The metallurgy of pearlitic rail steel following service in the UK

Abstract

To understand wear and rolling contact fatigue failures of rail steel it is vital that the behaviour of the steel under working loads is well characterised. Rail steel almost always fails while under high levels of compression, and its behaviour under these conditions cannot be investigated by standard materials tests at atmospheric pressure. In this work the characteristics of the near-surface region of one new and four used rails are examined using samples from rails which have been in service use in the UK. The shear strain and hardness variation with depth below the worn rail surfaces are presented, along with micrographs of the samples examined. The results presented here indicate that the used rails had a thin (up to 180 microns) deformed layer at the worn surface where the hardness was approximately 1.5 times the original (bulk) hardness. The depth of strained, hardened material was deeper at the gauge corner than on the rail head. A thin white surface layer (known as the white etching layer) with very high hardness (up to 1040HV) was observed on the surface of one of the used rails. These results have application in the modelling of rail failure by wear and in modelling rolling contact fatigue crack initiation, and can therefore be used to improve rail maintenance planning and risk assessments.