Effect of Nickel Addition and Porosity on Fracture Behaviour of Molybdenum Alloyed Powder Metallurgical Steel

Şadi Karagöz; Ridvan Yamanoğlu; Alpay Yilmaz; Ş. Hakan Atapek

doi:10.3139/120.110123

Article

Effect of Nickel Addition and Porosity on Fracture Behaviour of Molybdenum Alloyed Powder Metallurgical Steel

Şadi Karagöz , Ridvan Yamanoğlu , Alpay Yilmaz and Ş. Hakan Atapek

Published/Copyright: May 26, 2013

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From the journal Materials Testing Volume 52 Issue 4

Abstract

In the study for this contribution, good mechanical properties have been obtained from Mo (and Cu) alloyed PM-steels after suitable heat treatment. The influence of two to four weight percent nickel additions in these Mo (and Cu) alloyed PM-steels on the mechanical properties have been studied. The influence of such an alloying modification on the defect characteristics has also been investigated. The heat treatment of the steel material has been realized via a novel way, i.e. with the sinter-hardening method. The mechanical properties like tensile strength, matrix microhardness, and toughness have been measured. Transverse rupture tests have been implemented for toughness measurement while the transverse rupture strength data has been obtained by using the Weibull statistics. Microstructural studies have been performed with various microscopy techniques, where the general steel matrix was observed to exist of tempered martensite, bainite, residual austenite, and micropores. The amount of pores was measured with image analysis technique, while the amount of retained austenite was measured with the magnetic saturation method. The results show that the values of the transverse rupture test are determined primarily by pores/pore agglomerates that fit big size defect criteria. On the other hand, a positive effect of increasing Nickel content has been observed on the resistance against fracture.

Kurzfassung

Für den vorliegenden Beitrag wird gezeigt, dass sich durch Legieren mit Molybdän und Kupfer eines pulvermetallurgischen Stahles nach geeigneter Wärmebehandlung hervorragende mechanische Eigenschaften erzielen lassen. Der Einfluß eines Nickelzusatzes zwischen zwei und vier Prozent auf die mechanischen Eigenschaften solcher Werkstoffe wurde untersucht, ebenso wie der Einfluss der Legierungsmodifikationen auf die Charakteristika von Defekten. Die Wärmebehandlung wurde mittels eines neuen Verfahrens realisiert, dem so genannten Sinterhärten (sinter-hardening). Es wurden die mechanischen Eigenschaften der Werkstoffe, wie die Zugfestigkeit, die Mikrohärte des Gefüges und die Zähigkeit gemessen. Es wurden Biegeversuche zur Bestimmung der Zähigkeit durchgeführt, wobei die Biegebruchfestigkeit mittels Weibull-Statistik ermittelt wurde. Außerdem wurden Gefügeuntersuchungen mit verschiedenen Mikroskopiertechniken durchgeführt, wobei festgestellt wurde, dass die Matrix aus angelassenem Martensit, Bainit, Restaustenit und Mikroporen besteht. Die Porenanzahl wurde mittels Bildanalyseverfahren bestimmt, während der Restaustenit mit Magnetsonden ermittelt wurde. Die Ergebnisse zeigen, dass der Probenbruch vor allem durch Poren bzw. Porenansammlungen bestimmt ist, die die Kriterien für größere Defekte erfüllen. Außerdem wurde ein positiver Einfluss von Nickel hinsichtlich des Widerstandes gegen Bruch beobachtet.

Prof. Dr. Şadi Karagöz, born in Bolu-Turkey, graduated as M.Sc. at the Montanuniversität in Leoben, Austria, where he achieved also his doctoral degree. He worked as guest scientist at the Max Planck Institute for Metal Research in Stutgart. In 1984 he joined Yildiz University in Istanbul, Turkey. In 1993 he went to Kocaeli University, Izmit, Turkey, to build up the Department of Metallurgical and Materials Engineering where he was the head. He is now working at the Marmara University, Technology Faculty, Mechatronics Department, Istanbul.

Dipl.-Ing. Ridvan Yamanoğlu, born in Bilecik, graduated from the Kocaeli University, Izmit, Department of Metallurgical and Materials Engineering in 2002. He received his M.Sc. degree from the Kocaeli University, Izmit, in the same department. He has been working at Kocaeli University, Izmit, Dept. of Metallurgical and Materials Engineering since 2002.

Dr. Alpay Yilmaz, born in Istanbul, graduated from Technical University, Istanbul in 1996. He received his M. Sc. and Dr. Degrees from the Kocaeli University in Izmit, Dept. of Metallurgical and Materials Engineering. He is since 2007 in the Office of Technical Project and Administration, Turkish Land Forces Command, Ankara.

Dipl.-lng. Hakan Atapek, born in Adana, graduated from the Kocaeli University, Izmit, Department of Metallurgical and Materials Engineering in 2003. He received his M.Sc. degree from the Kocaeli University, Izmit, in the same department. He has been working at Kocaeli University, Izmit, Dept. of Metallurgical and Materials Engineering since 2003.

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Published Online: 2013-05-26

Published in Print: 2010-04-01

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https://doi.org/10.3139/120.110123