2. Description of the phenomenon

The two aging modes are distinguished by the presence or absence of strain hardening, but they share a number of common features and consequences for mechanical properties.

The term "ageing" is reserved for the evolution over time between ambient temperature and 300°C of the properties of ferritic or ferrito-perlitic steels. The properties concerned are physical: resistivity, internal friction, thermoelectric power, etc., and mechanical: yield strength, resistance, elongation, impact strength, etc.