The wear resistance and worn metallography of pearlite,bainite and tempered martensite rail steel microstructures of high hardness

In order to find out whether it is worthwhile to produce premium rail steels harder than 36–39 HRC and to discover the best microstructure for wear-resistant rail an experimental Cr-Mo alloy rail steel was heat treated to pearlite, bainite and tempered martensite. Each microstructure was prepared at hardness levels of 38, 42 and 45 HRC. These were tested in a dual disk-on-disk machine that closely simulates wheel-rail contact in curves at 1/10 scale. Wear rates were established for dry, grease-sand and pure grease environments. Dry wear rates decreased significantly with increasing hardness in high rails with tempered martensite or bainite microstructures but were almost independent of hardness for pearlite in the range tested. Lubrication reduced the wear rates by up to two orders of magnitude for all microstructures. It is concluded that pearlite gives the best dry wear performance, and there is no advantage in increasing the hardness beyond 38–40 HRC. The superior performance of pearlite in dry wear appears to be due to a very pronounced work hardening near the wearing surface. Electron microscopy reveals a marked refinement in the pearlite microstructure near the wearing surface, and this may explain the high work hardening observed.