Flywheels are/were available in steel, and aluminum. I am assuming that your question is more along the lines of if it was cast or forged. As far as I am aware all were cast. The aluminum flywheels that are available may come as a cast or forged option, but I do not think there were any forged steel flywheels, although I may be mistaken on that. What engine specifacly are you seeking a flywheel for?