The influence of magnetic austempering on microstructure and mechanical properties of austempered ductile cast iron (ADI)

Austempered ductile cast iron (ADI) has emerged as an important engineering material in recent years because of its excellent mechanical properties such as high strength with good ductility, good wear resistance, and better fracture toughness. Even though ADI has excellent mechanical properties, its thermal conductivity is lower. Also ADI has a microstructure that consists of ferrite and austenite. Since austenite transforms into martensite during machining operation, tool life will diminishes. It is well known that fully ferrite structure has higher machinability and higher thermal conductivity than mixed structure. Many studies have shown that in presence of magnetic field decomposition of austenite to ferrite is accelerated. In this study the possibility of producing the austenitic free ADI with higher thermal conductivity and machinability by austempering of ductile cast iron in magnetic field has been explored.; In this investigation, one batch of a nodular or ductile cast iron samples was processed by conventional austempering process at three different temperatures. Another batch of ductile cast iron samples were austempered at three different temperatures as before in the presence of magnetic field 20 Tesla. It was observed that after the magnetic field treatment a fully ferritic structure ADI (austenite free) can be developed. Also microstructures, mechanical properties, fractography and thermal conductivity of these samples were compared with the conventionally treated samples.