Process of aging and respectively of alteration of physical and mechanical properties over time which is achieved after heat treatment and subsequent quenching to room temperature.

If the aging temperature is held, carbon and nitrogen are formed after some time in form of carbides, nitrides or carbon nitrides in the iron lattice. The defining factors influencing quench aging are nucleation (see also Nucleation conditions), growth of nuclei and overaging.

Quench aging increases the deformability resistance of steel and its coercive force. The effect of quench aging can be considerably increased by high over-saturation of carbon and nitrogen as well as aging under tension.