The aim of this study was to propose potential materials for use in the automotive industry, specifically alloys applied in the production of valve seat inserts. The research was divided in steps according to standard powder metallurgy technique: selecting components for the studied alloys, acquisition and preparation of each of the metal powders, physical and microscopic characterization of the components, defining the proportions to be used, a mixture of alloys, compaction in uniaxial presses, sintering the parts according to thermal cycle and specific atmosphere, hardness tests, resistance to radial compression and microstructural analysis using scanning electron microscopy. The powders mixtures were basically iron powder mixed with high-speed steels type AISI M3/2, D2 and M2. The valve seat inserts made with the alloy M3/2 showed to be more advantageous in relation to the other mixtures in terms of hardness and transverse rupture strength.

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.

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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.

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