| 1. |
- Dimitrios, Nikas, et al.
(författare)
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Effect of annealing on microstructure in railway wheel steel
- 2022
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Ingår i: 42Nd Riso International Symposium On Materials Science. - : Institute of Physics Publishing (IOPP). ; 1249
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Konferensbidrag (refereegranskat)abstract
- Railway wheels are commonly made from medium carbon steels (similar to 0.55 wt.% C), heat treated to a near pearlitic microstructure with 5-10% pro-eutectoid ferrite. During the operation of freight trains, where block brakes are used, high thermal loads occur together with the high contact stresses, which combined can affect the mechanical properties of the material. In this study, the effects of annealing on local microstructure and mechanical properties in pearlitic railway wheel steel were investigated using electron microscopy and micro-hardness. It is found that after annealing at 650 degrees C, the room temperature hardness reduces about 25%, accompanied by significant spheroidization of cementite in the pearlitic colonies, though the size and the orientation gradients of the pearlitic colonies have not changed much. The relationship between the microstructural changes and the mechanical properties are discussed.
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| 2. |
- Goel, Sneha, 1993-, et al.
(författare)
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The Effect of Location and Post-treatment on the Microstructure of EBM-Built Alloy 718
- 2018
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Ingår i: Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives. - Cham : Springer. - 2367-1696 .- 2367-1181. - 9783319894799 - 9783319894805 ; , s. 115-129
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Konferensbidrag (refereegranskat)abstract
- Additive manufacturing (AM) of Ni-based superalloys such as Alloy 718 may obviate the need for difficult machining and welding operations associated with geometrically intricate parts, thus potentially expanding design possibilities and facilitating cost-effective manufacture of complex components. However, processing AM builds completely free from defects, which may impair mechanical properties such as fatigue and ductility, is challenging. Anisotropic properties, microstructural heterogeneities and local formation of undesired phases are additional concerns that have motivated post-treatment of AM builds. This work investigates the microstructural changes associated with post-treatment of Alloy 718 specimens produced by Electron Beam Melting (EBM) for as-built microstructures at 3 build heights: near base plate, in the middle of build and near the top of the build. Two different post-treatment conditions, hot isostatic pressing (HIP) alone and a combined HIP with solutionising and two-step aging were examined and compared to the results for the as-built condition. The influence of various post-treatments on minor phase distributions (δ, γ″, carbides), overall porosity, longitudinal grain widths and Vickers microhardness was considered. The HIP treatment led to significant reduction in overall porosity and dissolution of δ phase, which led to appreciable grain growth for both post-treatment conditions. The variation in hardness noted as a function of build height for the as-built specimens was eliminated after post-treatment. Overall, the hardness was found to decrease after HIP and increase after the full HIP, solutionising and aging treatment, which was attributed to dissolution of γ″ during HIP and its re-precipitation in subsequent heat treatment steps.
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| 3. |
- Hanning, Fabian, et al.
(författare)
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The Effect of Grain Size on theSusceptibility Towards Strain Age Crackingof Wrought Haynes® 282®
- 2020
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Ingår i: SPS 2020. - Amsterdam : IOS Press. - 9781643681467 - 9781643681474 ; 13, s. 407-416
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The effect of grain size on the suceptibility towards strain age cracking (SAC) has been investigated for Haynes® 282® in the tempeature range of 750 to 950°C after isothermal exposure up to 1800s. Grain growth was induced by heattreating the material at 1150°C for 2h, resulting in a fourfold increase in grain size. Hardness was significanlty reduced after heat treatment as compared to millannealed material. Large grain size resulted in intergranular fracture over a widertemperature range than small grain size material. Ductility was lowest at 850°C, while lower values were observed to be correlated to increased grain size. The rapid formation of grain boundary carbide networks in Haynes® 282® is found to be notable to compensate for higher local stresses on grain boundaries due to incresedgrain size.
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| 4. |
- Dimitrios, Nikas, et al.
(författare)
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Characterization of deformed pearlitic rail steel
- 2017
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Ingår i: IOP Conference Series. - : Institute of Physics Publishing (IOPP). ; 219:1, s. Art no:UNSP 012035-
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Konferensbidrag (refereegranskat)abstract
- Pearlitic steels are commonly used for railway rails because they combine good strength and wear properties. During service, the passage of trains results in a large accumulation of shear strains in the surface layer of the rail, leading to crack initiation. Knowledge of the material properties in this region is therefore important for fatigue life prediction. As the strain is limited to a thin surface layer, very large strain gradients can be found. This makes it very difficult to quantify changes in material behavior. In this study hardness measurements were performed close to the surface using the Knoop hardness test method. The orientation of the pearlitic lamellas was measured to give an overview of the deformed microstructure in the surface of the rail. Microstructural characterization of the material was done by optical microscopy and scanning electron microscopy to evaluate the changes in the microstructure due to the large deformation. A strong gradient can be observed in the top 50 μm of the rail, while deeper into the rail the microstructure of the base material is preserved.
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| 5. |
- GUNNARSDÓTTIR, SOFFÍA ARNÞRÚÐUR, 1987, et al.
(författare)
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Towards Simulation of Geometrical Effects of Laser Tempering of Boron Steel before Self-Pierce Riveting
- 2016
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Ingår i: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 44, s. 304-309
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Konferensbidrag (refereegranskat)abstract
- The automotive industry is continuously developing and finding new ways to respond to the incremental demands of higher safety standards and lower environmental impact. As an answer to weight reduction of vehicles, the combination of boron steel and composite material is being developed along with their joining process, self-pierce riveting. Boron steel is an ultra-high strength material that needs to be locally softened before the joining process. However, the joining process deforms the part. This paper investigates factors affecting the geometrical deformation during the tempering process and lists important phenomena that need to be included when simulating the tempering process.
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| 6. |
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| 7. |
- Klement, Uta, 1962, et al.
(författare)
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EBSD Analysis and Assessment of Porosity in Thermal Barrier Coatings Produced by Axial Suspension Plasma Spraying (ASPS)
- 2017
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Ingår i: Materials Science Forum. - : Trans Tech Publications. - 1662-9752 .- 0255-5476. - 9783035711295 ; 879, s. 972-977, s. 972-977
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Konferensbidrag (refereegranskat)abstract
- Axial suspension plasma spraying (ASPS) is a relatively new, innovative sprayingtechnique which has produced thermal barrier coatings (TBCs) with attractive properties such ashigh durability and low thermal conductivity. Using a suspension, it is possible to spray with finerpowder particles resulting in coatings that have a columnar microstructure and contain a wide rangeof pore sizes, both nm- and μm-sized pores. To optimize the thermal properties and to maintainthem during service of the components, it will be important to design TBCs with optimal porosity.Hence, an important part in the assessment of ASPS coatings is therefore the characterization of themicrostructure and how it is build up, and the determination of porosity. Both aspects are addressedby performing measurement on splats and ASPS-coating using electron backscatter diffraction(EBSD) technique and by measuring porosity by Mercury Intrusion Porosimetry (MIP).
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| 8. |
- Ryttberg, Kristina, 1977, et al.
(författare)
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High strain rate deformation induced by high-velocity forming of 100Cr6 steel
- 2008
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Ingår i: proceedings of The 9th International Conference on Technology of Plasticity (ICTP), Gyeongju, Korea, September 7-11, 2008. - 9788957081525 ; , s. On CD or www.ictp2008.org-
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Konferensbidrag (refereegranskat)abstract
- This paper concerns the development of the near-net-shape manufacturing technique of high-velocity forming. The microstructural response to the high strain-rate deformation was evaluated for 100Cr6 steel in two differently heat treated conditions: spheroidise annealed (hardness 250 HV) and quenched and tempered (330 HV). A high-velocity pressing machine was used to conduct the forming tests on cylindrical specimens. By applying different impact velocities on samples with varying sizes deformation mechanisms could be related to strain and strain rate. Extreme localization of deformation resulting in white etching bands was seen in quenched and tempered samples but not in spheroidise annealed samples. Furthermore, the strain and strain rates were shown to affect the tendency for extreme localization. No white etching bands were found in samples strained to less than 1. Appearance of white etching bands could be seen in the macroscopic shape of the samples where the more homogeneously deformed samples showed a typical barrel shape while the strongly localized samples were slightly more bell shaped. It can be concluded that for high-velocity forming to be applicable to 100Cr6 steel a careful choice of the combination strain/strain rate needs to be made.
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| 9. |
- Ryttberg, Kristina, 1977, et al.
(författare)
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Microstructure and texture development during ring rolling of 100Cr6
- 2008
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Ingår i: Ceramic Transactions. - 1042-1122. - 9781574982961 ; 200, s. 301-309
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Konferensbidrag (refereegranskat)abstract
- Pre-turned 100Cr6 steel rings with spheroidised annealed microstructure have been cold ring rolled to two levels: expanding the outer diameter by 10 and 20%. The final microstructure was shown to be varying throughout the cross-section of the ring, where the largest deformation was found close to the surface of the inner diameter. This was reflected in the hardness profile showing the highest hardness values close to the inner surface. Scanning electron microscopy showed that the microstructure below the surface of the outer diameter consisted of a greatly refined ferrite. Close to the surface of the inner diameter the structure was even more refined. Electron back scatter diffraction together with X-ray diffractometry showed that cold ring rolling changed the existing texture of the ring blanks, where {110}-planes were parallel to the axial direction of the rings, towards {110}-planes becoming parallel to the rolling direction. This resulted in a weak {110}-texture. Close to the surface of the outer diameter the greatly refined ferrite had decomposed into a more random orientation distribution.
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| 10. |
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