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PEREIRA, JOÃO M.B. ; PACHECO, CLARA JOHANNA ; ARENAS, MONICA P. ; ARAUJO, JEFFERSON F.D.F. ; PEREIRA, GABRIELA R. ; BRUNO, ANTONIO C. (2017).
Resumo: We have built a scanning dc-susceptometer for magnetic characterization of millimeter-scale samples. Using samples with few millimeter-thick slabs, the setup used is able to apply perpendicularly to the sample uniform dc magnetic fields up to 500 mT. It has a scanning range of 100 mm × 100 mm with micrometer resolution. In the present configuration, the dc-susceptometer is equipped with a pair of commercial Hall effect sensors forming an axial gradiometer. The measured output noise at 6.0 Hz is about 1.0 µTrms/√Hz in an unshielded environment and the magnetic moment sensitivity is 8.8 × 10−11 Am2. In particular, we used it to characterize heat-resistant steels, used as radiant tubes in steam reformer furnaces. We measured the cross-section of tube samples with progressing states of aging from as-cast to state VI. Measuring their susceptibilities, we detected a ferromagnetic layer at the external tube wall on aged samples. We were able to establish a relation between the magnetic response and the microstructural change of the steel.
DAS CHAGAS ALMEIDA, TATIANA; BANDEIRA, MERLIN CRISTINA ELAINE ; MOREIRA, ROGACIANO MAIA ; MATTOS, OSCAR ROSA. (2017).
Resumo: CO2 corrosion is an important process affecting oil and gas industries. Understanding the role of CO2 in the mechanism of carbon steel dissolution may contribute to better predict corrosion rate. Impedance, local pH and weight loss tests were measured using X65 carbon steel at pH 4 in the presence and absence of CO2, including high CO2 pressure experimental conditions. The results did not evidence a direct reaction of CO2 on the free iron surface.
DILLE, J ; Areiza, M.C.L. ; TAVARES, S.S.M. ; Pereira, G.R. ; DE ALMEIDA, L.H. ; Rebello, J.M.A. (2017).
Resumo: Duplex stainless steels are high strength and corrosion resistant alloys extensively used in chemical and petrochemical industries. However, exposition to temperatures in the range 300–1000 °C leads to precipitation of different phases having a detrimental effect on the mechanical properties and on the corrosion resistance of the alloy. In this work, the microstructural evolution during aging of a UNS S32304 lean duplex stainless steel was investigated by scanning electron microscopy, transmission electron microscopy and magnetic force microscopy. Formation of secondary austenite as well as Cr2N and Cr23C6 precipitation and, consequently, a decrease of ferrite volume fraction were observed. EDX analysis indicated that secondary austenite is depleted in chromium which is detrimental to the corrosion resistance of the alloy. A variation of magnetic properties and Eddy current measurement parameters during aging was simultaneously detected and can be explained by the decrease of ferrite volume content. Therefore, Eddy current non-destructive testing can be successfully applied to detect the formation of deleterious phases during aging.
DA ROCHA, ELISA PINTO ; HOSKEN, CAMILA MARTINS ; da Cunha Rocha, Adriana ; da Rocha Santos, Andrea Pedroza ; DE CASTRO, JOSE ADILSON. (2017).
Resumo: Aiming to reducing the gas emissions in the steel mill, in the present study the kinetic behavior of self-reducing pellets containing elephant grass coal and iron ore was investigated through kinetic isotherms for different temperatures. The pellets were isothermally treated in different time intervals for X-Ray diffraction and SEM analyzes. The results obtained by XRD showed that the higher mass of iron in the sample was achieved until the first 24 min. The SEM analysis allowed visualizing the presence of a metallic porous structure closer to edge and whiskers in the center of sample.
de Assis, Kioshy S. ; LAGE, MARCELLA ARAUJO ; GUTTEMBERG, GERALDO ; DOS SANTOS, FABRÍCIO PINHEIRO ; Mattos, Oscar R. (2017).
Resumo: Fracture mechanics concepts applied to tests in aggressive environments are a challenge for integrity analysis. Specifically about hydrogen, the concentration of this element in defects or in trapping sites can cause unexpected failure. The present paper presents results showing the influence of hydrogen in the reduction of fracture toughness and a discussion about how to deal with it in high strength alloys. The results show that the hydrogen reduces the plasticity and consequently the applications of CTOD concepts are questionable for the studied materials.
