Effects of Quenching Temperature and Cooling Rate on the Microstructure and Mechanical Properties of U75V Rail Steel

In order to investigate the effects of quenching temperature and cooling rate on the microstructure and mechanical properties of the U75V rail steel, Gleeble-3500 thermal simulator and tensile tester were applied and the dynamic CCT curves were obtained. The results show that low quenching temperature of 750 °C narrows the range of the cooling rate of only pearlite transformation, and the pearlite interlamellar spacing decreases with an increase in the cooling rate or the quenching temperature in this range. The minimum value of the pearlite interlamellar spacing is found to be 0.101 μm. At three quenching temperatures of 810, 780, and 750 °C, the microhardness increases with an increase in the cooling rate. In addition, the starting transformation temperature from austenite to pearlite does not exceed 700 °C, and the end temperature does not drop below 500 °C. The mechanical properties including yield strength, tensile strength, and total elongation of the selected specimens are improved as the pearlite interlamellar spacing decreases and meet the requirements. For the field production of the U75V rail steel, higher quenching temperature and a cooling rate of 3–5 °C/s are the best choices.