Abstract
This study investigated the two-step minima that appear in the creep rate vs. time curve of 25Cr–20Ni–Nb–N steel at 873 K under 280 MPa. The dynamic microstructural changes in this steel during creep were investigated and the correlations with the creep rate at each stage were discussed. Based on the precipitation behavior and the change in kernel average misorientation and grain orientation spread values, precipitation strengthening by NbX in the grain interior and softening by dynamic recovery were suggested as the causes of the first local minimum in the creep rate. Dynamic recovery was potentially facilitated by the high amount of initial strain. By considering the precipitation behavior on the grain boundary and its interaction with dislocations, grain boundary precipitation strengthening by M23C6 carbide was determined to cause the second local minimum, followed by acceleration of the creep rate due to local deformation near the grain boundary, resulting in formation of voids on the grain boundary.
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