RESUMO Este trabalho teve como finalidade avaliar a influência do tamanho médio dos grãos na susceptibilidade à corrosão do aço inoxidável austenítico AISI 316L, cujo material é bastante utilizado em juntas soldadas, em temperatura ambiente e em baixíssimas temperaturas (condições criogênicas) por apresentar excelente resistência à corrosão e boa ductilidade. Para tanto, amostras foram simuladas termicamente em uma Gleeble 3800 nas temperaturas de 900 °C e 1200 °C sob o tempo de permanência de 0, 5, 20 e 100 segundos, controlando a taxa de resfriamento para em torno de 20 ºC/s e sendo em seguida submetidas à análise de metalografia e de corrosão por técnicas eletroquímicas de polarização linear, usando uma solução de 3,5% de cloreto de sódio (NaCl). Além disso, foram realizados ensaios por análise de Raios-x nas amostras de maior e menor susceptibilidade à corrosão para verificação microestrutural. Os resultados mostraram que as amostras submetidas a 1200 ºC apresentaram um aumento no tamanho médio dos grãos em relação às amostras de 900 ºC, tendo uma menor susceptibilidade à corrosão, exceto para a condição de 1200 ºC a 100 s. Entretanto nas amostras com 1200 ºC a 100 s foram constatados carbonetos por análise de Raios-x e por fim, foi observado o fenômeno de corrosão por pite em todas as amostras.

ABSTRACT The purpose of this work was to evaluate the influence of the average grain size on the corrosion susceptibility of AISI 316L austenitic stainless steel, which is widely used in welded joints, at room temperature and at very low temperatures (cryogenic conditions) because it has excellent corrosion resistance and good ductility. For this, samples were thermally simulated on a Gleeble 3800 at temperatures of 900°C and 1200°C under the residence time of 0, 5, 20 and 100 seconds, controlling the cooling rate to around 20°C/s followed by metallography and corrosion analysis using linear polarization electrochemical techniques using a solution of 3,5% sodium chloride (NaCl). In addition, tests were performed by x-ray analysis on samples of greater and lesser susceptibility to corrosion for microstructural verification. The results showed that the samples submitted to 1200ºC presented a bigger increase in the average grain size in relation to the samples of 900ºC, having a lower susceptibility to corrosion, except for the condition of 1200ºC to 100s. However in the samples with 1200ºC to 100s, carbides were detected by X-ray analysis and finally, the corrosion phenomena were observed by pitting in all samples.

Through microsatellite analysis of 53 monoclonal populations of Trypanosoma cruzi, we found a remarkable degree of genetic polymorphism with no single multilocus genotype being observed more than once. The microsatellite profile proved to be stable during 70 generations of the CL Brener clone in culture. The microsatellite profiling presented also high diagnostic sensitivity since DNA amplifications could be achieved with less than 100 fg DNA, corresponding to half parasite total DNA content. Based on these technical attributes the microsatellite assay turns out to be an important tool for direct typing T. cruzi in biological samples. By using this approach we were able to type T. cruzi in feces of artificially infected bugs and in single cells sorted by FACS. The microsatellites have shown to be excellent markers for T. cruzi phylogenetic reconstruction. We used maximum parsimony based on the minimum number of mutational steps to build an unrooted Wagner network, which confirms previous conclusions based on the analysis of the D7 domain of the LSU rDNA gene that T. cruzi is composed by two major groups. We also obtained evidence that strains belonging to rRNA group 2 are subdivided into two genetically distant clusters, and that one of these clusters is more related to rRNA group 1/2. These results suggest different origins for these strains.