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On the relation between composition, oxidation and machinability of tool steels
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
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2008 (English)Conference paper (Refereed)
Place, publisher, year, edition, pages
National Category
Materials Engineering
URN: urn:nbn:se:uu:diva-172424OAI: oai:DiVA.org:uu-172424DiVA: diva2:514617
The 13th Nordic Symposium on Tribology, Tampere, Finland, June 10-13, 2008
Available from: 2012-04-10 Created: 2012-04-10 Last updated: 2016-04-12
In thesis
1. On the Machinability of High Performance Tool Steels
Open this publication in new window or tab >>On the Machinability of High Performance Tool Steels
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The continuous development of hot forming tool steels has resulted in steels with improved mechanical properties. A change in alloying composition, primarily a decreased silicon content, makes them tougher and more wear resistant at elevated temperatures. However, it is at the expense of their machinability. The aim of this study is to explain the mechanisms behind this negative side effect.

Hot work tool steels of H13 type with different Si content were characterised mechanically, and evaluated analytically and by dedicated machining tests. Machining tests verified that materials with low Si content displayed reduced machinability due to their stronger tendency to adhere to the cutting edge. Three hypotheses were tested.

The first hypothesis, that the improved toughness of the low Si steels is the reason behind their relatively poor machinability, was rejected after machining tests with one low Si steel heat treated to the same relatively low toughness as conventional hot work tool steels.

The second hypothesis, that a change in oxidation properties, also associated with the change in Si composition, lies behind the reduced machinability was investigated by dedicated tests and evaluations. It was found that the oxide thickness increased with reduced Si content and that there was an enrichment of Cr at the oxide/steel interface. The differences in oxide thickness and the possible differences in oxidation properties may influence the machinability of the materials through their different abilities to adhere to the cutting edge.

The third hypothesis, that a high enough temperature to initiate phase transformation from ferrite to austenite is generated during machining of the tool steels, was also investigated. This may lead to a reduced machinability because higher austenite content is directly related to higher compressive stresses and higher cutting forces. This causes accelerated tool wear. This hypothesis was verified by ThermoCalc calculation of austenite content in the steels, which showed a good agreement with Gleeble compression tests and cutting force measurements.

This thesis confirms that a reduced Si content in conventional H13 steel improves the toughness, reduces the oxidation resistance and lowers the ferrite-to-austenite transformation temperature. The reduction in austenite temperature is probably the most important factor behind the reduced machinability. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 58 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 927
hot work tool steels, alloying composition, machinability
National Category
Research subject
Materials Science
urn:nbn:se:uu:diva-172427 (URN)978-91-554-8349-4 (ISBN)
Public defence
2012-06-04, Häggsalen, Ångströmlaboratoriet, Uppsala, 12:00 (Swedish)
Available from: 2012-05-08 Created: 2012-04-10 Last updated: 2012-08-01Bibliographically approved

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