Study of the influence of steel chemical and structural heterogeneity on fracture toughness of railway wheels

The effect of structural and chemical heterogeneity of steel on the fracture toughness of the railway wheel was studied. The formation of a heterogeneous microstructure is associated with the presence of dendritic liquation of elements in the metal structure. The metal of the samples, which is characterized by the lower value of fracture toughness, in addition to sorbitol-like pearlite with excess ferrite on the boundaries of the “former” austenite grains, has acicular morphology (bainite structures) of the structure. They were concentrated, mainly, in microvolumes enriched with manganese. The acicular structure in the samples with high values of fracture toughness was not observed. The chemical composition of the sample’s structural component was studied. Areas with an acicular structure had an increased content of manganese compared to pearlite and ferrite located nearby. It was proved that liquation phenomena in the metal of the railway wheel rim with increased content of alloying elements (carbon, silicon, and manganese) were the CAUSE for the formation of the metal heterogeneous microstructure after thermal products hardening, and the presence of areas with bainite structures negatively affects the fracture toughness of the railway wheel rim metal.