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Structure and properties of welded joints of steam turbine rotor
Machala, Jan ; Hutařová, Simona (referee) ; Juliš, Martin (advisor)
This thesis deals with the assessment of the structural-mechanical properties of welded joints of steam turbine rotor. Experimental weld material is low alloy steel 30CrMoNiV5-11 in the state after the artificial degradation. The theoretical part of the literary researches the issue, focusing on the weldability of different types of steel used in the energy industry, the metallurgical processes in welding and provides an overview of the most important methods of welding. Great attention is paid to the evaluation of weld quality in accordance with relevant standards and destructive and non-destructive testing of welded joints. In the experimental part of this work was carried out measurements of hardness and microhardness of the weldment by Vickers and evaluation of the microstructure by light microscopy. The obtained values and information about the properties of the material after artificial degradation were compared with previously obtained experimental results in the default state (after annealing).
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Present Trends of Methods for Hardness Measurement
Brzobohatý, Tomáš ; Doležal, Pavel (referee) ; Hutařová, Simona (advisor)
Purpose of this thesis is created view of present methods of hardness measurement and to describe them in more detail. Firstly this thesis deals with representatives of standard and for many years used methods of hardness measurement and hardness evaluation which are used today, too. Secondly this thesis is focused on modern methods, and their successful working experience is question of time.
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Influence of Explosive Hardening on the Structure and Characteristic of Hadfield Steel in Terms of use in the Railway Transport
Havlíček, Petr ; Podrábský, Tomáš (referee) ; Nesvadba,, Petr (referee) ; Schmidtová,, Eva (referee) ; Stránský, Karel (advisor)
The high alloyed austenitic manganese steel, the Hadfield steel, thanks to its good wear resistance of the work surface and maintaining the high toughness of the internal material in the same time, is successfully applied for casted crossings. The crossings are the most dynamic stressed components in the railway turnouts. Thanks to low surface and sub-surface hardness the occurrence of plastic deformation and the progressive wear of the crossing running surfaces can be found since the initial stages of the crossing operational life. One possibility how to increase the surface and the sub-surface hardness and this way improve the dimensional stability and the crossing lifetime as well is to apply the explosive hardening of the crossing running surfaces. The technology mentioned above means the application of the explosives in the imminent nearness to the running surface of the crossing, when the high pressure wave acting within the extremely short period actuates the plastic deformation of the material structure. The work deals with analysis of influence of explosive hardening on the structure and characteristic of Hadfield steel. The explosive hardened samples have the surface and the sub-surface hardness checked and the microscopic analysis and X – ray diffraction is applied, including the TEM analysis as well carried out by the transmission electronic microscope. The characteristics experimental testing including outcomes from assessment of the contact – fatigue load of the explosive hardened Hadfield steel samples are the part of the work as well. As an experiment final part the outcomes of the long –term validation, the surface hardness and wear of the crossing running surfaces of the explosive hardened crossing already installed into the Czech Republic railway track are introduced as well.
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The Influence of Structure and Heat Treatment on Properties of Steels for Bearings
Pytlíčková, Kateřina ; Dočkal, Ing, Michael (referee) ; Věchet, Stanislav (advisor)
Heat treatment influences structure and characteristics of treatmented material. Good heat treatment of steels for bearings ensures hardness of matrix 60 - 65 HRC, whereas structure has be formed by tempered fine needle-shaped martensite with definite part of residual austenite. Carbides should be evenly dispersed, they mustn´t create carbide network and carbide lines. Quality of steels for bearings is also influenced by volume and morphology of inclusions in the matrix. In this diploma thesis various conditions of heat treatment were to be set up with the aim of choose the optimal ones. These ensures perfect martensite transformation and full hardening of all component. Quenching from 760 °C – 770 °C was quite unsatisfactory. At this temperature resulting structure was ferritic-perlitic, because martensite transformation did not pass. Too long hold on hardening temperature also had unfavourable influence on resulting structure and characteristics. In this case, structure was created by very coarse needle-shaped martensite. Coarsening of martensite needle locally exceeded maximum allowed level. In the structure there was also possible to watch partly soluted globular carbides. Optimal heat treatment is quenching from 850 °C – 870 °C followed by tempering at 220 °C. Resulting structure quite agree with above-mentioned needs. This heat treatment can be recommended for technical practise.
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Surface hardening os steels by YbYAG fiber laser
Hromada, Martin ; Daněk, Ladislav (referee) ; Mrňa, Libor (advisor)
Diploma thesis is focused on laser hardening by Yb:YAG fiber laser. Experiment is based on hardening of testing pieces made of steel 12 050 with different parameters of distance and movement speed of laser head. In theoretical part are described principle of laser, types of lasers, laser technology in industry, types of lasers, types of hardening and types of hardness measuring. In practical part are firstly evaluated macrostructure and microstructure photos and Vickers hardness. In conclusion are analyzed the results of laser hardening and after that the best laser hardening parameters were selected.
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Heat treatment of tool steels
Tobolík, Stanislav ; Pacal, Bohumil (referee) ; Molliková, Eva (advisor)
This thesis deals with the properties of ledeburitic chrome-vanadium tool steel after heat treatment. Theoretical part contains charakterization of ledeburitic steels, the posibility of manufacturing and heat treatment. There are also briefly describes the principles of the test methods, which were used. The practical part is focused on describing the results of 12 sample groups, with different heat treatment. The results are compared in the final discussion.
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Heat treatment of aluminum castings
Mátl, Vojtěch ; Pernica, Vítězslav (referee) ; Kaňa, Václav (advisor)
This bachelor thesis deals with the topic of heat treatment of aluminium castings. The first part of this thesis comprises of casting alloys and casting technology summary, followed by description of aluminium heat treatment. The second part descibes an experimet, that examins the effect of conditions during aging upon final aluminium alloy properties.
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Characterization of heat treated Ni-P coatings with different phosphorus contents.
Žilinský, Martin ; Kosár, Petr (referee) ; Wasserbauer, Jaromír (advisor)
The aim of this work was the characterization of heat–treated, electroless nickel–phosphorus coatings of different phosphorus content. In the theoretical part of this work, the substrate for the nickel–phosphorus coating, namely the AZ91 alloy, is discussed. Further, the deposition of the nickel–phosphorus coating on the substrate, the components of the nickel baths and their influence on the phosphorus content of the deposited coating nickel–phosphorus, is analyzed. Attention is also paid to the structure of this coating depending on the phosphorus content. Heat–treatment and its influence on the hardness of this coating is also discussed. At the end of the theoretical part, the current research in the field of nickel–phosphorus coatings, is described. The experimental part of this work describes the pre–treatment of samples and their characterization. Using a scanning electron microscope, the phosphorus content of the heat–treated coatings was determined. Furthermore, the microhardness of heat–treated nickel–phosphorus coatings was measured. X–ray diffraction analysis determined microstructure and crystallite size of the phases present in coatings after heat–treatment.
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