Innovative analysis of Luders band behaviour in X80 pipeline steel

In this study, the influence of Luders bands, which are frequently observed after the pipe coating process, is investigated. Stratified tensile test specimens, machined from different locations across the thickness of an X80 line pipe, were tested. The Luders bands were observed by using a digital image correlation (DIC) in the specimen machined from halfway across the pipe wall thickness. The specimens from the selected locations related to the Luders bands were studied and compared by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and standard mechanical testing. The results display that the microstructure, lattice constant, dislocation density and Schmid factors change when the Luders bands pass through the tensile test specimen, which brings about the difference in mechanical properties. The study of the influence of Luders bands on microstructures and mechanical properties enables better understanding of the strain-ageing mechanism.