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Compared HAZ the methods of welding TIG, MAG and CMT
Šoulák, Petr ; Sigmund, Marian (referee) ; Kubíček, Jaroslav (advisor)
The bachelor thesis was to compare the HAZ size for the TIG, MAG and CMT methods. The welded materials were low carbon steel and austenitic stainless steel. Samples of 250x50 mm size and 2 mm thick were welded with butt weld without a gap. In the first part of experiment, samples were welded at the same welding speed. The second part concerned only CMT, where the optimal welding speed was used. For selected samples, the HAZ size was measured and compared in macroscopic images.
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Measurement of oxygen activity in ferro-alloys
Žák, Štěpán ; Čamek, Libor (referee) ; Záděra, Antonín (advisor)
The thesis deals with determination of the oxygen content in ferro-alloys with emphasis on direct oxygen activity measurement in the meltage. The practical part of the thesis contains statistical analysis of oxygen activity values measured in austenitic and duplex stainless steel meltages. The measurements were done in vacuum furnace before vacuuming and afterwards. Statistically significant dependency of oxygen activity on the temperature of meltage was discovered among the values measured after the vacuuming. Therefore, its value can be predicted based just on the temperature of the meltage. No statistically significant dependency was found among the values measured before vacuuming (except for the low Chromium austenitic stainless steel meltages). Hence, other factors need to be considered when predicting oxygen activity before vacuuming.
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Microstructural stability of austenitic steels during fatigue loading
Kudelka, Martin ; Válka, Libor (referee) ; Pantělejev, Libor (advisor)
This diploma thesis studies the structure of selected austenitic stainless steels which were fatigued at room and depressed temperatures. The theoretical part is divided into three parts. The first one defines the austenitic stainless steels with accent to their chemical composition and microstructure. Second part is dedicated to deformation-induced martensite formation. The third part shows the mechanisms and stages of damage due to cyclic straining. The experimental part is focused especially on the observing of microstructural changes by methods of colour metallography and their relation to stress-strain response of material under selected conditions of fatigue loading. Series of samples of 304 and 316L steels were prepared by colour etching and their microstructures were documented using optical microscopy. Then the semi-quantitative measurements of presence and morphology of deformation-induced martensite were done and the results were discussed and correlated with fatigue damage level.
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The influence of mechanical alloying on contamination of powder mixtures and bulk materials
Kubíček, Antonín ; Hadraba, Hynek (referee) ; Moravčík, Igor (advisor)
This thesis deals with the influence of process parameters on the contamination level of powder materials produced by mechanical alloying (MA) technology. For this purpose austenitic stainless steel 316 L and equiatomic CoCrFeNi high-entropy alloy (HEA) were prepared by high-energy ball milling. Both materials were milled in argon and nitrogen atmospheres from 5 to 30 hours. Spark plasma sintering method (SPS) was then used for consolidation of chosen powder samples. Chemical analysis of contamination within MA was carried out using combustion analysers for determination of carbon, oxygen, and nitrogen contents after different lengths of milling. Also differences in chemical composition of powder and corresponding bulk samples were measured. The microstructure analysis using scanning electron microscopy (SEM) of both powder and bulk materials was executed with focus on oxide and carbide presence and dispersion. Increasing content of carbon with increasing milling time was observed across all measured samples. This contamination is attributed to using milling vial made of tool steel AISI D2 (containing 1,55 wt. % of carbon). Increase of carbon content within consolidation using SPS was also observed. Milling of specimens using N2 as milling atmosphere caused higher contamination level in both AISI 316 L and HEA compared to milling in argon.
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Recovery and recrystallization of austenitic steel 08Cr18Ni10T
Čech, Jan ; Gregor, Martin (referee) ; Foret, Rudolf (advisor)
This thesis deals with influences of graded deformations, temperatures and holding times on the grains and subgrains size in steel 08Cr18Ni10T. In literary part of the thesis there are described static and dynamic annealing treatments, then also austenitic stainless steels and some selected types of their processing. In experimental part there is studied grain size on differently deformed samples annealed in temperature range 1050–1200 °C for 10, 50 and 100 minutes. Analysis of present structures units was perform by EBSD. Except of that, there were realized chemical analysis of selected inclusions and also hardness test were realised. Achieved measurement shown, that grain size of chosen steel is depended on all 3 variable values.
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Short Crack Growth in Materials for High Temperature Applications
Mazánová, Veronika ; Obrtlík, Karel (referee) ; Krupp, habil Ulrich (referee) ; Polák, Jaroslav (advisor)
Pokročilá vysoce legovaná austenitická nerezová ocel Sanicro 25 s Fe-Ni-Cr matricí byla studována za podmínek nízkocyklové únavy za pokojové a vysoké teploty 700 °C. Široká škála moderních experimentálních technik byla použita ke studiu vzájemně souvisejících efektů chemického složení slitiny, mikrostrukturních změn a deformačních mechanismů, které určují odolnost materiálu vůči poškození. Hlavní úsilí bylo zaměřeno na studium iniciace únavových trhlin a růstu krátkých trhlin, tedy dvě stádia, která hrají zásadní roli ve výsledné celkové délce únavového života materiálu v provozu. • Vnitřní deformační mechanismy byly korelovány s vývojem povrchového reliéfu, který je pozorován ve formě persistentních skluzových stop na povrchu. Bylo zjištěno, že vysoce planární charakter dislokačního skluzu způsobuje vysokou lokalizaci cyklické plastické deformace do persistentních skluzových pásů, což v důsledku vede k nukleaci “Stage I” trhlin, která je spojena s přítomností persistentních skluzových stop na povrchu ve všech studovaných vzorcích. Bylo zjištěno, že praskání dvojčatových hraníc je taktéž spojeno s přítomností persistentních skluzových stop podél povrchové stopy dvojčatové roviny. • Interkrystalická iniciace únavové trhliny byla pozorována pouze zřídka, a to za podmínek zatěžování amplitudami vysoké deformace. Bylo zjištěno že interkrystalická iniciace je spojena s přítomností persistentních skluzových stop na hranicích zrn. Hranice zrn praskají za podmínek externího tahového zatížení zejména z důvodu vysokého počtu nekompatibilit na hranicích zrn, které jsou způsobené tvarem persistentních skluzových stop. • Mechanismy růstu přirozených krátkých trhlin byly studovány na vzorcích vystavených nízkocyklove únava s nízkou i vysokou deformací. Role mikrostruktury byla analyzována pomocí experimentálních technik a diskutována. • Rychlosti šíření nejdelších trhlin byly měřeny na vzorcích s mělkým vrubem. Výsledky byly analyzovány použitím přístupů lomové mechaniky založených na amplitudě KI a J-integrálu stejně jako na amplitudě plastické deformace. Všechny přístupy byly diskutovány v souvislosti s Mansonovými-Coffinovými křivkami únavové životnosti. Jednoduchý mocninový zákon růstu krátkých trhlin založený na amplitudě plastické deformace ukazuje velice dobrou korelaci se zákonem únavové životnosti. • Byla studována role oxidace v podmínkách cyklického zatěžování za vysokých teplot. Bylo zjištěno, že křehké praskání zoxidovaných hranic zrn hraje hlavní roli v počátečních stádiích nukleace trhlin. Později po iniciaci se dráha růstu trhliny mění preferenčně na transkrystalickou. Dráha šíření trhlin je velmi podobná dráze zjištěné při cyklování za pokojové teploty.
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Stick welding carbon and high-alloy steels
Hendrych, Marek ; Vaněk, Mojmír (referee) ; Kubíček, Jaroslav (advisor)
This thesis deals with analysis of manual metal arc welding method or method 111. In the research part of this thesis are discused principles of this method, welding power sources and additional welding material-coated elecrodes. Further the thesis is focused on the weldability of steels, especially carbon steels and austenitic stainless steels. In the experimental part was accomplished measurement of operational characteristics of coated electrods. Measurement was carried out on sample of cabon steel S235JR according to ČSN EN and austenitic stainless steel X5CrNi18-10 accordig to ČSN EN. The evaluation envolves a comparison of the results and their justifications.
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On the analysis of thin-wall parts sawing
Spáčil, Radek ; Dvořáková, Jana (referee) ; Píška, Miroslav (advisor)
Master‘s thesis deals with sawing of the thin-walled parts with high speed steel slitting saw. At first the most used conventional and unconventional possibilities of materiál cutting are described by a form of search. The next chapter describes forces arising from splitting saw machining, including their dependence on a specific cutting force, a chip cross section and a engagement angle. The second part of the thesis deals with the technological improvement of the cutting process, where three possible solutions are considered – geometry of the cutting tool, PVD coating deposition of the cutting tool and process fluid change. In the experimental part non coated slitting saw with burrs, non coated deburred slitting saw and coated slitting saws are compared. Used coatings were Ti(C,N), Cr-Al-Si-N, Al-Cr-B-N, and TripleCoating Cr, which is consisting of three layers TiN + (Al,Ti)N + Cr-Al-Si-N. The experiment has shown that the cutting forces inceases as the edge radius and wear level of the cutting tool increases. Coated cuttung tools has shown lower differences between the first and the last cut. Slitting saws have been also used in real cutting process to verify experimental results.
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Influence of chemical composition, casting temperature and the used deoxidation on technological properties of austenitic chrome-nickel steels
Myška, Martin ; Dulava, Martin (referee) ; Záděra, Antonín (advisor)
The thesis deals with austenitic stainless steel ČSN 42 2930, ASTM A351 CF8 and evaluates its mechanical and technological properties. The first part of this work is focused on properties of austenitic steels, it describes the process of melting and casting of steel on the basis of the realized experiments. It also deals with the mechanical properties of the used steel. The second section of the thesis is dedicated to the historical development of the maximum fluidity tests and main factors affecting the maximum fluidity of alloys. Maximum fluidity values have been processed on the basis of different casting temperatures of the maximum fluidity tests of the used steel. The third part of the work examines the effect of the casting temperature on the feeding distance of the used steel as well as the influence on its shrinkage rate.
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