Effects of Heating Rate on Microstructure and Fracture Toughness of Railway Wheel Steel

The microstructure and fracture toughness K IC (or K Q) of railway wheel steel with 0.53 wt pct C were studied under various heating rates. The effects of the heating rate on the grain size and the relation between the grain size and the fracture toughness were discussed. The results show that rapid heating not only refines the grains but can also result in more homogeneous grains. The cleavage fracture toughness strongly relates to the grains with larger size. It can be observed that under different heating rates, the fracture toughness K Q increases with decreasing average diameter of the top 5 pct grains D 5. K Q (MPa m1/2) = 194.3–29.8 ln(D 5) when D 5 is in the range of 30 to 73 μm. This result can be interpreted by the cleavage fracture critical event, which is grain-sized crack propagation controlled.