抄録
Structures and strength of welded joints of ductile irons have been experimentally investigated which were electron-beam welded using Ni insert plates of 0.2 to 0.5 mm in thickness and then annealed for 1h at various temperatures from 823 to 1 123K. Acicular martensitic structures and high carbon martensitic structures were observed in the bond and around the spheroidal graphites in the heat affected zone, respectively. After annealing at higher temperature than 973 K, these martensites were completely disappeared and fine cementite and graphite particles were precipitated in both bead and bond zones. The hardness in the bond decreased to similar values in the bead and base metal zones by annealing at higher temperature than 923 K. The tensile strength of welded joints in which Ni plates of 0.30 to 0.35 mm thick had been inserted were almost recovered to the strength of base metal by annealing. Fine blowholes which were observed in the bead did not affect the tensile strength of annealed specimens. Charpy impact values of as-welded specimens were less than 20 J/cm2, while the values of annealed ones were kept at more than 60 J/cm2.
