is used as a protective gas in light materials to prevent combustion and to evaporate the laser material. This means that power is the determinant of cutting speed; more power equals faster speed.
Laser power increases steadily in various applications. This development gives laser users reason to choose their processing needs, because they can now regard nitrogen-assisted gases as an effective way to process steel.
Factors to be considered
In order to make the right decision between oxygen and nitrogen, the following criteria must be considered:
(1) Processing speed
(2) Secondary operation, including required edge quality
(3) Operating cost
Let's examine these three factors in detail:
Processing speed. As mentioned earlier, the oxygen cutting speed is limited by the applied power, while the nitrogen cutting speed is directly related to the power. In some cases, the higher laser power of cutting thin steel with nitrogen allows laser users to expect processing speed to be three to four times faster than that with oxygen. However, cutting steel with nitrogen laser is not limited to thin materials. Nitrogen can be used as an auxiliary gas for thicker steels, and the maximum thickness depends on the available laser power. Although nitrogen can provide faster processing speed in steel, up to 1/8 inch, thick materials are not. In this case, oxygen will provide faster processing speed as material thickness increases.
Secondary operation. Nitrogen will provide high quality edge quality without any impurities. This edge is very easy to accept powder coatings and ensures proper welding surface. This cutting method usually does not require any secondary operation. However, the oxide surface produced by oxygen cutting will affect powder coatings and welding. Generally, steel larger than 14 needs to be removed for powder coatings.
Operating cost. The main influence factor of operation cost is auxiliary gas consumption. There is a significant difference between oxygen and nitrogen. Oxygen treatment can lead to the lowest operating costs, because gas consumption rates can be 10 to 15 times lower than nitrogen requirements. Generally speaking, as the thickness increases, the consumption of nitrogen-assisted gases increases.
The Right Choice
Taking into account all factors, the following decisions can be made:
In thin steel, if laser users can increase their processing speed and produce more and better quality parts at the same or slightly higher cost, nitrogen should be strongly regarded as an auxiliary gas. With the increase of material thickness, decision-making becomes more challenging. If the components to be manufactured require secondary operation, the user must weigh the cost of additional process and processing to determine whether the cost of additional nitrogen in laser cutting process will provide the most cost-effective solution.
All these factors must be weighed in order to make the most cost-effective decision. But all this boils down to - most importantly - assisted nitrogen providing the best experience for laser cutting users.