Ultrahigh-strength steels in the design of durable machines
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
Arina auditorium (TA105)
Topic of the dissertation
Ultrahigh-strength steels in the design of durable machines
Doctoral candidate
Master of Science (Technology) Lassi Keränen
Faculty and unit
University of Oulu Graduate School, Faculty of Technology, Materials and Mechanical Engineering
Subject of study
Machine design
Opponent
Professor Reijo Kouhia, Tampere University
Second opponent
Doctor Tuomas Rantalainen, Terästorni Oy, Lappeenranta
Custos
Professor Emil Kurvinen, University of Oulu
Ultrahigh-strength steels in the design of durable machines
This dissertation explores the utilization of ultrahigh-strength steels in different machines, focusing on how the welding affects their final properties. The wide-ranging research combines steel research and machine design, bringing valuable contributions to practical design work involving ultrahigh-strength steels. The machinery industry is a significant industry for Finland, which together with the metal industry accounts for one-third of Finland’s exports. In Finland, investment machines of very high quality are typically manufactured, requiring high productivity and efficiency.
The aim of the study was to facilitate the use of new ultrahigh-strength steels. Modern society relies heavily on various machines, which are wanted to be high in productivity and efficiency. At the same time, there is a need to reduce the emissions caused by machinery, transport and industry. Ultrahigh-strength steels allow machines and equipment to be made more durable, lighter, safer, more competitive and environmentally friendly, which reduces emissions starting from steel production.
However, the use of ultrahigh-strength steels is slowed down by the need for more precise design, from concept design to material selection, strength calculation, and manufacturing. Many machines are made by welding, which introduces a lot of heat into the material. Since the strength of ultrahigh-strength steels is often based on heat treatments, the heating caused by welding changes the properties of the steel, such as toughness and strength, and causes residual stresses. These changes are not yet fully understood and significantly affect the durability of welded machine parts.
The research tested ultrahigh-strength steels at different operating temperatures between -80 °C and +1000 °C, both unwelded and welded. The effects of welding on the residual stress state of ultrahigh-strength steel were also investigated through measurements. In addition, case studies demonstrated the potential of ultrahigh-strength steels in various machines.
The doctoral dissertation offers new methods for designers to utilize ultrahigh-strength steels more efficiently. The developed models can be used to assess the final material properties, strength, toughness, and the effects of welding at different operating temperatures. By utilizing these methods, machine design and manufacturing can be optimized more efficiently, leading to improved performance, safety and environmental friendliness. The results are also significant for the industry, as they provide ways to meet increasing performance and environmental demands.
The aim of the study was to facilitate the use of new ultrahigh-strength steels. Modern society relies heavily on various machines, which are wanted to be high in productivity and efficiency. At the same time, there is a need to reduce the emissions caused by machinery, transport and industry. Ultrahigh-strength steels allow machines and equipment to be made more durable, lighter, safer, more competitive and environmentally friendly, which reduces emissions starting from steel production.
However, the use of ultrahigh-strength steels is slowed down by the need for more precise design, from concept design to material selection, strength calculation, and manufacturing. Many machines are made by welding, which introduces a lot of heat into the material. Since the strength of ultrahigh-strength steels is often based on heat treatments, the heating caused by welding changes the properties of the steel, such as toughness and strength, and causes residual stresses. These changes are not yet fully understood and significantly affect the durability of welded machine parts.
The research tested ultrahigh-strength steels at different operating temperatures between -80 °C and +1000 °C, both unwelded and welded. The effects of welding on the residual stress state of ultrahigh-strength steel were also investigated through measurements. In addition, case studies demonstrated the potential of ultrahigh-strength steels in various machines.
The doctoral dissertation offers new methods for designers to utilize ultrahigh-strength steels more efficiently. The developed models can be used to assess the final material properties, strength, toughness, and the effects of welding at different operating temperatures. By utilizing these methods, machine design and manufacturing can be optimized more efficiently, leading to improved performance, safety and environmental friendliness. The results are also significant for the industry, as they provide ways to meet increasing performance and environmental demands.
Last updated: 16.1.2025