The correlation between Charpy impact energy and microstructural heterogeneity in the vicinity of fusion line for X80 girth welds at brittle-to-ductile transition region

Abstract

This study investigates the correlation between Charpy impact energy and microstructural heterogeneity in the vicinity of fusion line (FL) for X80 steel girth welds to determine accurate absorbed energy values and minimize the apparent scatter at brittle-to-ductile transition region. The results indicate that both the total impact energy and stable crack growth energy demonstrate a linear dependence on the proportion of FL in the crack propagation path, while the crack initiation energy remains largely unaffected. Furthermore, fractographic observations reveal that the fracture mode transition from ductile dimples to cleavage fracture is a key factor contributing to the high scatter of Charpy impact values in the FL region. Specimens with lower impact toughness exhibited numerous cleavage facets and secondary cracks near the primary crack. In contrast, specimens with higher impact toughness exhibited more tortuous primary crack path. In summary, the scatter in Charpy impact energy at the FL region is influenced by the microstructural characteristics along the crack propagation path and the degree of crack tortuosity.