Wear resistance of pearlitic rail steels.

Modern railway transportation has imposed severe work conditions on the track. Wear of rails has become an important and costly phenomenon. Recent developments in the manufacture of rail steels have refined the interlamellar spacing to produce harder and more wear resistant pearlitic steels. Despite better nominal properties shown by bainitic and martensitic steels, pearlitic steels have shown lower wear rates. The aim of this study is to explain the mechanisms for the wear performance by observing how the lamellar pearlitic microstructure adapts to the wear loading. Four pearlitic rail steels, with similar chemical composition but with different hardnesses and 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 effect of these realignments on the surface was to present an increased area fraction of hard cementite lamellae to the surface. Thinner cementite lamellae, associated with low interlamellar spacings, were easier to blend before fracturing. A relationship between the bulk hardness (HV) and the reciprocal root of the mean true interlamellar spacing has been proposed for fully pearlitic steels. Wear rates were found to be a function of the original bulk hardness, rather than the increased hardness of the plastically deformed layers. Also, wear rates were reduced as hardness increased by reducing the interlamellar spacing. Pure sliding and rolling-sliding wear tests ranked the four steels correctly. Furthermore, qualitative comparisons between experimental wear rates and those obtained in-track trials show the same scale in reduction of wear with increased hardness.