Interrupted ageing in steels: Hardness improvement and microstructural stabilization

Similarly to aluminium alloys, interrupted ageing in steels may increase hardness by 10%. By adding an intermediate stage between quenching and tempering, where quenched martensite is left to age at room temperature, carbon forms finer precipitate microstructures, which become more stable at room temperature. Using thermoelectric power to model carbon segregation to dislocations, it appears that room temperature ageing increases the number of effective nucleation sites for the subsequent tempering stage, as reflected in the microstructure and hardness.