Ductile–brittle transition behavior of the heat-affected zone in X80 automated GMAW girth welds

The ductile–brittle transition of the heat-affected zone (HAZ) in an X80 automated gas metal arc welding (GMAW) girth weld was investigated by instrumented Charpy impact testing, fractography, M–A quantification, and EBSD. The 50% energy transition temperature (ETT 50 ) was −48°C. Stable crack-propagation energy decreased continuously with decreasing temperature, whereas crack-initiation energy decreased stepwise. M–A area fractions were 4.75% in the CGHAZ and 5.22% in the ICCGHAZ, which showed a more continuous necklace-like distribution along prior-austenite grain boundaries. EBSD revealed reduced lattice misorientation and crack deflection with decreasing temperature. At −100°C, crack traces showed geometrical compatibility with candidate {111}, {310}, and {123} plane families.