Wear and Shelling Behavior in Pearlitic and Bainitic Rail Steels with Various Tensile Strengths

Abstract

Resistance to wear and surface damaging (shelling) in pearlitic and bainitic steel rails with various tensile strengths ranging from 850 to 1400 MPa were examined by wear and rotating contact fatigue tests. The pearlitic steels showed better wear resistance than the bainitic steels for all the test conditions tested, although the amount of wear varied according to the strength range and contact pressure used in the wear tests. The wear behavior of the pearlitic steels was roughly described by a Holm's-type equation (W=kP/H; where W: amount of wear, P: contact pressure, H: hardness and k: constant), while that of the bainitic steels showed complex dependencies on the strength and contact pressure. The bainitic steels, however, showed superior damage resistance to the pearlitic steels for all the test conditions tested: at a fixed tensile strength of 850 MPa, significant shelling was observed in the pearlitic steel after 200 h testing, while no damage was detected in the bainitic steel even after 500 h. The resistance to shelling of the pearlitic steels was improved by strengthening, but the opposite trend was obtained in the bainitic steels. These results were analyzed taking work hardening on the sample surface into consideration. Additionally, the formation behavior of the "white phase", which was the martensite phase formed on the rail-head surface by friction between rails and wheels, was compared in pearlitic and bainitic steels and discussed metallurgically.