Thermal Modification to Increase the Strength of Carbonitrided Surface Layers with a High Retained Austenite Content by Tempering
Research Topic
| Short Title | CNThermMod |
| Start of Project | Q4/2024 |
| Funding | FVA-Nr. 513/VI, IGF-Nr. 01IF23451N Federal Ministry for Economic Affairs and Climate Action, BMWK |
| Project Partner | Leibniz-Institut für Werkstofforientierte Technologien, IWT |
| Contact | Dr.-Ing. T. Tobie |
Project Description
In recent years, carbonitriding has been established as a highly effective process for producing case-hardened gears with the strongest possible surface layer strengths. The process involves the simultaneous modification of the chemical composition of the surface layer with carbon and nitrogen, resulting in a significantly higher retained austenite content after hardening. This is due to the high carbon and nitrogen contents in the surface area, which significantly lower the martensite start temperature of the steel. Concurrently, the formation of carbide, carbonitride and nitride precipitates in the surface layer influences the strength properties of the components.
Carbonitriding can be used to produce variants with varying degrees of carbide, carbonitride and nitride precipitation in the surface layer, although the formation and adjustment of these mixed microstructures is not yet fully understood.
Investigations carried out as part of research project FVA 513 III (IGF 17903 N) [Sad17] on gears tempered at high temperatures showed, on the basis of a few spot tests, comparatively high pitting resistance values and improved grindability. However, no systematic investigations have been carried out to explain this phenomenon from a materials science point of view. Furthermore, no research has been carried out to determine the optimum tempering temperature and time to achieve optimum gear load capacity.
The resulting need for research with a focus on the systematic investigation of gear load capacity and the derivation of optimum tempering conditions for carbonitrided gears will be addressed by this research project. The scientific, technical and economic benefit of this research project is the utilization of increased gear load capacity with the simultaneous benefits of hard finishing.
Literature
[Sad17] Saddei, P.; Schurer, S.; Güntner, C.: Randschichtgefüge - Alternative mehrphasige Randschichtgefüge beim Einsatzhärten zur Steigerung der Festigkeitseigenschaften von verzahnten Getriebebauteilen. Abschlussbericht; Forschungsvorhaben Nr. 513 III. Forschungsvereinigung Antriebstechnik e.V. (FVA), Frankfurt (2017).