Precipitation hardening, also known as age-hardening, involves quenching an alloy to increase its hardness over time through nucleation and growth of precipitates. It involves three main steps: solution treatment to dissolve precipitates, quenching, then aging at a lower temperature which allows precipitation to occur. During aging, carbon diffuses from ferrite forming cementite precipitates within the ferrite matrix, increasing the alloy's hardness. The rate of precipitation depends on temperature and free energy, with moderate temperatures and energies allowing the most rapid hardening. Over-aging can cause hardness to decrease if aging is done for too long.