Abstract: The high-temperature creep and interrupted creep tests of P91 steel were carried out under the stress of 145 MPa at 620 ℃. The evolution of small-angle grain boundary during creep was investigated by electron backscatter diffraction (EBSD) technique. Meanwhile, the misorientation distribution in the EBSD image was introduced to characterize the dislocation density of small-angle grain boundary with the misorientation of adjacent grains from 0.5° to 5°. By these methods, the relationships between the boundary dislocation density, the number of small-angle grain boundaries, plastic strain, and internal microstructure evolution were discussed during creep. Besides, the influence of calculation step size on the boundary dislocation density was analyzed in detail. The results manifested that the dislocation density at the small-angle boundaries increased rapidly from the primary creep to the beginning of the secondary creep. Then, it reached a peak when the creep rate was minimum. Afterwards, it decreased slowly and then remained constant until the creep rupture. Moreover, it indicated that the smaller the step size of EBSD, the more accurate the dislocation density value can be obtained.
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2018, Vol. 32 
