Defect formation mechanisms in lamellar graphite iron related to the casting geometry

Abstract

Although lamellar cast iron has been used in advanced applications for about 20 years, our knowledge about the mechanisms affecting microstructure and defect formation is relatively limited. The present paper summarises some solidification-related phenomena from a series of recently published peer-reviewed papers and scientific theses and suggests a mechanism of defect formation which is dependent on the shape of the solidifying casting geometry. When shrinkage porosity or metal expansion penetration occurs, evidence of material transport in the intergranular zone of primary equiaxed austenite grains in the casting and in the intergranular regions between the sand grains in the mould material is seen. Material transport occurs across the casting-mould interface, where the existence of or the permeability of the primary columnar zone determines if material transport can take place.

Keywords:

• Lamellar graphite iron
• Shrinkage porosity
• Metal expantion penetrayion
• Defect formation mechanisms
• Primary austenite grains
• Equiaxed zone
• Columnar zone
• Columnar to equiaxed transition

Acknowledgement

The present work is performed within a collaboration project in the Casting Innovation Centre, where the collaborating partners are the University of Jönköping, Swerea Swecast AB and the Swedish Foundry industry. All collaborating partners and financiers are gratefully acknowledged.