Engenharia Mecânica
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Navegando Engenharia Mecânica por Assunto "Aço - Tratamento térmico"
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- ItemAnálise da influência de tratamento térmico na resistência à corrosão-erosão do aço inoxidável AISI 304(Universidade Federal do Espírito Santo, 2008-12-18) Louzada, Dímisson Abreu; Macêdo, Marcelo Camargo Severo de; Franco, Sinésio Domingues; Bozzi, Antônio CésarThis work intends to evaluate the damaged caused by the erosion-corrosion process of a stainless steels AISI 304, under four microstructures conditions, used in various applications by the erosion, corrosion, and erosion-corrosion rates. With these rates it is possible to verify if there is a synergistic effect under the test conditions. For that reason, a slurry pot tester was useful. The experiments were performed at an impact of 7,5 m/s at room temperature. The abrasive particles of quartz used are in granulometric range 150 μm and an average sand concentration of 4 % wt. The corrosion and erosion-corrosion tests were performed in a solution of sodium chloride and acetic acid with 10-3 mol/l of sodium thiosulfate which is used to simulate the effect of the H2S presence. The samples obtained from dowel steel are cylindrical with 4,76 mm diameter and were weighted before and after each test. The erosion rate is in good agreement with the literature and is higher for solubility samples. The erosion rate is higher than the corrosion rate. The synergistic effect was observed for the test conditions.
- ItemAnálise de difusividade térmica em aço duplex UNS S32304 submetido a diferentes processos de soldagem TIG e tratamento térmico(Universidade Federal do Espírito Santo, 2016-05-13) Bolsanello, Marilia Fernandes; Passos, Carlos Augusto Cardoso; Orlando, Marcos Tadeu D'Azeredo; Macêdo, Marcelo Camargo Severo de; Rossi, Jesualdo Luiz; Passamai Junior, José LuisThermal diffusivity of UNS S32304 stainless steel was evaluated with the purpose ofaggregate knowledge to the development of the radioactive material transportation containment receptacles project.The Flash Lased Method was used, which is based on unidimensional thermal diffusivity equation analytical solution. A carbon dioxide laser with Gaussian profile was used, with 10−6𝑚wavelength, 10√2𝑊𝑚2⁄intensity and 10√2𝑊𝑚2⁄diameter.A sample of material was analyzed as received, in order toobtain a reference diffusivity value, and to compare with the value provided by the supplier, which ensured the method effectiveness. Thereafter, a sample welded by TIG autogenous process, with argon shield gas, was tested to analyze the welding process influence under thermal diffusivity. A sample welded by the same procedure, but heat treated under 600 °C for 8 hours and cooled by air was also analyzed, to evaluate the effect of these steels exposure to high temperatures after welding. To do so, in both welded samples, points with variable distance to sample middle were taken, including molted zone, heat affected zone and base metal. Finally, obtained results were compared to previous optical microscopy, ray X diffraction characterization, micro hardness and residual stresses analysis. It could be observed that thermal diffusivity was affected not only by welding process but also by heat treatment. Most of the points presented reduced thermal diffusivity, assigned to a material thermal conductive reduction, harmful for the use in question, once it will respond slowly to thermal changes. The heat treated sample presented diffusivity values closer to the material as received, qualitative similar results were also observed on residual stresses tests, where thermal treatment equalized materials stress state. Besides that, the molting zone point, at the sample only welded, presented a thermal diffusivity value above the one founded at base metal, which can be related to structural changes caused by heating. Nevertheless, those are partial conclusions, reinforcing the need of deeper studies concerning stainless steel UNS S32304 thermal diffusivity.
- ItemAvaliação das propriedades mecânicas do aço inoxidável duplex UNS S32304 submetido à soldagem TIG e diferentes temperaturas de tratamento térmico(Universidade Federal do Espírito Santo, 2019-03-11) Caetano, Gabriela Aksascki; Luz, Temístocles de Sousa; Orlando, Marcos Tadeu D'Azeredo; Furtado, Henrique Silva; Cavichini, Arthur Sant’Ana; Martinelli, Antonio Eduardo; Alves, Haimon Diniz LopesThe duplex stainless steel UNS S32304 has been investigated as a candidate for external construction of areceptacle for transporting radioactive material associated with the future Brazilian Multipurpose Nuclear Reactor(RMB), as it presents the combination of excellent mechanical properties and high resistance to corrosion, as a consequence of its ferritic-austenitic biphasic structure.The outer shell construction of this receptacle provides for the use of welded UNS S32304 steel sheets.In order to evaluate the effect of post-weld heat treatments on the mechanical properties and to guarantee the reliability of the weld in this material, plates of UNS S32304 with a thickness of 1.8 mm were welded by autogenous GTAW process with pulsed current with direct polarity, shieldinggaswith a mixture of argon and 2% of nitrogen and an automatic drive system with digital control of the parameters.The specimens were heat treated for 8 h at 600, 650, 700 and 750 ° C in a programmable muffle furnace, with accuracy of ± 5 ° C followed by air cooling.The sampleswere submitted to stress tests in the thermal-mechanical simulator using Gleeble®model 3500 and 3800 in the Brazilian Nanotechnology National Laboratory and Brazilian Synchrotron Light Laboratory, located at the Brazilian Center for Research in Energy and Materials. Hardness measurements were made the Vickers microhardness test with load of 1006 gf for the profile and loads of 1 and 2 gf for phase individual analysis. The microstructural characterization was done stereoscopy, optical microscopy and scanning electron microscopy. Phase quantification was performed by image processing and analysis using the FIJI -ImageJ and SVRNA software. It was verified that the increase of the heat treatment temperature promoted the increase in the content of the austenitic phase and consequently the increase of the ductility, increase of the hardening coefficient, reduction of the hardness and reduction of the mechanical strength
- ItemCorrelação entre a resistência à corrosão e as tensões residuais de um aço inoxidável lean duplex uns s32304 submetido à processo de soldagem TIG e diferentes condições de tratamentos térmicos e resfriamento(Universidade Federal do Espírito Santo, 2016-02-24) Merlo, Panmela Pereira; Macêdo, Marcelo Camargo Severo de; Orlando, Marcos Tadeu D'Azeredo; Ponzio, Eduardo ArielHeat treatment and welding process can promote the precipitation of secondary phases in duplex stainsless steels, resulting in the phenomenon ofsensitization,whichis detrimental tothecorrosion resistance of the material. In this work, the UNS S32304 steel samples were subjected to heat treatments at temperatures of 475, 600 and 750 ° C for 8 hours, air or seawater cooled and the GTAW welding process followed by the same treatments. In order to evaluate the resistance to localized corrosion were performed electrochemical tests of the type DL-EPR. After DL-EPR was possible to calculate the degree of sensitization(DOS) of the samples and it was found in general that the elevated heat treatment temperature caused an increase in localized corrosion. The samples subjected to the welding processand heat treatment had a superior sensitizationthan the samplestreated only, and that the cooledair obtained DOS higher than cooled in seawater. The residual microstressesin ferrite introduced a compatible DOSbehavior in only treated samples
- ItemEfeito da temperatura de tratamento térmico na corrosão localizada do aço inoxidável duplex UNS S31803 avaliado por espectroscopia de impedância eletroquímica(Universidade Federal do Espírito Santo, 2015-09-18) Helker, Paulo Victor Toso; Macêdo, Marcelo Camargo Severo de; Cotta, Rômulo Almeida; Ponzio, Eduardo ArielThis study evaluated the comparative results obtained from the DL-EPR techniques and electrochemical impedance spectroscopy, in terms of behavior susceptibility to localized corrosion of UNS S31803 duplex stainless steel. Also sought the relationship between the heat treatment, microstructure and sensitization. For these samples were heat treated at the temperatures 645 ° C, 820 ° C and 960 ° C for 12 hours besides the sample under the condition "as received". These treatments resulted in the precipitation of sigma phase. DL-EPR tests were conducted in a 2 M H2SO4 solution + 0.5M NaCl + 0.01 M KSCN in order to quantify the degree of sensitization after heat treatment, and testing electrochemical impedance spectroscopy in the same solution, however the open circuit potential (OCP) and the potential of +350 mVsce where the samples are passive, in order to verify that the results were consistent with those obtained with DL-EPR. The samples suffered a considerable change in the proportion of ferrite-austenite due to heat treatment. Thus, the EIS results were evaluated with caution, in order to consider that effectively attacked areas experienced great variation, which should be appropriately compensated before evaluating the results
- ItemEfeito da velocidade de resfriamento após tratamento térmico em alta temperatura na resistência à corrosão localizada do aço UNS S31803(Universidade Federal do Espírito Santo, 2014-02-25) Garcia, Davi Pereira; Macêdo, Marcelo Camargo Severo de; Pardal, Juan Manuel; Tavares, Sérgio Souto MaiorDuplex Stainless Steel have both phases ferrite and austenite in his microstructure in almost equal proportions, allowing it to have great strength corrosion and mechanical resistance , being extremely used in petrochemical and chemical industries. When exposed to high temperatures they are subject to microstructural changes making his properties to be modified. In this work localized corrosion resistance of the duplex stainless steel UNS S31803 heat treated by high temperature(1300◦C) for 30 minutes followed by different cooling rates is studied.Somesamples were solution treated at 1000◦C for 1 hour and fast cooled after the high temperaturetreatment.A wide range of microstructures,with differents morphologies and phase proportions, were obtained by this way, also this microstructural changes during cooling process have promoted the precipitation of deleteriusphases such as nitrides and sigma, making the corrosion strength to be altered.The intergranular corrosion resistance wasmeasured with DL-EPR technique,and pitting corrosion was made using potentiodynamic polarization both according to the standard ASTM.Besides these tests were made microhardness analysis,optical microscopy andscanning electron microscopy of the samples.
- ItemPerfis de tensão residual do aço duplex UNS S32304 submetido à processo de soldagem TIG e diferentes condições de tratamento térmico de tempera(Universidade Federal do Espírito Santo, 2015-05-13) Milagre, Mariana Xavier; Luz, Temístocles de Sousa; Orlando, Marcos Tadeu D'Azeredo; Macêdo, Marcelo Camargo Severo de; Rossi, Jesualdo LuizStructural failures can occur by a service and residual stressescombination effects. These are generated on the material after the non-uniform plastic deformation originated by mechanical, thermal or chemical process. In this work, the residualstresses mean valuesare investigated by X ray diffraction technique. Samples of duplex stainless steel UNS S32304 subjected to different heat treatment conditions and TIGwelding process are used. From the total mean stress values the residual stress profiles are obtained. This was possible by the 420 austenite plane behavior analysis with CuKαradiation (ߣ̅= 0.1542nm) and the 211 ferrite plane analysis with CrKαradiation (ߣ̅= 0.2291 nm). The samples were heat treated at475 °C, 600 °C and 750 °C for 8 hat air atmosphere and cooled in sea water. The results were analyzed by the sen²ψmethod and indicate that the thermal and microstructural variations related to different experimental conditionschange thematerial total mean residual stresses and consequently the stress profile