MICROSTRUCTURE AND WEAR-RESISTANCE OF PEARLITIC RAIL STEELS

Despite competition from bainitic and martensitic steels, pearlitic mi crostructures 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 a ims to explain the mechanisms for the wear performance by observing ho w the microstructure adapts to the wear loading. Four pearlitic rail s teels, with similar chemical compositions but with different interlame llar spacings, have been examined. Wear tests have been performed unde r both pure sliding and rolling-sliding conditions, the latter designe d to simulate track conditions. The worn surfaces and the plastically deformed subsurface regions have been examined by optical metallograph y and scanning electron microscopy. It was observed that the plastic d eformation produced considerable fracturing and realignment of the har d 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 p resent 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.