In contrast to solidification cracks, liquation cracks occur in the partially melted zone and the heat — affected zone and can be either interdendritic or intergranular in nature. An example of an interden­dritic liquation crack in a nickel-chromium alloy is given in Figure 2 (top), while intergranular liquation cracks in a pressure vessel steel are shown in Figure 8. The liquation cracks in Figure 8 are caused by the presence of sulfur-rich inclusions that liquate in the partially melted and heat-affected zones of the weld.

Another variation of liquation-type cracking can occur via the partial dissolution of second-phase particles, that is, the constitutional liquation mecha­nism proposed by Savage and shown experimentally by Pepe and Savage.1,16,17 In this type of cracking, the
heat from welding partially solutionizes the second — phase particles in the heat-affected zone. The result­ing concentration gradient around the particle lowers the solidus (e. g., the effect of niobium on nickel-based alloys from NbC or Ni2Nb) locally.