Post-hot-deformation microstructure development in austenitic stainless steel

In the present work, austenitic stainless steel has been thermo-mechanically processed to study the post -deformation microstructure evolution at elevated temperatures. The samples were axially compressed (at a strain rate 0.1 s- 1) and isothermally held at temperatures 900, 1000 and 1100 degrees C, for different time spans (2-1000 s). The electron back-scattered diffraction technique has been used to study the microstructure of the thermo-mechanically processed samples. The result shows for temperatures of 900 degrees C and 1000 degrees C, the resultant microstructures are comprised of deformed grains for samples held for 2 s. However, at 1100 degrees C sample isothermally held for 2 s shows a nearly complete recrystallization. The grain average misorientation approach has been used to estimate the softening fraction caused by recrystallization. The average grain size of the thermo-mechanically processed samples reveals grain refinement for the samples processed at 900 degrees C and 1000 degrees C. In addition to the grain refinement, the samples processed at 1000 degrees C shows a more consistent grain size. At all three temperatures, the increase in the holding time leads to a gradual decrease in the fraction of low angle boundaries and a simultaneous increase in high angle grain boundaries (HAGBs). The HAGBs are mainly contributed by sigma 3 coincident site lattice boundaries. At the end, a discussion on post-deformation softening, considering strain-induced boundary migration, has been presented.