Abstract
The authors have studied on the tensile characteristics of the joints of the ferritic spheroidal graphite cast iron bonded with Ni-base brazing sheets and found that the tensile characteristics of the joints were comparable to those of the base metal. For application of the joints to the mechanical parts, it is necessary to make clear the dynamic characteristics of the joints. In this study, the ferritic spheroidal graphite cast irons were bonded with Ni-Si-B system brazing sheet at 1313 K in vacuum, argon gas and air. Effects of bonding time and bonding atmosphere on absorbed energy of the joints were investigated by Charpy impact test. Main results obtained are as follows: (1) When the cast irons were bonded for 2 minutes in vacuum, the absorbed energy of the joints was 12.6 J. This value was nearly equal to the Japanese Industrial Standard (JIS) value and nearly equal to that of the base metal. (2) When the cast irons were bonded for 10 and 30 minutes in vacuum, the scattering range of the absorbed energy was 5-6 J, the value was larger than that of the joints bonded for 2 minutes, and the average values of the absorbed energy were about 1/2 of that of the base metal. Because Fe3(C, B)s were precipitated in the base metal near the bond interface of the joints bonded for 10 and 30 minutes, the crack on the Charpy impact test was propagated in the precipitation zone of Fe3(C, B)s and the brittle fracture was caused. (3) When the cast irons were bonded for 2 minutes in argon and air, the absorbed energies of the joints were a small value of about 4.5 J. Because the liquid of the brazing metal emitted to the outside surface of the specimen was oxidized by air during the initial stage of the bonding, and the amount of the emission of the brazing metal was less than that of the joints bonded in vacuum. So, brazed metals contained B were remained in the bond interface and the fraction of Fe3(C, B) was increased. The cracks were propagated in the precipitation zone of Fe3(C, B) by Charpy impact test. So, the absorbed energy was decreased compared to that of the joints bonded in vacuum.
