The effect of progressive minor spheroidization on the dry-wear rates of a standard carbon and a Cr-Mo alloy rail steel

Abstract

Non-lubricated, laboratory wear tests were done on two partially spheroidized eutectoid rail steels to determine the effects of increasing fragmentation of both thick and thin lamellae on dry-wear properties. The tests simulated heavy-duty stress conditions on the outer (high) rail of sharply curved railway track. The first steel, of Standard carbon composition, was heat treated in both the hot-rolled (thick cementite lamellae) and oil-quenched (fine cementite lamellae) conditions, and significantly lower rates were obtained for partially spheroidized hot-rolled oil-quenched specimens of similar hardness. The wear rates of the partially spheroidized second steel, a Cr-Mo alloy, corresponded very closely to those indicated by the wear rate vs. hardness curve of the oil-quenched specimens. Thus, wear rates of partially spheroidized microstructures are not uniquely defined by initial hardness, and are indeed better defined by the hardness of the worn surface. Image analysis observations suggest that the mean ferrite path is also an influential parameter in controlling the wear rate, irrespective of initial lamellar thickness. This could also explain why pearlite of hardness 38 HRC has a superior dry-wear resistance to harder upper bainites and tempered martensites.