Retained Austenite - Residual Stress - Distortion Relationships in Carburized SAE 6820 Steel
Bibliographic record
Abstract
SAE 8620 steel is typically used in the carburized condition for powertrain applications in the automotive industry, e.g. gears, roller bearings, camshafts. Such steels always contain retained austenite to varying degrees in the as-hardened and also in the tempered microstructures. As well as retained austenite, heat treatment can produce residual stresses, which lead to distortion (size and shape). The intent of this study was to investigate the effect of heat treatment parameters on the amount of retained austenite, residual stress and distortion in carburized SAE 8620 steel. A specially designed specimen, the Navy C-ring, was used for this study. The steel was first normalized prior to machining the Navy C-ring specimens. The specimens were then heat treated by carburizing at 927°C or 954°C (1700°F or 1750°F) at four levels of carbon potential (0.9, 1.0, 1.1, 1.2) followed by oil quenching and tempering at either 149°C or 177°C (300°F or 350°F). The distortion of the C-ring was evaluated by dimensional measurements of the inner diameter, outer diameter, gap width and thickness for size distortion, as well as flatness, cylindricity and roundness for shape distortion. X-ray diffraction (XRD) techniques were used to determine the residual stress and the amount of retained austenite. The amount of retained austenite was also measured by optical metallography. The amount of retained austenite and the residual stress increased with increasing carburizing temperature and carbon potential and decreased upon tempering. There was not a significant further reduction in the amount of retained austenite and residual stress when the tempering temperature was increased from 149°C to 177°C. Distortion was influenced by both the amount of retained austenite and the magnitude of the residual stress. With increasing retained austenite/residual stress, the distortion became more serious. Based on the distortion data for 3 parameters (OD, gap width and flatness) for the quenched and tempered specimens, the amount of retained austenite for minimum distortion was approximately 25%.
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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 | 0.000 | 0.000 |
| 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".