A new understanding of intergranular stress corrosion cracking resistance of pipeline steel through grain boundary character and crystallographic texture studies

Abstract

The roles of grain boundary character and crystallographic texture on the intergranular stress corrosion cracking (IGSCC) of API X-65 pipeline steel has been studied using scanning electron microscope (SEM) based electron backscattered diffraction (EBSD) and X-ray texture measurements. It has been found that low angle and special coincident site lattice (CSL) boundaries, mainly Σ11 and Σ13 b and, possibly Σ5, are crack-resistant while the CSL boundaries beyond Σ13 b and the random high angle boundaries are prone to cracking. However, several cracks were found to have been arrested even when the random high angle grain boundaries were available for them, both at the crack-tips and areas immediately ahead of them, to continue propagating. Texture studies in the vicinities of these crack-arrest regions, as well as in the cracked areas, provided a new understanding of crystallographic orientation-dependent IGSCC resistance: the boundaries of {1 1 0}‖rolling plane (RP) and {1 1 1}‖RP textured grains, mainly associated with 〈1 1 0〉 and 〈1 1 1〉 rotation axes, respectively, were crack-resistant due to their low energy configurations, while the cracked boundaries were mainly linked to the {1 0 0}‖RP textured grains.