A Study of White Etching Areas in an Annealed 52100 Steel through High Pressure Torsion Processes

INTRODUCTION White Structure Flaking (WSF) is a type of surface damage responsible for some early failures in wind turbine gearbox bearings. WSF has been associated with microstructural changes registered close to the damaged surface that appear to be white after etching, hence the name White Etching Areas (WEAs). Local hydrogen liberation from lubricants [2] and adiabatic shear bands [3] have been related to WEAs development. Moreover, it is believed that local plastic deformation promoted by shear stress occurs during WEA formation [4]. WEAs can be observed in other mechanical applications such as rail tracks [5], hard turning machining [6] or steel discs processed by High Pressure Torsion (HPT) [7]. HPT, as a Severe Plastic Deformation process (SPD), produces extremely refined grain sizes through a combination of shear and compressive stresses. HPT allows a detailed record of the microstructure evolution after different strains to be determined, although it is limited by the final hardness admissible in the samples compared to the dies used to deform the workpieces. This study shows the initial results on the use of HPT to create WEAs in an annealed AISI 52100 bearing steel and their microstructural characterization.