The Role of Compounds in Graphite Formation in Cast Iron - A Review

The paper reviews original data obtained by the authors, from recent separate publications, specifically concerning graphite formation in the solidification pattern of industrial cast irons, focussing on grey iron versus ductile iron. Additional unpublished data and selected data from literature are represented in the paper. Complex compounds act as nucleation sites in commercial cast irons, generally in a three-stage graphite formation, but with different sequences: (1) first micro-compound formation is oxide/silicate in grey iron and sulphide in ductile iron; (2) the second compound nucleates on the first one, as complex manganese sulphide in grey iron and complex silicates in ductile iron; (3) graphite nucleation on the sides of stage 2 compounds, which have low crystallographic misfit with graphite. Resulphurization (Mn/S control), preconditioning with strong oxide forming elements (Al, Zr), more potent inoculants and inoculation enhancement with S, O and oxy-sulphide forming elements were found to be beneficial treatments especially in critical solidification conditions