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Alternative microstructures and their influence on mechanical properties of case-hardened gears

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Abstract

Case hardening is one of the most common heat treatment processes for highly loaded shafts and gears. Due to numerous investigations, a microstructure consisting of martensite with retained austenite (less than 30%) represents a high sustainable microstructure.

Besides this, there are some alternative microstructures compared to the commonly specified martensitic layer. The central question is how they influence the load carrying capacity of gears. A former research project was focused on the mechanical properties of carbonitrided parts by varying the amount of retained austenite. The investigations revealed that a microstructure containing a significantly increased amount of retained austenite can increase the flank load carrying capacity in comparison to standard case carburized gears. The tooth root bending strength was not influenced in a negative way.

A microstructure containing an increased amount of retained austenite can also be reached by gas carburizing. Furthermore, a variant containing bainite in the case hardened layer was adjusted. In an actual research project, the influence on the load carrying capacity of gears made out of the material 20MnCr5 was investigated in experimental test-runs, using spur gears. The results of the variants with alternative microstructure show some differences, e. g. in the hardness profiles, compared to results of standard case hardened gears. In comparison to the case hardened reference, the flank load capacity of the gears with the alternative microstructures showed increased flank load capacity numbers, whereas the tooth root bending fatigue was not influenced in a negative way.

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Funding

The presented work was sponsored by the “Arbeitsgemeinschaft industrieller Forschungsvereinigung e. V. (AiF)”, by funds of the “Bundesministerium für Wirtschaft (BMWi, IGF no. 17903 N)” and with an equity ratio by the “Forschungsvereinigung Antriebstechnik e. V. (FVA)”. The results shown in this work were taken from results of the research project FVA 513 III “Randschichtgefüge”. More detailed information is given in the final report.

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Authors and Affiliations

  1. Gear Research Centre (FZG), Technical University of Munich, Garching, Germany

    Christian Güntner, Thomas Tobie & Karsten Stahl

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  1. Christian Güntner
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  2. Thomas Tobie
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  3. Karsten Stahl
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Correspondence to Christian Güntner.

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Güntner, C., Tobie, T. & Stahl, K. Alternative microstructures and their influence on mechanical properties of case-hardened gears. Forsch Ingenieurwes 81, 245–251 (2017). https://doi.org/10.1007/s10010-017-0222-4

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