Grain boundary sliding during high-temperature tensile deformation in superplastic Fe-6.6Mn-2.3Al steel

In the present study, grain boundary sliding (GBS) occurring during high-temperature deformation, i.e., a critical strain and accommodation process of GBS, was investigated using Fe-6.6Mn-2.3Al (wt%) steel, which was recently reported as a superplastic steel. For this purpose, high-temperature interrupted tensile tests were conducted at 880 °C with an initial strain rate of 1 × 10−3 s−1, and the microstructures of the tensile specimens were then observed at room temperature as a function of the true strain (ε) at 880 °C. Variations in certain microstructural features with ε, in this case the maximum intensity of the orientation distribution function, the average grain size, the void fraction, the misorientation distribution, the aspect ratio of the grains and the kernel average misorientation, found that dislocation plasticity occurred up to ε = 0.69, followed by both GBS and grain rotation. This indicates that the critical strain for GBS (εGBS) is 0.69. GBS occurred via a dislocation accommodation process, i.e., the second type of Rachinger sliding, where the original shape of the grains is maintained and subgrains do not form during GBS.