The Effect of Mo on the Microstructure and Mechanical Properties of High-Manganese Railway Frog Steel Produced with the Thermal Mechanical Control Process

The aim of this study is to investigate the influence of Mo on the microstructure and mechanical properties of railway frog steel. To address the challenges of a coarse microstructure and alloy element segregation caused by the current casting method of railway frog steel, the application of thermal mechanical control process (TMCP) technology can achieve a uniform and refined microstructure and stable mechanical properties, which is progress for the development of high-manganese railway frog steel. The TMCP of four experimental steels with varying Mo contents of 0.02~1.01 wt.% was simulated using a Gleeble 3500. The mechanical properties were tested, and the microstructure of each sample was characterized. A single austenite formed in each Mo-containing steel. With the increased Mo content, the grain boundary carbides decreased due to the formation of carbides within the grains, and the austenite and twin sizes were refined. Moreover, grain boundary strengthening and dislocation strengthening increased, while solid solution strengthening and precipitation strengthening had little effect, leading to an increase in the final yield strength. The contribution of dislocation strengthening to the yield strength was 51~56%, indicating that dislocation strengthening was the most significant strengthening method in the high-manganese railway frog steel produced using the TMCP. The impact energy showed a trend of first increasing and then decreasing, and the impact energy reached the highest point when the Mo content was 0.30 wt.%. In addition, the mechanisms governing the effect of increased Si in controlling the final microstructure and mechanical properties are discussed.