sorry bud, missed your post. this is an oversimplification but it will help put things in perspective.

When you heat steel to hardening temperature the crystals line up into austenite. if you cool it slowly they take a structure that is not rigid, hard, or brittle. this is pearlite, which is very workable, soft, and tough. when you cool it quickly the structure taken is very rigid, hard, and brittle. this is martensite. there's a lot of stress in the steel in this phase so you heat it to the tempering temperature to relieve the stress in the martensite.

there's more to it like ferrite, cementite, bainite, carbides, impurities, quenching media, normalizing, tons of other crap that affects the way things work, but that's the jist of it.