Abstract
Nitriding is a common heat treatment process for highly loaded gears. A very hard compound layer with a thickness of a few microns is produced at the surface of the gear. In the underlying material areas, a diffusion layer with nitride precipitations is formed. This publication summarizes the state of knowledge of nitrided gears and gives an overview of the current state of research in the field of nitrided gears. It can be concluded that a high load carrying capacity of nitrided gears is dependent on an adequate NHD and a stable compound layer. However, due to the increased surface roughness after nitriding, the risk of micropitting increases, too. Therefore, it may be favourable to grind the gears after nitriding. Ground gears also can provide a high load carrying capacity, but it must be taken into account that the wear performance will decrease significantly, since it is mainly influenced by the compound layer. In addition, nitrided gears usually show a high sensitivity against local load peaks. Beyond creating a stable compound the layer, the realization of a sufficient nitriding hardness depth with larger gear sizes is a focus in the current field of research.
Highlights
Nitriding is – besides case hardening – a common heat treatment process for highly loaded gears
Similar to the wear tests, the nitrided gears performed significantly better in the micropitting test, compared to the case hardened gears
For many applications, nitrided gears are not machined after nitriding, so the gears must be prepared appropriately in order to achieve a high load carrying capacity
Summary
Nitriding is – besides case hardening – a common heat treatment process for highly loaded gears. Compared to case hardened gears, where a lot of research has been undertaken in the last years [2,3,4,5,6,7], the knowledge on the load carrying capacity of nitrided gears is rather limited. Within the German Drive Train Association (Forschungsvereinigung Antriebstechnik e.V.), the advantages, characteristics and possible shortcomings of nitrided gears were investigated in several research projects [1, 8,9,10,11] by means of experimental tests on the tooth flank as well as on the tooth root load carrying capacity. Centre distance Normal module Face width Number of teeth Normal pressure angle Helix Angle Used in Symbol [Unit] a [mm] mn [mm] b [mm] z1/z2 [-]
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