Examinations of casting cracks in a high alloy steel valve

Mustafa Çöl; Fulya Kahrıman; Mehmet Uygun; Serhat Adişen

doi:10.3139/120.110919

Article

Examinations of casting cracks in a high alloy steel valve

Mustafa Çöl , Fulya Kahrıman , Mehmet Uygun and Serhat Adişen

Published/Copyright: August 30, 2016

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From the journal Materials Testing Volume 58 Issue 9

Abstract

High alloy steels are widely used for high temperature and corrosion resistance applications in power plants, e. g., in chemical and petroleum industries. Mechanical properties of these alloys (e. g., hardness and tensile strength) can be altered by suitable heat treatment. This paper deals with failure investigations of a cast valve made of high alloy steel. The samples were taken from valve body and prepared by metallographic techniques. Microstructural defects causing cracking were investigated using light microscopy and scanning electron microscopy/energy dispersive X-ray spectrometry. Segregation areas at the grain boundaries in the microstructure of the material were observed. Casting was repeated by taking necessary measures during the production in order to eliminate these heterogeneous regions and then suitable heat treatment was applied to the part. The samples taken from the last part were also examined. As a result, a homogeneous microstructure was obtained and no macro or micro cracks were observed.

Kurzfassung

Hochlegierte Stähle werden breitflächig angewandt, um eine Hochtemperatur- und Korrosionsbeständigkeit von Komponenten in Kraftwerken in der chemischen und in der Petroindustrie zu erreichen. Die mechanischen Eigenschaften dieser Legierungen (wie bspw. die Härte und die Zugfestigkeit) können mittels geeigneter Wärmebehandlung geändert werden. Der vorliegende Beitrag beschäftigt sich mit Schadensuntersuchungen an einem gegossenen Ventil, das aus einem hochlegierten Stahl gefertigt wurde. Die Proben wurden aus dem Ventilkörper entnommen und für metallografische Techniken präpariert. Es wurden die mikrostrukturellen Defekte, die eine Rissbildung verursacht haben, mittels Licht- und Rasterelektronenmikroskopie sowie EDS untersucht. Hierbei wurden heterogene Zonen an den Korngrenzen in der Mikrostruktur festgestellt. Der Gießprozess wurde wiederholt, wobei die notwendigen Maßnahmen während der Produktion getroffen wurden, solche hetereogenen Zonen zu beseitigen und anschließend wurde eine geeignete Wärmebehandlung mit dem entsprechenden Teil durchgeführt. Aus dem verbesserten Gießprozess wurden Proben entnommen und untersucht. In diesen Proben wurden keine Makro- oder Mikrorisse beobachtet.

*Correspondence Address, Research Assistant Fulya Kahriman, Department of Metallurgical and Materials Engineering, Umuttepe Campus, Kocaeli University, 41380 Kocaeli, Turkey, E-mail: fulya.kahriman@kocaeli.edu.tr

Dr. Mustafa Çöl, born in 1962, graduated from İstanbul Technical University, Department of Metallurgical and Materials Engineering, Turkey. He received his MSc. and his PhD degree in Materials Science at RWTH Aachen Technical University, Germany in 1991 and 1995, respectively. He is currently working as Associate Professor in the Department of Metallurgical and Materials Engineering, Kocaeli University, Turkey. His research interests are casting processes, aluminum alloys and metal alloying.

Fulya Kahriman, born in 1981, graduated from Kocaeli University, Department of Metallurgical and Materials Engineering, Turkey. She received her MSc degree from the same department in 2008. She is currently working as a research assistant at Kocaeli University, Department of Metallurgical and Materials Engineering, where she is a PhD student. Her research interests are metallography, materials characterization, fractography and aluminum alloys.

Mehmet Uygun, born in 1988, graduated from Kocaeli University, Department of Metallurgical and Materials Engineering, Turkey. He is working as an engineer in a Ministry of the Republic of Turkey in Gümüşhane.

Serhat Adişen graduated from Yıldız Technical University, Department of Metallurgical Engineering, Istanbul, Turkey. He finished training in Quality Systems Management at Istanbul Technical University, Turkey in 2007–2008. He is working as Director of Quality at Akmetal Metallurgical Ind. Corp., Istanbul, Turkey. His research interests include quality management, manufacturing, business process improvement and innovation management.

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Published Online: 2016-08-30

Published in Print: 2016-09-07

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https://doi.org/10.3139/120.110919