Experimental study on the influence of thermal loading caused by shoe braking on microstructure and mechanical properties of railway wheels

This study aimed to investigate the impact of thermal loading resulting from shoe braking on ER8, SUPERLOS® and ER-TEN railway wheels. To assess the effects of exposure to temperatures ranging from 700 °C to 970 °C, a series of tests, including hardness, tensile, toughness, fatigue crack growth rate tests, and microstructural analysis, were conducted. Specimens were collected from both new wheels and wheels subjected to heat treatments to replicate the microstructural changes induced by shoe braking. The results revealed that the heat treatment at 700 °C caused a decrease in the hardness, yield strength, and ultimate tensile strength of the steels due to the formation of globular pearlite. However, a reversal of this trend was observed after heat treatments at 750 °C and 970 °C. Nonetheless, these properties remained lower than those of the un-treated condition, primarily due to the presence of globular pearlite. Regarding fracture toughness, ER8 and SUPERLOS® generally exhibited a decrease after the heat treatments, while ER-TEN showed an increase after heat treatments at 750 °C and 970 °C. Additionally, a slight increase in the crack growth threshold and sub-critical crack growth rate was observed after the heat treatments in all steels.