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Licensed Unlicensed Requires Authentication Published by De Gruyter November 21, 2017

Microstructural and mechanical characterization of the parabolic spring steel 51CrV4

Mikrostrukturelle und mechanische Charakterisierung des Parabelfederstahles 51CrV4
Aydın Kömeç, Kazım Dikçi, Ş. Hakan Atapek, Şeyda Polat and Gülşah Aktaş Çelik
From the journal Materials Testing

Abstract

Findings about the microstructural features of, spring steels are necessary for the producers to enhance their mechanical properties. There are several reports revealing the basic relation between microstructure and fatigue performance. However, the results are commonly obtained from universal test procedures and have limited use due to the lack of real service conditions. In this study, the microstructural features of 51CrV4 alloy, used as spring steel component, were investigated by metallographic examinations starting from raw material to the final product. Its fatigue behavior was investigated using a self-designed test machine and a test procedure approved by the automotive industry to simulate the service conditions. Fractographic examination of fatigue failed surface was carried out to specify the effect of microstructural features on the fracture. It was concluded that (i) both oxide and decarburization layers were minimized by shot peening and (ii) although tested samples had superior fatigue resistance and failed above 105 cycles limit, oxide layer played a major role for crack initiation.

Kurzfassung

Erkenntnisse über die mikrostrukturellen Merkmale von Federstählen sind für Hersteller notwendig, um die mechanischen Eigenschaften zu verbessern. Es existieren verschiedene Berichte über eine grundlegende Relation zwischen der Mikrostruktur und der Performanz bei Ermüdungsbelastung. Allerdings werden die Ergebnisse üblicherweise mit universellen Prüfprozeduren gewonnen und haben aufgrund fehlender realer Einsatzbedingungen nur eine begrenzte Anwendbarkeit. In der diesem Beitrag zugrunde liegenden Studie wurden die mikrostrukturellen Merkmale der Legierung 51CrV4, die für Federstahlkomponenten eingesetzt wird, mittels metallografischer Verfahren untersucht, und zwar beginnend vom Rohmaterial bis hin zum fertigen Produkt. Hierzu wurde die Lebensdauer unter Ermüdungsbeanspruchung mittels einer selbstgefertigten Prüfmaschine und einer von der Automobilindustrie anerkannten Prüfprozedur untersucht, um die realen Einsatzbedingungen zu simulieren. Es wurde eine fraktografische Untersuchung der Schwingbruchoberflächen durchgeführt, um die Auswirkungen der mikrostrukturellen Merkmale auf die Bruchoberfläche zu spezifizieren. Daraus wurde geschlossen, dass sowohl die Oxid- als auch die entkohlten Schichten durch Kugelstrahlen minimiert werden, und dass die Oxidschicht eine wesentliche Bedeutung für die Rissinitiierung hat, obwohl die geprüften Proben eine überragende Ermüdungsresistenz hatten und erst über dem Limit von 105 Lastwechseln versagten.


*Correspondence Address, Dr. Ş. Hakan Atapek, Department of Metallurgical and Materials Engineering, Umuttepe Campus, Kocaeli University, 41380 Kocaeli, Turkey, E-mail:

A. Aydın Kömeç, born in 1967, graduated from Istanbul Technical University, Department of Metallurgical Engineering, Turkey. He started working at TT Çelikyay Co. Düzce, Turkey in 1994 as production engineer and he is currently the plant manager.

Kazım Dikçi, born in 1973, graduated from Istanbul Technical University, Machine Programme, Turkey. He started working at TT Çelikyay Co., Düzce, Turkey in 1996 in Quality Department and he is currently the Quality and R&D manager.

Dr. Ş. Hakan Atapek, born in 1979, graduated from Kocaeli University, Department of Metallurgical and Materials Engineering, Kocaeli, Turkey. He received his MSc and PhD from the same department of Kocaeli University. He is currently working as Associate Professor in the Department of Metallurgical and Materials Engineering oft Kocaeli University. He was also a postdoctoral researcher at Karlsruhe Institute of Technology, Institut für Angewandte Materialien-Werkstoffkunde, Germany, from May 2012 to May 2013 and studied the physical metallurgy of precipitation hardenable copper alloys. His interests are in the metallic materials, materials characterization and fractography.

Dr. Şeyda Polat graduated from Middle East Technical University, Department of Metallurgical Engineering, Ankara, Turkey. She received her MSc and her PhD degree in Materials Science and Engineering at the University of Illinois in Urbana-Champaign, USA, in 1980 and 1987, respectively. She worked as a research scientist at BRISA Bridgestone Sabancı Tire Manufacturing and Trading Inc., Kocaeli, Turkey from 1988 to 2002. Then she became a faculty member at Kocaeli University, where she is currently working as Associate Professor in the Department of Metallurgical and Materials Engineering. Her research interests include phase transformations, composite materials, tire technology and materials characterization.

Gülşah Aktaş Çelik, born in 1989, graduated from Kocaeli University, Department of Metallurgical and Materials Engineering, Kocaeli, Turkey. She received her MSc from the same department, at which she s currently a PhD student and working as a research assistant.


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Published Online: 2017-11-21
Published in Print: 2017-11-15

© 2017, Carl Hanser Verlag, München