Abrasive wear resistance of austempered ductile iron at room temperature

The use of austempered ductile iron obtained by heat treating spheroidal-graphite cast iron is very important in the gear industry. However the nature of the bainitic structure, which is used to improve wear resistance, has never been fully identified. The aims of this study were: -     to optimize the upper bainitic structures in S. G. cast irons (usually called austempered ductile iron or A. D. I.) to have the best abrasive wear resistance at room temperature. -     to study the influence of the solidification cell characteristics upon these optimized structures. -     to determine the evolution of the microstructures during the abrasion test. Results clearly indicate the primordial influence of the retained austenitic phase. A high percentage of retained austenite promotes a high abrasive wear resistance. The analysis of the results shows that this austenitic phase is heterogeneous. The best abrasive wear resistance is associated with the lowest hardness value. During abrasion, austenite at or near the surface is gradually and partly transformed to martensite.