The effect on Fe–Cr phase separation of a uniaxial stress during thermal ageing at 4251C is investigated on a Fe–15Cr–5Ni steel, a model alloy of commercial 15-5 PH steel. The applied stress is shown to accelerate the ageing kinetics, and influence the morphology of Cr rich domains. A dependence of the phase separation decomposition kinetics on the relative orientations of the load and the crystal local orientation has also been observed