Microstructural evolution and adiabatic shear band formation in tempered AISI 4340 steel under high strain rate and elevated temperature impact
Bibliographic record
Abstract
Adiabatic shear bands (ASBs) are narrow zones of intense plastic deformation that form in structural materials subjected to high strain-rate impacts, often leading to catastrophic failure. While ASB formation at room temperature is well documented, their evolution under elevated temperatures remains inadequately understood. This study investigates the formation and microstructural evolution of ASBs in quenched and tempered AISI 4340 steel subjected to dynamic loading at both room temperature (25 °C) and elevated temperatures (300-600 °C) using a direct impact Hopkinson pressure bar (DIHPB). Comprehensive microstructural characterization using optical microscopy, SEM, TEM, HRTEM, and EELS reveals that ASBs consistently formed at all temperatures tested, though their morphology and internal structure evolved significantly with temperature. Room-temperature impacts led to white-etching ASBs characterized by ultrafine grain refinement, high dislocation density, and carbide dissolution. At elevated temperatures, both white- and black-etching recrystallized ASBs developed, including dynamic recovery, recrystallization, carbide retention, and reprecipitation. Despite coarser grains at high temperatures, ASBs maintained higher hardness than surrounding regions due to carbide reprecipitation effects. Microcrack initiation and propagation were observed within white-recrystallized ASBs at 600 °C, linked to carbide fragmentation and redistribution preceding the onset of high temperature effects. These findings highlight that while temperature minimally affects ASB susceptibility, it profoundly alters post-impact microstructural evolution. The results advance our understanding of thermomechanical responses in structural steels under extreme conditions and offer valuable insights for designing materials resistant to failure in high-temperature, high-strain-rate environments.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".