Forming mechanism of delamination cracks observed during tensile and fracture toughness testing of X70 pipeline steel
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In this study, we have investigated microstructures of the delamination cracks observed from tensile and fracture toughness test specimens using an API X70 pipeline steel. It is found that the delaminations observed from both tensile and toughness specimens are intergranular fractures. At the occurrence, characteristics of brittle fracture were observed, but it was found not to be a brittle fracture as the delaminations were induced by plastic deformation. It is shown that severe plastic deformation produced strain concentration around particles located along grain boundaries and caused decohesion between adjacent grains, resulting in intergranular fracture.
KeywordsSplit Delamination Brittle fracture Tensile test Toughness test Intergranular fracture
This research work was funded by TransCanada Pipelines Limited and the Canadian federal government Program of Energy Research and Development (PERD). We thank Dr. Chris DeBuhr at the Instrumentation Facility for Analytical Electron Microscopy (IFFAEM), University of Calgary, for taking SEM-based fractographs, and Muhammad Arafin at CanmetMATERIALS for technical advice.
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