Development of Ceramic Reinforced High Phosphorus Cast Iron Brake Shoe

摘要

To develop the high quality brake shoe for railroad applications, ceramic reinforced high phosphorus cast iron brake shoes were prepared, and their structures and properties were investigated. Porous ceramic preforms made of SiC were inserted in sand mold cavities, and melts of high P cast iron containing 3.3 mass%C, 1.7 mass%Si, 1.5 mass%Mn, 0.3 to 1.2 mass%P, 0.4 mass%Cr, 0.2 to 0.1 mass%V, 0 to 0.05 mass%B were cast at an atmospheric pressure. Pores of ceramic preforms were almost completely filled by each melt, because the size of pores was rather large, about 2 to 6 mm. The microstructure of each cast iron was composed of steadite, cementite and flaky graphite distributed in pearlitic matrix. The amount of steadite increased with the increase in P content of cast iron, the amount of cementite also increased with the addition of minute amounts of B and they were distributed among cellular or dendritic γ -graphite eutectic. The wear resistance and the braking ability of each specimen were evaluated by using an original braking test machine and a full-size braking test machine. The full-size braking test almost showed the same result as the original braking test. Properties of cast iron brake shoe improved with additions of about 0.6 mass%P and 0.05 mass%B. Furthermore, that properties at an initial braking speed of above 95 km/h effectively improved with the reinforcement by ceramic preforms. Properties of cast iron brake shoe enhanced with the increase in hard phases, viz., steadite and cementite distributed in pearlitic matrix. However the contact surface was heated over A_1 temperature at the speed of over 95 km/h and pearlitic matrix containing hard phases was softened, which reduced that properties. On the other hand, the ceramic preform was harder than hard phases, and it was more excellent in the heat resistance than pearlitic matrix. Therefore, ceramic reinforced cast iron brake shoes showed higher properties at the speed of over 95 km/h.