Este es un artículo publicado en acceso (Open Access) abierto bajo la licencia Creative Commons Attribution NonCommercial, que permite su uso, distribución y reproducción en cualquier medio, sin restricciones siempre que sin fines comerciales y que el trabajo original sea debidamente citado. Resumen: Los aceros API X70 son aplicados en fabricación y construcción de tuberías para el transporte de hidrocarburos, sin embargo, a un lapso de tiempo se degradan debido al medio ambiente al cual están expuestos; influyendo en la velocidad y tipo de corrosión sobre las superficies del metal base (MB), zona afectada por el calor (ZAC) y zona de fusión (ZF). A fin de conocer y evaluar la susceptibilidad a la corrosión en uniones del acero API X70 sometido a diferentes medios corrosivos, varias pruebas se llevaron a cabo por el proceso de soldadura de doble arco sumergido (DSAW, por sus siglas en inglés), las cuales fueron inmersas en diferentes electrolitos: Cloruro de Sodio (NaCl al 3,5%) y Agua (H 2 O) a temperatura ambiente para conocer su comportamiento. Se utilizaron técnicas electroquímicas de ruido electroquímico (RE) y curvas de polarización cíclica (CPC) para obtener velocidad y tipo de corrosión producida en cada una de las muestras analizadas, incluyendo las tres zonas: MB, ZAC y ZF. Además, se utilizaron técnicas de caracterización como microscopía óptica (MO) y microscopía electrónica de barrido (MEB) para el análisis superficial. La mayoría de las soldaduras presentan corrosión mixta, con mayores velocidades de corrosión en 3,5% de NaCl. Palabras-clave:Corrosión; Técnicas electroquímicas; Soldadura de doble arco sumergido. Corrosion Behavior of API X70 Steel Welded for Process Double Submerged Arc Immersed in Different Corrosives EnvironmentsAbstract: The steels API X70 are applied in construction and fabrication of pipeline for transport of hydrocarbons, however, to lapse time are degrade due to environment to which are exposed, influencing on mode and corrosion rate on surface base metal (BM), heat zone affected (HAZ) and fusion zone (FZ). In order to know and evaluate the corrosion susceptibility in joints of API X70 steel submitted to different corrosives environment, several tests were carried out by process of double submerged arc welding (DSAW), which were immersed in different electrolytes: Sodium Chloride (3.5% NaCl) and Water (H 2 O) at room temperature for know its behavior. Electrochemical techniques were used of electrochemical noise (EN) and cyclic polarization curves (CPC) to obtain mode and corrosion rate produced for each of the samples analyzed, included the three zones: BM, HAZ and FZ. Further, characterization techniques were used such as optical microscopy (OM) and scanning electron microscopy (SEM) for superficial analysis. The welds' majoirity have a mixed corrosion, with higher corrosion rate in 3.5% NaCl. Key-words:Corrosion; Electrochemical techniques; Double submerged arc welding. IntroducciónActualmente en la industria del petróleo, el empleo de materiales que sean capaces de satis...
Hybrid welding is a process used in aeronautical materials to obtain benefits such as complete penetration, narrow heat affected zones, reduce filler material used, among others, mainly due the ability of the process to control filler-metal additions and heat input in materials such as steels, titanium and aluminum alloys. Recently a new industrial revolution is taken place called manufacturing 4.0, the aeronautical and automotive industry have a great interest in all the pillars which making it up, one of the principal pillars is the big data analysis such as welding parameters applied in advances welding processes. The present work describes a welding optimization applying non-dominated sorting genetic algorithm-III (NSGA-III) to find and predict depth penetration (DP) and mechanical properties, specifically ultimate tensile strength (UTS) in ASTM 1520 steel welded by a hybrid laser arc welding with the objective to improve the weld quality. A diverse experiment were used in order to obtain a suitable model, considering welding speed (WS), wire feed rate (WF), voltage (V), current (A) and laser power (P). The experimental results demonstrated that the pareto front values obtained by NSGA-III improve the DP and UTS. Microstructural phases and mechanical properties were discuss to complement the values obtained and chosen.
The present work presents a theoretical and experimental study regarding the microstructure, phase transformations and mechanical properties of advanced high-strength steels (AHSS) of third generation produced by thermal cycles similar than those used in a continuous annealing and galvanizing (CAG) process. The evolution of microstructure and phase transformations were discussed from the behavior of intercritical continuous cooling transformation diagrams calculated with the software JMatPro, and further characterization of the steel by scanning electron microscopy, optical microscopy and dilatometry. Mechanical properties were estimated with a mathematical model obtained as a function of the alloying elements concentrations by multiple linear regression, and then compared to the experimental mechanical properties determined by uniaxial tensile tests. It was found that AHSS of third generation can be obtained by thermal cycles simulating CAG lines through modifications in chemistry of a commercial AISI-1015 steel, having an ultimate tensile strength of UTS = 1020–1080 MPa and an elongation to fracture of Ef = 21.5–25.3%, and microstructures consisting of a mixture of ferrite phase, bainite microconstituent and retained austenite/martensite islands. The determination coefficient obtained by multiple linear regression for UTS and Ef was R2 = 0.94 and R2 = 0.84, respectively. In addition, the percentage error for UTS and Ef was 2.45–7.87% and 1.18–16.27%, respectively. Therefore, the proposed model can be used with a good approximation for the prediction of mechanical properties of low-alloyed AHSS.
In the present work, a Cr+Mo+Si low-alloyed low-carbon steel was fabricated at laboratory scale and processed to produce multiphase advanced high-strength steels (AHSS), under thermal cycles similar to those used in a continuous annealing and galvanizing process. Cold-rolled steel samples with a microstructure constituted of pearlite, bainite, and martensite in a matrix ferrite, were subjected to an intercritical annealing (817.5 °C, 15 s) and further isothermal bainitic treatment (IBT) to investigate the effects of time (30 s, 60 s, and 120 s) and temperature (425 °C, 450 °C, and 475 °C) on the resulting microstructure and mechanical properties. Results of an in situ phase transformation analysis show that annealing in the two-phase region leads to a microstructure of ferrite + austenite; the latter transforms, on cooling to IBT, to pro-eutectoid ferrite and bainite, and the austenite-to-bainite transformation advanced during IBT holding. On final cooling to room temperature, austenite transforms to martensite, but a small amount is also retained in the microstructure. Samples with the lowest temperature and largest IBT time resulted in the highest ultimate tensile strength/ductility ratio (1230.6 MPa-16.0%), which allows to classify the steel within the third generation of AHSS. The results were related to the presence of retained austenite with appropriate stability against mechanically induced martensitic transformation.
In this paper the effect of hybrid laser arc welding on longitudinal joints for pipes of 1.27cm thick is investigated. For the investigation, an API X70 steel was welded with the HLAW process and then subjected to tensile, bending and micro hardness tests under standards for pipe manufacturing. Images of the weld seams were taken to observe the structure and size of the weld zones. Analysis was made by light microscopy to determine the phases present in the weld zones and to observe if there is a variation of grain size in the weld zones that adversely affects the mechanical properties of the API X70 steel. Results show that the mechanical properties of the joints meet the requirements for their use in pipe manufacturing; one reason is the low thickness of the weld zone that barely affects the original properties of API X70 steel. Also the presence of bainite in the microstructure of weld zones provides resistance to the joints.
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