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Orientador: Paulo R. Mei Observação: Faltam as páginas 94, 95 e 172 Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica Resumo: Estudou-se a relação entre a porcentagem de austenita retida e o desgaste abrasivo em ferros fundidos brancos contendo 12,5% de cromo; 2% de carbono e 0,6; 1,2 ou 1,8% de manganês. Manteve-se constante a fração volumétrica de carbonetos eutéticos de modo a destacar o efeito das mudanças estruturais da matriz. Realizaram-se ensaios do pino com sic ou Sílex. As amostras foram temperadas ou temperadas e revenidas de modo a se variar a porcentagem de austenita retida. A caracterização das amostras foi feita empregando-se análise termo diferencial, microscopia ótica e eletrônica de varredura, di fração de raios X, metalografia quantitativa, macro e microdureza. A microestrutura e o comportamento em desgaste das ligas com 0,6 e 1,2% de manganês foi semelhante verificando-se o aumento da porcentagem de austenita retida e a diminuição da taxa de desgaste com a elevação da temperatura de austenitização. Por sua vez, as amostras com 1,8% de manganês exibiram um máximo de dureza e um mínimo de austenita retida quando austenitizadas a 950 oCo A transição de desgaste moderado para desgaste intenso ocorreu quando a relação entre dureza do abrasivo e dureza do material tinha o valor 2,5 ao invés de 1 como encontrado na literatura. Este comportamento foi relacionado à ocorrência de microssulcamento ao invés de microcorte da austenita, ocorrendo a remoção de material por microestiramento ou microfadiga. Nas amostras revenidas observou-se o mesmo comportamento quando estas continham austenita. Na ausência da austenita a resistência ao desgaste aumentou com a elevação da dureza. Neste caso a transição desgaste moderado/desgaste severo ocorreu quando a relação entre dureza do abrasivo e dureza do material era 1. Abstract: Retained austenite content and abrasive wear relationship of 12.5 % Cr, 2.0 % C with 0.6, 1.2 and 1.8 % Mn, with 18 % eutetic carbide in white cast iron, were studied. The volumetric fraction of eutectic carbide content were kept constant in order to point out the abrasive wear behavior of bulk metal. Pin test with sic or flint were carried out. oil quenching followed by tempering at three different temperatures were caried out to produce. variable retained austenite content specimens. Thermodifferential analysis, optical and scanning electron microscopic examination, X-ray diffraction, quantitative metallography, macro and micro hardness testings were used for specimens characterization. Microstructure and wear behavior of 0.6 and 1.2 % Mn content samples were similar. The austenite content were increased for higher austenitizing temperatures. Hardness and wear resistance decreased when austenite content were increased. On the- other hand -l.8 Mn alloy presented a maximum in hardness and a minimum in austenite content at 950 °c quenching. Mild to severe wear transition occured when abrasive hardness to sample hardness ratio was 2.5 rather than 1.0, as stated in the literature. This behavior was related to microploghing instead of microcutting of austenite phase, due to microstretching or microcutting of cold worked austenite phase. Tempered samples showed same behavior as quenched only sámples in the presence of austenite. In the absence of austenite wear resistance increases when hardness increases. In this condition the ratio between abrasive hardness and sample hardness for the mild to severe wear transition was 1.0. Doutorado Doutor em Engenharia Mecânica

A significant part of the friction losses in the automotive engine results from the abrasive action of particles formed in the interface between cylinder and piston/rings. Those particles are responsible for axial grooves that are observed in the liners of used engines. The objective of this work was to get a better understanding of the wear mechanisms related to liner/bore grooving and to identify a laboratory testing setup that might reproduce them under controlled conditions. Specimens of Gray Cast Iron (GCI) and of AISI 1070 steel with matrix hardness close to that found in GCI (≈200HV30) were submitted to scratch tests in a tribometer. It was found that scratches performed under 20-50 mN indenter load were similar to grooves observed in cylinder liners. No sharp transition between abrasion mechanisms was observed. Calculation of material removal factor fab from optical profilometry resulted in values with a large dispersion; they could not be associated with different abrasion mechanisms.