Effect of Special Boundaries on γ → α Transformation in Austenitic Stainless Steel

Orientation microscopy (EBSD) has been used to investigate the structure of austenitic stainless steel containing 18% Cr and 9 wt % Ni after its long-term operation at high temperatures and neutron irradiation. The γ → α shear transformation has been implemented partially in the samples during deformation-free cutting. Austenite has decomposed due to isotropic stresses oriented normally to the surface under study. The precision of orientation relationships (ORs), such as Kurdjumov–Sachs, Nishiyama–Wassermann, Greninger–Troiano, and others during γ → α transformation has been comparatively analyzed. The Greninger–Troiano OR has been found to be the best possible OR describing the transformation in this case. The α phase has been shown to nucleate at coherent twin boundaries (Σ3 in the coincidence site lattice model) between austenite grains. This has determined the variants of the current ORs and the unambiguous crystallographic orientation of α-phase grains.