Maraging steels with 18wt%Ni and 10wt%Co are precipitation hardenable steels selected for special applications. These steels are quenched and aged in the 480 -600 o C range. Ti and Mo are added to precipitate during aging as fine Ni 3 (Ti,Mo) and Fe 2 Mo particles. Aging at high temperatures causes overaging due to coarsening of particles and austenite formation. SAE 4340 is a typical low alloy medium carbon steel for quenching and tempering. The best combination of mechanical properties is attained by quenching and tempering in the 650 -670 o C range. These two steels are selected for services where an optimum combination of mechanical strength, toughness and fatigue resistance is required. In this work, the austenitizing temperature in the quenching treatment was varied in order to evaluate the effects on microstructure and mechanical properties of both steels. The results showed that the effect of previous austenite grain size on the toughness was different in the two steels analyzed.
Os aços inoxidáveis superduplex (AISD) são materiais que aliam altos valores de resistência mecânica com elevados níveis de resistência à corrosão. Por tal motivo, esta família de aços inoxidáveis é muito utilizada em componentes de processo na indústria offshore. No entanto, existem grandes desafios na soldagem destes materiais em termos de produtividade e custos mantendo-se a qualidade da junta produzida. Atualmente, a proteção gasosa da raiz é efetuada até o último passe de acabamento na soldagem durante a pré-montagem e montagem de tubulações de AISD em plataformas offshore. Neste tipo de proteção são usualmente empregados os gases hélio, argônio e nitrogênio, ou misturas destes. O nitrogênio é tipicamente adicionado no gás de proteção em teores de até 3% de modo a promover a estabilização da fase austenítica na superfície da raiz da solda. Devido ao alto custo do gás de proteção utilizado, é necessário determinar o passe ou camada na qual a proteção gasosa na raiz seja efetiva em termos das propriedades mecânicas e da resistência à corrosão, considerando ser esta uma região crítica, que ficará em contato com o fluido operante durante o serviço do componente. Neste sentido, o presente trabalho apresenta os resultados da influência da utilização de gás de purga na raiz de juntas soldadas correspondente a uma tubulação de aço inoxidável superduplex (AISD) UNS S32750 de 9 mm de espessura de parede soldada pelo processo de soldagem TIG (GTAW). Foram avaliados o ciclo térmico, o teor de nitrogênio e a tenacidade ao impacto da raiz da solda em função do aporte térmico para diversas juntas soldadas com diferentes níveis de proteção gasosa na raiz. Deste modo, o presente trabalho tem como objetivo a redução de custos na soldagem de tubulações indicando até qual camada é requerida a proteção gasosa na raiz em função do aporte de calor empregado.
The hydrogen interaction in palladium alloys with addition of Ce, Zr and Y was studied. These alloys are produced by arc-melting and then cold rolled into thin foils. Heat treatment at 800ºC for 24h in air atmosphere is applied to induce internal oxidation. Hydrogen permeation tests and TDS (Thermal Desorption Spectroscopy) are carried out to evaluate hydrogen interaction with three different microstructures which can be characterized by dislocations, substitutional atoms and nanoxides. For alloys argon annealed, Ce is the element that delays the most hydrogen diffusion, followed by Zr and Y. However alloys with yttrium nanoxides exhibit the highest solubility and the smallest diffusivity due to their small size, spherical shape and dispersion throughout the matrix. Analyzing TDS curves, it is shown that nanoxides are irreversible traps that improve hydrogen stored on palladium alloys. Dislocations and impurity atom on solid solution have little binding energy that detraps hydrogen at smaller temperatures.
Este artigo apresenta o relato de experiência dos minicursos de programação e robótica para jovens meninas de Macaé e região. O objetivo desse trabalho é incentivar a formação de mulheres para as carreiras de ciências exatas, engenharias e computação, e divulgar os cursos de graduação em Engenharia oferecidos pela Universidade Federal do Rio de Janeiro (UFRJ) para essas jovens. Esses minicursos aconteceram em parceria com professoras de três escolas públicas e atingiram no total 50 jovens, sendo 35 do sexo feminino. Ao longo das aulas pôde-se observar o interesse das alunas pelas atividades realizadas nos cursos da Engenharia e a curiosidade por aprender mais sobre programação.
Duplex stainless steels are well known austenitic-ferritic alloys which combines good mechanical resistance and excellent corrosion resistance. Due to this fact, this steel family is widely employed in offshore piping applications. However, these alloys require great care in thermomechanical processing, such as welding, since they might present serious decrease in corrosion resistance and toughness at the welded joint when compared to the base metal. Undeniably, welding is one of the major processes employed in pipe and industrial equipment assembly, thus requiring higher expertise and caution in order to achieve the desirable good combination of properties of duplex stainless steel alloys. In this context, induction bending process comes as an e cient alternative to reduce the number of weld joints in piping designs. In this work, induction bent tubes were characterized after bending in temperatures inside and outside the standard recommended range, that is, between 950 and 1150°C. Microstructural characterization, mechanical testing and corrosion tests were performed, indicating that the properties of curved materials remained comparable to a solubilized state. Therefore, the electromagnetic induction bending process proves to be not only a viable tool in thermomechanical processing of these materials, but also more productive.
Duplex stainless steels are well known austenitic-ferritic alloys which combines good mechanical resistance and excellent corrosion resistance. Due to this fact, this steel family is widely employed in offshore piping applications. However, these alloys require great care in thermomechanical processing, such as welding, since they might present serious decrease in corrosion resistance and toughness at the welded joint when compared to the base metal. Undeniably, welding is one of the major processes employed in pipe and industrial equipment assembly, thus requiring higher expertise and caution in order to achieve the desirable good combination of properties of duplex stainless steel alloys. In this context, induction bending process comes as an efficient alternative to reduce the number of weld joints in piping designs. In this work, induction bent tubes were characterized after bending in temperatures inside and outside the standard recommended range, that is, between 950 and 1150°C. Microstructural characterization, mechanical testing and corrosion tests were performed, indicating that the properties of curved materials remained comparable to a solubilized state. Therefore, the electromagnetic induction bending process proves to be not only a viable tool in thermomechanical processing of these materials, but also more productive.
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