Oxidation behaviour of Al-alloyed ductile cast irons at elevated temperature

The oxidation resistance of ductile irons alloyed with aluminium in the range from 0.08 to 6.16 wt.% has been investigated by heating at 550 ◦C for periods up to 1270 h. Examination by light and SEM microscopy and EPMA indicated that two quite distinguishable layers of oxide were established at the surface. It was found that, in alloys containing aluminium, a very thin and adherent film of aluminium oxide is produced after a short period of heating, which protects the bulk of the alloy from further attack. It is believed that the oxidation resistance can be improved by increasing the aluminium content: an increase in aluminium content led to a decrease in the average thickness of the iron-rich oxide layer. It was also found that the Al addition improved decarburization resistance; after long times at 550 ◦C a nodular iron with a 6.16% Al content was free of decarburization. Copyright  2004 John Wiley & Sons, Ltd.