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Fatigue behavior of high strength steels (S460, S690 and S960) after corrosion
Benešová, Anna ; Květoň, Josef (referee) ; Seitl, Stanislav (advisor)
The subject of this diploma thesis is the issue of the interaction of fatigue stress and corrosion on high-strength steel. Specifically, S 460, S 690, S 960 were selected. This work presents the results of fatigue experiments on test samples that were degraded by four types of corrosion, mainly in artificial atmospheres. Subsequently, fatigue models were calculated from these data, which describe the fatigue behavior of these steels and were compared with each other. At the end, photographs of fracture surfaces of broken samples of these steels were taken, which were analyzed and their fatigue behavior was discussed with their help together with the created fatigue models.
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Plasma cutting of high strength steels
Šmak, Martin ; Herčík, Tomáš (referee) ; Kubíček, Jaroslav (advisor)
Cutting of steel is one of the fundamental operations within steel processing and steel product manufacturing. The cutting of high-strength steels represents a significant technological problem since the application of many methods produces an extensive amount of heat that is introduced into the material. The heat may significantly impact the mechanical properties of the steel. The thesis is focused on the application of the method of plasma cutting on high-strength steels. In the theoretical part of the present thesis, the common methods of cutting of steel and the plasma cutting technology are described. The parameters influencing the process of plasma cutting and their impact on the quality of the section are discussed. Furthermore, the concept of a heat-affected zone in the context of the plasma cutting method is concerned. The experimental part deals with the influence of plasma cutting on the hardness of certain types of high-strength steels. Three types of high-strength steels were used for the experiments: ARMOX 500 T, STRENX 650 MC E, and XAR®450. The sections were performed with two different cutting speeds. The size of the heat-affected zone and the hardness in the different areas of the section were evaluated. The results show that the plasma cutting is suitable for cutting of high-strength steels if appropriate parameters are selected. The influence of this method on the mechanical properties of certain high-strength steels is shown and discussed.
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Design of Conveyor Semi-Trailer
Nepovím, Ondřej ; Kovář, Stanislav (referee) ; Pokorný, Přemysl (advisor)
The first part of the thesis focuses on a research study of high-strength steels. The thesis also includes a conceptual design of the supporting structure of a transshipment trailer, which uses high-strength materials. This design is compatible with the Herkul trailer produced by the company NovaSteel s. r. o. and distributed by the sales network of Romill Brno, spol. s r.o. In its final part, the thesis deals with a stress analysis of the proposed design of the transshipment trailer. Stress-strength and deformation tests were carried out by means of the finite element method.
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Microstructure modifications of Al-Si-coated press-hardened steel 22MnB5 by laser welding
Šebestová, Hana ; Horník, Petr ; Mika, Filip ; Mikmeková, Šárka ; Ambrož, Ondřej ; Mrňa, Libor
Weld microstructure depends on the characteristics of welded materials and parameters of welding technology, especially on the heat input that determines the peak temperature and the cooling rate. When the coated sheets are welded, the effect of the chemical composition of the coating must be also considered even though its thickness is only a few tens of microns. During 22MnB5+AlSi laser welding experiments, the ferrite-stabilizing elements of coating modified the weld metal microstructure. Ferrite appeared in a quenched weld metal. The rapid cooling rate accompanying welding with a focused beam limited the homogenization of the weld metal which resulted in the formation of ferritic bands in the regions rich in Si and especially in Al. On the other hand, a high level of homogenization was reached when welding with the defocused beam. The ferritic islands uniformly distributed in the weld metal were formed at 0.4 wt% and 1.6 wt% of Si and Al, respectively. The doubled heat input reduced the Al content to 0.7 wt% insufficient for the ferrite formation at still relatively high cooling rates. Predicting the distribution of ferrite in the weld metal is challenging due to its dependence on various factors, such as cooling rate and the volume of dissolved coating, which may vary with any modifications made to the welding parameters.
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Evaluation of the quality of laser cutting surfaces
Krejčiřík, Marek ; Sigmund, Marian (referee) ; Kubíček, Jaroslav (advisor)
As the title implies, the topic to be solved in this diploma thesis was describing and evaluating the CO2 and fiber laser cutting technologies and their comparison with plasma and oxygen cutting, described in the standard ČSN EN ISO 9013. Samples of IMEX 700 high-strength fine-grain steel with a yield strength of 690 MPa were used and subjected to a final quality assessment. The diploma thesis is divided into two parts – theoretical and experimental. The theoretical part is mainly focused on a laser. Among other things, the principle of plasma and oxygen cutting was discussed. The cutting edges of samples cut by these methods were analyzed and compared in an experiment. Last but not least, the surface roughness, material hardness, and their measurement methods were discussed in the theoretical part. The final cuts after laser, plasma, and oxygen cutting were evaluated and compared in the experimental part. The roughness of the individual cuts was compared, and measured values were classified into the relevant quality classes specified by the standard EN ISO 9013. The thermal influence of the cutting joint, the width of the thermally influenced area and the hardness history were further evaluated parameters. The obtained results were discussed and summarized in the conclusion. Studied technologies were compared. Based on the experiment, fiber laser cutting was determined as the best choice regarding quality and economics.
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Welding of Al-Si coated high-strength steel 22MnB5
Šebestová, Hana ; Horník, Petr ; Mikmeková, Šárka ; Novotný, Jan ; Mrňa, Libor
Al-Si-based coatings are widely used as surface protection of steel sheets against high-temperature oxidation during the hot stamping process. Laser welding is a suitable technology for hardened components joining because it does not produce a wide heat-affected zone with a degraded microstructure. The highly concentrated energy of the laser beam is responsible for rapid heating and subsequent rapid cooling of material which results in insufficient homogenization of the weld metal. In Al-rich areas (Al originates from the coating), ferritic bands are formed in the dominantly martensitic matrix. These bands decrease the strength of laser weld by more than one third compared to the base metal. The low-power electric arc placed immediately behind the laser beam can help to achieve a slower cooling of the weld metal, reduce the ferritic bands and increase the strength of weld joints up to 90 % of base metal tensile strength.
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Plasma cutting of high strength steels
Šmak, Martin ; Herčík, Tomáš (referee) ; Kubíček, Jaroslav (advisor)
Cutting of steel is one of the fundamental operations within steel processing and steel product manufacturing. The cutting of high-strength steels represents a significant technological problem since the application of many methods produces an extensive amount of heat that is introduced into the material. The heat may significantly impact the mechanical properties of the steel. The thesis is focused on the application of the method of plasma cutting on high-strength steels. In the theoretical part of the present thesis, the common methods of cutting of steel and the plasma cutting technology are described. The parameters influencing the process of plasma cutting and their impact on the quality of the section are discussed. Furthermore, the concept of a heat-affected zone in the context of the plasma cutting method is concerned. The experimental part deals with the influence of plasma cutting on the hardness of certain types of high-strength steels. Three types of high-strength steels were used for the experiments: ARMOX 500 T, STRENX 650 MC E, and XAR®450. The sections were performed with two different cutting speeds. The size of the heat-affected zone and the hardness in the different areas of the section were evaluated. The results show that the plasma cutting is suitable for cutting of high-strength steels if appropriate parameters are selected. The influence of this method on the mechanical properties of certain high-strength steels is shown and discussed.
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Hybrid welding of high-strength steels
Horník, Petr ; Šebestová, Hana ; Mrňa, Libor
High-strength steels represent a significant group of materials in the field of automobile construction, agricultural and construction machinery, mining conveyors or bridge construction. The excellent strength characteristics is achieved due to the very fine-grained structure ensured by microalloying and the controlled rolling process. In order to preserve the fine-grained structure and hence the required properties and minimize thermal distortions, it is advisable to use welding technologies that do not bring excessive heat to the material. At the same time, however, it is advisable to avoid large temperature gradients that support the formation of fragile microstructures. Therefore, an electric arc preheating is placed before the laser beam and its influence on the weld geometry and the heat-affected area is evaluated.\n
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Design of Conveyor Semi-Trailer
Nepovím, Ondřej ; Kovář, Stanislav (referee) ; Pokorný, Přemysl (advisor)
The first part of the thesis focuses on a research study of high-strength steels. The thesis also includes a conceptual design of the supporting structure of a transshipment trailer, which uses high-strength materials. This design is compatible with the Herkul trailer produced by the company NovaSteel s. r. o. and distributed by the sales network of Romill Brno, spol. s r.o. In its final part, the thesis deals with a stress analysis of the proposed design of the transshipment trailer. Stress-strength and deformation tests were carried out by means of the finite element method.
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