Hardening is a method to cool down rapidly with oil and water after making the steel glow. Generally, a good hardness can be expected from hardening and the abrasion resistance will be improved. However, hardening is not enough as it can be fragile and unstable, so heat it again to a certain temperature. That is called tempering. The steel will be toughened by tempering at approximately 600°after hardening. Also, when conducted together, hardening and tempering are referred to as thermal refining.