Yes / Tensile properties of powder metallurgy 3% manganese-0·8% carbon (content of green compact) steels were determined following laboratory sintering in (nearly) full, semiclosed containers with no getter powders in dry, 0-100% hydrogen-nitrogen atmospheres. Manganese was mixed with the NC 100·24 sponge iron powder as low carbon ferromanganese and carbon as a graphite addition. Dogbone compacts were pressed at 660 MPa, the sintering temperatures were 1120 and 1250°C and cooling rates ∼65 K min- 1. In specimens sintered in nitrogen containing atmospheres at 1120°C, final carbon content was ∼0·7% and for those processed at 1250°C ∼0·6%. Sintering in dry hydrogen resulted in lower carbon and oxygen contents. Independent of the H2/N2 ratio in the furnace atmosphere, however, all the specimens were ductile and exhibited similar strengths. Yield strengths R 0·2 were in the range: 426-464 MPa, tensile strengths Rm were 724-780 MPa and strains to failure were 1·6-2·0% after sintering at 1250°C. The 1120°C sintering temperature resulted in 10-15% lower strength values. The microstructures, significantly devoid of oxide networks, comprised mainly mixtures of bainite and fine (divorced) pearlite, with very little martensite and retained austenite. Reproducibly successful sintering of manganese containing compacts requires that reduction conditions exist at the sintering temperature. Ellingham Richardson diagrams dictate that the dewpoints of hydrogen required are-55 and-40°C at 1120 and 1250°C, respectively. A semiclosed container, how ever, ensures a different microclimate. It is suggested that then the initial relevant reactions there are: Mn[vapour]+H2O=MnO+H2, 3Fe2O3 +H2= 2Fe3O4+H2O, Fe3O4+H2=3FeO+H2O, FeO+H2= Fe+H2O and C+O2=CO2, which provide hydrogen andwater vapour,also within the pores. The manganese vapour further acts as a ‘shield’ by generating further hydrogen from the water vapour. The following reactions involving carbon monoxide are postulated above 927°C, when CO is a more effective reducing agent than hydrogen: C+H2O=H2+CO, 3Fe2O3+ CO=2Fe3O4+CO2, Fe3O4+CO=3FeO+CO2, FeO+CO=Fe+CO2 and C+CO2=2CO. Accordingly, irrespective of whether it is hydrogen or nitrogen in the semiclosed container, if there is a supply of carbon, reducing conditions prevail at the sintering temperature,embrittling oxidenetworks arenot formed and ductile manganese steels are processed.

Orientador: João Andrade de Carvalho Junior / Resumo: O nitrogênio (N) é um elemento fundamental para os seres vivos; contudo, o N disponível biologicamente é aquele conhecido como nitrogênio reativo (Nr). O presente trabalho propõe quantificar e analisar a variabilidade espacial da concentração e deposição atmosférica seca de nitrogênio reativo no estado de São Paulo, através de sua fase gasosa (HNO3; NH3; NO2) e particulada (NO3-; NH4+). Amostradores de coleta por Denuder (DELTA) foram distribuídos espacialmente em seis sítios de amostragem, abrangendo diferentes tipos de cobertura do solo e urbanização. As amostras foram coletadas ao longo de dois anos (2015-2017). A forma dominante de Nr inorgânico na atmosfera foi o NO2 gasoso em todos os locais de amostragem, o que representou 79% do total. As concentrações médias de NH3, HNO3, NH4+ e NO3− foram de 10%, 3%, 6% e 2% do total de Nr, respectivamente. A umidade relativa e a velocidade do vento foram significativas para explicar parte da variabilidade das concentrações de Nr na atmosfera, enquanto a precipitação foi importante apenas para a concentração de NO2. A deposição média de Nr seco no Estado de São Paulo foi de 8,9 kgN ha-1 ano-1. A maior deposição média de Nr foi encontrada no sudeste do Estado de São Paulo e está relacionada ao intenso tráfego de veículos, gerenciamento de resíduos e atividades industriais. Considerando a região onde a Mata Atlântica está localizada, este trabalho mostra que a deposição total de Nr seco por si só (sem considerar a deposição de espécie... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Nitrogen (N) is a fundamental element for living beings; however, the biologically available N is known as reactive nitrogen (Nr). The current work proposes to quantify and analyze the spatial variability of the concentration and dry atmospheric deposition of reactive nitrogen in the state of São Paulo, through its gas phase (HNO3; NH3; NO2) and particulate phase (NO3-; NH4+). Denuder collection samplers (DELTA) were spatially distributed in six sampling sites, covering different types of ground cover and urbanization. The samples were collected over two years (2015-2017). The dominant form of inorganic Nr in the atmosphere was gaseous NO2 in all sampling sites, what represented 79% of the total. The average concentrations of NH3, HNO3, NH4+ and NO3- were 10%, 3%, 6%, and 2% of the total Nr, respectively. The relative humidity and wind speed were significant to explain part of the variability of Nr concentrations in the atmosphere, while precipitation was important only for the concentration of NO2. The average of dry Nr deposition in the State of São Paulo was 8.9 kgN ha-1 year-1. The highest average deposition of Nr was found in the southeastern of São Paulo state and is related to the intense vehicle traffic, waste management, and industrial activities. Considering the region where the Atlantic Forest is located, this work shows that the total deposition of dry Nr by itself (without considering the deposition of wet or organic species) exceeded the critical load of Nr sugg... (Complete abstract click electronic access below) / Mestre