Este é um artigo publicado em acesso aberto (Open Access) sob a licença Creative Commons Attribution Non-Commercial, que permite uso, distribuição e reprodução em qualquer meio, sem restrições desde que sem fins comerciais e que o trabalho original seja corretamente citado. Resumo: Este trabalho constitui um estudo dos vergalhões CA-50 da classe dos aços SAE 1026. Para um melhor controle das propriedades mecânicas da junta soldada foi realizado este estudo, o conhecimento de certas variáveis é de grande importância para encontrar os parâmetros ideais de soldagem, e os respectivos resultados microestruturais e consequentemente sobre as propriedades mecânicas da junta soldada. Para realização deste estudo foi realizado um estudo do material como recebido para a fixação de uma base sólida de comparação. Foi realizada a soldagem do material utilizando como gás de proteção argônio com 20% de dióxido de carbono, o arame utilizado foi o cobreado ER70S-6, as juntas soldadas foram do tipo transpasse com monitoramento de temperatura através de termopares para dois aportes térmicos distintos. Um código numérico computacional foi desenvolvido para simular os fenômenos que ocorrem no processo (gradiente de temperatura, transformações de fases, transferência de calor). As juntas soldadas não apresentaram martensita como fase frágil, o metal de solda apresentou estrutura dendrítica, a ZTA apresentou duas regiões distintas com tamanhos de grão diferentes tudo isso devido ao gradiente de temperatura, que também originou características distintas do cordão de solda, ZTA, fases formadas e tamanhos de grão distintos. Palavras-chave:Soldabilidade; GMAW; Simulação computacional; Concreto armado. Numerical and Experimental Study of Microstructure Evolution and Properties of Welded Joints of Rebars by GMAW ProcessAbstract: This work is a study of rebar CA-50 class of steels SAE 1026. To better control the mechanical properties of the weld was carried out this study, knowledge of certain variables is very important to find the optimal parameters of welding, and the results microstructure and therefore on the mechanical properties of the welded joint. For this study was conducted a study of the material as received for establishing a solid basis for comparison. Welding the material using argon as protective gas of 20% carbon dioxide was performed, the wire used was ER70S-6 coppered, welded joints were of the type with crossover temperature monitoring thermocouple through two distinct thermal contributions. A computational numerical code was developed to simulate the phenomena occurring in the process (temperature gradient, phase transformations, heat transfer). Welded joints did not show how fragile martensite phase, the weld metal showed dendritic structure, the ZTA presented two distinct regions with different grain sizes all this due to the temperature gradient, which also originated distinct characteristics of the weld bead, ZTA, stages formed and different grain sizes.
Welding is a widely used process that requires continuous developments to meet new application demands of mechanical projects under severe conditions. The homogeneity of metallurgical and mechanical properties in welded joints is the key factor for any welding process. The applications of external magnetic fields, mechanical vibration, and ultrasound are the fundamental steps to achieve success in improving these properties. The present work aimed at determining suitable processing conditions to achieve the desired balance between metallurgical and mechanical properties of 304L steel in TIG (Tungsten Inert Gas) welding under the application of an external magnetic field. The microstructural characteristics of the weld bead were analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). In order to evaluate the mechanical properties of the welded specimen, its Vickers microhardness map and Charpy impact energy at −20 °C were obtained. In addition, corrosion tests were carried out in the saline medium to compare the corrosion resistance of the joint with that of the base metal and that without the magnetic field. It was found that the external magnetic field decreased the percentage of delta ferrite, improved the filling of the weld pool with the weld metal, and decreased the primary and secondary dendritic spacings. The Vickers microhardness value under the magnetic field was found to be lower than that without the magnetic field, and the Charpy test showed no significant variation in energy absorption. Moreover, the welded joint produced under the external magnetic field manifested less resistance to corrosion.
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%.
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