Masao Homma1, Tsuneo Ishida1 and Katsunobu Yamaya1
1The Reasearch Institute for Iron, Steel and Other Metals, Tohoku University, Sendai
This research was a fundamental analysis of the welding structures of flake graphite and spheroidal graphite cast irons to investigate the change of the graphite structure at the fusion bead, and to prevent flake graphite from being tranformed into eutectic graphite and spheroidal graphite from being collapsed. The heat-cycle was applied to the whole parts of samples in conformity with gas-welding, without the welding procedure.
The results are as follows:
(1) In the flake graphite cast iron, the amount of eutectic graphite increases with the increase of the maximum fusion temperature in air and in contact with the non-reducing flux. However, in the case of reducing fluxes, eutectic graphite hardly increases. Especially, when the amount of FeSi in the reducing flux is increased, a flake graphite similar to that of the original base metal is maintained. In the welding of cast iron, therefore, it is important to cover the fusion bead with the reducing and graphitizing flux during heat-cycle in order to prevent the formation of eutectic graphite which reduces the mechanical properties.
(2) During the welding of the spheroidal graphite cast iron, it is difficult to maintain the spheroidal graphite structure by covering the fusion bead with spheroidizing flux during the fusion period. However, it is possible to restore the original structure by treating it with the spherodizing flux just before cooling down, whatever heating and fusion may be carried out in air.
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