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The Changes in Structure of Steel P91 after Short Annealings
Král, Lubomír ; Čermák, Jiří ; Král, Petr
Phase composition of the steel P91 during annealing was studied with the aim to reveal the evolution of new phases. In this paper, the precipitation was characterized using energy-dispersive X-ray spectroscopy (EDS) and electron diffraction in transmission microscopy (TEM). Only Nb-rich particles were found in the studied samples austenitized at 1423 °C for 20h and water cooled. After tempering at 673 °C for 2 h, the formation mainly M3C type carbides and after tempering at 873 °C for 2 h, the formation of M7C3 and M23C6 was observed. These structure changes play an important role for stability and also carbon diffusion.
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Effect of grit blasting surface treatment on high temperature low cycle fatigue life of Inconel 713LC
Šulák, Ivo ; Obrtlík, Karel ; Čelko, L. ; Gejdoš, P.
This paper presents the results of high temperature low cycle fatigue tests carried out on Inconel 713LC. This polycrystalline nickel based superalloys is mainly used for high temperature applications such as disks, blades and vanes of gas turbine engines. These machine components are manufactured by investment casting and undergo a series of postcast processes to remove remnants of shells, oxides and other contaminants. Grit blasting is one of the most widely used and cheapest technology ensuring adequate cleaning of the surface and at the same time is used to treat the substrate surface prior to application of metalic bond coat and various protective coatings (like diffusion, overlay or thermall barier coatings). Low cycle fatigue tests were conducted on as-received and grit blasted material in fully reversed pull-push cycle in strain control mode with constant total strain amplitude and strain rate at 900 °C in air. Experimental data on fatigue life were evaluated and parameters of Baquin and Coffin-Manson curves were obtained for both tested materials. Specimen surface and cross sections of both treated and untreated materials were analysed prior to fatigue tests and also after testing by means of optical microscopy (OM), as well as scaning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) and Vickers microhardness was measured. Fatigue degradation mechanisms was documented in both materials and negligible effect of grit blasting on low cycle parameters was discussed.
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THE EFFECT OF THRESHOLD VALUE ON THE RESIDUAL FATIGUE LIFETIME OF RAILWAY AXLES
Pokorný, Pavel ; Náhlík, Luboš ; Hutař, Pavel
The fatigue failure of railway axles could have unaccepted consequences. Because of safe operation, it is important to determine the residual fatigue lifetime. The railway axle could contain some cracks either from manufacturing process or from previous service operation. Present defectoscopy can reliably detect only relatively long cracks (longer than 2 mm), see [1]. In other words, there is a risk that the existing crack is not detected by defectoscopy. For conservative establishment of the residual fatigue lifetime the crack, which could be not detected by defectoscopy, must be considered. This paper deals with an effect of the threshold value of fatigue crack propagation on the residual fatigue lifetime of railway axles. Two very commonly used materials for railway axles EA1N and EA4T steels are considered. The results of this paper could be used for safer operation of railway axles.
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Modified compact tension test: The influence of the steel bars position
Holušová, Táňa ; Seitl, Stanislav ; Fernández-Canteli, A.
Testing and analysis of fatigue behavior of homogeneous materials, such as concrete or other cement based composites, are one major problem being studied in this scientific field. In this contribution, adaptation of the compact tension test, well known its use in the testing of metallic materials, is pursued for crack propagation rate measurement on cement based composites using cylindrical specimens. In particular, the influence of the steel bars position on the fracture parameters is studied in the modified compact tension test. The numerical study is performed by ATENA 2D. The results are compared by Load-COD diagrams and the variation of the fracture parameters values is discussed.
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