Jueves, 21 de agosto de 2014
Hierro dúctil

Autor: Arias Fernández, Sergio

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.