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- Title
Ferrite Grain Size Distributions in Ultra-Fine-Grained High-Strength Low-Alloy Steel After Controlled Thermomechanical Deformation.
- Authors
Patra, S.; Roy, S.; Kumar, Vinod; Haldar, A.; Chakrabarti, D.
- Abstract
Plane-strain compression testing was carried out above, around, and below the A temperature with the deformation temperature, T, varying between 1323 K and 973 K (1050 °C and 700 °C), using Gleeble 3500, to develop uniform distribution of ultra-fine ferrite (UFF) grains. Prior austenite ( γ) grain structure, developed after soaking at 1473 K (1200 °C), was mixed in nature, comprising both coarse- and fine- γ-grain sizes. Applying heavy deformation in a single pass, just above the austenite-to-ferrite ( α) transformation temperature ( A), and cooling to room temperature resulted in the formation of UFF grain sizes (average α-grain size ~2 to 3 μm), with the largest grain sizes extending up to ~10 to 12 μm. Water quenching just after deformation prevented the coarsening of UFF grains and restricted the largest grain sizes to under 6 μm. Although the ferrite grain structures appeared homogeneous in slowly cooled samples (cooling rate (CR) 1 K/s), careful observation revealed the presence of alternate bands of coarse- (5 to 10 μm) and fine- α grains (<1 to 3 μm). The final α-grain size distributions were explained in view of the starting γ-grain size variation, dynamic recrystallization (DRX) of γ, dynamic strain-induced γ-to- α transformation (DSIT), and DRX of α and grain growth during slow cooling. Electron backscattered diffraction analysis (EBSD) revealed the presence of a large fraction (70 to 80 pct) of high-angle boundaries, having misorientation ≥15 deg. Compared to the use of the single, heavy deformation pass, the application of a number of lighter passes between A and A temperatures is more suitable in industrial rolling conditions, and also has the potential of developing UFF grains with high-angle boundaries.
- Subjects
STEEL alloys; FERRITES; PARTICLE size distribution; THERMOMECHANICAL properties of metals; DEFORMATIONS (Mechanics); TEMPERATURE effect; RECRYSTALLIZATION (Metallurgy); ELECTRON backscattering
- Publication
Metallurgical & Materials Transactions. Part A, 2011, Vol 42, Issue 9, p2575
- ISSN
1073-5623
- Publication type
Article
- DOI
10.1007/s11661-011-0668-1