Interfacial Reaction Between Cast Steel and Olivine Sand or Silica Sand

Abstract

Manganese in molten high manganese steel volatilized and penetrated mostly through the serpentine and the cracks in the olivine sand grains. The penetrated manganese lowered the melting point on the surface of the olivine sand grains, and a smooth shell (partly-fused layer) was formed at the metal-mold interface. After cooling, the shell easily peeled off from the casting without burning as a result of low affinity between the metal and shell. A similar reaction was observed both in green and calcined olivine sand, however, the shell was thinner on the green sand than the calcined olivine sand mold. The calcined sand caused neither blow holes nor pin holes, but the green sand may cause blow holes and pin holes from the dehydrated gas when the permeability is not sufficient in the mold.A comparison was made between the olivine sand and silica sand, and the effect of manganese coating on the olivine sand grains against burning was investigated in the present work. No burning took place between the olivine sand mold and low carbon steel, but a small quantity of manganese in steel diffused into olivine sand grains at the metal-mold interface. The low carbon steel penetrated into silica sand mold to combine with silica sand forming fayalite with a small quantity of manganese at the metal-mold interface. Manganese in molten high manganese steel diffused into the mold to combine with silica sand grains as 2MnOSiO2. High-manganese cast steel did not penetrate into silica sand mold because of the low pressure of molten metals. Manganese-coating on the olivine sand grains prevented the burning of low carbon steel.