5-8 September 2022
Wyndham Grand Salzburg Conference Center
Europe/Vienna timezone

Contact fatigue in carbonitrided steels and the influence of retained austenite

6 Sep 2022, 15:45
25m
Room 2

Room 2

Oral Presentation Thermochemical treatment (carburizing, carbonitriding, nitrocarburizing, nitriding) SURFACE ENGINEERING

Speaker

Emil STÅLNACKE (Swerim AB)

Description

Carbonitriding has shown great potential to further increase service life of components exposed to contact fatigue. In this project, the rolling contact fatigue properties of case hardened and carbonitrided 18CrNiMo7-6 were investigated. The aim was to qualitatively assess the impact of retained austenite on micropitting damage to further understand the underlying mechanisms of the carbonitriding process. In regular case hardening, it was found that high retained austenite reduces the degree of micropitting damages significantly, due to the mechanical-induced transformation of austenite into martensite. This was also found in in carbonitrided samples, but the results were further influenced by precipitation of chromium carbonitrides. These precipitate as nitrogen disassociates from the ammonia in the carbonitriding atmosphere into the steel. Indication were found that the size of these precipitates controls the impact they have on the resulting fatigue properties. The resulting hypothesis is that for lower ammonia content, <3%, the precipitates remain small (<10 μm) and provide a dispersion hardening effect with excellent enhancement of performance. On the other hand, at higher ammonia atmosphere contents, >5%, more of these precipitates grow large (>100 μm), thus providing sources for crack initiation and slightly reduce the fatigue strength compared to if they remained small.

Speaker Country Sverige
Register for the Tom Bell Young Author Award (TBYAA)? No

Primary author

Emil STÅLNACKE (Swerim AB)

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