| 1. |
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| 2. |
- Ekengren, Jens, 1976-, et al.
(författare)
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Assessment of strength and inclusions of tool steels in very high cycle fatigue
- 2009
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Ingår i: Proceedings of the 8th International Tooling Conference, Vol 1. - Aachen : Verlag Mainz, Wissenschaftsverlag. - 9783810793058
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Konferensbidrag (refereegranskat)abstract
- Fatigue strength is an important material property for many tooling applications, particularly in high performance applications. The research in Very High Cycle Fatigue (VHCF) has demonstrated that the traditional fatigue limit may not be valid for many materials subjected to 107 or more load cycles. Presently, both materials data and mechanism knowledge is missing on VHCF applications, even though many components are run at these life lengths. The fatigue strength is commonly controlled by different defects initiating failure, as in well controlled laboratory experiments may be internal inclusions. In this paper VHCF experimental testing was accomplished by the use of ultrasonic fatigue testing run at 20 kHz allowing long life evaluation within reasonably short test time. Fatigue strength, failure mechanisms and inclusion content were accordingly assessed. Fatigue strength data on H13 tool steel are presented, as well as a statistical approach considering available defect distribution and load distribution in the critically stressed volume, important to both steel supplier and end-user.
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| 3. |
- Ekengren, Jens, 1976-, et al.
(författare)
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Detecting large inclusions in steels : evaluating methods
- 2009
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Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 80:11, s. 854-858
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Tidskriftsartikel (refereegranskat)abstract
- 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
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| 4. |
- Ekengren, Jens, 1976-, et al.
(författare)
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Estimating the volume distribution of large defects using Generalized Extreme Values
- 2011
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Ingår i: Extremes. - 1386-1999 .- 1572-915X.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The presence of defects, such as oxides and other non-metallic inclusions, is an important factor in determining the properties of steels. Due to improvements in the manufacturing of high-quality steels, the amount of large defects has decreased and therefore it has become increasingly difficult to accurately determine their distribution using conventional methods. Previously, a method for estimating the distribution of large defects using a conversion from the Gumbel distribution has been presented. However, it has been shown that the Gumbel distribution is not always appropriate for modelling the sizes of the largest defects and that the Generalized Extreme Values (GEV) distribution should be used instead. In this work a more general method for the estimation of the total volume distribution of large defects isproposed, showing how the volume distribution may be calculated from the estimated parameters for the GEV distribution. The new method is applied to the results of a series of specimens made from high-quality tool steel tested in ultrasonic resonance fatigue. Possible methods for obtaining the confidence limits of thevolume distribution are also discussed.
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| 5. |
- Ekengren, Jens, 1976-, et al.
(författare)
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Influence of life length on estimated defect distribution in a low defect steel material
- 2011
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Ingår i: Proceedings of the Fifth International Conference on Very High Cycle Fatigue. - Berlin : Deutscher Verband für Materialforschung und -prüfung. - 9783981451603 ; , s. 177-182
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Konferensbidrag (refereegranskat)abstract
- This paper reports on results of very high cycle fatigue tests on a steel with a relatively low number of defects per unit volume. Two series of newly designed dog-bone specimens, with low stress gradients, were tested at two constant stress levels, aiming at providing fatigue life lengths of 106–108 cycles and 107–109 cycles, respectively. Fatigue-initiating defects on the fracture surfaces were measured and the corresponding size distributions were analysed to investigate the influence of the elevated stress level needed to achieve shorter life lengths. The presented results indicate a difference between the distribution of initiating defects in the long and shorter life length test series. The main conclusion is that fixed stress level fatigue testing to life lengths around 107 cycles may be a suitable method to estimate the content of large defects in low defect steel materials, provided a suitable test specimen geometry with low stress gradients is used.
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| 6. |
- Ekengren, Jens, 1976-, et al.
(författare)
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Relating gigacycle fatigue to other methods in evaluating the inclusion distribution of a H13 tool steel
- 2007
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Ingår i: Fourth International Conference on Very High Cycle Fatigue (VHCF-4). - : TMS (The Minerals, Metals & Materials Society). - 9780873397049 ; , s. 45-50
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 7. |
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| 8. |
- Mussa, Abdulbaset
(författare)
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A study on wear characteristics of high strength steels under sliding contact
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the last decades, significant improvements regarding the design, materials and technology of rock drills have been made. Likewise, in sheet metal forming, forming tools experience very high contact pressures when processing high strength steel sheets. In both applications components operate under extremely tough contact conditions that result in an accelerated component failure. Enhancements on mechanical properties of components material subjected to extreme contact conditions are highly required in order to withstand the application loads and prevent severe wear.The present thesis was focused on understanding of machinery component damage mechanisms under severe contact conditions. A case study of worn components used in rock drilling and sheet metal cold work was carried out. Thread joints from rock drilling and punches from sheet metal pressing were selected for the investigation. For these components, sliding contact under high contact pressure is a common load condition under the components usage. Then, to understand and quantify the influence of contact parameters, load and surface quality on material performance, laboratory simulations were performed. The results were used for a comparative analysis of the typical damage mechanisms observed in the tests and the case study of the components.The case study results showed that the threaded surfaces underwent severe plastic deformation due to the high-pressure sliding contact. The microstructure beneath the worn surface was altered and surface cracks and delamination were frequently observed at the worn surface. The dominant damage mechanism found on the investigated punches was adhesive wear. Material transfer adds friction stresses at the punch surface and ultimately, with repeated punch strokes, it leads to initiation and propagation of fatigue cracks.Wear process in thread joint and punch wear was simulated using the SOFS. The worn specimens tested experimentally showed similar wear mechanisms obtained in the case study. The thread joint wear simulation showed that the total damage at the worn surface was a result of adhesive wear, plastic deformation, and initiation and propagation of fatigue cracks. In addition, the results showed that the type of motion had a significant influence on the worn volume and crack initiation, and more severe wear was observed at reciprocal motion. The punch wear simulation showed that the friction quickly increased as work material from metal sheets transferred to the disc surface. The rate of the material transfer was strongly dependent on the combination of sheet material and tool steel. Further, the present experimental simulations were applicable to characterize and predict wear of components in the application.
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| 9. |
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| 10. |
- AlMotasem, Ahmed Tamer, et al.
(författare)
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Adhesion between ferrite iron-€“iron/cementite countersurfaces : A molecular dynamics study
- 2016
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Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 103, s. 113-120
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Tidskriftsartikel (refereegranskat)abstract
- The adhesive properties of Fe(110)/Fe(110) and Fe3C(001)/Fe(110) countersurfaces have been investigated by using classical molecular dynamics simulations. The simulation results show that Fe3C/Fe exhibits a relatively lower adhesion compared to the Fe/Fe. Additionally, the temperature dependence of the adhesive properties between 300–700 K has been examined. The results demonstrate that, with increasing the temperature, the values of the adhesion force and the work of adhesion continuously decrease in the case of Fe3C/Fe; they initially slightly increase up to 500 K then decrease in the case of Fe/Fe. Furthermore, the effect of lattice coherency between Fe/Fe has been examined and found to slightly reduce the adhesion. These results explain how carbides improve galling resistance of tool steel observed during dry sliding.
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| 11. |
- AlMotasem, Ahmed Tamer, et al.
(författare)
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Atomistic insights on the wear/friction behavior of nanocrystalline ferrite during nanoscratching as revealed by molecular dynamics
- 2017
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Ingår i: Tribology letters. - New York : Springer. - 1023-8883 .- 1573-2711. ; 65:3, s. 101-
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Tidskriftsartikel (refereegranskat)abstract
- Using embedded atom method potential, extensive large-scale molecular dynamics (MD) simulations of nanoindentation/nanoscratching of nanocrystalline (nc) iron have been carried out to explore grain size dependence of wear response. MD results show no clear dependence of the frictional and normal forces on the grain size, and the single-crystal (sc) iron has higher frictional and normal force compared to nc-samples. For all samples, the dislocation- mediated mechanism is the primary cause of plastic deformation in both nanoindentation/nanoscratch. However, secondary cooperative mechanisms are varied significantly according to grain size. Pileup formation was observed in the front of and sideways of the tool, and they exhibit strong dependence on grain orientation rather than grain size. Tip size has significant impact on nanoscratch characteristics; both frictional and normal forces monotonically increase as tip radii increase, while the friction coefficient value drops by about 38%. Additionally, the increase in scratch depth leads to an increase in frictional and normal forces as well as friction coefficient. To elucidate the relevance of indentation/scratch results with mechanical properties, uniaxial tensile test was performed for nc-samples, and the result indicates the existence of both the regular and inverse Hall-Petch relations at critical grain size of 110.9 angstrom. The present results suggest that indentation/scratch hardness has no apparent correlation with the mechanical properties of the substrate, whereas the plastic deformation has.
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| 12. |
- AlMotasem, Ahmed Tamer, et al.
(författare)
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Nanoindentation and nanoscratching of a ferrite/austenite iron bi-crystal : An atomistic study
- 2018
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Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 127, s. 231-239
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 13. |
- AlMotasem, Ahmed Tamer, et al.
(författare)
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Tool microstructure impact on the wear behavior of ferrite iron during nanoscratching : An atomic level simulation
- 2017
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 370-371, s. 39-45
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, molecular dynamics simulations were used to investigate the impact of the tool microstructure on the wear behavior of ferrite workpiece during nanoscratching. The tool microstructure was modified by varying the carbide (cementite) contents. The simulation results show that dislocations are the primary mechanism for plastic deformation of the workpiece material. It is found that total dislocation length varies significantly depending on the carbide content in the tool. Furthermore, other tribological phenomena were also observed to depend on the carbide contents. For example, the average value of frictional forces decreased while the normal force increases with increasing carbide contents, and hence the friction coefficient was decreased. Additionally, the shape and size of lateral and frontal pileups are lowered. The structural analysis of the pileup region reveals the loss of long range order and start of amorphisation. The temperature distribution of the pileup regions showed an increase of the pileup temperature when carbide is added into tool. The wear volume is considerably reduced when the carbide content increases. The average scratch hardness was found to decrease and the result was analyzed with the theoretical Taylor hardening model.
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| 14. |
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| 15. |
- Bergström, Jens, 1954-, et al.
(författare)
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Galling in sheet metal forming
- 2008
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Ingår i: Proceedings of the IDDRG 2008 Conference. - Olofström : Industriellt utvecklingscentrum i Olofström AB. - 9789163329487
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 16. |
- Chai, Guocai, 1956-, et al.
(författare)
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Crack Initiation in Bulk Matrix of Austenitic Stainless Steel during Very High Cycle Fatigue
- 2023
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Ingår i: Materials Performance and Characterization. - : American Society for Testing Materials. - 2379-1365 .- 2165-3992. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- In the very high cycle fatigue regime, fatigue crack initiation in high-strength steels is usually correlated to a subsurface inclusion with a fine granular area (FGA). Localized stress-strain concentration at the subsurface inclusion is a critical factor. Fatigue crack initiation with an FGA in the bulk matrix without any defect has rarely been reported. In this paper, a fundamental study on the formation of FGAs in the bulk matrix of an austenitic stainless steel has been carried out using a progressive stepwise load-increasing test with a cycle step of about 108 cycles. FGA formation in the subsurface bulk matrix has been observed. The micro structural damage in the fatigue-tested specimens has been studied using the electron channeling contrast imaging electron microscopy technique. Strain localization and grain fragmentation are the main processes for the formation of FGAs. Local plasticity exhaustion leads to crack initiation due to local stress concentrations. This method can also be used to predict the fatigue damage process, especially the damage rate in individual specimens.
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| 17. |
- Chai, Guocai, et al.
(författare)
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Formation of fine granular area in a non-defect matrix of austenitic stainless steel during very high cycle fatigue
- 2023
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Ingår i: Fatigue & Fracture of Engineering Materials & Structures. - : John Wiley & Sons. - 8756-758X .- 1460-2695. ; 46:6, s. 2364-2373
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Tidskriftsartikel (refereegranskat)abstract
- A fine granular area, FGA, is a typical phenomenon observed at the very high cycle fatigue fracture crack origin with a subsurface defect in the material. The FGA has been widely investigated, and different mechanisms have been proposed. In this paper, the formation of FGA in a non-defect matrix of one austenitic steel during very high cycle fatigue was studied using a progressive stepwise load-increasing method and electron scanning microscopy/electron channeling contrast imaging (ECCI) technique. A nano rough surface area or FGA at the fatigue crack origin has been observed in the subsurface matrix without any defect. It is a new phenomenon. A mechanism was proposed using the dislocation plasticity theory. The formation of FGA in a non-defect matrix is a localized plasticity exhausting process by strain localization, grain fragmentation, stress concentration and nano crack initiation and propagation along low-angle grain boundaries.
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| 18. |
- Chantziara, Katerina, 1993-, et al.
(författare)
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A case study of mechanical and thermal fatigue of press hardening dies
- 2022
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Ingår i: IOP Conference Series: Materials Science and Engineering. - : IOP Publishing. - 1757-8981 .- 1757-899X. ; , s. 1-10
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 19. |
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| 20. |
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| 21. |
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| 22. |
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| 23. |
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| 24. |
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| 25. |
- Gåård, Anders, 1977-, et al.
(författare)
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Wear mechanisms in galling : cold work tool materials sliding against high-strength carbon steel sheets
- 2009
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Ingår i: Tribology letters. - : Springer. - 1023-8883 .- 1573-2711. ; 33:1, s. 45-53
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Transfer and accumulation of adhered sheet material, generally referred to as galling, is the major cause for tool failure in sheet metal forming. In this study, the galling resistances of several tool steels were evaluated against dual-phase high-strength carbon steel using a SOFS tribometer, in which disc-shaped tools were slid against a real sheet surface in dry sliding test conditions. Three different frictional regimes were identified and characterized during sliding, and any transition in friction corresponded to a transition in wear mechanisms of the sheets. The performance of the tools depended on load, material and the particular frictional regime. Best overall performance was obtained by nitrogen-alloyed powder metallurgy tool steel.
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| 26. |
- Hanson, Magnus, et al.
(författare)
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Comparison of two test methods for evaluation of forming tool materials
- 2007
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Ingår i: Tribotest. - : Wiley. - 1354-4063 .- 1557-685X. ; 14:3, s. 147-158
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Tidskriftsartikel (refereegranskat)abstract
- Two test methods often used to simulate the tribological performance of forming tool materials are compared in this investigation through an evaluation of the friction and wear properties of four tool steels in dry sliding. One test (slider-on-flat-surface (SOFS)) utilises a vertical disc sliding on a horizontal flat test surface, and the other (load scanner (LS) tests) utilises two crossed cylindrical rods. The test conditions were selected as equal as possible for the two tests, and the following conclusions are made.Somewhat unexpectedly, the friction and wear results differed substantially between the two tests. The SOFS test showed a better potential to evaluate wear resistance since one test sample is in continuous contact with the other. The LS test can generate higher contact pressures since the two rods contact each other in an unworn condition throughout the whole test stroke.LS indicate that two hard and smooth tool steels tested against each other generally give low friction and good galling resistance. The two hard couples tested sustained the highest loads without any detectable surface damage. For the same combinations of hard steels, SOFS gave a higher friction due to the wear of the disc. The carbides in the disc material resist wear better than the matrix and will consequently wear the disc by abrasion, which adds to the friction.The above conclusions are drawn from a rather limited examination using only one set of test parameters. In fact, the two tests are both very flexible as to the way they can be used, and they both have advantages and limitations in tribological studies. They should rather be considered complementary than competitive.
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| 27. |
- Javadzadeh Kalahroudi, Faezeh, et al.
(författare)
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High-Nitrogen PM Tool Steel : A Comparison Of Microstructure And Mechanical Properties Of As-HIPed And HIPed Followed By Hot Working
- 2022
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Ingår i: World PM 2022 Congress Proceedings. - : European Powder Metallurgy Association (EPMA). - 9781899072552
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 28. |
- Javadzadeh Kalahroudi, Faezeh, et al.
(författare)
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On the microstructure and high cycle fatigue of near-net shape PM-HIPed Inconel 625
- 2023
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 886
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigated the microstructure and fatigue behavior of PM-HIPed Inconel 625. The microstructure was composed of γ phase and (Mo, Nb) carbonitrides located mostly on prior particle boundaries. Despite the presence of these carbonitrides, the samples showed good tensile properties with high elongation. Two different surface conditions, pickled and machined, were used for high cycle fatigue testing under a four-point bending test. The results indicated that pickled samples had 6% lower fatigue strength (at 106 cycles) with three times higher standard deviation compared to the machined ones. Fatigue failure mechanisms were found to be dependent on surface conditions and showed different failure modes due to non-metallic oxide inclusions and surface defects in samples with machined and pickled surfaces, respectively. The effect of type, size, and location of defects, multiplicity of crack initiations, as well as surface roughness were analyzed and discussed.
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| 29. |
- Karimi Bakhshandi, Reza, et al.
(författare)
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Failure analysis of two cylindrical impact pistons subjected to high velocity impacts in drilling applications
- 2022
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Ingår i: Engineering Failure Analysis. - : Elsevier. - 1350-6307 .- 1873-1961. ; 140
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Tidskriftsartikel (refereegranskat)abstract
- Top hammer drilling is a common method to drill holes in rock formations in mining and civil engineering applications. Failure of drilling machine components has a significant impact on the cost and period of the operation. Internal components of percussive hammers experience extreme loading conditions during their service life. The focus of the present case study is to characterize failure mechanisms of two cylindrical impact pistons subjected to impact loading. The investi-gated components were manufactured from two different steel grades, a surface hardened low alloyed high strength steel and a through hardened cold work tool steel.Failure of both pistons started with degradation of the impact surfaces in term of cavitation erosion and localized surface fatigue phenomena. Subsequently, chipping and removal of material from impact surfaces resulted in formation of semi-spherical holes and craters on both surfaces.Radial and hoop cracks started to develop from cavities on the impact surface. The radial cracks then propagated parallel to the impacting surface in the longitudinal direction of the piston. Once the cracks formed at the impact surface, the damage was controlled by impact fa-tigue. Fatigue beach marks were identified on the fracture surface of failed component.
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| 30. |
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| 31. |
- Karlsson, Patrik, 1973-, et al.
(författare)
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Galling resistance and wear mechanisms for cold-work tool steels in lubricated sliding against high strength stainless steel sheets
- 2012
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Ingår i: Wear. - Amsterdam : Elsevier. - 0043-1648 .- 1873-2577. ; 286-287, s. 92-97
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Tidskriftsartikel (refereegranskat)abstract
- Tool damage in sheet metal forming of stainless steel is of high concern for the forming industry. In the present work, ingot cast AISI D2 and advanced powder metallurgy tool steel (PM) cold-work tool steels were evaluated and ranked regarding wear mechanisms and galling resistance. Wear tests were performed using a slider-on-flat-surface (SOFS) tribometer in sliding against austenitic–ferritic (duplex) stainless steel sheets at different contact pressures in lubricated conditions. The best galling resistance was observed for the nitrogen alloyed PM tool steels. Abrasive scratching of the tool surfaces and transfer of sheet material due to adhesive wear were the main metal forming tool surface damage mechanisms. By increasing the hardness of one PM sheet metal forming tool grade, the galling resistance was enhanced.
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| 32. |
- Karlsson, Patrik, 1973-, et al.
(författare)
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Influence of size and distribution of hard phases in tool steels on the early stage of galling
- 2012
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Ingår i: TOOL 2012. - Knittelfeld : Verlag "Gutenberghaus". - 9783901384523
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Konferensbidrag (refereegranskat)abstract
- In sheet metal forming processes, contact pressures are relatively high and total sliding distances are long, which demands tool steels to prevent tool damage and to resist galling. Galling is related to microscopic and macroscopic material transfer, but, the mechanisms of initiation are not thoroughly understood.To investigate galling initiation, lubricated sliding testing in the Slider-On-Flat-Surface (SOFS) tribometer was performed for ingot cast (IC) AISI D2 type and nitrogen alloyed powder metallurgy (PM) tool steel. The sheet grade was EN 1.4509 ferritic stainless steel. To reveal mechanisms in the early stages of galling initiation, transfer and accumulation of sheet material to the tool surfaces were characterized using AFM and SEM.It was found that already after a short sliding distance, transfer of sheet material occurred covering both the matrix and the hard phases. Macroscopic analysis of the contact area showed that initial material transfer and further lump growth occurred at positions corresponding to high plastic strains in the sheet material. Even though initial material transfer was observed for both tested tool steels, the sliding distance to the point where transfer and further lump formation occurred was longer for the PM tool steel. This was discussed in correlation to differences in size and distribution of the hard phases in the tool steels, which was confirmed by AFM and SEM.
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| 33. |
- Karlsson, Patrik, 1973-, et al.
(författare)
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Influence of work material proof stress and tool steel microstructure on galling initiation and critical contact pressure
- 2013
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Ingår i: Tribology International. - Amsterdam : Elsevier. - 0301-679X .- 1879-2464. ; 60, s. 104-110
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Tidskriftsartikel (refereegranskat)abstract
- 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
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| 34. |
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| 35. |
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| 36. |
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| 37. |
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| 38. |
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| 39. |
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| 40. |
- Lindvall, Fredrik W., 1980-, et al.
(författare)
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Study of the influence of contact geometry and contact pressure on sliding distance to galling in the Slider-On-Flat-Surface wear tester
- 2013
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Ingår i: Tribology Transactions. - London : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 56:6, s. 1137-1145
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 41. |
- Lindvall, Fredrik W., 1980-, et al.
(författare)
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The effect of grinding and polishing procedure of tool steels in sheet metal forming
- 2010
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Ingår i: ICTPM 2010. ; , s. 603-612
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Konferensbidrag (refereegranskat)abstract
- The surface finish of tools in sheet metal forming has a large influence on the performance of the forming tool. Galling, concern of wear in sheet metal forming, is a severe form of adhesive wear where sheet material is transferred on to the tool surface. By polishing the tools to a fine surface finish, material pick-up has traditionally been reduced, but some surface preparations withstand adhesive wear better. To investigate the effect on galling performance of different surface preparations lubricated tests have been performed using a strip reduction rig. Two different tool materials, Vancron 40 and Vanadis 6 and up to ten different grinding and polishing treatments were tested against AISI 316 stainless steel. The tests showed that an optimum surface preparation might be found at the transition between abrasive and adhesive wear.
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| 42. |
- Lindvall, Fredrik W., 1980-, et al.
(författare)
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Tool steel and contact geometry influence on galling initiation in lubricated sliding on carbon steel sheets
- 2009
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Ingår i: Proceedings of the 8th International Tooling Conference, Vol 1. ; , s. 189-198
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Konferensbidrag (refereegranskat)abstract
- In sheet metal forming operations, sliding contact may cause adhesive wear of sheet materials with transfer of worn material to the tool surface, a wear damage process named galling. It results in loss of product quality, process performance and tool lifetime. The industrial experience of the optimal combination of sheet metal grades, tool steel grades, tool geometry and lubrication to increase the tool performance is not clearly understood. Accordingly, simulation of wear of sheet metal forming operation in laboratory conditions in order to quantify tendency of a tool material to galling is not a trivial problem neither. In the present study two tool steel grades, an ESR made 8%Cr cold work tool steel and a superior PM made high speed steel, were tested with different test tool geometries to obtain different contact pressure conditions. A slider on flat sheet (SOFS) test equipment was utilized, where a disc made of tool steel was slid along lubricated carbon steel sheets of different strengths. The sliding tool discs were prepared so that one elliptical and two linear contacts were simulated, in order to study their influence on distance to galling initiation. Normal and friction force data were collected, galling initiation was detected by analysis of the friction curve and verified by SEM and OP analysis of the tool surfaces and sheet sliding tracks. It was found that under selected test conditions, galling initiation was remarkably dependent on tool material as well as geometry.
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| 43. |
- Mardinoglu, Adil, 1982, et al.
(författare)
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An Integrated Understanding of the Rapid Metabolic Benefits of a Carbohydrate-Restricted Diet on Hepatic Steatosis in Humans
- 2018
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Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131 .- 1932-7420. ; 27:3
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Tidskriftsartikel (refereegranskat)abstract
- A carbohydrate-restricted diet is a widely recommended intervention for non-alcoholic fatty liver disease (NAFLD), but a systematic perspective on the multiple benefits of this diet is lacking. Here, we performed a short-term intervention with an isocaloric low-carbohydrate diet with increased protein content in obese subjects with NAFLD and characterized the resulting alterations in metabolism and the gut microbiota using a multi-omics approach. We observed rapid and dramatic reductions of liver fat and other cardiometabolic risk factors paralleled by (1) marked decreases in hepatic de novo lipogenesis; (2) large increases in serum beta-hydroxybutyrate concentrations, reflecting increased mitochondrial beta-oxidation; and (3) rapid increases in folate-producing Streptococcus and serum folate concentrations. Liver transcriptomic analysis on biopsy samples from a second cohort revealed downregulation of the fatty acid synthesis pathway and upregulation of folate-mediated one-carbon metabolism and fatty acid oxidation pathways. Our results highlight the potential of exploring diet-microbiota interactions for treating NAFLD.
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| 44. |
- Medvedeva, Anna, 1981-, et al.
(författare)
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High-temperature properties and microstructural stability of hot-work tool steels
- 2009
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 523:1-2, s. 39-46
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Indexable insert tools for machining operations are in service exposed to high temperatures and cyclic mechanical loads. Secondary hardening steels such as hot-work steels are commonly used for tools subjected to thermal exposure. However, these steels, highly alloyed with strong carbide forming elements as Cr, V and Mo, are generally difficult to machine and machining represents a large fraction of the production cost of a tool. Thus, the present study concerns the development of a new steel with improved machinability and meeting the requirements for high-temperature properties. Softening resistance of the THG2000 and QRO90 tool steels, commonly used in hot-work applications, and a newly developed tool steel MCG2006 with lower alloying content of carbide forming elements, was investigated by tempering and isothermal fatigue testing. Mechanisms of high-temperature softening of the tested tool steels were discussed with respect to their microstructure and high-temperature mechanical properties. Carbide morphology and precipitation as well as dislocation structure were determined using transmission electron microscopy and X-ray line broadening analysis. No difference in softening behaviour was found among the QRO90 and MCG2006 regarding hot hardness measurements. The THG2000 indicated some stabilization of the hardness between 450 and 550 °C and a considerable hardness decrease at higher temperatures. The short-time cyclic softening in isothermal fatigue was controlled by dislocation rearrangement and annihilation. The alloying composition of the steels presently tested had no influence on the dislocation density decrease. The long-time softening was affected by the material's temper resistance and strongly depended on the carbide morphology and their over-ageing resistance. The QRO90 with greater molybdenum and lower chromium contents than in the THG2000 show the best resistance to softening among the tested grades at all temperatures. The MCG2006, leaner alloyed with the carbide forming elements and alloyed with 4 wt% nickel, has better temper resistance than THG2000 at higher temperatures and longer tempering times.
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| 45. |
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| 46. |
- Medvedeva, Anna, 1981-, et al.
(författare)
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Influence of nickel content on machinability of a hot-work tool steel in prehardened condition
- 2011
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Ingår i: Materials & design. - Amsterdam : Elsevier. - 0264-1275 .- 1873-4197 .- 0261-3069. ; 32:2, s. 706-715
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, the influence of nickel content on the machinability of a prehardened hot-work tool steel was investigated. The machinability with varying nickel content from 1 to 5 wt% was characterized in end milling and drilling by evaluating tool life, cutting forces, and tool/chip interface temperature.Nickel content showed to have a positive effect on the machinability of the hot-work tool steel; with increasing nickel content in the steel, the longer tool life was reached in end milling and drilling operations. Machining the higher nickel containing steels generated lower cutting forces and tool/workpiece interface temperature. In addition, less adhesive wear and built-up edge formation were observed on the tools.The difference in the steel machinability was discussed in terms of their microstructure and mechanical properties. Increasing nickel content tends to decrease the carbon in the martensite and to retain a fine distribution of small primary carbides. It resulted in a reduction in yield strength with increasing nickel content related to the cutting force reduction and machinability improvement.
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| 47. |
- Medvedeva, Anna, 1981-, et al.
(författare)
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Stress relaxation resistance for improved fatigue performance of shot peened tool components
- 2008
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Ingår i: Proceedings of the 10<sup>th</sup> International Conference on Shot Peening, 15-18 September, Tokyo, Japan, 2008. - Tokyo : Academy Common Meiji University. ; , s. 286-295
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Konferensbidrag (refereegranskat)abstract
- Shot peening is an extensively used process in the production of mechanical components to improve their fatigue strength at ambient temperature. At higher working temperatures of some mechanical components, e.g. from 300 to 600°C, the influence and behaviour of the compressive residual stresses are more uncertain, since they tend to relieve at higher temperatures. The response to shot peening induced residual stresses of low alloyed and hot work tool steels was evaluated with respect to stress relief heat treatments and isothermal high temperature fatigue testing. Not only the residual stresses, but also the material substructure and its dislocation characteristics are of importance. Dislocation structures were determined using X-ray diffraction to explain the preference of the different steel grades. Also, results obtained from bending fatigue testing at ambient temperature of tool components after shot peening and stress relief heat treatments demonstrated the different ability of retaining the fatigue strength.
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| 48. |
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| 49. |
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| 50. |
- Mussa, Abdulbaset, et al.
(författare)
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Development of a new PM tool steel for optimization of cold working of advanced high-strength steels
- 2020
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Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 10:10
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, Uddeholm Vancron SuperClean cold work tool steel was investigated concerning wear resistance and fatigue strength, using laboratory and semi-industrial tests. The Uddeholm Vancron SuperClean was designed with the help of ThermoCalc calculations to contain a high amount of a carbonitride phase, which was suggested to improve tribological performance of this tool steel. In order to investigate the tested steel, galling tests with a slider-on flat-surface tribotester and semi-industrial punching tests were performed on an advanced high-strength steel, CP1180HD. Uddeholm Vanadis 8 SuperClean containing only a carbide phase and Uddeholm Vancron 40 containing a mixture of carbides and carbonitrides were also tested to compare the performance of the tool steels. The microstructure and wear mechanisms were characterized with scanning electron microscopy. It was found that the carbonitrides presented in Uddeholm Vancron SuperClean improved its resistance to material transfer and galling. Semi-industrial punching tests also confirmed that Uddeholm Vancron SuperClean cold work tool steel also possesses enhanced resistance to chipping and fatigue crack nucleation, which confirms the beneficial role of the carbonitride phase in wear resistance of cold work tool steel.
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