Dynamic restoration mechanisms in a Ti-Nb stabilized ferritic stainless steel during hot deformation

The effect of strain and deformation conditions on the microstructure and texture evolution of a 21% Cr Ti-Nb stabilized ferritic stainless steel was investigated in order to identify the dynamic restoration mechanisms taking place during high temperature deformation. Plane strain hot compression tests were carried out at 950 and 1050 °C at strain rates of 0.1 s−1 and 10 s−1 to the true strains of 0.2, 0.5, 1 and 1.5. The deformed specimens were examined using electron backscatter diffraction and transmission electron microscopy. The microstructure and texture development depended on the deformation conditions. Under the highest Zener-Hollomon parameter (8.91×1017 s−1) the restoration mechanism was dynamic recovery. However, at the highest strain of 1.5, continuous dynamic recrystallization and geometric dynamic recrystallization occurred, whereas under the lowest Zener-Hollomon parameter (4.67×1014 s−1) the initiation of continuous dynamic recrystallization was observed at 0.2 strain and dynamically recrystallized grains were detected already at the strain of 1. The size of subgrains decreased with increasing strain and increasing Zener-Hollomon parameter, and the stage at which a steady state was achieved, varied depending on the Zener-Hollomon parameter. Intense dynamic recovery and continuous dynamic recrystallization under plane strain deformation conditions were found to lead to the formation of intense α and ε fiber textures with a very weak γ fiber. Further, the possibility for the occurrence of discontinuous dynamic recrystallization is discussed.