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Fatigue, defects and failure mechanisms in high strength tool steels at different fatigue life regimes
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).ORCID iD: 0009-0001-6982-3625
2024 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Fatigue response of metallic materials is considered of significant importance, particularly for high-demanding applications. It is proved that most of the engineering materials do not exhibit a conventional fatigue limit in the high cycle fatigue regime, but rather display a continuously decreasing stress-life response at even longer lifetimes. Consequently, investigations of the various failure mechanisms taking place are essential, especially at the high and very high cycle fatigue regimes.The development of new ultrasonic testing equipment made the fatigue testing beyond 107 life cycles possible in a much shorter time, enabling testing with fatigue fractures at stress levels lower than the traditionally proposed “fatigue limit”. Nowadays, a classification of fatigue life regimes in Low Cycle Fatigue (LCF), High Cycle Fatigue (HCF) and Very High Cycle Fatigue (VHCF) is commonly used. The main reasons for this specific grading are: i) the need for safe design of components and ii) the fact that the failure mechanisms are particular in each of the LCF, HCF and VHCF regimes.The main goal of the present thesis is to address the fatigue response of high strength tool steels. Considering the novel alterations in composition and production methods in alloy development, materials of high-quality are continuously being introduced to the market; understanding the fatigue response of these materials is crucial for potential utilization across diverse industries and applications. The generation of fatigue experimental data, the analysis of the different types of fatigue initiation defects found in each material, as well as the investigation of the fatigue mechanisms occurring during cyclic loading are the main subjects analyzed throughout the present study. 

Abstract [sv]

Utmattningsegenskaper hos metalliska material anses vara av stor betydelse, särskilt för krävande tillämpningar. Det är visat att de flesta konstruktionsmaterial inte uppvisar en konventionell utmattningsgräns i området för högcykelutmattning, utan snarare uppvisar ett kontinuerligt minskande spänning-livslängd förhållande med längre livslängder. Följaktligen är undersökningar av de olika brottmekanismer som äger rum väsentliga, särskilt vid utmattningsregimer med höga och mycket höga livslängder.Utveckling av nya ultraljudsutrustningar gjorde utmattningsprovning utöver 107 livscykler möjliga på mycket kortare tid, vilket möjliggjorde provning med utmattningsbrott vid längre livstid och spänningsnivåer lägre än den traditionellt föreslagna "utmattningsgränsen". Nuförtiden används en indelning av utmattningsregimer i lågcykelutmattning (Low Cycle Fatigue LCF), högcykelutmattning (High Cycle Fatigue HCF) och utmattning vid mycket långa livslängder (Very High Cycle Fatigue VHCF). De huvudsakliga skälen till denna indelning är: i) behovet av säker design av komponenter, och ii) det faktum att brottmekanismerna är speciella i var och en av LCF-, HCF- och VHCF-regimerna. Det främsta målet med denna avhandling är att adressera utmattningsegenskaper hos höghållfasta verktygsstål. Med tanke på nya sammansättningar och produktionsmetoder i legeringsutvecklingen introduceras material av hög kvalitet kontinuerligt på marknaden; att förstå utmattningsresponsen hos dessa material är avgörande för potentiella användningar inom olika industrier och applikationer. Genereringen av experimentell utmattningsdata, analysen av de olika typerna av initieringsdefekter som hittats i varje material, såväl som undersökningen av utmattningsmekanismerna som uppstår under cyklisk belastning är huvudämnena som analyseras genom hela denna studie.

Place, publisher, year, edition, pages
Karlstads universitet, 2024. , p. 34
Series
Karlstad University Studies, ISSN 1403-8099 ; 2024:13
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-99279DOI: 10.59217/fvip8564ISBN: 978-91-7867-455-8 (print)ISBN: 978-91-7867-456-5 (electronic)OAI: oai:DiVA.org:kau-99279DiVA, id: diva2:1849972
Presentation
2024-06-13, 11D121, Andersalen, 09:15 (English)
Opponent
Available from: 2024-05-28 Created: 2024-04-09 Last updated: 2024-05-28Bibliographically approved
List of papers
1. A case study of mechanical and thermal fatigue of press hardening dies
Open this publication in new window or tab >>A case study of mechanical and thermal fatigue of press hardening dies
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2022 (English)In: IOP Conference Series: Materials Science and Engineering, 2022, Vol. 1238, no 1, p. 1-10, article id 012025Conference paper, Published paper (Refereed)
Abstract [en]

Press hardening provides ultra-high strength steel components, typically boron steels, of complex geometries. In the process, the steel sheet is heated in a furnace to the austenitization temperature, transferred to the press, then simultaneously formed at high temperature and cooled in the die. Life limiting factors for the press hardening dies are mechanical fatigue, thermal fatigue, and wear. In the present case study two die segments were selected where critical damages were mechanical and thermal fatigue, respectively. The dies were made of a H13 type premium hot-work tool steel with complex heated die technology, die design integrating an advanced cooling system, for pressing automotive frame parts.

The first die failed due to mechanical loading with a crack initiated from the ejector pin area. The die design, the mechanical loads, the elevated temperature, and the tool steel crack resistance are main factors to consider. In the second die cracks initiated from an ejector pin hole, as well, due to thermal cycles causing alternating compressive and tensile stresses at the surface, which led to crack nucleation because of the accumulation of local plastic strain in the surface.

National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-99227 (URN)10.1088/1757-899x/1238/1/012025 (DOI)
Conference
International Deep-Drawing Research Group Conference (IDDRG 2022) 06/06/2022 - 10/06/2022 Lorient, France
Available from: 2024-04-07 Created: 2024-04-07 Last updated: 2024-05-10Bibliographically approved
2. High and very high cycle fatigue behavior of an additively manufactured hot-work tool steel
Open this publication in new window or tab >>High and very high cycle fatigue behavior of an additively manufactured hot-work tool steel
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(English)Manuscript (preprint) (Other academic)
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:kau:diva-99228 (URN)
Available from: 2024-04-07 Created: 2024-04-07 Last updated: 2024-04-25Bibliographically approved
3. High-Nitrogen PM Tool Steel: A Comparison Of Microstructure And Mechanical Properties Of As-HIPed And HIPed Followed By Hot Working
Open this publication in new window or tab >>High-Nitrogen PM Tool Steel: A Comparison Of Microstructure And Mechanical Properties Of As-HIPed And HIPed Followed By Hot Working
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2022 (English)In: World PM 2022 Congress Proceedings, European Powder Metallurgy Association (EPMA) , 2022Conference paper, Published paper (Other academic)
Abstract [en]

High-nitrogen-chromium alloyed powder metallurgy (PM) tool steels offer many attractive features including high strength and corrosion resistance. The PM route offers various advantages such as advanced alloy composition, high homogeneity, and well-defined size distribution of hard phase particles. This study presents microstructure and mechanical properties of a PM Cr-Mo-V-N alloy. The conventional manufacturing route for this alloy is hot isostatic pressing (HIP) followed by hot working. To investigate the possibility of near-net-shape manufacturing, a comprehensive comparison of the performance was made between steels produced by as-HIPed and HIPed followed by hot working. Both steel types were heat treated in the same way to obtain martensitic matrix with limited retained austenite. In the present investigation, microstructure and phase analyses were performed by X-ray diffraction and scanning electron microscopy. Mechanical tests were carried out by hardness measurements and tensile fatigue tests in the very high cycle fatigue regime using ultrasonic fatigue testing. 

Place, publisher, year, edition, pages
European Powder Metallurgy Association (EPMA), 2022
Keywords
Chromium alloys, Corrosion resistance, Corrosion resistant alloys, Fatigue testing, High strength alloys, High-cycle fatigue, Hot isostatic pressing, Microstructure, Molybdenum alloys, Molybdenum compounds, Scanning electron microscopy, Tensile testing, Tool steel, Ultrasonic testing, Advanced alloys, Alloy compositions, Alloyed powder, Hard phase, High homogeneity, High strength, Corrosion resistances, High-nitrogen, Microstructures, Mechanical properties, Phase particles; Size-distribution, Powder metallurgy
National Category
Metallurgy and Metallic Materials Other Materials Engineering
Research subject
Materials Engineering; Materials Science
Identifiers
urn:nbn:se:kau:diva-95204 (URN)2-s2.0-85160795406 (Scopus ID)9781899072552 (ISBN)
Conference
World PM 2022 Congress and Exhibition, Lyon, France, October 9-13, 2023.
Funder
Knowledge Foundation, 20190033
Available from: 2023-06-12 Created: 2023-06-12 Last updated: 2024-04-12Bibliographically approved
4. Very HIgh Cycle Fatigue (VHCF) behavior of high strength alloys: A literature review
Open this publication in new window or tab >>Very HIgh Cycle Fatigue (VHCF) behavior of high strength alloys: A literature review
2023 (English)Report (Other academic)
Abstract [en]

Very High Cycle Fatigue (VHCF) response of metallic materials is considered of significance importance, particularly for high- demanding applications. Since it is proved that most of the engineering materials do not exhibit a conventional fatigue limit, but rather display a continuously decreasing stress-life response at longer lifetimes. Consequently, the investigation of the various mechanisms are taking place during VHCF is essential. The primary object of the present effort is to explore and summarize recent developments and current status of the VHCF phenomenon in high strength alloys.

The development of the new ultrasonic machines made the fatigue testing beyond 107 life cycles possible in a very shorter time, leading to fatigue fractures at stress levels lower than the traditionally proposed “fatigue limit”. Nowadays, a classification between Low Cycle Fatigue (LCF), High Cycle Fatigue (HCF) and Very High Cycle Fatigue (VHCF) is commonly used. The main reasons for this specific grading are: i) the need for safe design of components and ii) the fact that the failure mechanisms are particular in each of the LCF, HCF and VHCF regimes.

Ultrasound machines, also called piezoelectric, are resonance fatigue testing machines reducing the testing time at least 400 times compared to the conventional machines operating at frequencies up to 20 kHz.

The crack initiation stage is one of the most investigated subjects when it comes to VHCF. Usually, the fatigue initiates from a defect (inclusion, pore, grain boundary triple points), while up to 99% of fatigue life is consumed in that stage. Different models have been proposed in the literature regarding the evolution of events that contribute to the fatigue crack initiation and growth. Proposed models are such as the ODA, the polygonization, continuous grain refinement with local plasticity, the matrix fragmentation and the NCP numerous cyclic pressing. Several studies have assessed the different models and further enriched the knowledge in the VHCF field.

In the present literature review effort, the main VHCF mechanisms of crack initiation and growth as well as the proposed models are presented and analyzed. Moreover, the VHCF response and the recent experimental results referring to the most used engineering alloys, e.g. steels, Ti, Ni, Al and Mg alloys, are described, with a main attention to steels. The different testing parameters and the way they affect the VHCF response are also presented.

Finally, the literature review is concluded by presenting the new challenges and directions for future work in the field, especially under the light of the new low-carbon society.

Abstract [en]

Very High Cycle Fatigue (VHCF) response of metallic materials is considered of significance importance, particularly for high- demanding applications. Since it is proved that most of the engineering materials do not exhibit a conventional fatigue limit, but rather display a continuously decreasing stress-life response at longer lifetimes. Consequently, the investigation of the various mechanisms are taking place during VHCF is essential. The primary object of the present effort is to explore and summarize recent developments and current status of the VHCF phenomenon in high strength alloys. 

The development of the new ultrasonic machines made the fatigue testing beyond 107 life cycles possible in a very shorter time, leading to fatigue fractures at stress levels lower than the traditionally proposed “fatigue limit”. Nowadays, a classification between Low Cycle Fatigue (LCF), High Cycle Fatigue (HCF) and Very High Cycle Fatigue (VHCF) is commonly used. The main reasons for this specific grading are: i) the need for safe design of components and ii) the fact that the failure mechanisms are particular in each of the LCF, HCF and VHCF regimes. 

In the present literature review effort, the main VHCF mechanisms of crack initiation and growth as well as the proposed models are presented and analyzed. Moreover, the VHCF response and the recent experimental results referring to the most used engineering alloys, e.g. steels, Ti, Ni, Al and Mg alloys, are described, with a main attention to steels. The different testing parameters and the way they affect the VHCF response are also presented. 

Finally, the literature review is concluded by presenting the new challenges and directions for future work in the field, especially under the light of the new low-carbon society. 

Place, publisher, year, edition, pages
Karlstads universitet, 2023. p. 66
Series
Karlstad University Studies, ISSN 1403-8099 ; 2023:33
Keywords
Very High Cycle Fatigue (VHCF), Crack Initiation, Fatigue fracture, High strength alloys
National Category
Materials Engineering Metallurgy and Metallic Materials Mechanical Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-97258 (URN)978-91-7867-416-9 (ISBN)978-91-7867-417-6 (ISBN)
Available from: 2023-11-01 Created: 2023-11-01 Last updated: 2024-04-12Bibliographically approved

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Chantziara, Katerina

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