Steels don't necessarily need a lot of carbon to work harden. Stainless steels are an example of this. Stainless steels that are of low carbon can work harden readily. You do need to exceed the elastic limit to work harden. That is you need permanent (plastic) deformation to occur to work harden.

I'm not aware of any hardening from age in the alloys common to barrels. There are age hardening aluminums that harden over time, usually at elevated temps.

Last edited by Chuck H; 02/26/12 10:25 AM.