Divorced Eutectoid on Heat-Affected Zone of Welded Pearlitic Rails

Abstract

Welds in heavy haul rails are usually associated with accelerated wear and are a common source of defects, justifying a careful study of their characteristics. Heat-affected zones usually present hardness loss, corresponding to a spheroidized cementite region. The literature acknowledges that this is a consequence of the welding heat input but without further explanations. However, in order to control this loss, the mechanisms of microstructural changes need to be fully understood. This paper clarifies the mechanisms for the formation of the spheroidized region in the heat-affected zone of pearlitic welded rails, using as an example a flash butt-welded rail. The weld surroundings had its microstructure characterized and the correspondent hardness measured. Those microstructures were then simulated using a quenching dilatometer for three different rails. The results make it clear that the spheroidized microstructure is a consequence of the divorced eutectoid transformation, which is at a maximum at the end of the eutectoid gap.