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1Cr15Ni36W3Ti was thermally exposed at 580 ℃ and 680 ℃,respectively,up to 3000 h.The γ\'phase and intergranular TiC carbides continuously coarsened during exposure.None of η,laves or σ phase was discovered in the exposed samples,indicating good microstructure stability under the present exposure conditions.The ripening process of the γ\'phase could be well modelled utilizing the LSW theory.The evolutions of the yield and tensile strengths were monotonous during exposure at 580 ℃.However,a transition point in strengths was detected in the tensile samples exposed at 680 ℃ for 300 h.Accordingly,the critical γ\'diameter was measured to be 13-14 nm.The γ\'/dislocations interaction mechanism transformed from shearing to looping with the γ\'diameter exceeding the critical point.The combination of the weakly coupled dislocations model and the Orowan looping model yielded a critical diameter of 13.1 nm which coincided well with the measured one,indicating the applicability of these two strengthening models for 1Cr15Ni36W3Ti.The present exposure conditions did not exert a profound effect on the fracture mode.All the tensile samples underwent a typically ductile fracture with a dimple pattern dominating the fracture surface.The dispersed deformation induced by the prevalence of dislocation looping in the over-aged tensile samples retarded the propagation of intergranular cracks.The declined precipitation hardening increment and the enhanced deformation homogeneity partially recovered the tensile ductility in the over-aged samples exposed at 680 ℃.