Grain Boundary Microstructural Control through Thermomechanical Processing in a Titanium-Modified Austenitic Stainless Steel

Abstract

The present study discusses the grain boundary microstructural control in a 15Cr-15Ni-2.2Mo-Ti modified austenitic stainless steel (commonly known as alloy D9) through a one-step thermomechanical treatment. The experimental methodology adopted in this investigation was based on the strain annealing approach in which a small amount of strain (5 to 15 pct) was imparted on the solution-annealed (SA) sample. The cold-deformed samples were subsequently annealed at various temperatures (1173 to 1273 K) for different time periods (0.5 to 2 hours). It was observed that annealing after 5 pct deformation induces anomalous grain growth with a moderate increase in number fraction of coincidence site lattice (CSL) boundaries. However, a prestrain of 10 to 15 pct followed by annealing at 1273 K for 0.5 to 2 hours was found to be a suitable thermomechanical processing schedule to increase the number fraction of CSL boundaries (particularly Σ3 and its variants) significantly. Further, the well-connected network of random grain boundaries present in the SA specimen was substantially disrupted in these processing conditions due to the incorporation of Σ3 and its variants. The preceding results were discussed with reference to strain-induced grain growth vis-a-vis strain-induced boundary migration (SIBM) following deformation and annealing.