Material heated and allowed to cool gradually. Large crystals form. Atoms able to reposition themselves. Material tougher and more ductile.
Material heated and cooled quickly in cold water. Small, regular crystals form due to large number of dislocations. Material is harder and more brittle.
Material is heated and quenched. Reheated and allowed to cool slowly. Retains strength and ductility.
Mechanical work carried out in a crystalline metal makes it harder. Repeated stress creates extra dislocatiions which get entangled and stop eachother moving. Material is less ductile.