Modelling of precipitation kinetics and age hardening of Fe-12Ni-6Mn maraging type alloy

The precipitation hardening effect occurring in Fe-12Ni-6Mn maraging steel has been quantified in the present work. The model obtained can be applied to the entire aging period. Precipitate growth and precipitation fraction as functions of time and temperature have also been quantified. Time-temperature-precipitation diagrams with respect to precipitate size and fraction are proposed. The precipitation fraction at peak hardness has been estimated, together with the precipitate size. Results show that the precipitation process is far from complete when peak hardness is reached. At the lower temperature of 400 deg C, aging produces precipitates at a higher fraction and of larger size than those produced at 450 and 500 deg C, which explains why aging at 400 deg C gives a stronger hardening effect.