This research is about a costly problem in the automotive industry due to tool fracture during the splines cold rolling of steel shafts. The objective is to study the cause of this failure and propose solutions that can be implemented in the workshop.The writing starts with a brief introduction of the companies involved in shafts production and problem solving. It introduces the cold rolling process and its advantages on splines manufacturing, and it goes through relevant material and process characteristics that help to determine the cause of tool fracture.In order to understand the process failure and production flow, it has been necessary to build up an Ishikawa diagram with possible tool fracture causes. After collecting and analysing the data about the machine tool, cold rolling process and work-piece and rolling tool materials, tests and experiments have been done.It has been considered that there is a rolling tool fatigue that causes tool fracture. Beside tool fracture, two more problems with production flow instability and the right side rolling tool have been detected. Testing the material hardness of the work-piece has shown continuous hardness fluctuations from the supplier. Rolling tool misalignment has been measured by using a vernier caliper measurement device. Rolling tools material hardness analysis shows that tool is very hard and it is possible to use a tougher material which responds better to cyclic loads.Leax has tried to solve the problem by testing another lubrication and tool coatings. A modal analysis test has been performed in order to find the natural frequency of the work-piece which possibly may lead to vibration and over loading one of the rolling tools.The conclusion that has been reached is that main cause of fracture is rolling tool fatigue due to cyclic loads and it is important to use other rolling tool material. The other two detected problems, production flow instability and rigth side rolling tool fracture, should be considered as a part of the problem in order to significantly increase tools life and stabilize production flow rate.

Intercritically austempered ductile iron (IADI) with a matrix microstructure of ferrite plus metastable austenite has an excellent combination of strength and toughness. The high strength and good ductility of this material is due to the transformation of metastable austenite to martensite during deformation. In the present study, the transformation of austenite to martensite for intercritically austempered ductile irons of varying alloy chemistry (varying amounts of nickel and/or manganese) were examined using in-situ neutron diffraction under strain-controlled loading at VULCAN at the Spallation Neutron Source at Oak Ridge National Laboratory (ORNL). Both diffraction and tensile data were collected and synced using the VDRIVE software (a proprietary ORNL software package). The single peak fit method was employed in the analysis of the diffraction data. In this thesis, the stress and strain for the start of the transformation of metastable austenite to martensite were determined. The development of residual stresses during deformation and the elastic diffraction constants for both the ferrite and austenite phases were also determined. The material was characterized using optical microscopy, backscattered imaging in the scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy. / Master of Science

<blockquote><div><div>Methods and techniques for tailoring the surface morphology of metallic surfaces are determined in part by the complex behavior of elemental interactions in conjunction with electrochemical reactions. In this work, we show how the surface morphology can be predicted based on experimental data resulting from polarization curves and compositional differences of Fe- and Ni-based superalloys. Electrochemical treatments utilizing NaCl as the electrolyte were adapted using parameters such as the pitting resistance equivalent (PRE) number and polarization curves to obtain both rough and smooth surfaces. Utilizing these metrics, we electrochemically etched Inconel 600, SS304, Inconel 718 and Inconel 625 obtaining average surface roughness values that ranged from 0.05 to 57.4 μm indicating the success of tailoring the technique to obtaining rough and smooth surfaces. The effect of current density, current pulsing, and temperature were varied to elucidate roughness and pitting behavior, and strong correlations to the PRE number and polarization curve properties of the alloy were observed. Heat treatments and subsequent evolution to the microstructure in the form of grain growth and precipitation altered the etching behavior. These techniques can be used in preventing corrosion failure and enhancing electrochemical machining</div></div></blockquote>

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18986号 / 工博第4028号 / 新制||工||1620(附属図書館) / 31937 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 辻 伸泰, 教授 田中 功, 教授 乾 晴行 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第20476号 / エネ博第345号 / 新制||エネ||69(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー社会・環境科学専攻 / (主査)教授 石原 慶一, 教授 野平 俊之, 准教授 奥村 英之 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

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[pt] O aço inoxidável hiper duplex UNS S33207 é utilizado na indústria de óleo e gás para operações de poços em águas ultraprofundas devido às suas excelentes propriedades mecânicas e resistência à corrosão. Aços inoxidáveis duplex quando submetidos a ciclos térmicos que atingem temperaturas próximas à temperatura de ferritização seguido de resfriamento rápido, apresentam matriz ferrítica e diferentes morfologias de austenita, como Widmanstätten, alotriomórfica e intragranular, além da precipitação de nitretos de cromo. É importante destacar que no caso de aços inoxidáveis duplex, entre os elementos químicos presentes em solução sólida, o nitrogênio possui extrema importância na formação da fase austenítica. Sendo também responsável pela alta resistência à nucleação de pites. Portanto as atmosferas nas quais são realizados os tratamentos térmicos ou quando ciclos térmicos são aplicados a estes aços, podem ter efeito sobre a dessorção ou absorção de nitrogênio, influenciando assim a resistência à corrosão. Nesta dissertação foi analisado o aço hiper duplex UNS S33207 tanto na condição de como recebido, assim como tratado termicamente nas temperaturas de 1380 graus Celsius e 1390 graus Celsius em quatro atmosferas diferentes: ar atmosférico, argônio, nitrogênio e argônio com 5% de nitrogênio. A caracterização microestrutural foi realizada por microscopia ótica, e eletrônica de varredura (MEV) além de difração de elétrons retro-espalhados (EBSD). Foram também realizados ensaios de dureza, microdureza e teste de corrosão de acordo com a norma ASTM G48. Após o tratamento térmico o balanço entre as fases ferrita e austenita se alterou. Devido à alta taxa de resfriamento, a fase ferrítica se tornou mais abundante na condição de termicamente tratada. A influência das atmosferas se mostrou mais evidente em relação a austenita não dissolvida após o tratamento térmico. As amostras tratadas com atmosferas de nitrogênio apresentaram maior percentual de austenita não dissolvida do que as amostras tratadas em ar atmosférico ou mesmo em argônio puro, estas últimas apresentaram menor percentual de austenita não dissolvida. O teste de corrosão ASTM G48 indicou maior perda de massa nas amostras tratadas termicamente. Dentre estas condições, as que tiveram influência das atmosferas contendo nitrogênio apresentaram melhor resistência a corrosão. Os pites em todas as amostras iniciaram na interface gama /delta com propagação para o interior dos grãos ferríticos. O objetivo principal desta dissertação é correlacionar a influência de diferentes atmosferas na porcentagem das fases transformadas em função tratamentos térmicos nas propriedades de corrosão. / [en] Hyper duplex stainless steel UNS S33207 is used in the oil and gas industry in ultra-deep well operations due to its excellent mechanical properties and corrosion resistance. When stainless steels are subjected to thermal cycles reaching temperatures close to the ferritization temperature, then followed by fast cooling, the microstructure transforms. The ferritic matrix and different austenite morphologies will occur during cooling, such as Widmanstatten, allotriomorphic, and intragranular, in addition to chromium nitride precipitation. It is essential to highlight that for duplex stainless steels, among the chemical elements in solid solution, nitrogen is vital in the austenitic phase precipitation. It is also responsible for the pitting corrosion resistance. Therefore, the atmospheres in which heat treatments are carried out or when thermal cycles are applied to these steels can affect nitrogen desorption or absorption, thus influencing corrosion resistance. In this dissertation, UNS S33207 hyper duplex stainless steel was analyzed in the asreceived condition and as heat-treated at 1380 Celsius degrees and 1390 Celsius degrees in four different atmospheres: atmospheric air, argon, nitrogen and a mixture of argon and 5 percent nitrogen. Microstructural characterization was performed by optical microscopy and scanning electron microscopy (SEM) in addition to electron backscatter diffraction (EBSD). Hardness, microhardness, and ASTM G48 corrosion tests were also performed. After the heat treatment, the balance between the ferrite and austenite phases changed. Due to the fast cooling rate, the ferritic phase became more abundant in the heat-treated condition. The atmosphere influence was more evident on the primary austenite after the heat treatment. The samples heat treated with nitrogen atmospheres presented a higher percentage of primary austenite than the samples heat-treated in atmospheric air, or even in pure argon, the latter gave the lowest fraction of remaining austenite. The ASTM G48 corrosion test indicated a more significant mass loss in the heat-treated samples. Among these samples, those that were heat-treated in atmospheres containing nitrogen presented better corrosion resistance. The pitting in all samples nucleated at the gama / delta interface. The pitting then propagated into the ferritic grains. This dissertation main objective is to correlate the influence of the different atmospheres on the percentage of phases transformed as a function of heat treatments and the effect on corrosion properties.

String cheese, a Mozzarella cheese, has the unique ability to string in fibrous strands when pulled apart. Graders judge string cheese by its stringy texture; samples with copious amounts of string are awarded high ratings. But just as the texture of natural cheeses softens with time, the stringy texture of string cheese can diminish with age too. Age related softening in cheese is due primarily to an important biochemical event known as proteolysis, which is attributed to inherent milk proteinases, residual coagulant activity, and enzymes from the lysis of starter culture microorganisms. It is hypothesized that a post manufacture heat treatment of string cheese could inactivate these proteolytic enzymes and slow or eliminate proteolysis during storage. Therefore, the main objective of this study was to determine the effects of a post manufacture thermal dip treatment on proteolytic activity in packaged, commercial string cheese. Proteolysis was examined qualitatively by Urea-PAGE electrophoresis, quantitatively by measuring percentage of water-soluble nitrogen (%WSN), and by using a scoring method to analyze stringy texture during refrigerated storage. Fresh, commercial string cheese was sourced on two separate occasions and treated six days after manufacture. Treatment consisted of dipping the packaged cheese sticks in water baths at 55°C, 75°C, and 95°C for 30 and 60 seconds. String cheese that did not undergo treatment served as the control. Treated and control cheeses were stored at 4°C until sampling for Urea-PAGE, WSN extraction, and texture analysis on days 1, 11, 22, 29, 49, 91, and 172 after treatment. The degree of β-CN breakdown was not observed to be different between all treatment levels throughout the storage period. This was not expected since Mozzarella cheese exposed to a higher temperature should have more plasmin activity than that of cheese exposed to a lower temperature. There was a trend of slightly more intact αs1-CN in the most severely treated string cheese (95°C for 60s) when compared to the control at the final time point of the study. This suggests the possibility of successful inactivation of residual coagulant, intracellular enzymes, or other proteolytic enzymes in the string cheese at this treatment. However, only storage time had a significant effect on %WSN (p The research completed in this study provides insight of the proteolytic effects from a thermal treatment process applied post string cheese manufacture. Though relationships between the treatments to the extent of secondary proteolysis and stringy texture were not significant, it was still found that there was more intact αs1-CN due to one of the treatments. These results suggest that it is possible that the use of other heat treatment parameters, longer storage period, or a combination of the two could show a significant relationship between thermal treatment and proteolysis. These results also suggest that further work to improve shelf life of string cheese or other cheese varieties through the concept of a post manufacture heat treatment may be promising.