Why do steel castings shrink more than gray-iron castings as they solidify?

Steel castings exhibit higher linear shrinkage—typically around 1.5 percent—compared to the approximately 1 percent shrinkage observed in gray-iron castings.1

This difference is primarily due to the unique composition of gray iron. Gray cast iron contains a significant amount of graphite, which exists as flakes embedded within the metal matrix. During the solidification process, the formation of these graphite flakes helps to offset the natural contraction of the metal, resulting in less overall shrinkage compared to steel, which lacks this expansive graphite component.21

Additionally, because steel requires higher tapping temperatures to ensure sufficient fluidity for filling thin sections, the molds used for steel must be more heat-resistant than those used for gray iron.1