Dynamic normal grain growth in BCC interstitial-free steel during hot deformation




Rupp, Ryann Elizabeth

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Concurrent plastic deformation at elevated temperature can produce dynamic normal grain growth (DNGG). DNGG significantly impacts microstructure by accelerating grain growth and/or evolving texture. Both of these were observed in an interstitial-free steel deformed in uniaxial tension at 850°C at a constant true-strain rate of 10⁻⁴ s⁻¹. Two complementary analysis methodologies were used to investigate DNGG and its mechanisms. The first analysis method determined the contributions from (i) lattice rotation during slip and (ii) DNGG to texture evolution during high-temperature deformation. Lattice rotation and DNGG were isolated by determining the texture of three states: (i) undeformed (recrystallized), (ii) deformed at room temperature, and (iii) deformed at high temperature. The second analysis method segmented EBSD data into individual grains, which included their sizes and orientations. This analysis method probed the relationships between crystallographic orientation and changes in grain area fraction, number fraction, and size with strain. A statistical analysis identified the characteristics of grains that were preferred for growth in order to investigate DNGG and its mechanisms. DNGG preferentially grew grains of specific orientations at the expense of other orientations. Grains that preferentially grew by DNGG were observed to be from orientations with specific crystallographic planes parallel to the plane of the sheet material. Grains oriented with the {111}, {332}, or {322} planes parallel with the plane of the sheet material were preferred for growth. Among grains with these planes parallel to the sheet plane, a specific subset of orientations were most preferred for growth. The reference orientations most favored for growth depended on the initial recrystallized texture relative to the specimen tensile direction. Subgrains were observed to occur in grains during hot deformation and concurrently with DNGG. High-resolution EBSD (HR-EBSD) resolved subgrains and associated hot deformation substructure that is hypothesized to be important to DNGG.


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