Microstructural evolution of two-way cold rolled 12Cr ODS steel under 1073–1373?K annealing

摘要

Microstructural evolution and hardness variations of cold rolled 12Cr ODS steel with 60%–90% thickness reductions after 1073–1373?K annealing were systematically studied by electron backscatter diffraction technique, transmission electron microscopy, and Vickers hardness measurements. Recovery took place with heating up to 1273?K in specimens with 60% thickness reduction accompanying with gradual hardness decrease, and followed by recrystallization at 1373?K with an evident hardness reduction. By contrast, regarding specimens with 75% and 90% thickness reductions, recrystallization was observed at 1273?K which is 100?K lower than that of 60% thickness reduction, and 400?K lower than that of as-fabricated specimen without further cold rolling, indicating that a higher thickness reduction stimulated the onset of recrystallization at a lower temperature. Furthermore, partial recrystallization was characterized at 1073?K and 1173?K in the specimen with 90% thickness reduction, which produced equiaxed grain bands along the final rolling direction with none/lower density of oxide particles, and full recrystallization occurred at 1273?K and above, forming coarse elongated grains with high density of oxide particles and a smaller fraction of equiaxed grains. These bimodal grains were probably ascribed to heterogeneous distribution of oxide particles in the matrix, which were partially dissolved during cold rolling process, and re-precipitated after the thermal annealing.