Improving strength of rail steel and investigation of main mechanical and microstructural properties

Rail transportation systems in Turkey are constantly developing as a result of the increase of demand in high-speed trains and heavy-loading transportation. As there are high contact pressures between the rail and the wheel, the components wear out rapidly according to the higher loads. To prevent these, it is desired to develop critical parts of rail systems with high wear resistance and strength values to extend their service life. For this purpose, methods such as increasing the carbon content in the rail composition, reducing the space between the lamellae in the pearlitic microstructure, and hardening the head of the rails have been studied. However, conducted studies have reached saturation and alternative microstructures such as bainitic microstructures have begun to be investigated all over the world. In this study, it is aimed to obtain a bainitic microstructure by performing isothermal transformation in high carbon rail steel, which is frequently used in high-speed railway lines, instead of developing a new alloy. The combined high tensile strength and toughness by changing the microstructure is an important parameter to extend the service life of the components. To obtain different bainitic microstructures, various heat treatment processes conducted to the extracted specimens. In order to minimize the number of experiments, Taguchi experimental design method was used. After heat treatment processes, metallographic examination, hardness, impact, and tensile tests were carried out to clarify mechanical characteristics of the materials. In Taguchi method to determine the S/N ratios, obtained yield, and ultimate tensile stresses, hardness values, impact test results are used as an input parameter. In conclusion developed rail steels show improved mechanical properties than the conventional ones and the optimum parameters for heat treatment processes are clarified with the conducted.