How to tell if flywheel is iron or steel

I have a 11" flywheel from a 69 383 that i'm thinking about using. I'm sure its not the original wheel but i'm not sure if its iron or steel. It has the numbers 40 30467 stamped into it but I haven't been able to find anything online. The pressure plate was yellow and diaphragm type.
Is there any easy way to tell what its made of?