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Estimating inclusion content in high performance steels
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
2008 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Non-metallic inclusions in steel pose a major problem for the fatigue resistance, especially regarding fatigue at very long lives corresponding to low cyclic stress levels, as well as being detrimental to material toughness and polishability.

The largest inclusions are quite rare, which makes conventional detection methods timeconsuming if reliable results are to be obtained. Based on surface scanning using light or electron microscopes, these methods provide results that have to be converted to reflect the statistical volume distribution of inclusions.

Very high cycle fatigue (in the order of 109 cycles or more) using ultrasonic fatigue at 20 kHz has been found efficient at finding the largest inclusions in volumes of about 300 mm3 per specimen. The inclusions found at the fatigue initiation site can then been used to estimate the distribution of large inclusions using extreme value statistics.

In this work, a new method for estimating the volume distribution of large inclusions is presented as well as a suggested ranking variable based on the volume distribution.

Results from fatigue fractography and area scanning methods are compared to the endurance limit at 109 cycles for a number of batches from two high performance steels.

In addition, the extreme value distributions of fatigue initiating inclusions in six high performace steels, produced by different routes, are presented. It is shown that all modes of the Generalized Extreme Values distribution can be found in different materials. This result shows that the assumption of mode I distribution, also known as Gumbel or Largest Extreme Value distribution, must be substantiated.

Place, publisher, year, edition, pages
Karlstad: Karlstad University , 2008. , p. 18
Series
Karlstad University Studies, ISSN 1403-8099 ; 2008:50
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-3520ISBN: 978-91-7063-207-5 (print)OAI: oai:DiVA.org:kau-3520DiVA, id: diva2:158965
Presentation
2008-12-19, Ljungbergssalen, 21A 244, Karlstads universitet, Karlstad, 13:15 (Swedish)
Opponent
Available from: 2009-02-05 Created: 2009-02-05 Last updated: 2011-11-29Bibliographically approved
List of papers
1. Relating gigacycle fatigue to other methods in evaluating the inclusion distribution of a H13 tool steel
Open this publication in new window or tab >>Relating gigacycle fatigue to other methods in evaluating the inclusion distribution of a H13 tool steel
2007 (English)In: Fourth International Conference on Very High Cycle Fatigue (VHCF-4) / [ed] John E. Allison, J. Wayne Jones, James M. Larsen & Robert O. Ritchie, TMS (The Minerals, Metals & Materials Society) , 2007, p. 45-50Conference paper, Published paper (Refereed)
Abstract [en]

Inclusions play a crucial role for the fatigue properties of high strength steel, but to find the largest inclusions by microscopy measurements large areas have to be examined.In this study ultrasonic gigacycle staircase fatigue testing has been used to find large inclusions in an H13 tool steel. The inclusions have been examined in SEM and their size distribution modeled using methods from extreme value statistics. The inclusion distribution obtained from the fatigue crack surfaces is compared to distributions acquired by microscopy study of cross sections as well as ultrasound immersion tank measurements and to the corresponding staircase fatigue data via the Murakami √Area model.It is shown that the fatigue method more effectively finds large inclusions than the other methods. It is also shown that the correlation between predictions of inclusion sizes by the √Area model from stress levels and fatigue initiating inclusions is weak forthis material.

Place, publisher, year, edition, pages
TMS (The Minerals, Metals & Materials Society), 2007
Keywords
non-metallic inclusion, steel, gigacycle fatigue
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-3516 (URN)978-0-87339-704-9 (ISBN)
Conference
Fourth International Conference on Very High Cycle Fatigue (VHCF-4)
Available from: 2009-02-05 Created: 2009-02-05 Last updated: 2017-12-06Bibliographically approved
2. Detecting large inclusions in steels: evaluating methods
Open this publication in new window or tab >>Detecting large inclusions in steels: evaluating methods
2009 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 80, no 11, p. 854-858Article in journal (Refereed) Published
Abstract [en]

The distributions of large non-metallic inclusions in two steel grades have been investigated using light optical microscopy, scanning electron microscopy and ultrasonic fatigue testing in the gigacycle range. The different methods have inherently different capabilities for finding inclusions in different size ranges. A measure of the distribution of large inclusions is proposed as the size S at which half of the fatigue specimens are expected to contain at least one inclusion of size S or larger, corresponding to 50% failure probability. Values of S are obtained using the volume distribution estimated by the three methods. Extrapolation from microscopy measurements on surfaces agree with fatigue fractography results regarding density of large inclusions, as measured by the proposed ranking variable S

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2009
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-3517 (URN)10.2374/SRI09SP079 (DOI)
Note

Vid tidpunkten för författarens licentiatseminarium, förelåg detta delarbete som manuskript. This paper was first published as a manuscript at time for the author's licentiate seminar.

Available from: 2009-02-05 Created: 2009-02-05 Last updated: 2017-12-14Bibliographically approved
3. Extreme value distributions of inclusions in six  steels
Open this publication in new window or tab >>Extreme value distributions of inclusions in six  steels
2012 (English)In: Extremes, ISSN 1386-1999, E-ISSN 1572-915X, Vol. 15, p. 257-265Article in journal (Refereed) Published
Abstract [en]

There is a prevailing assumption that the largest inclusions in steel volumes follows mode I of the Generalized Extreme Values (GEV) distribution. In this work, the GEV distributions of non-metallic inclusions in six different high performance steels, of different grades and processing routes, were investigated by means of fractography of inclusions causing failure in ultrasonic fatigue testing to one billion cycles and all three modes of the GEV were found for the different steel grades. Values of the shape parameter ξ of the GEV distribution as high as 0.51 (standard deviation 0.11) were found in one steel grade. Thus, the present results show that the assumption of GEV-I (Gumbel, LEVD) distribution has to be substantiated before being used to estimate the size of the largest inclusions.

Keywords
Extreme values – Non-metallic inclusions – Steel
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kau:diva-8200 (URN)10.1007/s10687-011-0139-5 (DOI)000303585200006 ()
Available from: 2011-09-09 Created: 2011-09-09 Last updated: 2017-12-08Bibliographically approved
4. Finding non-metallic inclusions in clean steel
Open this publication in new window or tab >>Finding non-metallic inclusions in clean steel
2008 (English)Report (Other academic)
Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2008
Series
Karlstad University Studies, ISSN 1403-8099 ; 2008:51
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-3519 (URN)978-91-7063-208-2 (ISBN)
Available from: 2009-02-05 Created: 2009-02-05 Last updated: 2011-11-22Bibliographically approved

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Ekengren, Jens

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