Prediction of Cross-Section-Dependent ADI Microstructures by Experimental Heat Treatment Simulation

Abstract Heavy section Austempered Ductile Iron (ADI) components may contain pearlitic or a mixed microstructure (mixture of pearlite and ausferrite) in their centres besides ausferrite. As a result, mechanical properties are not homogeneously distributed across the thicknesses of the components. The oversizing of the components therefore leads to unnecessary material expenses in foundries. In order to avoid the complex manufacturing process of heavy section ADI components and subsequent investigations, preliminary tests were performed with smaller test samples. Here, temperature-time curves were detected during heat treatment at different depths. Material samples of the customised composition were heat treated in a dilatometer under the same heat treatment conditions according to different sections of the cast component. A variation of the quenching rates was conducted to investigate the influence on the mixed microstructure formation and ratio of pearlitic and ausferritic microstructures. A comparison of the conventionally heat-treated and dilatometer produced microstructures proved the successful application for heavy section parts and enables microstructure predictions with small samples only. In this way, there is no requirement of expensive tests with high-mass components.