Determination of Synergistic Effects of Austempering + Cryogenic Heat Treatments Applied to R260 Rail Steel

In this study, commercially obtained R260 grade rail steels were subjected to cryogenic treatment after isothermal holding at different austempering times. The effects of cryogenic treatment applied to the test specimens for five hours at -70 ℃ after austenitisation at 950 ℃ for five minutes, followed by austempering heat treatment at 350 ℃ in a neutral salt bath with different isothermal holding times (30-180 min) on microstructure, mechanics and crystallography were investigated. When the SEM microstructures of the alloy were examined, it was observed that with increasing isothermal retention times, significant subbainite transformation was completed, and hardnesses increased. While the untreated sample had a hardness value of 269 HV1, the hardness was measured as 607 HV1 with an increase of 226% after 180 min austempering and cryogenic processes. As a result of XRD measurements, it was determined that the amount of intermediate carbides and residual austenite decreased with increasing heat treatment time and improved mechanical properties.