Investigation into microstructure and mechanical properties of heavy section nickel alloyed austempered ductile iron in accordance with austempering parameters

Austempered ductile iron (ADI) is one of the most widely used types of ductile iron produced by austempering heat treatment. ADI heavy section parts are employed in different industries owing to their unique mechanical properties.

Cooling rate in thick parts is significantly low, so heavy section ductile iron parts should have an adequate austemperability for preventing pearlite formation in the middle of the casting. In order to achieve the proper austemperability and fully ausferritic structure, alloying elements like nickel are added to the melt.

The objective of this work is to study the role of austempering parameters on nickel alloyed ADI specimens fabricated from 75-mm-thick Y-block. Austempering temperature and time as main parameters in the austempering process are taken as the control variables. The heat treatment of austempering was performed at 320°C and 380°C for 60, 120, 180, and 240 min. It was possible to determine the best austempering conditions among those investigated in the paper, and the results showed that austempering at a higher temperature contributes to higher strength and hardness compared to lower austempering temperature. Furthermore, specimens that were austempered at 320°C for 120 min had better mechanical properties among other samples.