The strength of the diffusion bonded joints of ductile cast irons having the strength of 360 (FCD 37) or 490 MPa (FCD 50) and the ductile cast iron to a mild steel had been investigated in the 1st report. In this report, the effects of the post bond heat treatments-annealing for ferritization and normalizing for structure changing of matrix-have been studied. The results obtained are as follows; (1) The tensile fracture of the joints which were annealed after that bonding carried out using the insert metals of Ni or Fe foils occurred in the base metal. However, both joints without a insert metal and with Cu foil fractured at the bonding interface. (2) When the ductile cast irons were directly bonded without a insert metal the joint strength after annealing depended on the volume fraction of graphites which precipitated on the bonding interface by decomposition of Fe3C during annealing, and abruptly deteriorated with increasing the fraction of these graphites. This graphite volume fraction increased in proportion to the pearlite volume fraction around bonding interface before annealing. (3) As to the joints of the ductile cast iron to the mild steel, the joint strength after annealing depended on the bondability between the ductile cast iron and the insert metal. Except the insert metal of Cu foil, the tensile fracture occurred at the mild steel side away from the insert metal. (4) The tensile strength of ductile-ductile joints increased as the volume fraction of pearlite formed in matrix by normalizing for structure changing incrased and was the same as that of the base metal up to 550 MPa. When the strength of the base metal was higher than 550 MPa the joint strength reached the plateau value of 85% of the base metal strength. (5) On the other hand, the strength of both joints without the insert metal and with Cu foil did not exceed 80% of the base metal strength of 430 to 1000 MPa.
