Taku Ohide

Directional cellular solidification of eutectic and hypereutectic mottled cast irons

Abstract Directional solidification experiments were conducted on Fe-C eutectic and hypereutectic alloys to investigate the mechanism of the formation of a mottled structure, the growth pattern and the microstructures. The effects of manganese, silicon and the growth rate on the transition in eutectic growth from the stable Fe-C to the metastable Fe-Fe 3 C type were investigated. The mottled structures formed by the cellular mode of solidification can be classified into three types. The compositional change during solidification in the cast iron due to the segregation of the alloying elements (in this case, Mn and Si) which occured in the melt between the leading eutectic cells result in the change of the eutectic solidification temperature. If the effect of the compositional change on the eutectic solidification temperature is sufficient, the eutectic mode of solidification in the cast iron may be changed from one to the other. The mechanism of the formation of a mottled structure may be explained in terms of this conception.