Nitriding properties required:
Wear resistance, anti-seizure properties, corrosion resistance, fatigue resistance.
Computer-regulated nitriding has made great headway in the automotive branch often replacing traditional gas nitriding, salt bath and ion (also known as plasma) nitriding, as well as carburizing. A number of automotive manufacturers are specifying surface properties that would be difficult or impossible to achieve without the use of controlled nitriding methods. Besides, close tolerances specified for a number of critical components call for, among other factors, close temperature control. The Nitrex series of nitriding furnaces is capable of achieving temperature uniformity within ± 3° C throughout the retort.
Case study:
In non-alloyed steels and cast irons, Nitreg® nitriding produces practically only a compound layer composed of γ‘ or ε+γ‘ nitrides. The su
rface hardness is not very high (HV1 = 320 – 380 for mild steel, 400 – 580 for cast iron), but sufficient to improve wear resistance considerably. At the same time, in conditions of insufficient lubrication, the resistance to galling, or seizure, is strongly improved. A typical example is a clutch hub made of low carbon steel. The requirement is a 6 μm minimum compound layer, and passing a specified long-term wear test. In the first approach, by one supplier, plasma nitriding was employed. However, the required case depth uniformity over the whole profile of the spline teeth could not be met. Nitreg® proved to be superior with respect to white layer requirements and the layer itself was found to be more uniform, especially in the fillets. After the test involving 1500 load cycles, the Nitreg® nitrided surface was still free of any signs of wear.
