Comparison of high-cycle fatigue properties of continuous casting and mould casting axle steels

It is a challenge to ensure that the mechanical properties of continuous casting axle steel are comparable to those of mould casting axle steel. Thus, the high-cycle fatigue fracture behavior of high-speed railway axle steels manufactured by continuous casting and mould casting was studied by using rotating-bending fatigue test and fatigue crack growth (FCG) test. The results showed that both the tensile strength and fatigue strength of the trial continuous cast steel was lower than those of the mould cast steel, while the fatigue crack growth rate of the former was slightly higher than that of the latter. SEM analysis of all the fatigue fractured specimens revealed that most of them initiated from specimen surface matrix. Both the average prior austenite grain size and cementite size of the continuous cast steel were slightly larger than those of the mould cast steel, although both of the microstructures were high-temperature tempered martensite. Further analyses of both metallographic rating and the statistics of extremes methods of non-metallic inclusions showed that the inclusion size of the continuous cast steel was notably larger than that of the mould cast steel. Therefore, in order to replace the mould cast process with the continuous casting process, it is necessary to further optimize the chemical composition, continuous casting process and heat treatment parameters to obtain excellent metallurgical quality and structural properties.