Implementation of the magnetic Barkhausen noise technique for microstructural characterization of rail steel

Abstract

In the present work the feasibility of using Magnetic Barkhausen Noise (MBN) to identify variations in the microstructure of a commercial rail steel has been studied. To achieve this purpose a brand new rail, reference R260 was sectioned to obtain two samples that were subjected to quenching and normalizing heat treatments. The hardness and microstructure of the specimens were evaluated by conventional destructive and nondestructive evaluation. The MBN technique's sensibility to characterize different microstructures was studied, and the results were contrasted with hardness and residual stress measurements. The envelope of MBN signals proved to be useful to detect the presence of martensite at the surface of rail sections, mainly because of the high density of dislocations that is typical of this micro constituent in comparison with pearlite of ferrite. The MBN signals showed strong correlation with the changes in hardness and microstructure of the samples, being the normalized sample the one with the highest amplitude signal of MBN. In contrast, the quenched sample with martensite microstructure had a lower MBN intensity. The results of this work show the potential of MBN for nondestructive evaluation (NDE) of rails in the field, which could improve the capacity of early detection of defects in railway systems.