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When copper is heated to cherry red, it resets the crystalline structure. Quenching it has nothing to do with annealing it, it is only done so you can handle it sooner. Quenching it or letting it air cool has the same effect. When this crystalline structure is shattered, the copper work hardens. This is why hammering it, bending it back and forth, or even burnishing it will work harden it. As far as I know this is the only way to harden copper. The same principle is true for copper alloys and also silver and maybe gold, but I'm not sure about other non ferrous metals.
Work hardening copper does get it much harder than soft copper. But thats relative. Annealed copper is almost like solder. But work hardened brass is ALWAYS going to be harder than work hardened copper, and work hardened tin bronze is ALWAYS going to be harder than both.
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