Navegando por Autor "Cardoso, Rogério Antão"

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Characterization of austenite decomposition in steels with different chemical concepts and high potential to manufacture seamed pipes for oil and gas industry.
(2019) Cardoso, Rogério Antão; Faria, Geraldo Lúcio de
This work presents the characterization of austenite decomposition kinetics in two steels during continuous cooling considering non-deformed austenite grains. Two different chemical concepts of steels were evaluated: low carbon - high manganese and a relatively new concept based on low carbon - low manganese - high niobium contents. Dilatometric experiments, microstructural characterization procedures and microhardness tests were carried out. Experimental and calculated CCT diagrams were plotted and the adapted JMAK model was applied aiming to predict the austenite decomposition kinetics. The low carbon - high manganese steel was the most sensitive to the applied cooling rates and, due to that, presented the higher grain refinement and hardness increasing after continuous cooling. These results highlight that the Mn content decreasing may promote a potential loss of grain refinement in procedures of continuous cooling where the structure recrystallization does not occur, as in some welding procedures or conventional heat treatments applied in the seamed pipe manufacturing process.
Development of an oxidation method for prior austenite grain boundary revelation.
(2018) Faria, Geraldo Lúcio de; Cardoso, Rogério Antão; Moreira, Paulo
The prior austenite grain size is a very important quantitative parameter which has a great influence on steel final microstructure and properties. Therefore, its measurement is a useful metallographic tool. To measure the austenitic grain size, it is necessary to reveal the prior austenitic grain boundaries by applying contrast methods. The technical literature reports many limitations to achieve satisfactory results using known methods that are, generally, susceptible to steel chemical composition and processing routes. In this context, this study proposed an oxidation method to reveal the prior austenite grain boundaries in different steel grades. This method was evaluated in the samples of AISI 4340 and AISI 1030 steels. Aiming to confirm the proposed technique efficiency, a parallel and classical method, based on picric acid etching, was applied to same steels. In the suggested oxidation method, the samples were mechanically ground, polished, and then austenitized in an argon atmosphere with low oxygen partial pressure. The obtained results confirm the success of the proposed method for both studied steels.