Difference between Hardened and Case-hardened

Hardened

Part of speech: verb

Definition: To become hard (tough, resistant to pressure).

Part of speech: adjective

Definition: Unfeeling or lacking emotion due to experience; callous.

Example sentence: This nation has been through hard times. But those hard times have hardened our resolve. I'm ready to do the difficult work ahead. But I want to do that work with Barack Obama, and not a Tea Party ideologue. We can move America forward, but we can only do it together.

Case-hardened

Part of speech: adjective

Definition: Metal that is harder at its surface, due to a case hardening process.