A long slow cooling process anneals the metal by allowing the metal crystals time to grow larger. A fast cooling freezes the structure, keeping a finer structure.

Work hardening decreases crystal size by mechanically dislocating them.

Shot peening dislocates and puts the surface in compression.

The finer structure has more dislocation points, making it harder to permanently deform.

Lots of other details... Its been a long time.

87 Turbo Intercooled Raider, roller cam, torsen rear diff, LSD front diff, lockup auto with modified converter, V6 brakes, low transfer case gears...