Effect of as cast microstructure on tensile fracture morphology of Austempered Ductile Iron

The drawing shows SEM pictures of tensile fracture surface of Austempered Ductile Iron with different as cast microstructure after treatment at 920 ℃ / 2H + 280 ℃ / 1.5h.

It can be seen from the figure that ductile iron with different as cast microstructure has lower TA In the tensile fracture surface of austempered ductile iron, a large number of graphite peeled off under tensile stress and formed hemispherical graphite pits, while the graphite which did not fall off continued to be exposed in the form of graphite balls. Around the hemispherical graphite pits, there were obvious structural ups and downs and a large number of short and tortuous tearing edges.

At the same time, there are a small number of small dimples between the tearing edges, which shows the mixed fracture characteristics of cleavage and micropore polymerization. In addition, a large number of cleavage steps and cleavage surfaces can be observed in the fracture surface. Comprehensive analysis shows that the fracture mode of Austempered Ductile Iron with different as cast microstructure is quasi cleavage fracture at lower isothermal transformation temperature.