Residual stress and heat treatment – process design for bending fatigue strength improvement of carburized aerospace gears∗

B. L. Ferguson; A. M. Freborg; Zhichao Li

doi:10.3139/105.100435

Article

Residual stress and heat treatment – process design for bending fatigue strength improvement of carburized aerospace gears∗

B. L. Ferguson , A. M. Freborg and Zhichao Li

Published/Copyright: May 18, 2013

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From the journal HTM Journal of Heat Treatment and Materials Volume 62 Issue 6

Abstract

It is well established that carburization of low alloy steels promotes compressive residual surface stress upon quenching, and that compressive surface stresses enhance fatigue life. In an effort to build on these established facts, a project is in-progress to improve helicopter gear fatigue life the application of intensive quenching to achieve deeper compressive surface stress. Under US Army Sponsorship, DCT has demonstrated the feasibility of improving the bending fatigue life of Pyrowear 53 steel gears by achieving deeper compressive residual stress in carburized and quench hardened parts. Computer simulations of the conventional heat treatment practice and an intensive quenching process were conducted to analyze these heat treating processes in terms of metallurgical response and residual stress development. The timing and location of phase transformations during the quenching process was found to be critical to achieving the optimum residual stress state for service life. Beginning with simple notched bar coupons and progressing to full test gears, the physical bending fatigue results for these heat treated components are discussed in relation to the combined heat treatment residual and gear loading stresses from the computer simulations.

Kurzfassung

Es ist allgemein bekannt, dass beim Einsatzhärten niedriglegierter Stähle während des Abschreckens Druckeigenspannungen im Randgefüge aufgebaut werden und dass Druckeigenspannungen die Ermüdungslebensdauer verbessern. Ausgehend von diesem gesicherten Kenntnisstand soll in einer laufenden Untersuchung die Lebensdauer von Zahnrädern in Hubschraubergetrieben verbessert werden, in dem durch intensive Abschreckung tiefer reichende Druckeigenspannungen erreicht werden. Deformation Control Technology Inc. hat, gefördert durch die US Army, belegt, dass die Biegedauerfestigkeit von Zahnrädern aus dem Stahl Pyrowear 53 verbessert wird, wenn tiefere Druckeigenspannungen in einsatzgehärteten Teilen erreicht werden. Werkstoffverhalten und die Entwicklung der Eigenspannungen wurden für den herkömmlichen Wärmebehandlungsablauf und für eine Wärmebehandlung mit intensiver Abschreckung simuliert. Zeit und Ort der Phasenumwandlungen bestimmen danach entscheidend den für die Nutzungsdauer besten Eigenspannungszustand. Ergebnisse aus Dauerbiegeversuchen an entsprechend wärmebehandelten gekerbten Proben und Versuchsrädern werden mit den in der Simulation mit den Lastspannungen überlagerten Eigenspannungen aus der Wärmebehandlung verglichen.

^∗Lecture held at the 5^th Int. Conf. on Quenching and Control of Distortion and the European Conf. on Heat Treatment, 25–27 April 2007 in Berlin.

Dr. B. Lynn Ferguson is President and founder of Deformation Control Technology, Inc. (DCT). He has a Ph.D. in Materials Engineering from Drexel University. His areas of expertise include metallurgical engineering, powder metallurgy, forging preform design, structure/property relations, and finite element analysis.

Andrew M. Freborg is a Metallurgical Engineer from IIT. Formerly a Senior Process Metallurgist at Republic Engineered Steels, his background is in continuous casting and ingot casting of steel and in primary metal production. At DCT he has headed efforts in simulation of thermal barrier coatings and been an active user of our DANTE heat treatment simulation software.

Dr. Zhichao Li has a Ph.D. in Mechanical Engineering from Wright State University, and Bachelor and Master Degrees in Metal-forming from Harbin Institute of Technology. He has a strong background in computer analysis of metalforming and heat treat processes.

References

1. Freborg, A., et al.: Bending Fatigue Strength Improvement of Carburized Aerospace Gears. Proc. 23^rd ASM HTS Conf., Sept. 25–28, 2005, Pittbourgh, PA/USA, Herring, D. (Ed.), ASM Int., 2006, p. 186–195Search in Google Scholar

2. Dudley, Darle W.: Handbook of Practical Gear Design. McGraw-Hill Book Company, New York/USA, 1984Search in Google Scholar

Published Online: 2013-05-18

Published in Print: 2007-12-01

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https://doi.org/10.3139/105.100435