Nitrisering

Nitrisering is a thermochemical surface hardening process used to improve the wear resistance, fatigue strength, and corrosion resistance of steel and other ferrous alloys. It involves diffusing nitrogen into the surface layer of the material at elevated temperatures, typically between 480 and 580 degrees Celsius. This diffusion process forms a hard, nitrogen-rich layer known as the compound layer, which is primarily composed of iron nitrides. Beneath the compound layer, a diffusion zone forms where nitrogen is dissolved in the iron matrix, further enhancing the mechanical properties.

The nitriding process can be carried out using various methods, including gas nitriding, salt bath nitriding, and plasma nitriding. Gas nitriding, the most common method, involves exposing the parts to a nitrogen-rich atmosphere, often ammonia gas, in a sealed furnace. Ammonia dissociates at the elevated temperatures, releasing atomic nitrogen that diffuses into the steel surface. Salt bath nitriding uses a molten salt bath containing nitrogen-bearing compounds, while plasma nitriding utilizes a glow discharge to introduce nitrogen. The choice of method depends on factors such as the material to be treated, desired case depth, and production volume.

The nitrided layer is typically very hard and brittle, which can be a disadvantage in some applications. However, the underlying diffusion zone provides a tough substrate, preventing catastrophic failure. Nitriding is particularly effective for components subjected to high surface loads and abrasive wear, such as gears, camshafts, crankshafts, and cutting tools. The process is performed after heat treatment and machining, as it is a relatively low-temperature process that causes minimal distortion.