When oxygen-cutting mild steels and low-alloy steels, on the cut surface forms a thin oxide layer. In most cases, this does not cause any problems. However, it may lead to difficulties if the cut parts are to be painted or powder coated, in which case paint adhesion and, consequently, corrosion protection may be insufficient. Here, we can use high pressure nitrogen-cutting as an alternative to obtain oxidefree cuts. When cutting thick materials, however, the cutting speed will reduce. Modern high power lasers allow for the same cutting speeds and sometimes even higher cutting speeds when cutting thin material (thickness less than 0.08 in).
The surface condition of mild and low-alloy steels is important in laser cutting.
Oxygen-cutting of sheets with rust, for example, may cause dross and notches. Likewise, painted surfaces can also cause problems. This applies particularly to sheets coated with zinc primers and iron oxide shop primers. When oxygen-cutting, problems only occur when the paint layer faces the gas nozzle. The cuts then often exhibit dross and notches.
These problems do not occur when the paint layer is on the lower side of the sheet. It can avoide the problems with painte sheets by using high-pressure nitrogen- cutting, although the cutting speed will, of course, be lower.
Zinc coated mild steels, galvanised or hot dipped, cause considerable problems when cutting with oxygen. There is always dross formation and the cut surfaces may be quite rough. High-pressure nitrogencutting is therefore use in industry to cut zinc-coated steels. The cutting quality is acceptable and free of adhering dross.