Duplex and superduplex stainless steels are characterised by high corrosion resistance and high mechanical strength. However, these steels can suffer formation of secondary brittle phases when they reach temperatures between 600 and 950 °C, which can lead to the catastrophic service failure of components. In order to understand the influence of the mechanical history of the steel part, equal-channel angular pressing was applied followed by different thermal treatments. Microstructural characterisation was carried out on the ECAPed samples before and after thermal treatment. The analysis of the hardness evolution of the same samples was also evaluated.