Thermal fatigue evaluation of cast iron discs for railway vehicles

Thermal fatigue of brake discs for railway vehicles has been a troublesome problem since the advent of disc brake. To develop cast-iron brake discs with high heat resistance to thermal shock loading, three candidate materials with different components were developed. Main components of the cast irons are Fe, C, Si, Mn, Ni, Cr, Mo, Cu and Al. Mechanical and thermal properties were measured. Then thermal fatigue tests were carried out by a thermal fatigue test equipment developed by the authors. The possible temperature range of the equipment is 20∼1500 °C. Cylindrical solid specimens ϕ20×80 mm were heated by an induction coil and cooled in water. At an interval of 20∼30 thermal cycles, the surfaces of the specimens were examined with an optical microscope to check thermal cracks. To quantify the total length of cracks an image analyzing program that can measure the length of cracks from micrographs was developed. It was found the fatigue lifetime of cast iron can be elongated by regulating composition and metallurgical structures.