Aplicação de tratamento de revenido por indução em camada martensítica produzida por retificação em aço de trilho ferroviário

Abstract

WEL (White Etching Layers) consist of martensitic layers of high hardness and brittleness that can be observed on the surface of rails after the grinding process to correct their profiles and remove rolling contact fatigue defects. Its presence can cause the premature formation of cracks, shortening its service life and causing numerous damages to the railway system. The present work studied the application of inductive tempering treatment of WEL produced by grinding on a TR-68 rail, thus evaluating its effectiveness in reversing the hardness and brittleness of WEL layers. Initially, it was studied how to produce WEL by grinding with a flat grinder. At this stage, martensitic layers with a hardness of around 800 HV were obtained. In parallel, the surface heating process was studied in an industrial induction machine with a frequency of 25 kHz and 160 kW power. The results of heating the rail in its supplied condition supported the selection of parameters used in the inductive tempering process. As this type of equipment is most commonly used for the rapid austenitization of steel, it is important to find parameters that allow the maintenance of the original microstructure of the pearlitic steel. The last step involved applying inductive tempering to the ground sample with the thickest WEL formed in the grinding operation. At this stage, the induction tempering reduced martensite hardness to an average of 387 HV. This result points to the feasibility of inductive tempering treatment to treat ground railway tracks and indicates the possibility of correcting excessively high surface hardness.