Effect of Thermal Treatments and Carbon Potential on Bending Fatigue Performance of SAE 4320 Gear Steel

This project investigated the effect of carburizing carbonpotential and thermal history on the bending fatigue performance of carburized SAE 4320 gear steel. ModifiedBrugger cantilever bending fatigue specimens were carburized at carbon potentials of 0.60, 0.85, 1.05, and 1.25 wt. pet. carbon, and w...

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Bibliographic Details
Published in:SAE transactions 1999-01, Vol.108, p.547-556
Main Authors: Medlin, Dana J., Cornelissen, Bastiaan E., Matlock, David K., Krauss, G., Filar, Raymond J.
Format: Article
Language:English
Subjects:
Austenite
Bending
Carbon
Carburizing
Endurance
Fatigue
Heat treatment
Rapid quenching
Residual stress
Specimens
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Summary:This project investigated the effect of carburizing carbonpotential and thermal history on the bending fatigue performance of carburized SAE 4320 gear steel. ModifiedBrugger cantilever bending fatigue specimens were carburized at carbon potentials of 0.60, 0.85, 1.05, and 1.25 wt. pet. carbon, and were either quenched and tempered or quenched, tempered, reheated, quenched, and tempered. The reheat treatment was designed to lower the solute carbon content in the case through the formation of transition carbides and refine the prior austenite grain size. Specimens were fatigue tested in a tension/tension cycle with a minimum to maximum stress ratio of 0.1. The bending fatigue results were correlated with case and core microstructures, hardness profiles, residual stress profiles, retained austenite profiles, and component distortion. The lower case carbon contents resulted in higher bending fatigue endurance limits, a result attributed to lower retained austenite and higher residual compressive stresses. The lower carbon potential specimens experienced more dimensional distortion compared to the higher carbon potential specimens. The bending fatigue endurance limits of the reheated specimens were approximately 10% higher than those of the quenched and tempered specimens.
ISSN:0096-736X
2577-1531