Cryogenic Treatment of SG Iron for Disc Brake Application

Cryogenic treatment has a good potential to significantly increase the service life of automotive components, where friction and wear are the major factors in their operation leading to failure. Cryogenic treatment changes the surface as well as the core properties of the component in comparison with other treatments. It has significant improvement in wear and toughness. Numerous studies have been conducted on cryogenic treatment of steels and tool steels showing significant improvements in wear resistance, only minimal work has been done in cast irons. In this study, the effect of cryogenic treatment on the wear resistance, hardness, tensile strength, toughness and microstructure of spheroidal graphite iron was assessed. The deep cryogenic treatment was carried out at 87K for 12h and annealed in the chamber itself. The samples were tempered at 473K for 1 h. The hardness, toughness and tensile strength of base material, cryotreated and cryotreated tempered samples were measured using Rockwell hardness, Impact testing machine and Universal testing machine respectively. Wear studies were performed using pin-on-disc wear testing machine with EN 31 steel as the disc. There was a significant increase in hardness, toughness and tensile strength due to cryogenic treatment. The results indicate an improvement in the wear rate of SG iron of 6.1-38.2% due to cryogenic treatment where significant wear has occurred and further improved to 52.9% due to tempering after cryogenic treatment. This finds suitable for disc brake application in automobiles.