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Electron back-scattered diffraction and positron annihilation lifetime measurements were performed on the ferritic-martensitic 9 %Cr Eurofer steel processed by equal channel angular pressing (ECAP) at 550 A degrees C. The orientation imaging mapping images reveal ECAP-induced changes toward a more stable texture via rotation around aOE (c) 111 > and aOE (c) 110 > axes. These are accompanied by transformation of martensite into ferrite and a remarkable change in the bimodal distribution of grain misorientations with reduction of the fraction of high-angle grain boundaries. The positron annihilation measurements evidence the release of vacancies retained in the ECAP-processed material and their clustering into nanovoids in samples heat treated at T a parts per thousand yen 500 A degrees C. It is found that tensile strain applied at 600 A degrees C can inhibit this void formation in the ECAP-deformed material for 1 and 2 passes, but not in the case of 4 passes. A model for accounting the results is proposed.