2008 Volume 80 Issue 9 Pages 536-540
The austempered ductile iron (ADI) has been used as an industrial material, since it is a high strength material with good ductility and toughness. ADI, however, becomes very brittle when it is used in aquatic environments. In cast iron, a local cell is formed between the graphite and the matrix in acid solution and hydrogen is generated by the galvanic reaction. The experimental results suggest that the reduction of strength and ductility of the ADI may be caused by this hydrogen. Excellent properties of strength and ductility are observed even under aquatic environment in ADI with decomposed retained austenite which is produced by annealing at 673～723K after austempering (named ADI-AN). And the similar excellent tensile properties are observed also in the ADI without retained austenite which is produced by austempering at 653K after autenitizing at 1173K and cooling gradually to 1033K (named α-ADI). The strength and the toughness of ADI-AN in air are almost the same as those of the quenched and tempered ductile iron having sorbite structure. However, the toughness of α-ADI is higher than that of the quenched and tempered ductile iron with the same strength.
