MAURILIO PEREIRA GOMES

MAURILIO PEREIRA GOMES

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Influence of heat treatment on corrosion resistance of press hardened steel coated with AlSi and ZnNi
2017 - COUTO, CAMILA P.; COSTA, ISOLDA; COLOSIO, MARCO; GOMES, MAURILIO; ROSSI, JESUALDO; BOLSANELLO, MARILIA
The ultrahigh strength boron manganese steels, also known as PHS (press hardened steels), are strategic materials for the automotive industry, satisfying safety needs and fuel reduction requirements by means of the lightweight design concept, a current trend for new vehicles. It is possible by the hot stamping process which consists in heating a steel blank to the austenitization temperature, transferring it to press tooling, forming and quenching to fully martensitic transformation. At the end of process, the steel achieves tensile strength up to 1,500 MPa. The transference step from furnace to press is a critical stage because it might promote deleterious steel oxidation. The use of metallic coatings avoids this outcome. AlSi coatings have been the most applied on PHS. Alternative coatings such as electroplated ZnNi are under investigation to evaluate their potential for replacement of AlSi coatings, besides to keep up with the high projected world demand. Zinc based coatings are advantageous comparatively to AlSi ones because they provide cathodic protection to steel substrates. In this study the influence of hot stamping heat treatment on corrosion resistance of 25MnB5 steel coated by AlSi and electroplated ZnNi has been investigated. The tests include open circuit potential measurement, electrochemical impedance spectroscopy and anodic polarization curves. The samples have been tested as received and after the heat treatment which consists in heating the sample at 900°C by 10 minutes and then, fast cooling in water. It is expect that the heat treatment changes the corrosion resistance due to the intermetallics formation at the coating layer as a consequence of diffusion.
Valve seat insert: air quenching and characterization of components obtained with AISI M3:2 high-speed steel
2018 - GOMES, M.P.; SANTOS, I.P.; REIS, L.A.M.; COUTO, C.P.; BETINI, E.G.; MUCSI, C.S.; COLOSIO, M.A.; ROSSI, J.L.
The development of components ecologically correct is something more and more necessary. The first developement of valve seat inserts (VSI) take in account the use of cobalt and lead in its chemical composition. Such elements are avoided in the current applications due to its high cost and toxicological effects, respectively. In the present work was used VSI developed with a new chemical composition. The aim of this work were to air quench and characterize such components. The studied VSI were obtained with AISI M3:2 high-speed steel admixed with iron powder and another additives such as manganese sulphide, graphite, zinc stearate and carbides. All the air quenched VSI were double tempered, for one hour each, at seven equidistant temperature from 100 °C until 700 °C. The air quenched components had its mechanical and physical properties determined by means of its apparent density, apparent hardness and crush radial strength. The chemical composition was measured through the gases analyses and energy dispersive X-ray fluorescence spectrometry techniques. Microstructural and phase characterizations were performed with the support of optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. Regarding the VSI required properties, the best results were obtained with the components air quenched and double tempered at 600 °C.
Recycling process viability from zirconium alloys scraps of lathe melted in the vacuum arc remelting (VAR) furnace
2018 - REIS, L.A.M.; ALENCAR, M.C.; GOMES, M.P.; PEREIRA, L.A.T.; BARBOSA, L.P.; MUCSI, C.S.; ROSSI, J.L.
Pressurized water reactors (PWR) commonly use U235 enriched uranium dioxide pellets as a nuclear fuel, these are assembled and cladded in zirconium alloy (M5, Zirlo, Zircaloy) tubes and end caps. During the machining of these components, large amounts of turning lathe chips are generated which are contaminated with cutting fluid. Its storage presents safety and environmental risks due to its pyrophoric and reactive nature. Recycling industry has shown interest in its recycling due to its strategic importance of these scraps. This paper presents the steps on the recycling processes and the results for the search of an efficient way on the cleaning, quality control, manufacturing, and melting of electrodes for Vacuum Arc Remelting (VAR) furnace. The process starts with cutting oil washout and this step consists of a water dissolution followed by a degreasing process, the water rinse by continuous flow of water and finally drying in hot air. Process evaluation was first made by means the X-ray fluorescence tests in order to define the quality of the scraps that after washing were pressed in 20 mm diameter briquettes, melted and subjected to such analysis. The next step consists in the pressing with a die square section with 40 mm2 and 500 mm long, producing an electrode with 20% of the Zircaloy bulk density. The electrode was melted in a laboratory scale VAR furnace located at the CCTM – IPEN producing a 0.8 kg ingot. The microstructural and macro structural characterization is being done by analyzes performed in the optical microscope and scanning electron microscope (from portuguese Microscópio Eletronico de Varredura - MEV). Gas analyzes were carried out with the intention of evaluating possible gases resulting from the melting and evaluating their influence. X-ray diffraction analyzes were also performed to identify the phases present in the material after the melting process The authors conclude that the samples obtained from the fuel element industry can be melting in a VAR furnace reducing 40 times the storage volume, however, it is necessary to remelt the ingots by correcting their composition intended for reuse.
Effect of nitrogen addition to shielding gas on cooling rates and microstructure of thin plates of duplex stainless steel welded by pulsed GTAW process
2018 - BETINI, E.G.; GOMES, M.P.; MUCSI, C.S.; ORLANDO, M.T.; LUZ, T.S.; AVETTAND-FENOEL, M.; ROSSI, J.L.
The content of nitrogen to shielding gas and their effects on temperature distributions of the heat-affected zone of thin plates of duplex stainless steel during the pulsed GTAW process has been studied here. The duplex stainless steels have many features due to unique structural combination of austenite and ferrite grains. The phase balance can be easily altered to a mostly ferritic microstructures, depending on the welding parameters like shielding gas used. Microstructural examination showed that the austenite phase in the weld increases with the presence of nitrogen in the shielding gas. The additional nitrogen promoted the primary austenite formation and slightly increased the microhardness of the solidified zone. Microhardness mapping and metallographic imaging presented information about microstructures, confirming the formation of secondary phases and microstructure sensitization during thermal cycle in the temperature range 850-950°C. Two plates were welded using pure argon and pure argon plus 2% of nitrogen as shielding gas. The thermal profile had shown that N2-supplemented shielding gas lead to high peaks of temperature using similar welding parameters. The columnar and equiaxied ferrite grain size of solidified fusion zone was studied. Ferrite phase increased from 53 % in base metal to 78% to pure Ar and 63% using Ar+2%N2 as shielding gas. Control of ferrite in the welds is essential mainly to improve corrosion resistance.
Study of the thermal diffusivity variation in thin duplex steel plates welded by GTAW process
2016 - BETINI, E.G.; ROSSI, J.L.; MUCSI, C.S.; GOMES, M.P.; ORLANDO, M.T.; LUZ, T.S.
This study describes the experimental efforts in recording 2-dimensional temperature distribution in thin plates autogenous UNS S32304 steel during welding. The butt-welded autogenous joints were experimentally performed by the GTAW (Gas Tungsten Arc Welding) process with either argon or argon-2%nitrogen atmospheres. The increase of nitrogen mass in the heat affected regions after welding was measured suggesting a correlation with the change in the thermal diffusivity of the material. The laser flash method (LFM) was also used to determine the thermal diffusivity of the material in the thickness direction. The cooling rates of the temperature cycles were recorded by thermocouples embedded by spot welding on surfaces of the plate and connected to an acquisition multichannel data system. The temperature curves suggest a relationship between the microstructures in the solidified and the heat affected zone with the diffusivity variation. These measurements define key parameters regards the residual stress study after welded process.
Estudo de mancais para uso na barra de ensaio dinâmico de compressão SHPB
2016 - MUCSI, C.S.; ROSSI, J.L.; GOMES, M.P.; NOGUEIRA, E.J.; SOUZA, M.M.
Os ensaios de dinâmicos de compressão com alta taxa de deformação são essenciais para a caracterização de materiais que serão submetidos à esforços dinâmicos de compressão, quando utilizados em peças ou partes, notadamente na área bélica, mas também na construção de invólucros, para o transporte de materiais radioativos. E trabalho apresenta parte do processo de construção e testes de um equipamento SHPB, e tem por objetivo o desenvolvimento de uma metodologia para a determinação dos atritos estáticos entre as barras incidente e transmitida, no dispositivo de teste SHPB do CCTM-IPEN, e viabilizar o método de alinhamento destes componentes.
Heat treatment and characterization of sintered high-speed steel for valve seat insert application
2016 - GOMES, M.P.; ROSSI, J.L.; MUCSI, C.S.; SANTOS, I.P.; COLOSIO, M.A.; BETINI, E.G.
The aim of this work was the characterization of valve seat inserts (VSI) subjected to heat treatments. The VSI were produced with three different alloys modified from the AISI M3:2, M2 and D2. These alloys modifications were intended as an alternative to replace cobalt and lead used in the original alloy due to their high cost and toxicological effect. The VSI were submitted to different heat treatments, such as: air quenching and oil quenching, both followed by double tempering with different temperatures. The VSI mechanical and metallurgical properties were performed according to standardized apparent density (ASTM C 373-88), apparent hardness (ASTM E 92-82) and radial crush strength (MPIF Standard 35) tests. The VSI characterizations also were carried out using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and light optical microscopy (LOM). The VSI produced with alloy M3/2 showed the best results in the hardness test and radial crush strength.