Innovative analysis of Luders band behaviour in X80 pipeline steel

Abstract

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. ABSTRACTIn 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.

Effects of hydrogen on the mechanical response of X80 pipeline steel subject to high strain rate tensile tests

“…The critical dislocation velocity v cr can be determined from Equation according to Tien et al, ie, where E bd denotes the binding enthalpy of the dislocation with hydrogen and “|b|” is the magnitude of the Burgers vector. The mean dislocation velocity in the tensile tests can be calculated from Orowan's relationship where v D is the dislocation velocity and ρ mob is the density of mobile dislocations . Hydrogen requires at least 750 seconds to diffuse through an X80 sheet of thickness 2 mm.…”

“…where v D is the dislocation velocity and ρ mob is the density of mobile dislocations. 51 Hydrogen requires at least 750 seconds to diffuse through an X80 sheet of thickness 2 mm. It shows that no degradation occurred during the straining of the precharged specimens.…”

The Structure and Mechanical Properties of Low Carbon Steel after Controlled Rolling and Low-Temperature Treatment

“…Strain aging of the pipe incurred during coating heating could increase the yield strength of the pipe to some degree. This, in turn, increases the yield ratio (Y/T) and possibly worsens the deformability of the pipes [6].…”

Numerical study on the effect of the Lüders plateau on the ductile crack growth resistance of SENT specimens

“…It is well-known that most structural steels show obvious temperature dependent mechanical properties, such as yield stress, ductile-brittle fracture transition behavior. Previous investigations demonstrate that for some steels, the so-called Lüders plateau which is influenced by loading rate, ferrite grain size, yield stress, et al may occur in uniaxial tension test (Beardsmore et al, 2013;Dahl et al, 2018;Hallai and Kyriakides, 2013;Han et al, 2017;Liu et al, 2015;Mazière et al, 2017;Ren et al, 2015;Tsuchida et al, 2006). It has been reported that lowering testing temperature will increase the Lüders plateau length, see Fig.…”