The Effect of the Substitution of Silicon by Aluminum on the Properties of Lamellar Graphite Iron

In cast iron, silicon and aluminum are elements that promote graphite precipitation and strengthen the alloy by solid solution. In the present work, Si has been substituted by Al leading to values that easily surpass standard properties of Fe-C-Si gray cast irons, reaching a strength of 466MPa at moderate hardness (250HB) for an iron with 3.08% C, 3.15% Al and 0.16% Si. Sequences of heats increasing Al content were carried out. It was found that the UTS increases with the Al content, reaching a maximum at about 3% Al, after which it decreases. Graphite area measurements show a minimum at the maximum UTS, with graphite exhibiting random orientation. Carbides are avoided above 1.5% Al for very low Si content (about 0.2%) in Y2 keel blocks (25mm thickness). Plates as thin as 2.5mm were cast free of carbides from irons with more than 3% Al, which makes this material very desirable for thin wall castings. Additions of other elements were necessary, including 0.35% chromium, 0.55% manganese and 0.075% tin to obtain a pearlitic structure.