EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The cooling rate during the martensitic transformation has been shown to have a strong impact on the fatigue performance of case-hardened steels with differences of up to 20 % [1]. The mechanism for this increase is not fully understood. To clarify the underlying mechanism, the impact of cooling rates on the martensitic transformation in two high carbon steels (0.54 and 0.74 w% C) was studied. In-situ high energy x-ray diffraction (HEXRD) during dilatometer tests were conducted to study the transformation kinetics and the martensite tetragonality. A clear impact of the cooling rate on the tetragonality of martensite was found for both carbon contents. These results were supported by the analysis of the final microstructure by electron microscopy, focusing on the local tetragonality of martensite as determined by electron backscatter diffraction (EBSD) using the projective transformation approach by Winkelmann et al [2,3]. The combination of results from in-situ HEXRD with dilatometer tests and microstructure analysis will here be presented.

[1] Fahlkrans, Johan, et al. "Gas quench rate after low pressure carburizing and its influence on fatigue properties of gears." HTM Journal of Heat Treatment and Materials 68.6 (2013): 239-245.
[2] Winkelmann, Aimo, et al. "Mapping of local lattice parameter ratios by projective Kikuchi pattern matching." Physical Review Materials 2.12 (2018): 123803.
[3] Nolze, Gert, et al. "Tetragonality mapping of martensite in a high-carbon steel by EBSD." arXiv preprint arXiv:2011.10275 (2020).