Fatigue behavior and mechanism of KMN in a very high cycle regime

Pengfei Wang; Weiqiang Wang; Ming Zhang; Jianfeng Li

doi:10.3139/120.111117

Article

Fatigue behavior and mechanism of KMN in a very high cycle regime

Pengfei Wang , Weiqiang Wang , Ming Zhang and Jianfeng Li

Published/Copyright: December 28, 2017

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From the journal Materials Testing Volume 60 Issue 1

Abstract

The fatigue behavior of KMN with different heat treatments (marked as S and I) used in compressor blades was investigated in a very high cycle fatigue regime. It was found that the S-N curve of KMN-I had a slow decline after 10⁶ cycles, while the fatigue limit was observed in KMN-S. In order to explain the difference between the two steels, mechanical property tests, metallographic observation, and SEM analysis were carried out. The results showed that surface fractures were mostly observed in KMN-I, while interior cracks initiated from nonmetallic inclusions which were identified as MnS by SEM. In addition, the surface defects were simplified as cracks using fracture mechanics and the fatigue strength model with surface defects was modified, which proved to be more in agreement with the experimental results than the Murakami model.

Kurzfassung

Das Ermüdungsverhalten von KMN mit verschiedenen Wärmebehandlungen (markiert als S und I), wie sie für Verdichterschaufeln verwendet werden, wurde im Bereich sehr hoher Lastwechselzahlen untersucht. Es stellte sich heraus, dass die Wöhlerkurve von KMN-I eine leichte Absenkung nach 10⁶ Lastwechseln aufwies, während die Dauerfestigkeit von KMN-S erreicht wurde. Um die Unterschiede für die beiden Stähle zu erklären, wurden Prüfungen der mechanischen Eigenschaften, eine metallografische Untersuchung und REM-Analysen durchgeführt. Die Ergebnisse zeigen, dass Oberflächenrisse überwiegend im KMN-I zu beobachten sind, während interne Risse ausgehend von nichtmetallischen Einschlüssen, die mittels REM als MnS identifiziert wurden, auftreten. Zudem wurden die Oberflächendefekte als Risse vereinfacht, was zu besserer Übereinstimmung mit den experimentellen Ergebnissen führte als das Murakami Modell.

*Correspondence Address, Prof. Dr. Weiqiang Wang, School of Mechanical Engineering, Shandong University, 17923 Jingshi Road, Jinan, P. R. China, E-Mail: wqwang@sdu.edu.cn, batiworldwang@163.com

Pengfei Wang, born in 1990, studied Process Equipment and Control at Zhejiang University, China, from 2007 to 2011. In 2011, he graduated and received his Bachelor's degree. Then, he went to Shandong University, China for a doctoral degree. His main research areas are equipment failure analysis, safety evaluation and life assessment technology. He participated in the National Key Basic Research and Development Program (973 Program 2011CB013401) and many equipment fatigue failure analysis projects.

Prof. Weiqiang Wang, born in 1959, graduated from Shandong Institute of Chemical Technology, China, and received his Bachelor's degree in 1982. In 1990, graduated from East China University of Science and Technology and received his doctoral degree in Engineering. He is employed at Shandong University as Professor since 1997. His main research areas are engineering materials and structural failure, and service safety theory. He is lecturing at the School of Mechanical Engineering Shandong University and gives courses in process equipment safety technology, engineering materials and structural failure, elasto-plastic mechanics and systems safety engineering.

Dr. Ming Zhang, born in 1987, studied Process Equipment and Control at Shandong University, China, from 2004 to 2008. In 2008, he graduated and received his Bachelor's degree. In 2015, he graduated from Shandong University and received his doctoral degree in Engineering. His main research areas are equipment failure analysis, safety evaluation and life assessment technology.

Prof. Jianfeng Li, born in 1963, graduated from Shandong University of Technology, China and received his Bachelor's degree. In 1991and his doctoral degree in Engineering. In 2000, he went to Michigan University of Technology, USA, as a Postdoctoral Fellow. He is employed at Shandong University as Professor since 1995. His main research areas are environmentally conscious design and manufacturing, design for disassembly, remanufacturing and optimization of mechanical processing parameters.

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Published Online: 2017-12-28

Published in Print: 2018-01-04

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https://doi.org/10.3139/120.111117