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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 N 2-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.

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 sin2y methodology shown that the influence of the high welding temperature leads to compressive stresses for both phase of the duplex steels mainly in heat-affected zone. It was observed a high temperature peak and an increase of the mean residual stress after addition of nitrogen to the argon shielding gas.

The aim of this work was to study the valve seat insert (VSI) produced with three different alloys (mainly modified from the original AISI M3/2, M2 and D2 high-speed steels) from the mechanical and metallurgical point of view. 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 respectively. Such alloys have been developed for internal combustion engines VSI manufacture. The VSI studied in this work was previously produced by the powder metallurgy (P/M) route. The VSI production was performed using a uniaxial hydraulic press and a belt conveyor furnace. The VSI was submitted to metallic infiltration during the sintering process using copper as filler. The studies 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 produced with M3/2 alloy proved to be more advantageous considering the highest values obtained in the apparent hardness and radial crush strength tests.Keywords: powder metallurgy, characterization, valve seat insert, high-speed steel. ResumoO objetivo deste trabalho foi estudar o inserto para assento de válvula (do inglês VSI -Valve Seat Insert) produzido com três ligas diferentes (modificadas principalmente das ligas originais de aço rápido AISI M3/2, M2 e D2) do ponto de vista mecânico e metalúrgico. As modificações destas ligas foram pretendidas como uma alternativa para substituir o cobalto e o chumbo usados na liga original, devido ao seu custo elevado e efeito toxicológico respectivamente. Tais ligas têm sido desenvolvidas para a manufatura de VSI utilizados em motores à combustão interna. O VSI estudado neste trabalho foi produzido pela rota da metalurgia do pó (M/P). Este processo foi realizado utilizando-se uma prensa hidráulica de compactação e um forno contínuo de esteira. Os VSI foram submetidos a infiltração metálica durante a etapa de sinterização utilizando cobre como infiltrante. Os estudos foram determinados de acordo com testes padronizados, sendo eles: densidade aparente (ASTM C 373-88), dureza aparente (ASTM E 92-82) e resistência à ruptura radial (MPIF padrão 35). Os VSI produzidos com a liga M3/2 provaram ser mais vantajosos considerando-se os valores obtidos nos ensaios de dureza aparente e resistência à ruptura radial.Palavras-chave: metalurgia do pó, caracterização, inserto de assento de válvula, aço rápido.