The grain phase has a significant influence on the extent and mechanism of attack of low-cement castables with similar bond systems in a crucible corrosion test. The general corrosion mechanism, as determined by post mortem scanning electron microscopic examination of corroded samples and thermodynamic calculations for all four grain types examined (white-fused alumina (WFA), tabular alumina (TA), brown-fused alumina (BFA), and alumina-rich spinel (S)), involves initial reaction of the most penetrating slag (enriched in calcium, manganese, and iron, because these elements diffuse rapidly) with the fine alumina and calcium aluminates of the matrix, This reaction gives a CaO-rich local liquid, which can then react with each grain predominantly to form calcium hexaluminate (CA(6)) and hercynitic spinel, In the WFA system, a complete CA(6) laver forms around the grain, whereas in the TA system, this layer is incomplete, In both systems, extensive penetration occurs, although corrosion is low, In the BFA system, titanates are released from the grain into the bond, leading to increased densification of the refractory, via liquid-phase sintering, and consequent low penetration. Hoc-ever, the resulting fluid liquid dissolves easily in the slag, so that corrosive wear is high, even though a CA(6) layer forms around the grain. In the S grain system, uptake of the rapidly diffusing cations into the spinel crystal structure leads to silica-rich and viscous local liquid which leads to low penetration and corrosion.