Micro-shrinkage Porosity in Castings with Special Safety Requirements

Cast iron is a unique alloy that, depending on its nucleation capacity, can solidify according to the stable Fe-C-Si diagram with graphite formation, as well as in an intermediate state with graphite and cementite, or with the complete presence of carbides and austenite. These three solidification behaviours determine the final properties of the castings. Nowadays, classic casting systems, in which heat evolution occurs in the direction of the feeders, no longer have a place.

For competitive reasons, it is essential to design high-yield pattern plates, reduce the number of feeders, lower energy consumption, and avoid processes that do not add value, such as deburring, trimming, and degating, to produce castings in a lean manner without WIP. The only way to obtain sound castings with high yield is to combine heat evolution during solidification with the ability to form graphite. The isolated thermal pockets found in the last-to-freeze areas (LFA) and the corresponding contraction due to residual liquid must be compensated by graphite formation in these areas.

Controlling nucleation and graphite growth during the eutectic phase is essential to obtain flawless components and avoid further sorting of castings parts with porosity due to micro-shrinkage.