Microstructural Changes of Cast Iron Rotor Surfaces and Their Effects on Brake Performance and Wear Resistance

Rotor surface temperatures reaching above 700°C are not unusual for heavy-duty disc brakes in service, which are used in both heavy vehicles and high-performance passenger cars.

Brake rotors are conventionally composed of pearlitic gray cast iron. The over 700°C temperatures experienced in heavy-duty service cause microstructural changes in which the surface rotor material is transformed from pearl-itic to spheroidic cast iron. The objective of this study was to determine the effect of this transformation of rotor metallurgy on brake friction and wear. In this study, the normal and spheroidized rotors are coupled to a common semimetallic friction material, and the respective brake pairs are then evaluated for possible difference in friction and wear properties. Tests of rotors so transformed, either by heat treatment or by temperature cycling on a brake dynamometer showed no significant change in braking performance, but an increase of 15% in pad wear and a doubling of rotor wear over the untransformed rotors.