Metalsguy

If you look at our world of solids, as liquids in suspension, and metal is. We host it's "hardness, toughness, durability" through the tool's existence, in it's lifetime or our lifetime. Every time a hammer is struck, work hardening is incurred. What it strikes, with what force, and what frequency will determine an outcome i.e., two similarly Alloyed metals are struck, likely of similar harness, one will yield to the other, either "denting" or "flaking". It is not to say that a proven three generation hammer will one day reveal a flaw, as you are working, but to to smash your two favorite tools together will push the envelope. The word "flak" popularly (or unpopular) known to WW2 pilots, are metal flakes generated by hardened metals forced together by explosive force. Soft metal under force sprays, hard metal flakes. We are in a period economic and high quality tool production down-turn, less of our metal, do we know or understand, it's linage is far less regulated, respect what you have, and always wear safety protection.
PS The Hardness of a tool is generally set in the final "strike" in the factory, that creates it's final shape. This is why drop-forged hammers are superior, But, this is more of the story.