Reaktive Grenzschichten in metallischen Wälzkontakten
Zusammenfassung der Projektergebnisse
The selected case-hardened 20MnCr5 is seen as a kind of reference alloy for gear applications. The two selected alternative alloys, 36NiCrMoV1-5-7 and 45SiCrMo6, are industrially available steels without thermo-chemical treatments, susceptible to work hardening and bearing on solid solution strengthening. All three alloys were fully metallurgically characterized and are presented with information on their mechanical properties, including the recommended heat treatment procedures from their respective manufacturers. The 20MnCr5 was heat treated to yield different residual austenite contents. The tribological profiles under slip-rolling of different materials chosen for the project “Reactive Boundary Layers in Metallic Rolling Contacts” are presented and put more clearly into context with reference to available literature data. Therefore this current work focused on the development of pre-conditioning methods that aim to transfer the running-in process into the last steps of machining and finishing of the tribological surfaces by: a. work hardening and b. tribofilm formation, whereby these two concepts have thus far been effective in reducing friction and wear. It was shown that pre-conditioning through optimized work hardening led to reductions in the coefficients of friction in all pre-conditioned materials at all testing loads. Coefficients of friction at the end of endurance testing showed modest but consistent reductions for case-hardened 20MnCr5. The non-case-hardened alternative alloys showed reductions in coefficients of friction after cold work hardening to 3/4 their original values. This performance is equal to DLC-coated material equivalents. Even more impressive were the observed reductions in profilometric wear coefficients. This was again the case for all pre-conditioned materials at all testing loads. Both case-hardened 20MnCr5 and the non-case-hardened alternative alloys showed strong reductions in wear. In some cases, wear coefficients were reduced to 1/10 through work hardening. Pre-conditioning through the generation of protective chemical tribofilms led to reductions in the coefficients of friction at the end of endurance testing for the alternative alloys. In certain cases, these coefficients of friction were reduced beyond the 3/4 of the original values, previously observed. Friction results for pre-conditioned 20MnCr5 were more mixed, with reductions observed in only some cases, though no significant increases in friction were observed. Wear reductions were achieved for all materials through preconditioned tribofilms. The best results showed wear coefficients from pre-conditioning below 1/10 their original values, i.e. reduced to approximately 5%. The implication of this is that it is indeed possible to replace thermo-chemical treatments, which are time-, energy- and cost-intensive, as well as technically challenging, with a simple and effective pre-conditioning regime to yield equivalent, if not better, friction and wear performance in industrially available steels. The present test programme accumulated approximately 30.000 hours of slip-rolling endurance testing.
Projektbezogene Publikationen (Auswahl)
- Reactive Boundary Layers in Metallic Rolling Contacts, Gordon Research Conference: Tribology, 8 - 13 July, 2012, Waterville, ME, USA
J. Burbank, C. Scholz, M. Woydt
- Reactive Boundary Layers in Metallic Rolling Contacts, Society of Tribologists and Lubrication Engineers: 69th Annual Meeting and Exhibition, 18 - 22 May, 2014, Lake Buena Vista, FL, USA
J. Burbank, M. Woydt
- Reaktive Grenzschichten in metallischen Wälzkontakten, Gesellschaft für Tribologie e.V.: 55. Tribologie-Fachtagung, 22 - 24 September, 2014, Göttingen, Germany
J. Burbank, M. Woydt
- Comparison of slip-rolling behaviour between 20MnCr5 gear steel, 36NiCrMoV1-5-7 hot working tool steel and 45SiCrMo6 spring steel, WEAR, 328-329 (2015) 28–38
J. Burbank, M. Woydt
(Siehe online unter https://doi.org/10.1016/j.wear.2015.01.024)
