Influence of Ingate Size on the Formation of Micro Shrinkage Pore in Gray Cast Iron

Abstract

In this paper, the origin of micro shrinkage pores in gray cast irons is revealed, and a solidification process for the iron is proposed. Gray cast irons, casted under various casting conditions, were examined in terms of density and optical microscopy microstructures of the irons. The amount of the added inoculation agent affects the size and the number of graphite particles per unit area, but does not affect the volume fraction of the graphite. The density of the iron was affected by the cross-sectional area of the ingate, regardless of the amount of the added inoculation agent. When the cross-sectional area of the ingate is larger than the appropriate size, the density of the iron decrease. The reason is the formation of micro shrinkage pores in the iron. The relationship between the solidification process and micro shrinkage pores of the gray cast iron was discussed based on the above experimental results. When the completion of the solidification in the ingate occurs before than that in the cavity, the molten metal cannot flow between the cavity and the runner by passing through the ingate. Therefore, the expansion due to the crystallization of the graphite is equal to the shrinkage due to the crystallization of the austenite at the eutectic solidification in the cavity. As a result, gray cast iron without micro shrinkage pores was obtained.

 

This Paper was Originally Published in Japanese in J. JFS 90 (2018) 443–449.

Fig. 7 Schematic illustration of solidification process for gray cast iron of hypoeutectic composition.