The σ-Phase precipitation in 20% cold-worked 15Cr–15Ni titanium-modified austenitic stainless steel was studied during long-term aging treatment. During the isothermal aging stage, the amount of σ-Phase was significantly increased at beginning and gradually became constant. The aging time only slightly affected the size and morphology of the σ-Phase. Conversely, during the isochronal aging stage, the amount of σ-Phase grew rapidly with the increase in the aging temperature. The σ-Phase with a large amount of stacking faults was prone to nucleate around the(Ti, Mo)C particles or at the grain boundaries. The(Ti, Mo)C particles can act as effective nucleation sites, where the σ-Phase directly precipitates from the austenitic matrix. From this work, the growth of σ-Phase is found to be influenced by the aging temperature, and a new mechanism of σ-Phase precipitation from austenite has been proposed.
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