In the case of employing brake discs as a key component of mechanical brake equipment, the initiation of thermal cracking owing to repetitive thermal shock generated during braking may potentially lead to higher maintenance costs, worsened braking performance, and greater risk of railway accidents. The purpose of this study is to gain basic data to facilitate application of compacted vermicular (C. V.) graphite cast iron to brake discs in order to obtain high thermal crack resistance and improved lifetime. To this end, this study developed three types of C. V. graphite cast iron with differing content of key elements, including Ni, Cr, and Mo. Each test specimen underwent numerous tests for evaluation of materials characteristics, and the results were compared with those obtained for existing materials. The test results show that the thermal fatigue lifetime of material C is nearly double that of the conventional material. This demonstrates the suitability of material C as a material for brake discs in mid-to high-speed railway vehicles.

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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 φ 20 × 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.

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