Publication: Evaluation of impact and fatigue properties on austempered ductile iron
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2009
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2009
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Tutors
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Abstract
Austempered Ductile Iron (ADI) proved to be an excellent material as it possesses
attractive properties: high strength, ductility and toughness are combined with good wear
resistance and machinability. In this work impact and the fatigue properties have been
evaluated for low alloyed Austempered Ductile Iron. To do this, Charpy-type impact test for
austempered ductile iron was performed by the standard ASTM A 327M and Fatigue
Crack Growth Rates (FCGR) were measured by the standard ASTM E 647. It was found
that impact energy is related with the morphology of the graphite nodules in the
microstructure. In particular, the impact energy increases when the nodularity and the
nodule count increase, and the nodule size decreases. A clear relation with the amount of
retained austenite wasn’t found. For the fatigue properties it was found that these were
related with the morphology of microstructure (graphite nodules, amount of retained
austenite and its carbon content). However, it was observed that the the crack initiation
was mainly affected by the presence of defects as porosity or carbides. When the
preferential crack path was observed between two neighboring nodules, the crack growth
rate increased when two graphite nodules were closer. The growth of the crack depends
on the orientation of the ferrite laths, but, in this work, it was observed that the crack path
probably takes place along the austenite/ferrite interface. Furthermore, it was found that
the likelihood of crack formation, facilitated by decohesion of the graphite nodules,
increased with nodule size.
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Keywords
Mecánica de sólidos, Hierro dúctil, Ensayo de materiales, Resistencia de materiales