Relationship between grain boundary characteristic and liquation cracking susceptibility of alloy 625

• Ratios of CSL boundaries and Σ9 + Σ27 boundaries both increases with annealing time. • Melting temperature reduces in order of CSL boundary, random boundary, and NbC. • Liquation crack primarily occurs at random boundaries and hardly at CSL boundaries. • Effective distribution of CSL boundary reduces liquation cracking susceptibility. Liquation cracks often occur due to the local melting of segregated parts and constituents with low melting temperatures at the grain boundaries in the heat-affected zone (HAZ) of Alloy 625. Low-energy grain boundaries, called coincidence site lattice (CSL) boundaries, can reduce the intergranular segregation. Therefore, an effective distribution and large ratio of CSL boundaries (grain boundary character distribution, GBCD) can improve the liquation cracking susceptibility. The relationship between GBCD and liquation cracking susceptibility in the HAZ of Alloy 625 was examined by applying grain boundary engineering (GBE). The CSL ratio and Σ9 + Σ27 ratio increased with increasing annealing time and reached the maximum ratios after 48 h. Liquation cracking susceptibility was investigated using a hot tensile test with in-situ observations. The liquation crack was initiated in the locally melted part and propagated along the grain boundary. The crack tended to occur at random boundaries and the frequency was higher than those of the Σ9･Σ27 boundary. Besides, the Σ9･Σ27 boundary often acted as a barrier for the propagation from the random boundary. Thus, an effective distribution and increase of the Σ9･Σ27 boundary, which ha higher melting temperature, can reduce the liquation cracking susceptibility.