Austenite stability of austempered ductile iron (ADI) in sub-zero conditions

The use of Austempered Ductile Iron (ADI) in the manufacture of different types of components grows despite some limitations that hinder the full development of their potential. The eligibility of these grades for applications at low temperature operating conditions is still an open question.

Consequently, the effect of low temperatures in the behaviour of materials submitted to conditions that resemble those expected in some extreme applications should be analyzed. Test samples have been submitted to sub-zero thermal treatment at -20°C (-4°F) and -40°C (-40°F) in order to assess their influence in the mechanical properties of ADI 1000. But in actual working situations, most of the components undergo variable temperature conditions. So, a group of samples has also bee submitted to successive cycles of -40°C in order to, in a way, approach the thermal conditions that could be found in hard environments.

Moreover, some samples have been submitted to deep cryogenic treatment at -175°C (-283°F). Although not reachable in nature, this level of temperatures provides an interesting research field for the future development of austempered ductile iron. In order to simplify the presentation and interpretation of the results, the dynamic characterization (fatigue and fracture values) has not been considered in this study. It will be addressed in future investigation. The transformation of the austenite has been verified by metallographic techniques. The changes in mechanical properties have been significant and can be explained by this evolution.