Effect of microstructural characteristics and mechanical properties on the impact-abrasive and abrasive wear resistance of ultra-high strength steels

Thesis event information

Date and time of the thesis defence

Place of the thesis defence

Linnanmaa, auditorium L5. Remoten connestion: https://oulu.zoom.us/j/69320702588

Topic of the dissertation

Effect of microstructural characteristics and mechanical properties on the impact-abrasive and abrasive wear resistance of ultra-high strength steels

Doctoral candidate

Master of Science Oskari Haiko

Faculty and unit

University of Oulu Graduate School, Faculty of Technology, Materials and Mechanical Engineering Research Group

Subject of study

Materials Engineering

Opponent

Associate Professor Jens Hardell, Luleå University of Technology

Second opponent

Doctor Marke Kallio, Metso Outotec

Custos

Professor Jukka Kömi, University of Oulu

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Steel research for improved wear resistance in demanding applications

The primary aim of the thesis has been to provide new information regarding the wear of ultra-high strength steels in demanding wear conditions. The emphasis has been on understanding which features affect the abrasive and impact wear resistance of steels.

The efficiency of machinery has improved dramatically in many industrial sectors during the past few decades. Some examples are the applications used in mining and mineral handling as well as agricultural machinery. While the processes become faster and the machinery more powerful, the materials used in the applications face increasing requirements, especially regarding wear resistance. In addition, more advanced materials are required in mobile machinery for stronger, but lightweight structures to reduce emissions.

Ultra-high strength steels are important for various applications which are used in harsh conditions facing heavy wear. Several martensitic grade steels were tested in the study to gain more knowledge on their wear behavior. Moreover, novel carbide-free bainitic (CFB) concept steels were tested for wear performance. The wear tests were done at Tampere Wear Center (Tampere University) with application-oriented testing devices. Mechanical testing and material characterization were also included in the research work.

The results revealed that the initial hardness on the steels is a major factor in terms of wear resistance, but the work-hardening capability of steels was also found crucial. Retained austenite, tempering and prior austenite grain size were found to influence the wear of martensitic steels. New bainitic steels showed extremely promising wear test results, which was mainly attributed to the high work-hardening capability.

The research work provides new information, which can be utilized to develop even stronger and more durable wear-resistant steels. The results may also be used for improving other ultra-high strength steels, such as protection steels and automotive steels for increased safety. Furthermore, the research work on the novel bainitic steels should be continued to enable the use of CFB steels as wear-resistant materials.
Last updated: 6.9.2021