Hybrid control of graphite cast iron structure by partial melt treatment process

Abstract

The Modified Inmould Process, which forms a cast iron-graphite hybrid alloy with a spheroidal/flake graphite structure (SG/FG), has been developed by the author.1-3 Though this process can easily control the transitional structure of SG/FG, there are some mild restrictions caused by rapid collision during the mixing of molten metals in the mould on pouring. In this study, a new experimental process was designed to solve this difficulty. The plate-like mould cavity was separated into a reaction chamber (RC) and a product cavity by a thin dam. An alloy of FeSiMg for spheroidization of base molten metal was prepared in the reaction chamber. Molten metal was poured up from the bottom of the product cavity and a part of it flowed over the dam into the reaction chamber. After being spheroidized in the reaction chamber, spheroidal graphite (SG) iron melt flowed backward into the product cavity. The density of SG molten iron with a higher carbon equivalent value is generally lower than that of flake graphite (FG) molten metal. Thus SG molten metal moved into the upper end of the product cavity by replacement of the base metal, while the base metal remained stationary at the lower end of the cavity. As a result of the phenomena of flow, movement and replacement between mutual melts, a SG/FG transitional layer structure was formed, downward, throughout the cast product.