The research of Austempered Ductile Iron in the world began in the 60s of last century At the end of the s, the research focuses on the composition design, austempering process and equipment development, isothermal transformation mechanism, performance and application of austempered, so as to improve the applicability of austempered ductile iron, improve the performance advantages of austempered ductile iron, replace various alloy castings and reduce production costs.
The heat treatment process of ADI has been studied by foreign researchers. Putatunda S K and Yang J found that during the isothermal transformation of ductile iron, γ C – α B + γ HC and γ HC – α + ε occurred successively during holding for 1 ~ 4 h
At the same time, carbide will make ADI material brittle.
At the same time, the microstructure of ADI was analyzed by scanning electron microscopy (SEM) by yesca Gonzalez ma. It was found that the acicular ferrite observed under conventional optical microscope is composed of finer high carbon austenite sheets and ferrite sheets with a thickness of 0.2 ~ 1 μ m, and there is no ferrite / cementite grain boundary in pearlite at the austenite / ferrite grain boundary.