On the role of microstructural properties on mechanical behavior of API-X46 steel

The dependence of the mechanical properties respect to the microstructural orientation of a low carbon steel API-5L grade X46 pipe was assessed by Charpy impact and tensile strength tests, through the use of samples oriented in the longitudinal (L) and circumferential (C) directions. Also, a thorough microstructural and EBSD analysis were made. The steel presented anisotropic mechanical behavior, associated with the material forming process. The specimens oriented in the L direction, which is parallel to the microstructural banding, had a lower fracture resistance (KIC-CV) and tensile properties (YS) than the C oriented specimens. According to obtained results, it is concluded that the influence of microstructural banding and crystallographic texture varies the fracture toughness of a material at least 10% between the L and the C directions. Hence, the anisotropy coefficient “rrv” was introduced to correlate quantitatively the microstructural properties to the anisotropic behavior of the API-5L X46 steel. The fracture resistance and tensile strength are mainly influenced by crystallographic texture, while the tensile ductility is associated to the microstructural banding.