Mg添加過共晶球状黒鉛鋳鉄におけるグラファイトの核生成と形状変化の時間分解その場観察

抄録

  Nucleation position, floating and morphological change of graphite nodules during solidification of hypereutectic ductile cast iron with Mg addition was observed in-situ using synchrotron radiation X-ray imaging. Graphite nucleated on pre-existing inclusions (i. e. MgS and Mg-containing oxysulfide) in the melt around austenite dendrites and most of the graphite nodules floated due to the buoyancy force. The floating graphite nodules were engulfed or entrapped austenite dendrites within several seconds. Floating distance of graphite nodules was shorter than dendrite arm spacing. The nucleation events near the dendrites and solute exchange between austenite dendrites and graphite nodules resulted in the short floating distance. The engulfment / entrapment of graphite nodules into austenite dendrites promoted the secondary nucleation of graphite in the melt and consequently influenced size and number of graphite nodules. In addition, two different phenomena also contributed to the morphological transition from spheroidal shape. One is the coalescence of graphite nodules and the other is the growth of graphite nodules in the austenite.