The combination of high strength, good toughness, high specific strength, good wear resistance and high fatigue strength of austemperedis the key factor recognized by various industries and preparation enterprises. During more than 40 years since the isothermally quenched ductile iron was developed, many scholars and enterprise personnel have done a lot of research work in the selection of blank, preparation technology and microstructure, in order to further improve and improve the mechanical properties of austempered ductile iron. So far, there are many researches on improving the mechanical properties of Austempered Ductile Iron by improving the quality of austempered ductile iron, optimizing its heat treatment parameters and refining its matrix structure. On this basis, the effects of as cast microstructure, austempering process and casting wall thickness on the mechanical properties of austempered ductile iron were studied, and the correlation between different process factors and mechanical properties of austempered ductile iron was explored.
(1) After austempering at 920 ℃ / 2H + 280 ℃ / 1.5h, the fracture mode of ADI is quasi cleavage fracture. Among them, ADI produced by Ms = 0.25cm ductile iron has the strongest resistance to elastic deformation, with Rp0.2 up to 1268.8mpa, yield to strength ratio of 0.96 and e of 117.1gpa. However, it is found that the strength and toughness of austempered ductile iron obtained by Ms = 0.50cm and Ms = 0.75cm are relatively good, while those of MS = 1.00cm and Ms = 1.25cm are relatively poor. At the same time, with the increase of MS, the hardness of austempered ductile iron decreases gradually, but the change range is not large.
(2) After Austempering Ductile Iron with different process parameters, it was found that, with the increase of austempering temperature Ta, RM, Rp0.2, yield ratio, e and hardness of austempered ductile iron decreased gradually, a and Z decreased with the same austenitizing process parameters (920 ℃ / 1H or 920 ℃ / 2H) The fracture mode of austempered ductile iron changes from quasi cleavage fracture to dissociation fracture. In addition, when the austenitizing temperature T γ is 920 ℃, the tensile properties of ADI obtained by holding for 1 h is better than that by holding for 2 h. The specific performance is that RM, Rp0.2, yield ratio and E are higher, a and Z are larger, but the effect of austenitizing holding time on matrix hardness of austempered ductile iron is not obvious.
(3) After austempering at 920 ℃ / 2H + 280 ℃ / 1.5h for ductile iron with δ = 7mm, Φ 12mm and Φ 17mm, the fracture mode of austempered ductile iron is quasi cleavage fracture, but generally speaking, the mechanical properties of Austempered Ductile Iron with δ = 7mm and 12mm are better than those with δ = 17mm. When δ = 7mm, the Rp0.2 and yield ratio of austempered ductile iron are the highest; when δ = 12mm, RM, a, Z and e of austempered ductile iron are the largest.