A quench factor, Q, has been derived that quantifies the overall severity of the steel hardening process—quench severity by interrelating steel hardenability with quenching variables including: the specific quenchant being used, agitation, bath temperature, etc. In this analysis, quench severity is quantified by a so-called “quench factor” (Q) that is a single numerical value that effectively indicates the extent to which a given steel can be hardened. This article provides a description of the concept and an overall review of applications where it has been successfully applied.