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 R3 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 R3 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.

A Study on Microstructural Evolution and Dynamic Recrystallization During Isothermal Deformation of a Ti-Modified Austenitic Stainless Steel

“…The twins have both a straight and a curvilinear appearance, which indicates that both coherent and incoherent twins are present in the recrystallized grains. [27,28] The extent of recrystallization is much higher at a true strain of 0.8, though an appreciable amount of deformed grains still exist in the microstructure (Figure 3(c)). …”

Origin and Role of Σ3 Boundaries during Thermo-Mechanical Processing of a Ti-Modified Austenitic Stainless Steel

“…When a Σ9 boundary generated in this way encounters another Σ3 boundary, either a new Σ3 boundary or a Σ27 boundary results according to the relationship Σ3 + Σ9 = Σ3 or Σ3 + Σ9 = Σ27, respectively. However, from the statistics of the Σ3, Σ9 and Σ27 boundaries in various GBE microstructures, it is inferred that Σ3 + Σ9 = Σ3 occurs more frequently than Σ3 + Σ9 = Σ27 [9]. For example, the number fraction of Σ3 boundaries increases from 0.45 in the SA condition to 0.58 in the specimen shown in Fig.…”

Effect of grain boundary engineering on the microstructure and mechanical properties of copper containing austenitic stainless steel

“…In the recent past, some investigations have been carried out to study the role of grain boundary character distribution (GBCD) on the microstructure and tensile properties of various austenitic stainless steels [20][21][22]. In these papers, the CSL fraction and connectivity of high angle boundaries were studied with respect to the applied processing parameters and consequent improvement in properties were reported.…”