Influence of Gas Nitriding on Rolling Contact Fatigue: Application on Alloyed Steels for Gears

Gears are subjected to Rolling Contact Fatigue (RCF), meaning crack initiations and propagations due to repeated high sthresses at the geartooth surface. The resulting damages, characterized by material flaking known as micropitting and pitting, can generate noises in the gearboxes and in the worse...

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Bibliographic Details
Published in:Tribology & lubrication technology 2015-02, Vol.71 (2), p.20-20
Main Authors: Le, Marion, Ville, Fabrice, Kleber, Xavier, Cavoret, Jérôme, Sainte-Catherine, Marie-Christine, Briancon, Laurence
Format: Magazinearticle
Language:English
Subjects:
Alloys
Cementite
Crack propagation
Experiments
Fatigue failure
Gears
Grain boundaries
Mechanical properties
Metal fatigue
Networks
Precipitates
Precipitation
Propagation
Residual stress
Rolling contact
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Summary:Gears are subjected to Rolling Contact Fatigue (RCF), meaning crack initiations and propagations due to repeated high sthresses at the geartooth surface. The resulting damages, characterized by material flaking known as micropitting and pitting, can generate noises in the gearboxes and in the worse cases, premature tooth flank breakages at the origin of heavy maintenances. To avoid RCF failures, gear manufacturers use gas-nitriding to enhance the superficial mechanical properties. However, treating the 33CrMoV12-9 gear steel introduces a network of cementite precipitates at grain boundaries, which is not taken into account by gear designers. Surface observations of the micropits on the discs were carried out with an optical microscope during the tests. For similar mechanical properties, specimens with thin grain size and cementite networks have better resistance to micropitting, crack propagation, and therefore surface-originated pitting than those with coarser microstructures. Evidences support the statement of an effect of cementite on RCF, as if these precipitates make easier the crack growth.
ISSN:1545-858X