MAURILIO PEREIRA GOMES

MAURILIO PEREIRA GOMES

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Microstructural characterization of air quenched valve seat inserts obtained with AISI D2 tool steel
2017 - GOMES, M.P.; SANTOS, I.P.; COUTO, C.P.; BETINI, E.G.; COLOSIO, M.A.; ROSSI, J.L.
The obtention of valve seat insert (VSI) by powder metallurgy using a mixture of iron powder and tool steel is fulfilling the requirements for substitution of cobalt and lead in commercial parts, aiming cost reduction and avoid the lead toxicity. The aim of this work consisted of evaluate the influence of heat treatment on VSI obtained with AISI D2 tool steel powder. The AISI D2 tool steel powder was mixed with iron powder and additives such as manganese sulphide, zinc stearate, graphite and carbides. The heat treatment of the VSI consisted of air quenching followed by double tempering it at 500 °C. The microstructural characterization was performed using scanning electron microscopy and energy dispersive spectroscopy.
Effect of the cooling rates on heat-affected zone of UNS S32304 duplex stainless steel welded by pulsed GTAW process
2017 - BETINI, E.G.; GOMES, M.P.; REIS, L.A.; MUCSI, C.S.; ALENCAR, M.C.; ORLANDO, M.T.D.; LUZ, T.S.; AVETTAND-FENOEL, M-N.; ROSSI, J.L.
Two thin plates of UNS 32304 of duplex stainless steel were joined by pulsed gas tungsten arc welding (GTAW) using a mixture 98% of argon plus 2% of nitrogen as shielding gas or pure argon as purging gas at the bottom of the plate without filler metal. The temperature profile close and away from the weld pool was measured using K type (Ni-Cr) thermocouples, connected to a digital data acquisition system. The thermal cycles was recorded in the heat-affected zone (HAZ) at a distance in between 1 and 3 mm from the joint line. The cooling rate and holding time were studied with respect to the used purging gas. Experimental thermal profiles are in good agreement with literature values. The joints welded without any purging gas revealed high peak temperature and cooling rates. The present investigation showed that temperature peaks are comprised in the phase transformation temperature ranges for the welded duplex stainless steel.
Effect of nitrogen addition to shielding gas on cooling rates and in the microstructure of thin sheets of duplex stainless steel welded by pulsed gas tungsten arc welding process
2019 - BETINI, EVANDRO G.; GOMES, MAURILIO P.; MUCSI, CRISTIANO S.; ORLANDO, MARCOS T.D.; LUZ, TEMISTOCLES de S.; AVETTAND-FENOEL, MARIE-NOELLE; ROSSI, JESUALDO L.
The effect of the nitrogen content in the shielding gas and its effect on temperature distributions at the welded zone of thin sheets of duplex stainless steel have been evaluated. The duplex stainless steels have many features due to unique microstructural combination of austenite and ferrite grains. The phase balance can be easily shifted depending on the welding parameters. Two sheets 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 higher peaks of temperature using similar welding parameters. Microstructural examination showed that the austenite phase in the weld increased with the presence of nitrogen in the shielding gas. The added nitrogen promoted primary austenite formation and slightly increases the microhardness at the solidified zone. Microhardness mapping and metallographic imaging presented information about microstructures, confirming the formation of secondary phases during thermal cycle in the temperature range 850 °C and 950 °C. Control of ferrite amounts in the welds is essential mainly to improve mechanical properties and corrosion resistance of welding zones.
Study on welding thermal cycle and residual stress of UNS S32304 duplex stainless steel selected as external shield for a transport packaging of Mo-99
2019 - BETINI, E.G.; GOMES, M.P.; MILAGRE, M.X.; MACHADO, C.S.C.; REIS, L.A.M.; MUCSI, C.S.; ORLANDO, M.T.D.; LUZ, T.S.; MARTINEZ, L.G.; ROSSI, J.L.
Thin plates of duplex stainless steel UNS S32304 were welded using the pulsed gas tungsten arc GTAW process (butt joint) without filler addition. The used shielding gas was pure argon and 98% argon plus 2% of nitrogen. The thermal cycles were acquired during welding, in regions near the melting pool. This alloy is candidate for the external clad of a cask for the transport of high activity radiopharmaceuticals substances. For the residual stress measurements in austenite phase an X-ray diffractometer was used in a Bragg-Brentano geometry with CuKα radiation (λ= 0.154 nm) and for ferrite phase was used a pseudo-parallel geometry with CrKα radiation (λ= 0.2291nm). The results of residual stress using sin2 methodology showed that the influence of the high welding temperature leads to compressive stresses for both phases of the duplex steels mainly in the heat-affected zone. It was observed a high temperature peak and an increase of the mean residual stress after addition of ni-trogen to the argon shielding gas.
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.
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.
Heat treatment of sintered valve seat inserts
2018 - GOMES, MAURILIO P.; SANTOS, IGOR P. dos; COUTO, CAMILA P.; BETINI, EVANDRO G.; REIS, LUIS A.M. dos; MUCSI, CRISTIANO S.; COLOSIO, MARCO A.; ROSSI, JESUALDO L.
The characterization of sintered valve seat inserts (VSIs) after being subjected to different heat treatment operations has been carried out. The VSIs were obtained from three different alloys by mixing iron powder with AISI M3:2, AISI M2 high-speed steels, and AISI D2 tool steel. After sintering, the VSI were quenched in air followed by double tempering at seven different temperatures. The cooling rate during air quenching was measured by means of a thermocouple type k attached to a data acquisition system. The characterization of the mechanical and physical properties of the VSIs was achieved by measuring relative density, apparent hardness and crush radial strength. The resulting microstructures for the sintered parts were interpreted using the isothermal and continuous cooling transformation diagrams for similar alloys. The VSI obtained with AISI M3:2 and AISI M2 high-speed steels after air quenching and double tempering at 600 ºC showed the best results in terms of apparent hardness and crush radial strength.
Study of the thermal diffusivity variation in thin duplex steel plates welded by GTAW process
2018 - BETINI, EVANDRO G.; GOMES, MAURILIO P.; MUCSI, CRISTIANO S.; LUZ, TEMISTOCLES de S.; ORLANDO, MARCOS T.D.; ROSSI, JESUALDO L.
This study describes the thermal diffusivity of thin duplex steel plates in the thickness direction measured using the laser-flash method after welding. The work reports the experimental efforts in recording temperature profiles of the grade UNS S32304 duplex steel during autogenous welding. The butt weld autogenous joints were carried out by the GTAW (gas tungsten arc welding) process with either argon or argon - 2% nitrogen atmospheres. The amount of nitrogen in the heat affected regions, after welding, was measured and correlated with the variation of the thermal diffusivity of the studied material. The temperature profiles were obtained using k-type thermocouples connected to a digital data acquisition system. Different thermal cycles and thermal diffusivity values were observed in the heat-affected zone (HAZ) for both samples. In the solidified zone (SZ) was observed similar increase of the thermal diffusivity values for the plates welded with pure argon and argon plus nitrogen atmosphere.
Study on welding thermal cycle and residual stress of UNS S32304 duplex steel selected as external shield for a transport packaging of Mo-99
2017 - BETINI, EVANDRO G.; GOMES, MAURILIO P.; MILAGRE, MARIANA X.; MACHADO, CARULINE S.C.; REIS, LUIS A.M.; MUCSI, CRISTIANO S.; ORLANDO, MARCOS T.D.; LUZ, TEMISTOCLES S.; ROSSI, JESUALDO L.
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.