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Sadek, M., Bergström, J., Hallbäck, N. & Burman, C. (2018). 20 kHz 3-point bending fatigue of automotive steels. In: MATEC Web of Conferences: . Paper presented at 12th International Fatigue Congress, FATIGUE 2018, 27 May 2018 through 1 June 2018 (pp. 1-7). EDP Sciences, 165, Article ID 22020.
Open this publication in new window or tab >>20 kHz 3-point bending fatigue of automotive steels
2018 (English)In: MATEC Web of Conferences, EDP Sciences, 2018, Vol. 165, p. 1-7, article id 22020Conference paper, Published paper (Refereed)
Abstract [en]

The 20 kHz load frequency enables fatigue tests for very high cycle fatigue life, 109-1013 cycles, within conveniently short time. In automotive applications, many components are subjected to flexural loading and hence bending fatigue is an important test mode. Ultrasound fatigue test instruments have been used successfully in several assessments of fatigue strength and more commonly in uniaxial loading. Here, a 3-point bending fatigue test rig operating in resonance at 20 kHz load frequency has been designed to test plane specimens at R=0.1 loading. The test rig design and stress calculations are presented. Testing for fatigue strength was conducted using the staircase method with 15 specimens of each steel grade, specimens reaching 108 cycles were considered run-outs giving fatigue strength at 108 cycles. Additional 15 specimens of each grade were tested for S-N curves with the upper limit above 109 cycles. Two different common automotive steels, 38MnSiV5, a micro-alloyed ferritic-pearlitic steel, and 16MnCr5, a carburizing martensitic steel, were tested. The fatigue strengths achieved from the staircase testing are 340 and 419 MPa stress amplitudes for the 38MnSiV5 and 16MnCr5 steels, respectively. The S-N curves of the steels appear to be quite flat in the tested life range 107 - 109.

Place, publisher, year, edition, pages
EDP Sciences, 2018
Keywords
Automotive steels, Carburized steel, Ferritic-pearlitic steel, Three-point bending, VHCF, Binary alloys, Chromium alloys, Fatigue of materials, Fatigue testing, Ferrite, Ferritic steel, Pearlite, Silicon alloys, Stairs, Steel metallography, Steel testing, Pearlitic steels, Three point bending, Manganese alloys
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:kau:diva-68076 (URN)10.1051/matecconf/201816522020 (DOI)2-s2.0-85048089977 (Scopus ID)
Conference
12th International Fatigue Congress, FATIGUE 2018, 27 May 2018 through 1 June 2018
Available from: 2018-06-26 Created: 2018-06-26 Last updated: 2018-06-27Bibliographically approved
AlMotasem, A. T., Posselt, M. & Bergström, J. (2018). Nanoindentation and nanoscratching of a ferrite/austenite iron bi-crystal: An atomistic study. Tribology International, 127, 231-239
Open this publication in new window or tab >>Nanoindentation and nanoscratching of a ferrite/austenite iron bi-crystal: An atomistic study
2018 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 127, p. 231-239Article in journal (Refereed) Published
Abstract [en]

Molecular dynamics simulations are applied to investigate the wear/friction behavior of a ferrite/austenite iron bi-crystal, as a model system for duplex stainless steels. The plasticity of the ferrite phase is dominated by dislocations while both dislocations and stacking faults are the primary cause of plastic deformation of the austenite phase. Interestingly, the responses of tribological parameters vary depending on the scratch direction. For instance, the scratch hardness is increased by about 46% whereas the friction coefficient is reduced by about 22% when scratch starts from austenite to ferrite. At the interface, a local softening/hardening occurs because of dislocation-interface interaction. The present results demonstrate that martensitic phase transformation is responsible for experimentally observed high amount of ferrite of the pile-up.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-69118 (URN)10.1016/j.triboint.2018.06.017 (DOI)000442334100022 ()
Available from: 2018-09-07 Created: 2018-09-07 Last updated: 2018-09-13Bibliographically approved
Tofique, W., Bergström, J., Svensson, K., Johansson, S. & Peng, R. L. (2017). ECCl/EBSD and TEM analysis of plastic fatigue damage accumulation responsible for fatigue crack initiation and propagation in VHCF of duplex stainless steels. International Journal of Fatigue, 100, 251-262
Open this publication in new window or tab >>ECCl/EBSD and TEM analysis of plastic fatigue damage accumulation responsible for fatigue crack initiation and propagation in VHCF of duplex stainless steels
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2017 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 100, p. 251-262Article in journal (Refereed) Published
Abstract [en]

Fatigue test data of duplex stainless steel grades, LDX 2101 and 2304 SRG, in the Very High Cycle Fatigue (VHCF) regime is presented. Fatigue testing was conducted using ultrasonic fatigue test equipment operating at 20 kHz under fully reversed tension-compression load condition. Scanning Electron Microscope (SEM) analysis of the fracture surfaces and external surfaces of failed specimens was conducted. Electron Channelling Contrast Imaging (ECCI) and Electron Back Scattered Diffraction (EBSD) studies of the axially cut surface of the failed specimens was done to analyse the accumulation of plastic fatigue damage and fatigue crack growth in the grains adjacent to the external surface and crack initiation site. Transmission Electron Microscope (TEM) analysis of thin foils cut from failed specimens of LDX 2101 was carried out to examine the effect of fatigue loading on dislocation structure. SEM studies of the Crystallographic Growth Region (CGR) showed features like grain boundaries and fatigue striations on the fracture surfaces. SEM analysis of the external surfaces of fatigue loaded specimens showed inhomogeneous accumulation of plastic fatigue damage. ECCl/EBSD analysis showed Persistent Slip Bands (PSBs) in ferrite grains in LDX 2101 grade but no PSBs were observed in any grains of 2304 SRG specimens. The barrier effect of grain and phase boundaries on short fatigue crack propagation was observed. TEM analysis of thin foils cut from the failed specimens of LDX 2101 showed stacking faults in austenite grains and they were seen to stop at the grain and phase boundaries. (C) 2017 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Duplex stainless steel, High frequency testing, Crack initiation, Damage accumulation, Fatigue crack growth, Short cracks
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kau:diva-65533 (URN)10.1016/j.ijfatigue.2017.03.035 (DOI)000402217000024 ()
Available from: 2018-01-05 Created: 2018-01-05 Last updated: 2018-06-27Bibliographically approved
Tofique, M. W., Bergström, J. & Svensson, K. (2017). Very High Cycle Fatigue of cold rolled stainless steels, crack initiation and formation of Fine Granular Area. International Journal of Fatigue, 100(1), 238-250
Open this publication in new window or tab >>Very High Cycle Fatigue of cold rolled stainless steels, crack initiation and formation of Fine Granular Area
2017 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 100, no 1, p. 238-250Article in journal (Other academic) Published
Abstract [en]

Fatigue tests of cold rolled strip materials, a duplex stainless steel and a martensitic stainless steel, were performed using an ultrasonic fatigue test equipment operating at 20 kHz under a completely reversed tension compression load ratio R =-1. Fatigue test data (SN data) was generated in the VHCF regime and fracture surfaces of the failed specimens were investigated using a Scanning Electron Microscope (SEM). In the duple stainless steel grade, fatigue failures were found to be initiated at surface defects on the side surfaces or corners, created due to cold rolling, of the strip specimens. Features of a Fine Granular Area (FGA) were observed around the crack initiating surface defects on the fracture surfaces. In the martensitic stainless steel grade, fatigue crack initiation occurred due to aluminium-silicon oxide inclusions or surface defects created due to cold rolling of the material. In situ Focussed Ion Beam (FIB) technique was used to extract cross-sections from the FGA around the crack initiating defect on the fracture surface. Transmission Electron Microscope (TEM) investigations of the extracted cross-sections revealed FGAs in immediate vicinity of the crack initiating surface defects. The observed fine grained layers seemed to be composed of nano-sized grains and, thus, could be distinguished from the bulk material. The FGA around the surface crack initiating defects seems to have formed due to localized plastic deformation by stress concentration at the defects.

Place, publisher, year, edition, pages
oxford: Elsevier, 2017
Keywords
Duplex stainless steel, Martensitic stainless steel, Fatigue, High frequency testing, Crack initiation, Fine granular area
National Category
Other Materials Engineering
Research subject
Materials Engineering; Mechanical Engineering
Identifiers
urn:nbn:se:kau:diva-47126 (URN)10.1016/j.ijfatigue.2017.03.037 (DOI)000402217000023 ()
Funder
Knowledge Foundation
Available from: 2016-11-07 Created: 2016-11-07 Last updated: 2018-06-27Bibliographically approved
Tofique, M. W., Bergström, J., Burman, C., Hallbäck, N. & Gåård, A. (2016). Fatigue strength, crack initiation, and localized plastic fatigue damage in VHCF of duplex stainless steels. Steel Research International, 87(7), 899-910
Open this publication in new window or tab >>Fatigue strength, crack initiation, and localized plastic fatigue damage in VHCF of duplex stainless steels
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2016 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, no 7, p. 899-910Article in journal (Refereed) Published
Abstract [en]

The fatigue strength of two-duplex stainless steel grades, 2304 SRG and LDX 2101, with austenitic–ferritic microstructure is tested using ultrasonic fatigue testing equipment operating at 20 kHz. The testing is conducted in tension-compression mode with the load ratio R=-1. The fatigue strength is evaluated at 107, 108, and 109 load cycles and the estimates of fatigue strength are higher for the LDX 2101 grade. The fatigue crack initiation mechanisms are analyzed using a scanning electron microscope. The fatigue cracks, in all cases, appear to initiate due to accumulation of plastic fatigue damage at the surface. In the 2304 SRG grade, accumulation of fatigue damage occurs at the external surface of fatigued specimens in the form of extrusions at the grain/phase boundaries and in the form of individual slip lines in the austenite phase. Meanwhile, in the LDX 2101 grade accumulation of plastic fatigue damage in the form of extrusions and intrusions occurs mainly within the ferrite grain. When the crack is microstructurally short, the crack growth appears to be crystallographic in nature and the crack appears to change its direction propagating from one grain into another.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2016
Keywords
duplex stainless steel; ultrasonic fatigue testing; plastic fatigue damage; very high cycle fatigue; crystallographic crack growth
National Category
Metallurgy and Metallic Materials
Research subject
Materials Engineering; Mechanical Engineering
Identifiers
urn:nbn:se:kau:diva-38693 (URN)10.1002/srin.201500263 (DOI)000385610500010 ()
Projects
Very High Cycle Fatigue of Stainless Steels - an unknown life
Funder
Knowledge Foundation
Available from: 2015-11-23 Created: 2015-11-23 Last updated: 2017-12-06Bibliographically approved
Bergstrom, J., Burman, C., Svensson, J., Jansson, A., Ivansson, C., Zhou, J. & Valizadeh, S. (2016). Very High Cycle Fatigue of Two Ductile Iron Grades. Steel Research International, 87(5), 614-621
Open this publication in new window or tab >>Very High Cycle Fatigue of Two Ductile Iron Grades
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2016 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, no 5, p. 614-621Article in journal (Refereed) Published
Abstract [en]

Two ductile iron grades, EN-GJS-600-3 a ferritic-pearlitic grade, and EN-GJS-600-10 a silicon strengthened ferritic nodular iron grade, are studied in the very high cycle fatigue range using a 20kHz ultrasonic test equipment. Fatigue strengths and SN-curves are achieved, and fracture surfaces and microstructures are investigated. The ferritic grade with higher ductility displays a lower fatigue strength at 10(8) load cycles than the ferritic-pearlitic grade, 142 and 167MPa, respectively. Examination of fracture surfaces shows that fatigue failures are controlled by micropores in both of the ductile iron grades, while the graphite nodule distributions do not seem to influence the difference in fatigue strengths. Prediction of the fatigue strengths, using a model for ductile iron proposed by Endo and Yanase, indicates a large potential for improvement in particular for the ferritic grade.

Keywords
ductile iron, fatigue, very high cycle fatigue, microstructure
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:kau:diva-42622 (URN)10.1002/srin.201500163 (DOI)000375688300009 ()
Available from: 2016-06-03 Created: 2016-06-03 Last updated: 2017-11-30Bibliographically approved
Tofique, M. W., Bergström, J., Hallbäck, N. & Burman, C. (2014). Fatigue initiation and strength of duplex stainless steel strip specimens in the very high cycle fatigue regime. In: Very high cycle fatigue 6 (VHCF6): . Paper presented at 6th International conference on very high cycle fatigue (VHCF6), Chengdu, China.
Open this publication in new window or tab >>Fatigue initiation and strength of duplex stainless steel strip specimens in the very high cycle fatigue regime
2014 (English)In: Very high cycle fatigue 6 (VHCF6), 2014Conference paper, Published paper (Refereed)
Abstract [en]

Fatigue studies of cold-rolled duplex stainless strip steel were performed in the very high cycle fatigue life region. The duplex austenitic-ferritic microstructure gives this grade a combination of high mechanical strength and high corrosion resistance. Fatigue properties of thin steel strips are particular due to cold rolling introducing a very fine microstructure. Crack initiation and fatigue strength are controlled by steel microstructure and alloying. The initiation and growth of the very short initial fatigue crack in very high cycle fatigue are unclear and subject to different descriptions. Fatigue test data of thin strip specimens at very high fatigue lives are scarce due to testing difficulties. For practical reasons testing must be performed at ultrasound test frequencies which involves fixturing problems. A test setup including the load chain ultrasonic horn, fixture and specimen was designed for resonance with a horse-shoe design of a screw fixture. The design of the horse-shoe fixture and the specimens along with FEM calculation of eigenfrequency are presented. Fatigue testing was performed at 20 kHz in R=-1 conditions up to fatigue life of 107 to 5*109 cycles. Fatigue strength was tested and crack initiation was studied on the fracture surface using FEG-SEM at the initiation site.

Keywords
Very high cycle fatigue, initiation, ultrasonic fatigue testing, strip specimen
National Category
Other Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-34633 (URN)
Conference
6th International conference on very high cycle fatigue (VHCF6), Chengdu, China
Projects
Very high cycle fatigue of stainless steels - an unknown life
Funder
Knowledge Foundation
Available from: 2014-11-21 Created: 2014-11-21 Last updated: 2017-12-06Bibliographically approved
Karlsson, P., Krakhmalev, P., Gåård, A. & Bergström, J. (2013). Influence of work material proof stress and tool steel microstructure on galling initiation and critical contact pressure. Tribology International, 60, 104-110
Open this publication in new window or tab >>Influence of work material proof stress and tool steel microstructure on galling initiation and critical contact pressure
2013 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 60, p. 104-110Article in journal (Refereed) Published
Abstract [en]

EN 1.4301 (austenitic), EN 1.4509 (ferritic), EN 1.4162 (duplex) and EN 1.4310 C1000 (metastable austenitic) stainless steels were tested in lubricated sliding against an ingot cast EN X153WCrMoV12 and powder metallurgy nitrogen alloyed Uddeholm Vancron 40 tool steels to reveal critical to galling contact pressure, Pcr. The calculated Pcr were higher for steels with higher strength. At P>Pcr, due to plastic flow of sheet material, the tool is damaged substantially and wear-induced matrix damage causes rapid galling initiation. At P<Pcr, galling was not observed. The powder metallurgy tool steel was more resistant to galling against all tested stainless steels. Better performance was associated with fine and homogeneously distributed hard phases preventing intensive wear of the tool steel matrix.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2013
Keywords
Galling, Tool steels, Stainless steel, Wear
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-15340 (URN)10.1016/j.triboint.2012.10.023 (DOI)000315550700014 ()
Note

The article had the status accepted at the time of P. Karlssons licentiate defense.

Available from: 2012-10-26 Created: 2012-10-26 Last updated: 2018-01-12Bibliographically approved
Yong-an, M., Jens, B., Xiao-chun, W. & Luo-ping, X. (2013). Oxidation and Thermal Fatigue Behaviors of Two Type Hot Work Steels During Thermal Cycling. Journal of Iron and Steel Research International, 20(11), 90-97
Open this publication in new window or tab >>Oxidation and Thermal Fatigue Behaviors of Two Type Hot Work Steels During Thermal Cycling
2013 (English)In: Journal of Iron and Steel Research International, ISSN 1006-706X, E-ISSN 2210-3988, Vol. 20, no 11, p. 90-97Article in journal (Refereed) Published
Abstract [en]

Thermal fatigue test has been carried out on widely used hot work steel 4Cr5MoSiV1 and a low alloyed steel 3Cr3MoV in temperature range of 200 to 700 degrees C. Tempering resistance, as well as high temperature hardness/strength of steel specimens, works as a dominating material parameter on thermal fatigue resistance. During the heating period, high hardness can depress the inelastic deformation. This deformation is the origination of tensile stress, which acts as the driving force of heat checking during the cooling period. The cyclic strain-oxidation interaction can speed up the damage on surface defects, which plays an obvious role in initiation of thermal cracks. On 4Cr5MoSiV1 steel specimens, borders between the matrix and inclusions such as titanium compounds, or lager carbides such as primary carbides, are focused by strain and attacked by oxidation, and are main initiating places of cracks. While on 3Cr3MoV steel specimens, larger strain causes plastic deformation concentrating around grain boundaries. Then the following oxidation accelerates this grain boundary damage and creates cracks.

Keywords
thermal fatigue, hot work steel, oxidation, heat checking, thermal cycling, tempering resistance
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-38581 (URN)000327368000015 ()
Available from: 2015-11-30 Created: 2015-11-23 Last updated: 2017-12-06Bibliographically approved
Lindvall, F. W., Gåård, A., Krakhmalev, P. & Bergström, J. (2013). Study of the influence of contact geometry and contact pressure on sliding distance to galling in the Slider-On-Flat-Surface wear tester. Tribology Transactions, 56(6), 1137-1145
Open this publication in new window or tab >>Study of the influence of contact geometry and contact pressure on sliding distance to galling in the Slider-On-Flat-Surface wear tester
2013 (English)In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 56, no 6, p. 1137-1145Article in journal (Refereed) Published
Abstract [en]

One of the major causes of tool failure in sheet metal forming is wear in the form of galling. Galling is gradual buildup of adhered sheet material on the tool and leads to unacceptable scratches on the sheet surface and to components that fail to meet tolerances. Because it is difficult to reproduce operational and interactional conditions in laboratory test equipments it is hard to test, model, and predict galling initiation.Here the authors examine how changes from elliptical to line contact geometry influenced galling initiation under dry sliding by using a slider-on-flat surface (SOFS) wear tester. A micro clean tool steel was tested against ferritic low-strength and martensitic high-strength steel sheets.The sliding distance to galling initiation was extracted from friction data and verified by scanning electron microscopy (SEM) observations. The presence of adhesive wear on worn tools after completed tests was used as a criterion. Experimental results showed that the elliptical contact causes galling quicker than the line contact.Applicability of experimental results depends on the relevance of test conditions, so contact pressures calculated for the described tests were compared to calculated contact pressures in a semi-industrial U-bending test and to literature data relevant to industrial applications. Good agreement between values observed for SOFS and for most selected industrial applications was found, which assume that contact pressures typical for most common industrial applications can be successfully simulated by selection of tool geometry and normal load in the SOFS tester.

Place, publisher, year, edition, pages
London: Taylor & Francis, 2013
Keywords
galling, wear, sheet metal forming, friction
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-8970 (URN)10.1080/10402004.2013.827766 (DOI)000324614500023 ()
Available from: 2011-12-19 Created: 2011-12-19 Last updated: 2017-12-08Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-6029-2613

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