Resumo: O aço AISI 316L e Inconel 718 são metais de ampla aplicação na indústria. O estudo da soldagem dissimilar entre esses dois materiais é tecnologicamente importante para melhorar o desempenho da junta. Concentramos este estudo na avaliação da soldabilidade dissimilar desses materiais. Três amostras de AISI 316L e Inconel 718 soldadas usando processo multipass GTAW (Gas Tungsten Arc Welding) com diferentes parâmetros foram analisadas. Foram realizadas caracterização microestrutural, medidas da fração volumétrica da ferrita δ e fase Laves, espaçamento entre as dendritas de austenita, além da medição e análise das dimensões do metal de solda e da microdureza. A medição das dimensões do metal de solda e do espaçamento entre as dendritas mostrou que maiores aportes térmicos aumentaram as zonas fundidas e o espaçamento entre as dendritas de austenita. A fração volumétrica de ferrita δ diminuiu com o aumento do aporte térmico, enquanto que a fração da fase Laves aumentou. A microdureza apresentou variação significativa na poça de fusão devido a mudanças nas fases e na composição, conforme evidenciado pela análise de EDS nas juntas dissimilares.

Abstract: AISI 316L steel and Inconel 718 are metals of wide application in industries. The study of dissimilar welding between these two materials is technologically important to improve their joint performance. We focused this study on the evaluation of the dissimilar weldability of these materials. Three samples of AISI 316L and Inconel 718 welded using a multipass GTAW (Gas Tungsten Arc Welding) process with different parameters were analyzed. The microstructural characterization, measurements of the volumetric fraction of the δ ferrite and Laves phase, the spacing between austenite dendrites, in addition to measurement and analysis of dimensions of the welding zones and the microhardness were performed. The measurement of the weld metal dimensions and the dendrite spacing showed that higher heat inputs increased the dilution zones and the spacing between austenite dendrites. The volumetric fraction of the δ ferrite decreased with the increase of heat input, while the Laves phase fraction increased. The microhardness presented significant variation in the weld pool due to changes in the phases and composition, as evidenced by EDS analysis in the dissimilar joints.

Abstract ADI are the result of graphite nodules and ausferrite microstructure (acicular ferrite + retained austenite). Over the past few years, ADI has become an important material for engineering due to its excellent mechanical properties (outstanding ductility, high mechanical strength and good toughness) and low cost. It is known the discussion of process variables such as austempering time and temperature are extremely important for the microstructural and hardness study of these materials. Thus, in the present work, ADI cast iron was investigated under twelve different austenitic conditions, aiming to characterize the influence of the amount of austenite on the ferritic matrix on the mechanical property of hardness. The heat treatment parameters vary from three different times (40 min, 90 min and 180 min) under four temperatures (280ºC, 300 ºC, 320 ºC and 370ºC). Results show there is a decreasing of hardness linked to the increasing of retained austenite % volume. The greater amount of retained austenite % volume in the matrix was presented by sample A14, treated during 40 minutes under 370ºC and presenting 32.30% of this microconstituint. The amounts of each phase present in the studied materials were raised by quantitative metallography through the software Fiji-ImageJ, allowing a comparison of the results obtained by these two methods. Time differences on the austempering heating treatment did not show several implications on ADI microstructure. In addition, analyzes of the graphite nodules were performed.

Abstract With the growing industrialization, there is a constant increase in the world demand for iron ore, thus implying an increase in the volume of mining, resulting in the extraction of ores with higher levels of silicon, phosphorus and sulfur impurities. Therefore, it is highly relevant to use beneficiation techniques that allow the use of iron ores with high levels of impurities, and it is known that a widely used alternative is to perform a pre-treatment of iron ore particles in order to reach the limit of acceptable phosphorus before application in steel production. Therefore, this study aims to evaluate the pre-treatment process of iron ore particles aiming at reducing the phosphorus content using the bacterial strain burkolderia caribensis in contaminated iron ore samples. Through the rotatable central composite design technique, it was possible to evaluate the best conditions for the use of the bacterial strain to reduce the phosphorus content in the particles. The results indicated that the developed process has relevant applicability. The results contribute to a better understanding of the use of the bacterial strain as a pretreatment process to reduce the phosphorus content of iron ore particles and also to the development of new cleaner technologies.

With the growing industrialization, there is a constant increase in the world demand for steel, causing an increase on extraction of low-grade iron ores, which bear high levels of impurities. A feasible alternative is the use of residues from steel rolling processes (steelmaking mill scale) generated in the steel industry, which are composed of iron oxides consisting mainly of wustite (FeO), hematite (Fe2O3) and magnetite (Fe3O4). In line with the recycling of wastes, the application of heating by microwave energy in ironmaking processes consists in a promising new method developed in recent decades and is considered a cleaner technique. Therefore, this study aims to evaluate the self-reduction of mixtures composed of iron ore and steelmaking mill scale as iron source, together with coke fines as carbon source, heated using microwave energy. Through the rotational central composite design technique, it was possible to evaluate the best conditions for the use of steelmaking scale residue as well as the effect of the applied microwave energy power. The results indicated that the developed process has relevant utility with up to 41.48% of reduction obtained. The outcomes contribute to a better understanding of iron recovery from steelmaking residues in reduction processes using microwave energy for heating, providing significant insight for the development of new clean technologies.

Abstract In recent decades, microwave energy has been successfully experimented for mining and metallurgy processes and is considered a promising new method for ironmaking. In this context, in the present work, self-reducing mixtures composed of fines of iron ore and coke were prepared, intending to evaluate the degree of reduction of iron ore using microwave energy, applying different contents of coke, levels of power, and reaction times. For this, the degree of reduction was assessed as a function of these variables. Additionally, the reduction kinetics was investigated using chemical and diffusional models, and the microstructure of the samples was evaluated using scanning electron microscopy (SEM). The highest degree of reduction obtained after the experiments was greater than 60% and a statistical investigation showed that the reaction time is the factor with the greatest influence on these results, followed by microwave power and coke content. The investigation of the reaction kinetics showed that the process is chemically controlled, depending on the gasification steps governed by the Boudouard reaction. The images obtained by SEM led to the conclusion that the temperature inside the sample reached 1200°C. Pig iron was found both in the form of whiskers and in the form of metallic droplets.

Abstract Demand for iron ore worldwide has been steadily increasing, thus implying an increase in the volume of mining resulting in the extraction of ores with higher levels of silicon, phosphorus and sulfur impurities. An extensively used alternative is to perform a pre-treatment of the particles in order to reach the acceptable phosphorus limit in iron ore before its use in steel production. This study aims at the evaluation of the heating process and decrease of the phosphorus content of the particles using microwave energy in iron ore samples percolated by sulfuric acid followed by the leaching technique as a feasible route for the remotion of the phosphorus content in iron ore particles. Using the scanning electron microscopy (SEM) and statistical analysis techniques, it was possible to observe the characteristics of the iron ore particles after treatment with microwave energy. The results indicated that the developed process is feasible. The results of the kinetic simulation contribute to a better understanding of the phenomena of heating using microwave energy and also to the development of new cleaner technologies aiming to improve the efficiency of the acid baking - leaching technique for the reduction of the phosphorus content in iron ore particles.

Unlike the available mineral resources, the steelmaking processes have demanded raw material with lower phosphorus content to decrease the costs, energy use, and the residue generated within the steel plant. One alternative is to develop pretreatment of the iron ore concentrates producing raw materials with lower phosphorus. Depending on the mineral structure, a heat treatment combined with leaching could be an efficient way to achieve concentrates with low phosphorus (less than 0.01%), suitable for steelmaking processes. A fast and efficient way of applying energy to iron ore particles is the use of microwave to heat the particles. Thus, we propose a treatment using microwave heating while mixing with a dilute aqueous solution of sulfuric acid, followed by quenching during leaching with water, as a feasible route for the phosphorus removal from iron ore particles. We performed a design of experiment (DOE) to investigate the optimal conditions of heating and leaching, which maximize the rate of phosphorus removal. The structure of the iron ore particles after their treatment with microwave energy was observed by scanning electron microscopy (SEM). Thus, we analyze the optimal conditions for heating and leaching, the structure of the iron ore particles and which mechanism and rate equations are controlling the phosphorus removal. The results indicated that the average heating time is 10 min, the size of the crack of the order of 20µm and a leaching time of 8 min are adequate to achieve less than 0.01% of phosphorus. We demonstrated that under the most favorable combination of conditions for heating followed by leaching proposed in this study, the removal of the phosphorus content in the iron ore samples could reach 100%.