If there is no difference between parts with different materials, hardness, and different finishes, just make them options from a list on the drawing. One drawing, one part, one ERP record.
There is at least 50 years of research into part variation tracking. Here's a link to a section of a book on just this subject.
ERP: Tools, Techniques, and Applications for Integrating the Supply Chain ...
By Carol A Ptak, Eli Schragenheim
Publisher http://www.crcpress.com/product/isbn/9781420056020