The role of heterogeneity and pop-in events when assessing brittle fracture in the weld metal of multi-pass welds

Fracture toughness testing was conducted on 81 SE(B)-specimens extracted from the weld metal of an aged pressurizer weld, of which 42 were deep-cracked and 39 shallow-cracked specimens. The crack tips were positioned in distinct zones in the weld metal, which was achieved by polishing and etching the material to reveal prior-austenite grain boundaries prior to specimen manufacturing. Deep-cracked specimens with crack tips located in the as-welded zone and where dendrites exhibit a low inclination to the pre-crack plane, frequently showed pop-in events during testing. The length of these pop-ins correlated directly with the length of the weld zone in front of the crack tip. Toughness was evaluated both at the pop-in and at final failure, and values were assigned to the corresponding weld zones. The ductile-to-brittle transition temperature was determined separately for each zone, confirming that the as-welded zone with low dendrite inclination is the most critical in the aged weld. • Polishing and etching procedure used to precisely position specimens’ crack fronts in specific weld zones of weld metal of multi-pass welds. • Relating pop-in events in fracture toughness testing of multi-pass welds to specific weld zones of weld metal and proposing a procedure for their evaluation. • Evaluation of T 0 separately for each weld zone in weld metal and comparison to the standard approach.