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The Positive Effect of Nitrogen Alloying of Tool Steels Used in Sheet Metal Forming
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Sheet metal forming processes are mechanical processes, designed to make products from metal sheet without material removal. These processes are applied extensively by the manufacturing industry to produce commodities such as heat exchangers or panels for automotive applications. They are suitable for production in large volumes.

A typical problem in forming operations is accumulation of local sheet material adherents onto the tool surface, which may deteriorate the subsequent products. This tool failure mechanism is named galling. The aim of this work is to explain the mechanisms behind galling and establish factors how it can be reduced.

The focus of this work is on the influence of tool material for minimum risk of galling. Experimental tool steels alloyed with nitrogen were designed and manufactured for systematic tribological evaluation. Reference tool materials were conventional cold forming tool steels and coated tool steels. The sheet material was austenitic stainless steel AISI 304, which is sensitive for galling. A variety of lubricants ranging from low to high viscous lubricants were used in the evaluation.

The properties of the tool materials were characterized analytically and their tribological evaluation included industrial field tests and several laboratory-scale tests. The testing verified that nitrogen alloying has a very positive effect for improving galling resistance of tool steels. Tool lives comparable to the coated tool steels were achieved even with low viscous lubricants without poisonous additives.

The hypothesis used for the explanation of the positive effect of nitrogen alloying is based on the critical local contact temperature at which the lubrication deteriorates. Therefore, the contact mechanism at the tool-sheet interface and the local energy formation were studied systematically. Theoretical considerations complemented with FEA analysis showed that a small size of hard particles with a high volume fraction gives low local contact loads, which leads to low frictional heating. Also, an even spacing between the hard particles and their frictional properties are of importance. Nitrogen alloyed tool steels have these properties in the form of small carbonitrides.

The finding of this work can be applied to a wide range of applications that involve sliding metal contacts under severe tribological loading.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. , 56 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1045
Keyword [en]
galling, nitrogen, tool steel, sliding contact, metal forming
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
URN: urn:nbn:se:uu:diva-198747ISBN: 978-91-554-8673-0 (print)OAI: oai:DiVA.org:uu-198747DiVA: diva2:617657
Public defence
2013-06-12, Sal 2001 Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2013-05-21 Created: 2013-04-24 Last updated: 2013-08-30Bibliographically approved
List of papers
1. Influence of Nitrogen Alloying on Galling Properties of PM tool steels
Open this publication in new window or tab >>Influence of Nitrogen Alloying on Galling Properties of PM tool steels
2002 (English)In: -, 216-226 p.Article in journal (Refereed) Published
Abstract [en]

The objective of this study is to investigate the effect of nitrogen alloying of tool steels on their galling properties. Nitrogen is introduced to the steel composition by solid state nitriding  with ammonia gas at 550-600 oC. The base material composition is in powder form during nitriding. Different nitrogen contents are experimented. The hard phases present in steel composition are of type M(C,N) and M6C. The materials are consolidated by HIP process. Galling behaviour of the produced alloys is evaluated with slider-on-sheet tribological test method. As a reference for nitrogen alloyed compositions various PM tool steel grades and CVD coated tool steels are chosen. The ability of the test materials to avoid formation of galling adherants is tested against AISI 304 stainless steel with a low viscose lubricant. The test results show that nitrogen alloying increases manifold resistance against galling reaching equal behaviour as for CVD coated tool steels.

 

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2002
Keyword
carbonitride, PM tool steel, nitriding, galling, stainless steel
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-198744 (URN)
Conference
6th International Tooling ConferenceKarlstad 10-13 September 2002
Available from: 2013-04-24 Created: 2013-04-24 Last updated: 2013-05-13
2. Adhesion of selected PM tool steels and coated tool steels in sliding contact with stainless steel
Open this publication in new window or tab >>Adhesion of selected PM tool steels and coated tool steels in sliding contact with stainless steel
2003 (English)In: Int.Conference on Powder Metallurgy and Particilate Materials, Las Vegas, 2003, 2003Conference paper, Published paper (Other (popular scientific, debate etc.))
Identifiers
urn:nbn:se:uu:diva-24886 (URN)
Available from: 2007-02-08 Created: 2007-02-08 Last updated: 2013-05-13
3. Influence of tool steel microstructure on galling resistance against stainless steel.
Open this publication in new window or tab >>Influence of tool steel microstructure on galling resistance against stainless steel.
2003 (English)In: Int. Conference Leed-Lyon Symposium, Lyon, 2003, 2003Conference paper, Published paper (Other (popular scientific, debate etc.))
Identifiers
urn:nbn:se:uu:diva-24887 (URN)
Available from: 2007-02-08 Created: 2007-02-08 Last updated: 2013-05-13
4. Tool material aspects in forming of stainless steel with easy-to-clean lubricants
Open this publication in new window or tab >>Tool material aspects in forming of stainless steel with easy-to-clean lubricants
Show others...
2004 (English)In: Innovations in Metal Forming, Brescia, 2004Conference paper, Published paper (Other (popular scientific, debate etc.))
Identifiers
urn:nbn:se:uu:diva-24904 (URN)
Available from: 2007-02-08 Created: 2007-02-08 Last updated: 2013-05-13
5. The contribution of the surface properties of tool steels for galling behaviour in sheet metal forming
Open this publication in new window or tab >>The contribution of the surface properties of tool steels for galling behaviour in sheet metal forming
2006 (English)Conference paper, Published paper (Other (popular science, discussion, etc.))
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-24917 (URN)
Conference
Int. Conference Tooling Materials and their applications from research to market, Torino, 2006
Available from: 2007-02-08 Created: 2007-02-08 Last updated: 2016-06-23
6. Clean forming of stainless steel and titanium products by lubricious oxides
Open this publication in new window or tab >>Clean forming of stainless steel and titanium products by lubricious oxides
2012 (English)In: Proceedings of NORDTRIB, Trondheim: NTNU , 2012Conference paper, Published paper (Refereed)
Abstract [en]

Big social benefits can be attained through increased use of stainless steel or titanium in new sheet metal applications. Unfortunately, forming of these materials is often a challenging and costly operation, that can lead to environmental and health problems when solving the technical limitations. One possible method to overcome these problems is to use an oxide layer with optimised properties to reduce friction during forming, either as a substitute to lubricants, or acting as a conversion layer for environmental friendly lubricants. The most beneficial group of oxides for low friction is called lubricious oxides with a rutile crystal structure. Oxides of Ti, Mo, V, and Zn can build rutiles under certain contact temperatures during rolling and forming. The aim of this investigation is to evaluate if oxides designed on metal sheets display a lubricious effect under conditions similar to industrial forming processes. Preliminary evaluations show a beneficial influence of two oxides types, on stainless steel and on titanium. More work is needed to test the lubricating effect in other forming operations and to analyse the sustainability aspects for products manufactured with this alternative surface.

Place, publisher, year, edition, pages
Trondheim: NTNU, 2012
Keyword
lubricious oxides, friction, sheet metals, sliding contact, forming
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-198746 (URN)978-82-14-05270-1 (ISBN)
Conference
15th Nordic Symposium on TribologyTrondheim 13-15 June 2012; Trondheim, Norway
Available from: 2013-04-24 Created: 2013-04-24 Last updated: 2014-03-04Bibliographically approved

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Citation style
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