Effect of hot deformation and crystallographic texture on toughness anisotropy and fracture behavior of Nb+V microalloyed API X70 steel

Effect of Textures and Microstructures on the Occurrence of Delamination during and after Fracture Toughness Tests of API X80 Steel Plates

“…In order to achieve these goals, pipeline steels, such as API 5 L X80, X100, and X120, rely upon alloy design and Thermo-Mechanically Controlled Processing (TMCP) to produce grain refinement by controlled deformation of austenite during rolling [3,4]. In general, rolling of TMCP steel plates are carried out in two stages: first, rough rolling is performed in the temperature range of austenite recrystallization while alloying elements are in solution (normally above 1100°C); then, at lower temperatures (typically below 1000°C, sometimes in the intercritical range) finish rolling passes are executed, cold-working the matrix [4][5][6]. At these lower temperatures, the presence of precipitated carbides inhibit grain growth, and fine austenite grains, substructure, and dislocations assist the formation of a refined ferritic or bainitic structure, depending on the cooling conditions [4,7].…”

“…At these lower temperatures, the presence of precipitated carbides inhibit grain growth, and fine austenite grains, substructure, and dislocations assist the formation of a refined ferritic or bainitic structure, depending on the cooling conditions [4,7]. Because of the low-temperature rolling, diffusional phenomena are limited, and the deformed microstructure carries strong crystallographic textures, which lead to anisotropy and possibly a decrease of mechanical properties [4,5,8]. As such, numerous investigations have been performed recently to understand texture formation in TMCP steels and its correlation with mechanical properties, especially impact toughness behavior (Charpy tests) [5,6,[8][9][10].…”

“…Fracture toughness and how crack propagation occurs in steels, depend on their chemical composition [4,5,[11][12][13], resultant microstructures [4,5,[10][11][12]14], inclusions [4,5,11,12], grain morphology, e.g., pancaked or elongated [4,12], crystallographic textures [4,5,[10][11][12][13][14] and residual stresses produced after the TMCP process [15]. Moreover, many studies in the literature point out the crystallographic orientation as the major cause of delamination, i.e., the presence of 001 plane more specifically [5,8,11,[15][16][17][18]. Most of the literature presents impact toughness results from Charpy tests.…”

“…The best condition was found at 0° and then at 90° [17], where the fracture orientation factor, a factor used to characterize the anisotropy of the fracture strength based on <100>, presented lower values compared to 45° to RD, the direction in which maximum fracture orientation factor was obtained. Bakshi et al [5] studied the influence of the TMCP, microstructure and crystallography on an X70 also varying the orientation of the machined samples for Charpy impact tests. As many cited works, Bakshi et al [5] also reported that the presence of 001 plane induces delamination.…”

“…Bakshi et al [5] studied the influence of the TMCP, microstructure and crystallography on an X70 also varying the orientation of the machined samples for Charpy impact tests. As many cited works, Bakshi et al [5] also reported that the presence of 001 plane induces delamination.…”