Nitrocarburizing and High Temperature Nitriding of Steels in Bearing Applications
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Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Publicerad
2012
Författare
Flodström, Isabella
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
A group of steels used in bearing applications were subjected to three different heat treatments – gaseous ferritic and austenitic nitrocarburizing at 580 °C and 620 °C respectively and solution nitriding at 1100 °C. The aim was to improve wear and corrosion resistance of the steels and to evaluate for which steels the processes are most suitable. Both nitrocarburizing processes resulted in a thin compound layer with a hardness in the range of 800–1000 HV for all investigated steels. The hardest and deepest diffusion zones were obtained on the steels with the lowest carbon content. The best properties for bearing applications were obtained by austenitic nitrocarburizing which resulted in a thicker compound layer and a deeper nitrocarburizing depth than ferritic nitrocarburizing. Another advantage of austenitic nitrocarburizing is that it produces an austenitic layer below the compound layer. By tempering at 300 °C this layer can be transformed to a fine structure with hardness above 1000 HV. It was also established that both ferritic and austenitic nitrocarburizing improve corrosion resistance in neutral salt spray significantly. Solution nitriding was applied to one group of martensitic stainless steels and one group of heat resistant steels. All the steels were found to contain nitrogen after the treatment. Solution nitriding resulted in high hardness throughout the stainless steels, but also in grain boundary precipitates. The problem increased with increasing carbon content of the steel. Of the heat resistant steels, only M50 achieved the desired hardness.
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Ämne/nyckelord
Ytbehandlingsteknik , Konstruktionsmaterial , Materialvetenskap , Produktion , Surface engineering , Construction materials , Materials Science , Production