Delamination of pipeline steels : determination of an anisotropic cleavage criterion

Cleavage fracture anisotropy has been studied on a ferrite-bainite low alloy pipeline steel plate. Mechanical tests have been performed on smooth and notched bars taken along the three principal directions of the plate at temperatures between 20 °C and −196 °C, and analyzed by finite element calculations with an anisotropic plasticity model. The fracture mode of specimens tested along the normal direction differs from that of specimens taken along the two other directions, together with a lower critical cleavage stress. This difference seems to be related to microtexture anisotropy and might explain the sensitivity of this steel to delamination at low temperatures.