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Previous issue date: 2007-02-27 === The subject of this work was to study the mechanical properties, based in tensile and impact tests, of two stainless martensitic steels cast under designations of ASTM Standards, namely the CA15 steel, a steel with 12% of Cr, and the CA6NM steel, a steel with 12% Cr and 4% Ni. For both steel grades bar tests were machined out from Keel Block coupons test cast in sand molds bonded with no-bake resin, according to the ASTM designations. Before machining the Keel Blocks were heat treated according to the ASTM standards as following: solubilization, quenching and tempering. The effectiveness of the heat treatments and the results of the mechanical tests were evaluated by means of microstructural characterization using optical and scanning electron microscopies. The CA15 steel showed the presence of delta ferrite in the martensitic matrix, and a weak tendency to carbide precipitation. On the other hand, the CA6NM steel showed predominantly a martensitic structure and strong carbide precipitation. The effect of two quenching conditions, namely water and air, were investigated on the mechanical properties of CA15 and CA6NM steels and showed to be high significance. For both steels two distinct levels of tensile strength at room temperature were obtained, one inferior to 700MPa, and other superior around the 900MPa. In the CA15 grades were obtained higher values of area reduction and lower elongation values, when compared to the CA6NM grade. The tensile tests at higher temperature (500°C), led to a reduction of approximately 30% in the values of tensile strength for the CA15 steel. However, in the CA6NM steel, the reduction of the tensile strength was lower( less than 20%) due to presence of massive carbide precipitation. After impact tests at several temperatures for determination of the ductile-fragile transition temperature, according to the 20,6J criterion, the CA15 steel revealed a transition temperature beyond 10°C, while the CA6NM steel revealed values between -100 and -150°C. === A presente dissertacao, consiste no estudo das propriedades mecanicas, com base em ensaios de tracao e impacto de dois acos inoxidaveis martensiticos, fundidos sob designacoes da norma ASTM, o aco CA15, um aco com 12% de Cr e o aco CA6NM, um aco com 12% Cr, 4% Ni e 0,65% Mo. O trabalho atestou os dois acos CA15 e CA6NM, em condicoes equiparaveis de ensaios de tracao e impacto, a partir de corpos de prova tipo Keel Block fundidos em molde de areia aglomerada com resina, conforme as designacoes da norma ASTM. A efetividade dos tratamentos termicos e o resultado sob os ensaios mecanicos foram verificados por meio de ensaios de caracterizacao microestrutural: analise metalografica por microscopia otica e eletronica de varredura. No aco CA15 observou-se a predisposicao a obtencao de ferrita delta na matriz martensitica, e uma fraca tendencia a precipitacao de carbonetos. No aco CA6NM, tanto a microestrutura predominantemente martensitica, quanto a forte precipitacao de carbonetos, sao tracos marcantes. Os efeitos de dois meios de tempera: agua e ar, sob as propriedades mecanicas dos acos CA15 e CA6NM, foram investigados e se mostraram muito significativos. Para ambos os acos, duas classes de limites de resistencia a tracao em temperatura ambiente foram obtidas, uma inferior a 700MPa, e outra superior, em torno dos 900MPa. No aco CA15 obteve-se maiores valores de reducao de area e menores valores de alongamento, em comparacao com o CA6NM. Os ensaios de tracao a quente(500°C), revelaram uma reducao nos valores de limite de resistencia(em relacao ao obtido a temperatura ambiente), em torno dos 30% no aco CA15. Mas no aco CA6NM, a reducao do limite de resistencia atingiu valores baixos de ate 20%, devido a presenca massiva de carbonetos. Apos ensaio de impacto em diversas temperaturas, para determinacao da temperatura de transicao ductil-fragil segundo criterio 20,6J, o aco CA15 revelou temperaturas de transicao maiores que 10°C, enquanto que o CA6NM revelou valores de temperatura de transicao entre -100 e -150°C.
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