The Diploma thesis deals with the verification of Jominy end-quench test when analysis of hardenability of aluminium alloys is considered. The problem was solved experimentally, by developing end-quench curves of selected grades of aluminium alloys. Degree of hardenability of alloy is hardness after complete strengthening heat treatment. Samples of aluminium alloys commonly used for aircraft structures were prepared and then subjected to end-quench tests in various quenchants. On the basis of performed experiments, suitability of Jominy end-quench test for comparison of hardenability of alloys was found. Part of the thesis deals with the creation of equivalent cooling rate diagrams using the developed end-quench curves.

L’objectif de cette thèse est d’aboutir à une meilleure compréhension des mécanismes de ségrégation du bore aux joints de grains austénitiques (γGB) et de leur effet sur la décomposition de l’austénite. En effet, l’addition de très faibles quantités de bore comme élément d’alliage permet d’augmenter de manière remarquable la résistance mécanique des aciers à très haute résistance. Cet effet est lié à l’état du bore aux γGBs qui décale la cinétique de décomposition de l’austénite.Tout d’abord, la distribution du bore dans la microstructure a été identifiée de manière très précise à l’aide des analyses de la même zone par Nano-SIMS et par MEB. De plus, le couplage de la sonde atomique tomographique et du Nano-SIMS a apporté une meilleure quantification de l’état du bore dans la microstructure. Ces études ont été réalisées après différents traitements thermiques qui ont été conçus spécifiquement pour étudier séparément chaque mécanisme. L’ensemble de ces résultats permet d’écarter la contribution de la ségrégation hors équilibre et confirme la présence d’un équilibre local entre les γGBs et la solution solide dans leurs voisinages. Par conséquent, le niveau de ségrégation du bore aux γGBs est contrôlé par l’état de précipitation des borures qui définit la concentration du bore en solution solide.Par ailleurs, des mesures de DRX in situ et de dilatomètrie ont été effectuées afin de suivre les cinétiques de formation de la bainite. Les résultats montrent que la cinétique de formation de la bainite est retardée en augmentant la quantité de bore ségrégé, par contre l’augmentation de la taille de grain austénitique l’accélère. / The aim of this thesis is to lead to a better understanding of the mechanisms of boron segregation at austenite grain boundaries (γGB) and its effect on the austenite decomposition. Indeed, the small quantity of boron as alloying element remarkably improves the mechanical resistance of the advanced high strength steels. This effect is related to the boron state at γGBs, which delays the kinetics of austenite decomposition.The boron distribution in the microstructure was precisely identified thanks to the analyses of the same field by using correlative nano-SIMS and SEM. In addition, the coupling of APT and nano-SIMS provided a better quantification of the boron state in the microstructure. These studies were performed after different heat treatments, which were specifically designed to study separately each mechanism. The results excludes the contribution of non-equilibrium segregation mechanism on boron segregation at γGBs and confirm the local equilibrium between the γGBs and the solid solution at the γGBs vicinity. Consequently, the level of boron segregation at γGBs is controlled by boride precipitation, which controls the concentration of boron in solid solution.Measurements of in situ XRD and the dilatometry were performed in order to follow the kinetics of bainite formation. The specific heat treatments were applied before bainite formation in order to study the effect of boron segregated amount at γGBs and the austenite grain size. These results show that the kinetics of bainitic transformation is delayed by the increase of boron segregated amount. Whereas, the increasing of austenite grain size accelerates the kinetics of bainitic transformation.

Os aços da classe SAE 5120 são largamente utilizados para a produção de eixos e engrenagens de caixas de transmissão. As adições de nióbio e boro neste aço visam modificar a microestrutura e, consequentemente, alteram as propriedades metalúrgicas e mecânicas deste aço. Adições de nióbio ancoram o crescimento de grão austenítico, permitindo um aumento de produtividade no processamento visto que temperaturas de laminação e de tratamento térmico mais elevadas podem ser aplicadas sem que ocorra o crescimento de grão austenítico. O boro encontra-se tanto na forma solúvel como nãosolúvel nos aços. O boro solúvel aumenta a temperabilidade, devido à segregação deste elemento durante a solidificação nos contornos de grãos, retardando a nucleação da ferrita. O boro não-solúvel (combinado) também contribui para o ancoramento dos contornos de grãos austeníticos, visto que este se combina com o nitrogênio formando o BN cuja temperatura de solubilização é por volta de 1360ºC. O objetivo principal foi avaliar a cinética de transformação do aço SAE 5120 com a adição simultânea de boro e nióbio por meio da curva de transformação por resfriamento contínuo (CCT) a partir do campo austenítico (930oC). As amostras foram caracterizadas por microscopia óptica e microscopia eletrônica de varredura e por ensaios de dureza, possibilitando a construção da curva CCT para diferentes taxas de resfriamento. Na análise metalográfica observou-se a segregação de manganês e cromo da matéria-prima (estrutura bandeada) e a forte tendência de formação da bainita. Com o auxílio do programa de simulação termodinâmica computacional Thermocalc, foi possível simular as fases termodinamicamente estáveis, verificando que o boro e o nióbio formam precipitados estáveis em altas temperaturas (acima de 1150ºC), sendo os principais responsáveis pelo refino de grão. A temperabilidade e comportamento mecânico foram avaliados pelos ensaios Jominy e o ensaio de impacto Brugger, respectivamente. A influência dos elementos de liga nestes ensaios foi avaliada através de método de regressão linear por meio do software Minitab. / SAE 5120-alloyed steel is largely used to manufacture transmission gears and shafts for automotive industry. Alloying with niobium and boron is intentionally made to modify the microstructure and, consequently, promoting changes in metallurgical and mechanical proprieties. Alloying with niobium prevents austenitic grain growth (pinning effect), leading to an increase of productivity since higher rolling mill and heat treatment temperatures can be achieved. Boron can be found either soluble or insoluble in steels. Soluble B increases hardness, because it segregates to grain boundaries retarding the nucleation of ferrite. Insoluble B, on the other hand, also plays a role on avoiding austenitic grain growth due to its chemical reaction with N forming BN whose solubility temperature is around 1360ºC. The main target of this work was to evaluate the kinetics of phase transformations by continuous cooling transformation (CCT) from the austenitic field (930oC). The microstructure was analyzed by optical microscope, scanning eléctron microscope (SEM), and hardness testing, allowing building the CCT diagram with different cooling rates. It was observed by means of conventional metallography the segregation of Mn and Cr (banding) during solidification of the raw material and a strong propensity to form bainite. Using the Thermocalc software, it was possible to predict the thermodynamically stable phases, proving that boron and niobium form stable precipitates at high temperatures (above 1150ºC) responsible to decrease austenitic grain size. The hardenability and mechanical properties were investigated by Jominy and Brugger impact tests, respectively. The effect alloy adding in these tests were analyzed by linear regression in the software Minitab.

Os aços da classe SAE 5120 são largamente utilizados para a produção de eixos e engrenagens de caixas de transmissão. As adições de nióbio e boro neste aço visam modificar a microestrutura e, consequentemente, alteram as propriedades metalúrgicas e mecânicas deste aço. Adições de nióbio ancoram o crescimento de grão austenítico, permitindo um aumento de produtividade no processamento visto que temperaturas de laminação e de tratamento térmico mais elevadas podem ser aplicadas sem que ocorra o crescimento de grão austenítico. O boro encontra-se tanto na forma solúvel como nãosolúvel nos aços. O boro solúvel aumenta a temperabilidade, devido à segregação deste elemento durante a solidificação nos contornos de grãos, retardando a nucleação da ferrita. O boro não-solúvel (combinado) também contribui para o ancoramento dos contornos de grãos austeníticos, visto que este se combina com o nitrogênio formando o BN cuja temperatura de solubilização é por volta de 1360ºC. O objetivo principal foi avaliar a cinética de transformação do aço SAE 5120 com a adição simultânea de boro e nióbio por meio da curva de transformação por resfriamento contínuo (CCT) a partir do campo austenítico (930oC). As amostras foram caracterizadas por microscopia óptica e microscopia eletrônica de varredura e por ensaios de dureza, possibilitando a construção da curva CCT para diferentes taxas de resfriamento. Na análise metalográfica observou-se a segregação de manganês e cromo da matéria-prima (estrutura bandeada) e a forte tendência de formação da bainita. Com o auxílio do programa de simulação termodinâmica computacional Thermocalc, foi possível simular as fases termodinamicamente estáveis, verificando que o boro e o nióbio formam precipitados estáveis em altas temperaturas (acima de 1150ºC), sendo os principais responsáveis pelo refino de grão. A temperabilidade e comportamento mecânico foram avaliados pelos ensaios Jominy e o ensaio de impacto Brugger, respectivamente. A influência dos elementos de liga nestes ensaios foi avaliada através de método de regressão linear por meio do software Minitab. / SAE 5120-alloyed steel is largely used to manufacture transmission gears and shafts for automotive industry. Alloying with niobium and boron is intentionally made to modify the microstructure and, consequently, promoting changes in metallurgical and mechanical proprieties. Alloying with niobium prevents austenitic grain growth (pinning effect), leading to an increase of productivity since higher rolling mill and heat treatment temperatures can be achieved. Boron can be found either soluble or insoluble in steels. Soluble B increases hardness, because it segregates to grain boundaries retarding the nucleation of ferrite. Insoluble B, on the other hand, also plays a role on avoiding austenitic grain growth due to its chemical reaction with N forming BN whose solubility temperature is around 1360ºC. The main target of this work was to evaluate the kinetics of phase transformations by continuous cooling transformation (CCT) from the austenitic field (930oC). The microstructure was analyzed by optical microscope, scanning eléctron microscope (SEM), and hardness testing, allowing building the CCT diagram with different cooling rates. It was observed by means of conventional metallography the segregation of Mn and Cr (banding) during solidification of the raw material and a strong propensity to form bainite. Using the Thermocalc software, it was possible to predict the thermodynamically stable phases, proving that boron and niobium form stable precipitates at high temperatures (above 1150ºC) responsible to decrease austenitic grain size. The hardenability and mechanical properties were investigated by Jominy and Brugger impact tests, respectively. The effect alloy adding in these tests were analyzed by linear regression in the software Minitab.

Os aços com adição de boro temperados e revenidos têm sido utilizados em diversas aplicações que exigem um compromisso entre boas propriedades mecânicas e baixo custo, como por exemplo, indústria automotiva, de petróleo e na fabricação de plataformas marítimas e tubulações. Estudos termodinâmicos indicam que uma pequena adição de boro altera significativamente o diagrama de fases, aumentando a estabilidade dos carbonetos pela substituição de C por B na estrutura cristalina. A avaliação da cinética de precipitação foi realizada indiretamente pela medição da variação de resistividade elétrica de amostras tratadas em temperaturas de 790, 810 e 830°C. Foi possível traçar a curva de precipitação (JMAK) para cada temperatura e propor um diagrama TTP que indicou que as temperaturas testadas estão situadas na parte superior da curva \"C\". A confirmação do fenômeno de precipitação foi obtida por microscopia eletrônica de varredura (MEV-FEG), indicando que a técnica indireta foi eficaz para predição do fenômeno. A cinética de coalescimento foi avaliada em amostras tratadas em 880°C de forma direta, por microscopia óptica e microscopia eletrônica de varredura, e de forma indireta, por avaliação da energia absorvida em ensaio de impacto Charpy. A determinação da distribuição de tamanho de borocarbonetos em cada condição testada forneceu indícios de que o mecanismo de controle do crescimento é reação na interface. Foi possível, satisfatoriamente, correlacionar o tamanho médio de borocarboneto com a resistência ao impacto Charpy, indicando que a susceptibilidade à fragilização pelo coalescimento de borocarbonetos independe da região da barra laminada. / Boron added steels in quenched and tempered condition have been used in many applications with mechanical properties and low-cost requirements, i.e., automotive, petrochemical and O&G industries. Thermodynamic simulations have shown that boron addition promotes significant change in phase diagram due to carbide stability increase by replacement of carbon by boron. Precipitation kinetic was evaluated by electrical resistivity in samples heat-treated at 790°C, 810°C, and 830°C. It was possible to estimate the precipitation curve (JMAK) for each temperature and to propose a TTP diagram which indicates that tested temperatures were in the upper region of the C-shape curve. Precipitation phenomenon was confirmed by FEG-SEM analysis, indicating that electrical resistivity measurement was effective to evaluate precipitation at these conditions. Coarsening kinetic was evaluated in samples heat-treated at 880°C by Microscopy and by absorbed energy in Charpy impact test. The borocarbide size and distribution determination provided evidence of interface reaction-controlled mechanism. A correlation between absorbed energy in impact test and average borocarbide size was proposed, indicating that embrittlement susceptibility by borocarbide coarsening has no dependence of rolled bar region.

Abstract not available

<p>In this thesis a mixture density network has been constructed to predict steel hardenability for a given alloy composition. Throughout the work hardenability is expressed in terms of jominy profiles according to the standard jominy test. A piecewise linear description of the jominy profile has been developed to solve the problem of missing data, model identification from data based on different units and measurement uncertainty. When the underlying physical processes are complex and not well understood, as the case with hardenability modelling, mixture density networks, which are an extension of neural networks, offer a strong non-linear modelling alternative. Mixture density networks model conditional probability densities, from which it is possible to determine any statistical property. Here the model output is presented in terms of expectation values along with confidence interval. This statistical output facilitates future extension of the model towards optimisation of alloy cost. A good agreement has been obtained between the experimental and the calculated data. In order to ensure the reliability of the model in service, novelty detection of the input data is performed.</p>

In this thesis a mixture density network has been constructed to predict steel hardenability for a given alloy composition. Throughout the work hardenability is expressed in terms of jominy profiles according to the standard jominy test. A piecewise linear description of the jominy profile has been developed to solve the problem of missing data, model identification from data based on different units and measurement uncertainty. When the underlying physical processes are complex and not well understood, as the case with hardenability modelling, mixture density networks, which are an extension of neural networks, offer a strong non-linear modelling alternative. Mixture density networks model conditional probability densities, from which it is possible to determine any statistical property. Here the model output is presented in terms of expectation values along with confidence interval. This statistical output facilitates future extension of the model towards optimisation of alloy cost. A good agreement has been obtained between the experimental and the calculated data. In order to ensure the reliability of the model in service, novelty detection of the input data is performed.

Orientador: Sergio Tonini Button / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-09T12:42:48Z (GMT). No. of bitstreams: 1 Caminaga_Celio_D.pdf: 45945732 bytes, checksum: 36b9f4a15a23ccd9e0ad12b26cfe5931 (MD5) Previous issue date: 2007 / Resumo: A exigência por parte das montadoras por produtos com maior qualidade, a preços mais baixos e com diminuição do prazo de entrega, faz com que as indústrias de autopeças concentrem esforços na busca de processos e materiais alternativos. Os processos de forjamento a quente aliados aos aços microligados, que também são conhecidos como aços de alta resistência e baixa liga (ARBL), tem uma extensa aplicação em componentes automotivos. A proposta deste trabalho é estudar o comportamento microestrutural e mecânico (resistência e tenacidade) do aço microligado 27MnSiVS6, quando empregado no processo ausforming, a fim de analisar-se o desempenho do processo e a qualidade dos produtos, comparando-o com os processos de forjamento a quente e a morno. Os produtos forjados proveniente do processo de ausforming que foram submetidos aos ensaios de tração unidirecional, dureza, fadiga em flexão rotativa e tenacidade a fratura apresentaram as melhores propriedades mecânicas. A microscopia óptica e microscopia eletrônica (varredura e transmissão) que foram utilizadas para caracterização microestrutural dos produtos forjados demonstraram o refino dos grãos ferríticos, a presença de inclusões não metálicas (MnS) e a contribuição dos mecanismos de endurecimento ao limite de escoamento. Os testes estatísticos aplicados aos resultados permitiram concluir, que os produtos obtidos pelo processo de forjamento ausforming apresentam a melhor combinação de resistência mecânica e qualidade superficial dos produtos forjados, sem aumentar a carga de forjamento / Abstract: The demand of the automotive industry for parts with high overall quality, low costs and reduced time to market, forced the suppliers to search alternative materials and manufacturing processes. Hot forgings with microalloyed steels, also known as HSLA (High Strength Low Alloy), represent an extensive application in automotive parts. The main objective of this work is to study the workability of a microalloyed steel deformed by ausforming and compare the products microstructures and forming loads to those obtained by hot and warm forging. Results from preliminary upsetting tests confirmed the viability of this study. Finally forgings tests were held to define the forming load and to analyze products microstructures for these three processes. Forgings were analyzed by tensile tests, fatigue under cyclic flexion tests, and fracture toughness tests. Optical and electronic microscopy (SEM and TEM) applied to evaluate the forgings microstructure showed the ferritic grain refinement, the presence of non-metallic inclusions (MnS) and confirmed the contribution of hardening mechanisms to increase the yield strength of forging products. The statistical analysis of the experimental results showed that ausforming is a suitable process to substitute hot and warm forging since ausforming presented lower loads when compared to warm forging, and ausformed forgings presented the best combination of mechanical strength and surface quality, without a significant increase of the forging loads / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Powder metallurgy is a branch of metal forming technology where metal powders are used to manufacture parts and components. It is a flexible and economical technique for manufacturing complicated shapes. This present work focuses on press and sinter technology and forms a part of Höganäs’s efforts of modelling hardenability through quenching. It aims to reduce the number of experimental trials for optimising heat treatment. Hardenability is a measure of how much martensite can be formed during heat treatment, thereby making steels hard, tough and impart strength. The presence of alloying elements like carbon, manganese, chromium, molybdenum, and nickel affects the hardenability of the steel and improves performance like fatigue strength and corrosion resistance. These elements influence the critical cooling rate necessary to form martensite during heat treatment. Component geometry also influences hardenability. Depending on the surface area available to cool, and volume of component, cooling rates may locally be different thereby resulting in an inhomogeneous structure. The work focuses particularly on two grades of powders manufactured by Höganäs AB - Astaloy® CrA and Astaloy® CrS which are evaluated for their hardenability. The aim of this work is to take cooling conditions observed in the actual furnace, use them to predict the amount of martensite present and the martensite start temperature and then compare it with experimental results thereby linking experiment to simulations. For the experimental part, dilatometry was used. Quenching data is obtained from the furnace along with heat capacity of the component and are used as input in Abaqus, which gives us the cooling rates for the component in the furnace. This data is then utilised as an input to dilatometry, where the samples are representative of sections of component. After dilatometry, vital information like martensite start temperature is recorded and metallography is performed, where phase fraction is obtained. Hardness measurements are also performed to verify the phases present. Simulation tools like JMatPro and Thermo-Calc are employed to obtain data for correlation. An extensive study on the difference between them are also studied and presented. The data from simulation and actual experiment is compared and, Ms evaluated from JMatPro and Thermo-Calc for CrA shows a deviation of 12°C. For CrS samples, a higher deviation is observed, with JMatPro showing deviation of 44°C and Thermo-Calc, 52°C in respect to the measured values. For CrA, we observe a fully martensitic structure for the higher carbon samples, including ones alloyed with Ni. For samples with lower carbon, metallographic investigation results in an unclear picture as to if the structure observed is bainite or martensite. CrS samples are mostly martensitic with some bainite present. CrS samples alloyed with Ni and Cu show the least amount of bainite present. The phase fractions predicted by JMatPro show good agreement with results from metallography. Data from microhardness confirms the presence of phases present. Samples with low carbon are softest but show a great improvement in hardness when alloyed. Overall, simulations and actual experimental values are seen to be in good agreement, thereby establishing a strong foundation for future work, where actual components can be evaluated. Quenching conditions observed in the furnace are validated through this work. / Pulvermetallurgi är en gren av metallformningsteknik där metallpulver används för att tillverka delar och komponenter. Det är en flexibel och ekonomisk teknik för att tillverka komplicerade former. Detta nuvarande arbete fokuserar på press- och sinterteknik och är en del av Höganäs arbete med att modellera härdbarhet genom härdning. Det syftar till att minska antalet experimentella försök för att optimera värmebehandlingen. Härdbarhet är ett mått på hur mycket martensit som kan bildas vid värmebehandling, vilket gör stålen hårda, sega och ger styrka. Närvaron av legeringselement som kol, mangan, krom, molybden och nickel påverkar stålets härdbarhet och förbättrar prestanda som utmattningshållfasthet och korrosionsbeständighet. Dessa element påverkar den kritiska kylningshastighet som krävs för att bilda martensit under värmebehandling. Komponentgeometrin påverkar också härdbarheten. Beroende på den yta som är tillgänglig för kylning och volymen av komponenten, kan kylningshastigheterna lokalt vara olika, vilket resulterar i en inhomogen struktur. Arbetet fokuserar särskilt på två kvaliteter av pulver tillverkade av Höganäs AB - Astaloy® CrA och Astaloy® CrS som utvärderas för sin härdbarhet. Syftet med detta arbete är att ta kylförhållanden som observerats i den faktiska ugnen, använda dem för att förutsäga mängden närvarande martensit och martensitens starttemperatur och sedan jämföra den med experimentella resultat och därigenom koppla experiment till simuleringar. För den experimentella delen användes dilatometry. Släckningsdata erhålls från ugnen tillsammans med värmekapaciteten hos komponenten och används som indata i Abaqus, vilket ger oss kylhastigheten för komponenten i ugnen. Dessa data används sedan som indata till dilatometry, där proverna är representativa för sektioner av komponenten. Efter dilatometri registreras viktig information som martensitstarttemperatur och metallografi utförs, där fasfraktion erhålls. Hårdhetsmätningar utförs också för att verifiera de närvarande faserna. Simuleringsverktyg som JMatPro och Thermo-Calc används för att få data för korrelation. En omfattande studie om skillnaden mellan dem studeras och presenteras också. Data från simulering och faktiska experiment jämförs och Ms utvärderade från JMatPro och Thermo-Calc för CrA visar en avvikelse på 12°C. För CrS-prover observeras en högre avvikelse, där JMatPro visar en avvikelse på 44°C och Thermo-Calc, 52°C i förhållande till de uppmätta värdena. För CrA observerar vi en helt martensitisk struktur för de högre kolproverna, inklusive de som legerats med Ni. För prover med lägre kolhalt resulterar metallografisk undersökning i en oklar bild av om den observerade strukturen är bainit eller martensit. CrS-prover är mestadels martensitiska med viss bainit närvarande. CrS-prover legerade med Ni och Cu visar den minsta mängden bainit som finns närvarande. Fasfraktionerna som förutspåtts av JMatPro visar god överensstämmelse med resultaten från metallografi. Data från mikrohårdhet bekräftar närvaron av faser. Prover med låg kolhalt är mjukast men visar en stor förbättring i hårdhet när de är legerade. Sammantaget bedöms simuleringar och faktiska experimentella värden stämma överens, vilket skapar en stark grund för framtida arbete, där faktiska komponenter kan utvärderas. Släckningsförhållanden som observerats i ugnen valideras genom detta arbete.