球状黒鉛鋳鉄の溶湯結合部の組織に及ぼすけい素の影響

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With a view to investigating the influence of silicon on the graphite formation in spheroidal graphite cast iron, molten metals with different silicon content but fixed carbon content were bound to each other in W-type CO2 process sand mold at various joining temperatures. The variation of graphite structure in the joint zone was observed with optical and scanning electron microscopes. Gray cast iron or spheroidal graphite cast iron containing 2 or 5% silicon were joined at various combinations, and also spheroidal graphite cast iron containing 2.5% silicon was joined with Fe-20%Si alloy in both molten and solid states. In the molten state joining of gray cast iron with either spheroidal graphite cast iron or Fe-Si alloy, vermicular graphite was formed in the joint zone in all of the combination, mainly because of the decrease in magnesium content in this zone. This was noticed in both hypo- and hypereutectic compositions of spheroidal graphite cast iron notwithstanding the direction of silicon movement or diffusion during joining. Moreover, heavily branched vermicular graphite was formed markedly when the silicon moved in the reverse direction. It has been clarified also that the same tendency was remarkable when silicon moves toward the hyper-eutectic iron melt. No vermicular graphite was formed, however, in any case of joining of two spheroidal graphite cast irons. Moreover, when solid Fe-Si alloy bar was immersed in spheroidal graphite cast iron melt, the variation of silicon concentration was observed only at higher joining temperatures of more than 1,300°C. On the matrix of the joint zone containing 4 to 9% silicon, due to the diffusion of silicon the degree of graphite spheroidization improved and also the graphite nodule number increased.
日本鋳造工学会の論文

著者

大番屋嘉一
(株)神戸製鋼所加古川製鉄所

球状黒鉛鋳鉄の溶湯結合部の組織に及ぼすけい素の影響

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