The effects of cryogenic processing on the wear resistance of grey cast iron brake discs

Cryogenic processing has the potential to significantly increase longevity in many automotive components, where friction and wear are major factors in their operation and eventual failure. Cryogenic treatment affects the whole cross-section of the component and is inexpensive compared to other treatment processes. Whilst numerous studies have been conducted on cryogenic treatment of tool steels since the 1970’s, in many cases showing significant improvements in wear resistance, only minimal work has been done in cast irons. In this study the effects of deep cryogenic treatment (93 K) on the wear resistance of grey cast iron (SAE J431 G10) brake rotors was assessed and related to changes in their microstructure using optical microscopy. A comparative analysis using pin-on-disc testing was carried out on brake discs having undergone deep cryogenic treatment and those that had not, using chrome steel balls as the wear inducing body. The results indicate an improvement in the wear rate of grey cast iron of 9.1–81.4% due to deep cryogenic treatment where significant wear has occurred, although there was no significant change in the bulk hardness, matrix hardness or in the microstructure of the material under optical observation.