The decomposition of martensite during tempering or ageing is an important phenomenon as it leads to changes in the mechanical properties. These changes could take place during both steel manufacturing or in-service. Thus, their understanding is required to predict the material performance. Recent advances in the development of local electrode atom probes has led to a significant increase in the analysed volume of material (up to 100 millions of atoms) and at the same time reduced the acquisition times. This allows improvement in data statistics when investigating fine nanoscale features, such as solute segregation, clustering and ultrafine precipitation. Selected results of atom probe studies on the decomposition of martensite from bake hardening of a pre-strained Transformation Induced Plasticity (TRIP) steel and ageing of FeNiTiMnAl maraging steel are presented.