Influence of the microstructure on the rolling contact fatigue of rail steel: Spheroidized pearlite and fully pearlitic microstructure analysis

Twin-disc tests were carried out between two discs of rail steel (fully pearlitic and spheroidized microstructures) to investigate the effect of the flash-butt welded rail HAZ microstructure. The spheroidized cementite microstructure was obtained by heat-treating simulating the HAZ softer region. Ten tests were performed for each condition, considering maximum Hertz pressure of 1100 MPa, rotation speed of 400 rpm and slip of 0% and 1%. The results showed that the spheroidized cementite discs (with less hardness) presented more significant surface hardness due to deformation, more clearly for the tests carried out with 1% slip. This factor led to a cracking process for both heat-treated discs and counter-discs with a completely pearlitic microstructure. The number of cycles for the beginning of contact fatigue between the specimens compared to the untreated pairs proved to be statistically equal in the tests carried out with 1% slip. In tests without slip, however, this phenomenon did not occur, as the spheroidized discs showed a significant decrease in the number of cycles before the beginning of contact fatigue. Plastic deformation was observed around the fatigue cracks (even in the spheroidized microstructure's discs), and the presence of inclusions influenced the cracking process.