Facultad Regional San Nicolas
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Item Sensibilización y Corrosión en AISI 316L(Secretaría de Investigación, Facultad de Ingeniería, Universidad Nacional de Lomas de Zamora., 2024-07-30) Inés, Mariano Nicolás; Mansilla, Graciela AnalíaEste trabajo estudia la corrosión acelerada de acero inoxidable AISI 316L bajo exposición a una atmósfera salina durante 96h. Previamente, las muestras fueron solubilizadas a 1100°C durante 1h y luego enfriadas en agua o aire, seguidas de una sensibilización isotérmica a 650°C durante 6h. El análisis microestructural, mediante microscopía óptica y electrónica de barrido, reveló ataques severos en los bordes de grano austeníticos, atribuidos a la precipitación de distintos tipos de carburos de cromo y fases intermetálicas, como lo confirmó la difracción de rayos X. Los ensayos de corrosión indicaron que la muestra enfriada en aire presentó una mayor tasa de degradación y pérdida de masa, con un avance significativo de la corrosión intergranular, en comparación con la muestra enfriada en agua. Estos hallazgos destacan la influencia de los tratamientos térmicos sobre la susceptibilidad a la corrosión localizada.Item Hydrogen incidence on tensile strength behavior of AISI 316L stainless steel(2022-05-13) Inés, Mariano Nicolás; Mansilla, Graciela AnalíaMost paper in literature are devoted on the effect caused by chromium carbides on the tensile behavior of stainless steels, for example, it is known that the precipitation of M23C6, M6C and Sigma Phase are harmful under certain operative conditions, although there are only few papers related with hydrogen embrittlement in type 316L stainless steels. Even though hydrogen slightly modifies the mechanical behavior of these stainless steels, it should be considered to avoid significant economic losses. The aim of this work is to evaluate the effect on mechanical response of hydrogen charged AISI 316L stainless steel samples. To achieve homogeneous carbides precipitation, specific thermal treatments were conducted on as-received samples. Then three sets of samples were considered to carry out tensile tests. Before that, a group of heat-treated samples were hydrogen charged, in a 1N H2SO4 electrolytic solution with 0.25 g/L NaAsO2 as hydrogen promoter agent, using graphite anode and a constant current density of 35 mA/cm2 for 3.5 h. After tensile tests, the resulting fracture surfaces exhibited mixed ductile-brittle behavior in hydrogen charged samples in comparison with the ductile morphology obtained in uncharged ones. In addition, in hydrogenated samples cracks were found associated with fine chromium carbides, while ductile well-developed dimples were found in uncharged samples. In coincidence, there was a ductility loss in electrolytic hydrogen charged samples, which was not observed in those uncharged ones. In order to identify hydrogen - carbides interactions, a selective metallographic technique made it possible to find grain boundaries and carbides/matrix interfaces as the main hydrogen traps. Furthermore, differential scanning calorimetry (DSC) tests were performed to obtain hydrogen desorption temperatures. Results allowed to settle that those carbides developed during thermal treatments are responsible for deleterious hydrogen trapping that may cause mechanical failure on AISI 316L stainless steel.Item Incidence of heat treatment on the corrosive behavior of AISI 316L austenitic stainless steel(2023-06-30) Inés, Mariano Nicolás; Mansilla, Graciela AnalíaHeat treatments of AISI 316L samples were conducted at 900°C with slow cooling in air to induce varied precipitation of chromiumrich carbide particles at grain boundaries, resulting in a microstructure susceptible to intergranular corrosion. The corrosion behavior of the material in this state was investigated in a salt spray chamber containing 5% NaCl. The temperature inside the chamber was set at 35°C, while the saturated air temperature was recorded at 47°C. Samples were periodically extracted for observation and analysis using a stereoscopic magnifying glass, optical microscope, and scanning electron microscope. The results revealed the detrimental effect of chloride ions on the corrosion behavior of these stainless steels. Metallographic examination of corroded specimens after the salt spray test confirmed that the passive layer's breakdown was responsible for the intergranular corrosion occurring along preferential paths of chromium carbides.Item Salt spray test on AISI 316L stainless steel(2020-01-10) Inés, Mariano Nicolás; Mansilla, Graciela AnalíaDamage produced by rigorous working conditions can affect materials, especially when they are exposed to high temperatures, corrosive atmospheres and mechanical stresses. Austenitic stainless steels have variable chromium contents but greater than 16%, which allows the surface formation of a passivating thin layer of chromium oxide (Cr2O3) that protects the steel against corrosion during prolonged exposure to aggressive environments. From a metallurgical point of view, these steels meet the requirements to operate under prolonged exposures to high temperature and aggressive environments (depending on the steel grade), however attention must be paid to the precipitation of different carbides, such as M23C6 and M6C, and especially sigma () phase formation, since its precipitation produced chromium depleting zones which are very harmful in many applications, because it makes the material brittle and allows high corrosion penetration. Another consequence is sensitize hydrogen capture originated during corrosion. The aim of this work is to evaluate the corrosive behavior of an austenitic stainless steel (AISI 316L) that was first exposed to several heat treatments conditions and then was subjected to a spray saline solution of 5% NaCl, inside the chamber the temperature was set in 35ºC while the saturated air temperature was 47ºC. Characterization techniques such as optical and scanning electron microscopy were applied. Results allowed to establish the incidence on the corrosion rate of formed chromium carbides, that sensitize steel to the attack of chloride ions responsible of pitting corrosion by breaking of the passive layer thus helping a rapid corrosion rate.