Effect of Annealing Treatment on Σ3-Type CSL Boundaries and Its Interactions in 304HCu Grade Austenitic Stainless Steel
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This paper presents the results of a study on grain boundary characteristics in cold deformed and annealed 304HCu grade austenitic stainless steel (SS 304HCu) using electron backscatter diffraction. The microstructure exhibited an increasing fraction of Σ1 to 29 coincidence site lattice boundaries with annealing temperature, resulting up to ~60 pct at 1573 K with 92 pct contribution from Σ3-type twin boundary. However, the twin boundary interaction at the triple points with a network of Σ3–Σ3–Σ9 was found to decrease from 4 to 0.5 pct with annealing temperature. To understand the resultant boundary advancement of the Σ3 n (n = 1, 2, 3) boundaries, their migration was traced in the annealed specimen. However, in the specimen with extended annealing Σ3 boundary fraction was found to be higher with a concomitant decrease in the boundary fraction generated by the Σ3 interactions. In this study, a procedure to analyze the coherency of Σ3 boundaries and its interfaces that form due to Σ3 interactions has been evolved based on single-section analysis using the pole concentration across the grains. Further, a crystallographic description of the two planes meeting at the interface of Σ3-type boundary has been provided by adopting serial sectioning methods, which help to understand the morphological changes. The quantitative deviation from exact coherent Σ3 has been estimated to be within ~6 deg in this study.
The authors would like to thank Dr. G. Amarendra, Director, Metallurgy and Materials Group, and Dr. A. K. Bhaduri, Director, Indira Gandhi Centre for Atomic Research for their sustained support and encouragement during this work.
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