Splitting susceptibility in modern X80 pipeline steels

The microstructure and crystallographic texture of modern industrially produced API X80 grade pipeline steels were studied to identify the factors associated with the phenomenon known as splitting, which can occur on the fracture surfaces of Charpy, drop-weight tear test and full-scale fracture propagation tests. The steels investigated originated from full-scale production of line pipes, which had shown different levels of crack arrestability under full-scale burst test conditions. It was shown that a low Charpy impact transition temperature in the through thickness direction corresponded with a low susceptibility to splitting under conventional test methods and an increased resistance to ductile fracture propagation. The microstructural features shown to be consistent with an increased susceptibility to splitting included banding of the {001}<110> texture component in the microstructure and the presence of hard microstructure constituents being potential initiation sites for cleavage fracture. It is suggested that these results provide a viable test method to classify steel susceptibility to splitting and potential performance in full-scale ductile fracture tests.