Larry S:

An easy way to understand annealing is to look at it this way:

The ring on a Padlock is hardened steel. If you try cutting it with a hacksaw, about all you will do is polish it.

Now take a torch and heat that ring till it's red hot. Once it's red, slowly pull the torch away so that the ring slowly loses it's red color.

Once you turn off the torch, let the ring cool to room temp.

Now you can cut it with a hacksaw.

To bring the ring back to a hardened state, it must be properly heated and quenched (Cooled rapidly)