Wear Resistance of Pearlitic Steel Microstructures
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ABSTRACT 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 steels, with similar chemical composition but with different interlamenar spacings, have been examined. Wear test have been conducted under both pure sliding and rolling-sliding 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.
INTRODUCTION The more severe loading conditions of modem railway operations have generated an increase in the wear of rails. Wear occurs primarily in the high rails of curves due to severe wheel-rail contact that involves combined rolling and sliding under contact pressures which may exceed the yield strength of the rail steel. Several authors have studied the rail-wheel contact and associated wear. It has been widely accepted that a fine fully pearlitic microstructure presents better wear resistance than bainitic, martensitic or coarse pearlitic microstructures [1-3]. However there is still a lack of understanding of this behaviour. The work described in this study is primarily to explain the wear behaviour of microstructural features of pearlitic rail steels. It was observed that the plastic deformation produced considerable fracturing and realignment of the hard cementite lamellae 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 contact surface. Pure sliding tests were performed on a pin-on-disc wear machine. Rolling-sliding tests were performed on the Leicester rolling-sliding (LEROS) wear machine. Both machines were designed and built at the University of Leicester, England, UK.
MATERIALS Four fully pearlitic rail steels with similar chemical composition but with different interlamellar spacing and therefore different hardness were tested against a pearlitic wheel steel. All steel samples were taken from normal production. Table 1 shows the chemical 383 Mat. Res. Soc. Symp. Proc. Vol. 355 01995 Materials Research Society
composition and hardness of the steel samples.The hardness variation across the rail head for three of the steels was exploited to select reasonable variation between specimens. For the pure sliding wear tests, pins were machined from the rail heads with their long axis parallel to the rolling direction. Discs were machined from the oute
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