Steel

Although containing many other elements in combination with iron, it is the carbon content of steel which is the most important, and is largely responsible for the wide range of properties which can be obtained. Steel heat treatments fall into two broad categories, namely softening processes which are mainly utilised as intermediate heat treatments and hardening processes applied as part of the finishing operations given to a component.

The majority of steel is hardened by heat treatments that involve quenching of the product from the austenitising temperature. Oil remains the most common quenchant and has associated risks, beyond its inherent flammability. The main one involves the ingress of water (possibly from a leaking cooling system). In small quantities, water in the oil can lead to component cracking. Larger volumes can produce foaming of the oil bath and the attached risk that the mixture can overflow and cause a fire. In extreme situations, sufficient water can explosively form water vapour within the oil and be a source for a major fire or explosion.