Characteristics of hot cracking in dissimilar joint of A690 overlay and stainless steel clad

Hot cracks frequently encountered during nuclear vessel fabrication in dissimilar joints between Nb-containing A690 overlay weld and stainless steel clad. This phenomenon was duplicated in three-pass bead-on-plate SMA welds and confirmed by a mock-up test to identify the major type of hot cracking and to investigate the root cause of cracking. Microstructural studies showed that two types of eutectic reaction products, i.e., NbC or Laves phase, were formed and their contents increased with the dilution extent of stainless steel clad. In addition, all hot cracks observed near stainless steel clad were identified as a type of liquation cracks, associating with partial melting of Laves phase during subsequent weld passes. Since the proportion of Laves phase increased with the dilution, the greater liquation cracking tendency in dissimilar joint of A690 overlay weld to stainless steel clad was attributed to the increased Fe content of A690 weld near stainless steel clad.