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Galling resistance evaluation of tool steels by two different laboratory test methods for sheet metal forming
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
Dalarna University.
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
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2012 (English)In: Lubrication Science, ISSN 0954-0075, Vol. 24, no 6, 263-272 p.Article in journal (Refereed) Published
Abstract [en]

Adhesive accumulation of work material on the tool surface is today a major problem in many sheet metal-forming applications. Different laboratory test methods are used to investigate galling with respect to different tool materials, lubricants and process conditions. In the present study, the galling resistance of a modern nitrogen-alloyed powder metallurgy tool steel and an conventional ingot cast D2 type tool steel was evaluated under lubricated sliding against ferritic stainless steel sheets using a commercial pin-on-disc (POD) and an in-house made slider-on-flat-surface (SOFS) tribotester. The investigated tool steels ranked similarly in terms of galling resistanc in both test methods. However, sliding distances to galling were longer for the SOFS equipment due to continuous sliding on new lubricated sheet surface. Best performance was demonstrated by the powder metallurgy tool steel treated to 65 HRC. Differences in friction behaviour and galling initiation were analysed on the basis of the two different working conditions, i.e. open (SOFS) and closed (POD) tribosystems. Copyright © 2012 John Wiley & Sons, Ltd.

Place, publisher, year, edition, pages
John Wiley & Sons, 2012. Vol. 24, no 6, 263-272 p.
Keyword [en]
slider-on-flat-surface, pin-on-disc, sheet metal forming, galling, stainless steel
National Category
Tribology
Research subject
Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-15338DOI: 10.1002/ls.1180ISI: 000308637600002OAI: oai:DiVA.org:kau-15338DiVA: diva2:562933
Available from: 2012-10-26 Created: 2012-10-26 Last updated: 2014-06-17Bibliographically approved
In thesis
1. The early stage of galling
Open this publication in new window or tab >>The early stage of galling
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In sheet metal forming (SMF) of materials such as stainless steels there is a major problem with transfer and accumulation of sheet material to the metal forming tool surface. The problem is known as galling; a kind of severe adhesive wear, which results in severe scratching of produced parts. In this thesis, galling observed in contacts between tool steels and stainless steel sheets under lubricated sliding conditions was studied, focusing on the early stage of galling. It was found that changes in friction cannot be used as galling indicator in the early stage of galling because transfer and accumulation of sheet material happens even though friction is low and stable. The progression of galling is influenced by tool steel damage occurring around the tool steel hard phases caused by sheet material flow, which results in formation of wear-induced galling initiation sites. A correlation between the critical contact pressure to galling and sheet material proof stress was found. Galling happened at lower pressures for sheet material with lower proof stress possibly due to easier sheet material flow, resulting in quicker tool damage. Material transfer and tool steel damage were delayed for tool steels comprising homogenously distributed, small and high hard phases. Additionally, the galling resistance was higher for tool steels with higher hardness due to decreased tool steel damage. In a comparison between observations of the worn tool surfaces after wear tests and calculations in FEM it was found that material transfer did not take place at regions with highest contact pressures but at regions with highest plastic strains. The results obtained in this thesis indicate that tool steel damage and sheet material flow occurring in the contact during sliding are important factors influencing galling.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2012. 41 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2012:51
Keyword
Galling, Stainless steel, Tool steel, Friction, Sliding wear, SOFS, Tribology, Wear
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-15345 (URN)978-91-7063-462-8 (ISBN)
Presentation
2012-12-07, Eva Erikssonsalen, 21A 342, Karlstads Universitet, Karlstad, 13:15 (English)
Opponent
Supervisors
Available from: 2012-11-21 Created: 2012-10-26 Last updated: 2012-11-21Bibliographically approved
2. The influence of tool steel microstructure on galling
Open this publication in new window or tab >>The influence of tool steel microstructure on galling
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In sheet metal forming (SMF) of materials such as stainless steels there is a major problem with transfer and accumulation of sheet material to the metal forming tool surface. The problem is known as galling; a sort of severe adhesive wear, which results in severe scratching of produced parts. In this thesis, the overall aim was to gain knowledge of the influence of tool steel microstructure on galling initiation under sliding conditions. It was discovered that material transfer and tool steel damage caused by sheet material flow creating wear-induced galling initiation sites occurred in the early stage of galling. The galling resistance was higher for tool steels with higher matrix hardness due to better resistance to tool steel damage. Initial friction and critical contact pressure to galling was influenced by the strength of the sheet material. Material transfer happened at low pressures and the friction value was high in a case of sheet materials with lower proof strength, possibly due to the sheet contact against the tool steel matrix resulting in high adhesion and quicker tool damage. It was demonstrated that, in addition to hardness of the tool steel matrix and sheet material proof strength, tool steel microstructural features like size, shape, distribution and height of hard phases are important parameters influencing galling. Tool steels comprising homogeneously distributed, small and high hard phases better prevented the contact between sheet material and the tool steel matrix. Thus, a metal to metal contact with high friction was more efficiently avoided, which resulted in better tool performance.

 

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2014. 42 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2014:35
Keyword
Galling, Microstructure, Material transfer, Tool steel, Stainless steel, Metall transfer
National Category
Tribology
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-32113 (URN)978-91-7063-568-7 (ISBN)
Public defence
2014-08-29, Ljungbergsalen, 21A 244, Universitetsgatan 2, Karlstad, 10:15 (English)
Opponent
Supervisors
Available from: 2014-06-17 Created: 2014-05-19 Last updated: 2014-06-17Bibliographically approved

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