An investigation on ductility-dip cracking in the base metal heat-affected zone of wrought nickel base alloys-part I: metallurgical effects and cracking mechanism

Ductility-dip cracking (DDC) in the heat-affected zone (HAZ) of NiCr15Fe-type alloys was studied using the programmable-deformation-crack (PVR) and the strain-to-fracture (STF) test. This paper concentrates on the cracking morphology and the effect of metallurgical factors for DDC susceptibility. The obtained results are discussed in the context of the underlying cracking mechanism. Evidence was found that DDC in the heat-affected base metal occurs due to a relative grain boundary movement, which induces high strain buildup at grain boundary triple points, subsequent cavity formation, and intergranular crack propagation. Base metal grain size and intergranular carbide precipitation are shown to have a significant effect on DDC susceptibility and are discussed in the context of the observed grain boundary sliding mechanism.