Os aços-ferramenta têm importante participação no mercado mundial de aços. São usados na indústria metal-mecânica como ferramentas de corte, moldes, punções, matrizes, etc. Devido ao uso de grande responsabilidade, é importante discutir a relação entre microestrutura e propriedades mecânicas, porque é uma prática comum na indústria especificar os tratamentos térmicos com base principalmente na dureza final do material, sem considerar que para um mesmo valor de dureza um aço-ferramenta pode apresentar diferenças nas propriedades mecânicas, dependendo do ciclo de tratamento térmico aplicado. Logo, esta seleção de tratamento térmico é um aspecto tecnológico relevante no desempenho de aços-ferramentas.Os materiais selecionados foram os aços VND, Calmax, VF-800 e Vanadis 10, sendo os três primeiros produzidos por fundição – rota convencional e o último produzido por processo de pressão isostática a quente (HIP) – rota sinterizada.O objetivo deste trabalho foi avaliar o tratamento térmico, a microestrutura e as propriedades mecânicas destes quatro açosferramenta para trabalho a frio, para determinar o tratamento térmico capaz de promover a melhor relação dureza-tenacidade. Os resultados mostraram para o aço VND a possibilidade de se trabalhar com nível de dureza um pouco superior ao recomendado pelo fabricante, com sensível melhora nos parâmetros de resistência sem, no entanto, a ocorrência de um decréscimo importante em termos de tenacidade. Para o aço Calmax os resultados mostraram a possibilidade de trabalhar com dureza um pouco inferior à recomendada pelo fabricante, com significativa melhora nos parâmetros de tenacidade, sem a ocorrência de um decréscimo na resistência. Para os aços VF-800 e Vanadis 10, os resultados obtidos utilizando-se temperatura de revenimento inferior à recomendada pelo fabricante mostraram um ótimo desempenho em todos os ensaios, com particular atenção aos resultados de energia absorvida. / Tool steels have important participation in the worldwide market of steels. They are used by metal-mechanical industry as cutting tools, molds, punches, dies etc.Due to the use of great responsibility, it is important to discuss the relationship between microstructure and mechanical properties because it is a common practice in industry to specify heat treatments based mainly in the final hardness of the material without considerations about that for the same value of hardness a tool-steel can present differences in mechanical properties, depending on the heat treatment cycle applied. Thus, the selection of the heat treatment is a relevant technological aspect in the performance of tool steels. The materials selected were VND, Calmax, VF800 and Vanadis 10, being the three first produced by hot ingot casting followed by hot working - conventional route, and the last one by hot isostatic pressing (HIP) process – sintering route. The aim of this work was to evaluate the heat treatment, microstructure and mechanical properties of these four tool steels for cold work application in order to determine the heat treatment able to promote the best relationship hardness-toughness. The results have shown for VND steel the possibility of working with hardness slightly higher than that recommended by the manufacturer, with sensible improvement of strength without, however, the occurrence of an important decrease in toughness. For the Calmax steel the results have shown the possibility of working with hardness values slightly lower than that recommended by the manufacturer, with significant improvement in toughness, without the occurrence of a strength decreasing. For the steels VF-800 and Vanadis 10, the results of lower temperature of tempering than the recommended by the manufacturer have indicated good performance in all mechanical tests, with attention to the absorbed energy results.

Additive manufacturing technologies place materials at the direct point of need of the warfighter, enabling the development of optimal, situation-specific means to produce and repair parts of Army and DoD weapons systems. In the case of solid-state AM, a full understanding of the metallic powder is critical with producing ideal consolidated material properties reliably and repeatably. By way of iteratively coupling computational models with supportive experimental testing, one can rapidly archetype differences in processing methods, alloy compositions, and heat treatments for metallic powders that serve as feedstock for these AM technologies. Through the combination of thermodynamic models, advanced characterization, and dynamic nano-indentation, representative correlations are established between microstructural features and mechanical properties, enabling the development of enhanced feedstock materials that can achieve the specific needs of the warfighter efficiently without forfeiting quality. This represents both a holistic and a materials-by-design approach to AM through the deliberate use of computation to drive down the discovery process and allow feedstock powders to be engineered with specific properties dictated by Army requirements for performance. In a case study of Al 6061, unique observations were made through the combination of modeling and experimentation. It was discovered that the precipitation kinetics were greatly accelerated in powders and therefore, typical heat treatment processes used for cast-aluminum alloys were not valid. Due to this shift in precipitation sequences, high-temperature treatment was limited to discourage precipitate and grain coarsening. Additionally, when compared to typical cast Al 6061, the main precipitation hardening phase shifts from Mg2Si to Al4Cu2Mg8Si7, changing how aging mechanisms were accounted for. These conclusions were supported by both the computational models and experimental results. Through the generation of numerous data, the models were calibrated, enabling more efficient and precise development of tailored material characteristics from specific microstructural features to serve as an input in a holistic through-process model for a solid-state AM process and guide future experimentation.

<div>Self-pierce riveting as a relative new technology has been used by automotive industry for decades. Because of the several benefits of the SPR technique, it has been widely used for joining the similar or dissimilar materials to satisfy the light-weighting requirements of automobile. There were many researchers and automotive manufacturers that had been investigated the SPR by experiments and applied this technique to their products. The SPR was designed for joining the materials with sufficient ductility because the joining process was going to introduce the large plastic deformation on the joint button area. Die casting aluminum alloy products became more and more popular to be used for structural components. However, the casting aluminum components have relative low ductility than the wrought alloy product. The cracking problems were easy to occur during the riveting process.</div><div><br></div><div>In terms of the cracking issues on die casting aluminum products, an analysis was conducted in this study to investigate the influence of composition on cracking problem. And the cracking mechanism was also analyzed and summarized. Corresponding to the influence of silicon content difference and silicon morphology, heat treatment was used to modify the eutectic silicon morphology of the casting aluminum alloys to improve the rivetability. Once the silicon network was broken by the heat treatment, the rivetability of die casting aluminum was drastically increased and the cracks on joint button were also suppressed. Under the effect of heat treatment, the joint performance was tightly related to the variation of the eutectic silicon phase and the cracks on the joint button. The joint strength was obtained by shear test to investigate the influence of heat treatment and die depth. A novel cracking statistics has been generated and used to calculate the cracks on the joint button. Eventually, a comprehensive joint performance was obtained by taking into consideration of joint strength, heat treatment and die depth.</div><div><br></div><div>Finally, the simulation of the SPR process was conducted and analyzed by FORGE. The die depth as the variable was used to investigate the strain and fracture distribution in</div><div>cross-section view of the joint. In terms of the initial results of the simulation, the die cavity with various sidewall incline angles was simulated to find the optimal die cavity geometry in order to improve the rivetability of the bottom material sheet.</div>

Os aços-ferramenta têm importante participação no mercado mundial de aços. São usados na indústria metal-mecânica como ferramentas de corte, moldes, punções, matrizes, etc. Devido ao uso de grande responsabilidade, é importante discutir a relação entre microestrutura e propriedades mecânicas, porque é uma prática comum na indústria especificar os tratamentos térmicos com base principalmente na dureza final do material, sem considerar que para um mesmo valor de dureza um aço-ferramenta pode apresentar diferenças nas propriedades mecânicas, dependendo do ciclo de tratamento térmico aplicado. Logo, esta seleção de tratamento térmico é um aspecto tecnológico relevante no desempenho de aços-ferramentas.Os materiais selecionados foram os aços VND, Calmax, VF-800 e Vanadis 10, sendo os três primeiros produzidos por fundição – rota convencional e o último produzido por processo de pressão isostática a quente (HIP) – rota sinterizada.O objetivo deste trabalho foi avaliar o tratamento térmico, a microestrutura e as propriedades mecânicas destes quatro açosferramenta para trabalho a frio, para determinar o tratamento térmico capaz de promover a melhor relação dureza-tenacidade. Os resultados mostraram para o aço VND a possibilidade de se trabalhar com nível de dureza um pouco superior ao recomendado pelo fabricante, com sensível melhora nos parâmetros de resistência sem, no entanto, a ocorrência de um decréscimo importante em termos de tenacidade. Para o aço Calmax os resultados mostraram a possibilidade de trabalhar com dureza um pouco inferior à recomendada pelo fabricante, com significativa melhora nos parâmetros de tenacidade, sem a ocorrência de um decréscimo na resistência. Para os aços VF-800 e Vanadis 10, os resultados obtidos utilizando-se temperatura de revenimento inferior à recomendada pelo fabricante mostraram um ótimo desempenho em todos os ensaios, com particular atenção aos resultados de energia absorvida. / Tool steels have important participation in the worldwide market of steels. They are used by metal-mechanical industry as cutting tools, molds, punches, dies etc.Due to the use of great responsibility, it is important to discuss the relationship between microstructure and mechanical properties because it is a common practice in industry to specify heat treatments based mainly in the final hardness of the material without considerations about that for the same value of hardness a tool-steel can present differences in mechanical properties, depending on the heat treatment cycle applied. Thus, the selection of the heat treatment is a relevant technological aspect in the performance of tool steels. The materials selected were VND, Calmax, VF800 and Vanadis 10, being the three first produced by hot ingot casting followed by hot working - conventional route, and the last one by hot isostatic pressing (HIP) process – sintering route. The aim of this work was to evaluate the heat treatment, microstructure and mechanical properties of these four tool steels for cold work application in order to determine the heat treatment able to promote the best relationship hardness-toughness. The results have shown for VND steel the possibility of working with hardness slightly higher than that recommended by the manufacturer, with sensible improvement of strength without, however, the occurrence of an important decrease in toughness. For the Calmax steel the results have shown the possibility of working with hardness values slightly lower than that recommended by the manufacturer, with significant improvement in toughness, without the occurrence of a strength decreasing. For the steels VF-800 and Vanadis 10, the results of lower temperature of tempering than the recommended by the manufacturer have indicated good performance in all mechanical tests, with attention to the absorbed energy results.

Neste trabalho foram estudados os efeitos causados pelo tratamento térmico na argila STx-1b-Li+ na condutividade de filmes argila/alginato de sódio. O argilomineral STx-1b foi submetido à substituição isomórfica do cátion Na+ por Li+ e posteriormente ao tratamento térmico em diferentes temperaturas. As argilas STx-1b-Li+ não tratada e tratada termicamente foram caracterizada por difração de raios-X (DRX) e termogravimetria (TG). As curvas TG mostraram que o argilomineral STx-1b-Li+ apresentou três perdas de massa que podem ser atribuídas à água adsorvida na argila, a água de hidratação dos íons Li+ e a água estrutural da argila. Para as argilas STx-1b-Li+ tratadas termicamente não foi observado a perda de massa associada à água quimicamente ligada aos contra-íons Li+. Estes resultados estão em concordância com os obtidos por DRX, onde observou-se uma diminuição no espaçamento interlamelar nas argilas tratadas termicamente. Em adição, foram preparados filmes de alginato de sódio com as argilas STx-1b-Li+ não tratada e tratada termicamente e estes foram caracterizados por calorimetria exploratória diferencia (DSC) e espectroscopia de impedância eletroquímica (EIE). As curvas DSC mostraram um aumento na temperatura de transição vítrea (Tg) dos filmes com o aumento da temperatura utilizada no tratamento das argilas. Este aumento nos valores de Tg é um indicativo que a mobilidade das cadeias diminuiu nos filmes polímero/argila que contém argilas tratadas em temperaturas mais elevadas. A espectroscopia de impedância eletroquímica (EIE) foi usada para avaliar-se a condutividade iônica dos filmes. Os resultados indicaram que os filmes contendo argilas que foram tratadas com temperaturas mais altas apresentaram menor condutividade. / In this work the effects caused by the heat treatment in STx-1b-Li+ clay on the conductivity of sodium alginate/clay were studied. The clay mineral STx-1b was submitted to isomorphous substitution of the Na+ for Li+ cation and subsequently to heat treatment at different temperatures. The STx-1b-Li+ clays untreated and heats treated were characterized by X-ray diffraction (XRD) and Thermogravimetric Analysis (TG). The TG curve showed that the clay mineral STL-1b-Li+ had three mass losses which can be attributed to adsorbed water in the clay, the water of hydration of the Li+ ions and structural clay water. To STx-1b-Li+ clays heat treated there were no mass loss associated to the water chemically bound to Li+ counter ions. These results are in agreement with those obtained by XRD, which it was observed a decrease in interlayer spacing in the heat treated clay. In addition, they were prepared sodium alginate films with STx-1b-Li+ clays untreated and heat treated and these films were characterized by Differential Scanning Calorimetry (DSC) and Electrochemical Impedance Spectroscopy (EIS). DSC curves showed an increase in glass transition temperature (Tg) of the films with temperature increasing used in the treatment of clays. This increase in Tg value is an indicative that the mobility of the chains had decrease in the polymer/clay films which contains heat treated clays at higher temperatures. The electrochemical impedance spectroscopy (EIS) was used to evaluate the ionic conductivity of the films. The results indicate that films containing clays which have been treated at higher temperatures had lower conductivity.

"The thesis includes fundamental work in the following, · Development of materials database which includes the main parameters of the various heat transfer models · Validation and testing of the system capability and accuracy by means of various case studies A computer aided heat treatment planning system (CAHTPS) is developed to assist the heat treatment process. The temperature distribution inside the furnace and the temperature of the various parts in the load can be determined. The various models for the heat treatment are analyzed and the various parameters in the equations are classified. The majority of the equations parameters were properties of various metals and non metals. Hence an extensive database is developed so as to assist the models. The remaining physical conditions dependent parameters of the models were analyzed and the effects due to change in the conditions and these parameters are tested and studied by various case studies. The change in the loading pattern effects and change in the load quantity effects for the various cases are presented. The thesis work establishes the system’s application scope and the accuracy to be used in the current heat treatment industries."

"Surface contamination during the heat treatment process can greatly affect the quality of the heat treated parts. Although cleaning the post-heat treated parts is considered a value added process in heat treatment, cleaning parts prior to heat treatment is also important and can influence the outcome of subsequent processes. A series of experiments has been designed to determine the effects of the surface contaminants on nitriding. Nitralloy-135 steel was selected to evaluate the cleaning methods and the effects on the result of subsequent nitriding process. The samples were contaminated with a variety of contaminants, including rust preventive oil, cutting fluid and rust. The contaminated samples were cleaned using either acid or alkaline cleaner. Both cleaned and contaminated samples were nitride in the furnace. To determine the effect of contaminants on gas nitriding, weight gain and the surface hardness were measured. Nitrogen flux was also calculated. The results show that the acid cleaning effectively removes the rust layer. Rusted parts had lower nitrogen absorption than that of the cleaned samples. The parts contaminated by the oil did not reveal any effect on the nitrogen uptake. The surface hardness (Rc) did not show a significant difference between the heavily rusted sample and the clean sample. It has been observed that the nitrogen flux is smaller due to the rust layer on the heavily rusted samples."

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / Includes bibliographical references. / M.S.

No description available.

The study involves two different approaches to increasing cottage cheese yields by the inclusion of whey proteins in the curd. They were the use of high heat treated skim milk and ultrafiltered skim milk retentates for cottage cheese making. Increasing the pasteurization temperature of skim milk from 61.8 to 79.4 C for 30 minutes resulted in 15.6% increase in cultured cottage cheese yields. However, the high heat cheese exhibited variable quality and was generally inferior to the control. Cheese making from high heat skim milk was done by cutting at the A.C. end point and using 30 ml of rennet per 454 kg of skim milk. There appeared to be no relationship between the rate of heating to 79.4 C and the quality of cottage cheese produced. Skim milk was concentrated by ultrafiltration to 12, 16, and 20% solids. The 20% retentate was produced by concentrating skim milk 5:1 and then subjecting it to diafiltration with an equivalent volume of deionized water. The acidification of the retentates was accomplished by metering concentrated hydrochloric acid into the vortex of the centrifugal Culture growth in 20% retentates was inhibited below and soluble phosphate seemed to be an important factor in this inhibition. The yield trials indicated that the increase in yields over cultured cottage cheese made from skim milk was 12.4, 15.3, 5.6 and 1.6% for 16 % cultured, 16 % direct acid, 20% cultured and 20% direct acid cottage cheeses made from retentates. The lower yield increases from 20% retentates was because of the shattering of the curd while cooking, and the diffusion of the whey proteins. While the quality of cultured cottage produced by ultrafiltration was as good as the cultured cottage cheese from skim milk, the direct acid cottage cheeses were much inferior. Considering both high heat treatment of skim milk and ultrafiltration for increasing cottage cheese yields, ultrafiltration seems to be the better method owing to the much better quality of cheese produced. To obtain maximum benefits from ultrafiltration, problems of lactic culture growth in retentates must be solved and non conventional cooking methods have to be developed for handling curds from high solids retentates.