I have a question, for the same metal material, when will the elastic modulus will be changed? in another words, in what kind of processing or machine condition will the elastic modulus be changed? for example, to machine elements(gear, bearing ...), when the part surface is case hardened,will the elastic modulus be changed? if not, how can the difference of hardness between case hardened surface and without hardened substrate be reflected in FEM analysis? how can the case hardened surface parameters affect the contact stress when two part are brought to contact?

Thank you, for you help very much!