MICROSTRUCTURE AND WEAR-RESISTANCE OF PEARLITIC RAIL STEELS

Despite competition from bainitic and martensitic steels, pearlitic microstructures remain dominant for railway track. Techniques developed over recent years have progressively refined the interlamellar spacing to produce harder, more wear-resistant pearlitic steels. This study aims to explain the mechanisms for the wear performance by observing how the microstructure adapts to the wear loading. Four pearlitic rail steels, with similar chemical compositions but with different interlamellar spacings, have been examined. Wear tests have been performed under both pure sliding and rolling-sliding conditions, the latter designed to simulate track conditions. The worn surfaces and the plastically deformed subsurface regions have been examined by optical metallography and scanning electron microscopy. It was observed that the plastic deformation produced considerable fracturing and realignment of the hard cementite lamellae. The softer ferrite matrix was severely deformed, allowing a reduction in the interlamellar spacing on approaching the worn surface. The effect of these realignments on the surface was to present an increased area fraction of hard cementite lamellae on planes parallel to the surface. Thinner cementite lamellae, associated with low interlamellar spacings, were easier to bend before fracturing. It is believed that shear ductility plays an important role in the period of time that any particular volume of material remains at the surface before becoming a loose particle.