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

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 Sigma 11 and Sigma 13b and, possibly Sigma 5, are crack-resistant while the CSL boundaries beyond Sigma 13b 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}parallel to rolling plane (RP) and {1 1 1}parallel to RP textured grains, mainly associated with < 110 > and < 111 > rotation axes, respectively. were crack-resistant due to their low energy configurations, while the cracked boundaries were mainly linked to the {1 0 0}parallel to RP textured grains. (c) 2008 Elsevier Ltd. All rights reserved.