It is the first time in our country to austemper the rare earth magnesium nodular iron at lower temperature and obtain the mixed structure of carbide ferrite and austenite. Then, by means of alloying, the problem of hardenability of thick gear was solved. Up to now, a lot of research work has been done on the chemical composition, molten iron melting, isothermal transformation technology and microstructure of Austempered Ductile Iron in China, which has greatly promoted the development of ADI in China’s manufacturing industry.
In terms of chemical composition, Zhu Junxian studied the effects of Si content and isothermal time on the mechanical properties of austempered ductile iron. It was found that with the increase of Si content, ADI not only improved the mechanical properties at room temperature, but also improved the mechanical properties and low temperature impact toughness after cold treatment. However, when w (SI) > 3.39%, it had little effect on the mechanical properties of ADI. At the same time, the mechanical properties of ADI obtained by isothermal transformation for 2 h before and after cold treatment are the best.
Huang Zhide studied the microstructure and mechanical properties of Austempered Ductile Iron with Cu Ni alloy. It was found that the addition of Cu and Ni could optimize the quality of nodular cast iron, and the spheroidization rate of ADI after austempering reached 2 grades, and the sphere diameter reached 1.5 ~ 2.6 μ M. meanwhile, the σ B of ADI could reach 930 ~ 1020mpa, δ could reach 9.7% ~ 16.6%, Hb could reach 269 ~ 321, α K could reach 142 ~ 149j / cm ~ 2.
The mechanical properties of Austempered Ductile Iron with Cu Nb, Cu NB Mo and Cu Mo alloying ADI were studied by ZHY casting. It was found that the mechanical properties of Austempered Ductile Iron with Cu and Nb elements were better than those with other alloy elements within the casting wall thickness ≤ 25 mm. The austempered ductile iron with σ b > 1200 MPa, δ > 12%, α k > 140 J / cm ~ 2 can be obtained at 350 ℃ The impact toughness can reach 39.2 J / cm2 at low temperature (- 60 ℃). At the same time, it is found that the two-step isothermal quenching technology can increase the quenching diameter of ductile iron with Cu, Nb and Mo elements to 45 mm and 65 mm respectively.
