The Investigation On Novel Heat Treatment Processes Of Austempered Ductile Iron (ADI)

Austempered ductile cast iron (ADI) has emerged as an important engineering material in recent years. Because of its excellent properties, unique advantage of reducing noise, attractive lower production cost, ADI has got more and more applications in various industries, and production increases by 25% every year all over the world.However, ADI still belongs to new material. Some issues about application and specific principles are still needed to be explored. Main contents in this paper are as followed:Firstly, this paper mainly focused on the effects of heat treatment process on microstructures and properties of ADI, especially novel methods, rules and principles, in order to further improve properties.Secondly, two-step austempering process is adopted, namely, the samples are austempered in lower temperature salt bath for a moment after austenitizing, then the salt bath is heated to a higher temperature immediately. Compared with traditional austempered process, this new method would obtain much finer structure with nearly same volume fraction of retained austenite in matrix and carbon content of austenite. High hardness and better ductility are obtained with this method, which would not be gained with traditional process.Thirdly, induction surface hardening is carried out on ADI. Two processes (induction surface hardening and two-step induction surface hardening) are adopted to explore the effect of different induction surface hardening processes on the surface structure and hardness. Results show that in condition of maintain inner ductility, surface hardness and wear resistance are obviously improved with two-step induction surface hardening, which has great significance in enlarging the application of ADI.The principles and effects of different processes on structure and mechanical properties are mainly summarized. Discussion and analysis are carried out about the phenomenon and principles from theoretical view.