Influence of electron beam welding parameters and metallurgical factors on intergranular liquation cracking susceptibility of cast alloy 718

The factors affecting intergranular liquation cracking susceptibility in electron beam welds were investigated for cast alloy 718. The materials used were as-received plates and heat-treated plates with three different levels of grain size. Liquation cracking susceptibility in HAZ was evaluated by a bead-on-plate test and a restraint/relaxation U-type hot cracking test. The penetrated shapes in the welds were classified into wine cup-like Type W and nail head-like Type N. For a given beam current, Type w and Type N were observed at the lower and higher welding speeds, respectively. Welding defects, i.e., underfills and microcracks were seen in the electron beam welds. Compared with Type W, the liquation cracking was more sensitive for the Type N bead cross sectional shape. Furthermore, it easily occurred at grain boundaries in Region II, i.e., very near the nail head necked part. According to the restraint/relaxation U-type hot cracking test, the liquation cracking susceptibility decreased with decreasing grain size or with homogenization heat treatment. These results suggested that the liquation cracking susceptibility in cast alloy 718 electron beam welds could be improved by using the Type W bead cross sectional shape, a decreasing the grain size and using appropriate heat treatment before welding.[PUBLICATION ABSTRACT]