Studies on twinning and grain boundary character distribution during anomalous grain growth in a Ti-modified austenitic stainless steel

Solution-annealed alloy D9 (a 15Cr-15Ni-2.2Mo-Ti-modified austenitic stainless steel) samples were subjected to annealing in the temperature range 1173-1273 K with and without 5% prior deformation. Anomalous grain growth (AGG) was observed in these processing conditions. Electron back scattered diffraction (EBSD) analysis revealed that the proportion of Σ3 boundaries increased during AGG. This was attributed to the formation of new annealing twins during grain growth. Fraction of Σ27 boundaries remained constant in all processing conditions, whereas the fraction of Σ9 boundaries increased marginally at higher annealing temperatures. This indicates that only a few interactions between Σ3 boundaries happened during grain growth. The AGG in alloy D9 during annealing is attributed to inhomogeneous distribution of local strain in material coupled with intrinsic misorientation dependant boundary mobility. The inhomogeneous grain size distribution in the solution-annealed specimen would have provided the 'size-advantage' so that bigger grains could grow abnormally during annealing.