Browsing by Author "Goldenstein, Helio"
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Item Effects of different cooling rates on the microstructure, crystallographic features, and hydrogen induced cracking of API X80 pipeline steel(2021) Ramirez, Mario F.G.; Hernández, José W.C.; Ladino, Duberney H.; Masoumi, Mohammad; Goldenstein, HelioHydrogen-Induced Cracking (HIC) is a primary failure mechanism of pipeline-welded joints in the absence of external loading in the oil and gas exploration industries. Three different cooling rates after austenitization were used to simulate in the laboratory different regions of the heat-affected zone (HAZ) formed when welding an API X80 pipeline steel specially designed to enhance the HIC resistance. The samples were characterized with regard to microstructure and crystallography as well as HIC resistance. The HIC resistance test used NACE TM0284-2011 methodology. The microstructure and its homogeneity varied as a function of cooling rates. Samples containing inclusions and segregation zone from the segregation bands of specimens showed reduced HIC resistance, while specimens containing only acicular ferrite and granular bainite coupled with the absence of segregation zone showed significant improvement in HIC resistance. The best HIC resistance results came from samples presenting fine acicular ferrite consisting of fine interlocking plates, with divergent crystallographic orientations, preventing the formation of localized strain distribution inside the grain and at grain boundaries. It was also found that a large proportion of medium-angle boundaries prevent microcrack initiation and the transgranular mode of crack propagation.Item Electrochemical characterization of 13Cr low-carbon martensitic stainless steel - Corrosion study with a mini-cell setup(2022-11) Calderón Hernández, José Wilmar; González Ramírez, Mario Fernando; Sepulveda Castaño, Jorge Mauricio; Santos Martines, Juan David; Quispe Avilés, Janeth Marlene; Magnabosco, Rodrigo; Goldenstein, Helio13Cr low-carbon martensitic stainless steels also known as supermartensitic stainless steels (SMSS) have superior properties than conventional martensitic stainless steels. The SMSS have better weldability and corrosion resistance. Nevertheless, corrosion resistance depends on phases transformations which are induced generally by heat treatments. In this work, the electrochemical properties of a SMSS were evaluated as a function of the tempering temperature (400 °C–700 °C). The susceptibility to intergranular corrosion was determined throught the degree of sensitization (DOS) using the Double Loop - Electrochemical Potentiokinetic Reactivation technique (DL-EPR) in a conventional three electrodes corrosion cell. On the other hand, the pitting susceptibility was evaluated by potentiodynamic polarization using a homemade corrosion mini-cell (based on a sessile electrolyte droplet), thus avoiding crevice problems typically seen with conventional arrangements. Imaging the microstructure with SEM, XRD analysis and thermodynamic and kinetic simulations were performed to understand the microstructural transformations and their relationship with corrosion resistance. The most severe sensitization occurs at the temperature where reversed austenite transformation is highest.