The Performance and Microstructure Research on Air-cooling Bainitic Steels for Rails

The paper introduces the mechanical properties and microstructure of two bainitic steels which we have designed for switch rails. All steels are made in vacuum induction furnace to produce about 30 kg ingots. After being forged with air cooling, specimen is made for all experiments. The results of tensile and Charpy U notch (CUN) impact test show that the two bainitic steels have higher strength and CUN toughness than that of current premium rail steels. The UTS varies between 1 280 MPa and 1 337 MPa, and the good value for the elongation at fracture, 16%, is obtained. The value of CUN toughness is 20 J·cm -2 and 46 J·cm -2 respectively. The fracture toughness ( K IC ) of the second bainitic steel at -20℃ is also noteworthy, which is up to 42 MPa m1/2. The transmission electron micrograph shows that microstructures of the two bainitic steels consist of ferrite laths and ″thin film″ type of retained austenite. Meanwhile, the bainitic basic units are distinguished in ferrite laths.In the end, the conclusion says that the two kinds of bainitic steel can be used to make switch rails.