Evaluation of s355nl Steel Welded by Flux Cored Arc Welding Using Different Tubular Wires

High strength low alloy (HSLA) steels are used in several industrial sectors, as they have good mechanical strength and easy weldability. This HSLA is present in several areas, such as naval, petrochemical, piping, and civil construction. S355 NL steel is HSLA grade and has its application in the manufacture of the Brazilian submarine. For the manufacture and finishing of a Brazilian submarine, countless welds are performed during the assembly steps. The welding process currently applied is FCAW (Flux Cored Arc Welding), and the currently applied filler metal is of French origin. However, this import, from France to Brazil, makes manufacturing costs high and the waiting time for the imported product to arrive is long. Thus, in this work, the idea was to characterize a national filler metal (Brazilian) that similarly maintained the microstructure and consequently its mechanical and electrochemical properties concerning the imported filler metal (French). Therefore, the present work aimed at the microstructural, mechanical, and electrochemical characterization of S355NL structural steel welded by the FCAW process with national tubular wire (Brazilian) and imported tubular wire (French). We performed microstructural characterization with the aid of optical microscopy (OM) and scanning electron microscopy (SEM). For the mechanical characterization, we performed the following tests: tensile test, Vickers hardness, and impact at room temperature and -40ºC. In the electrochemical characterization, it generated polarization curves where the samples were exposed to a 3.5% NaCl solution to test the behavior in corrosive media. The results showed that the wires, national and imported, behaved homogeneously and uniformly concerning the mechanical properties. In the electrochemical part, the national material presented in the weld metal a corrosion current density interesting. Therefore, the national tubular wire is a promising filler metal for the welding application of this Brazilian submarine

Study of the properties of anodic oxide films grown in different acid electrolytes on the biomaterial Ti-50Zr at.%

Studies on the influence of the nature of the growth electrolyte on the properties of oxide films grown on the Ti-50Zr at.% alloy were carried out. The results obtained through the different measurements done (chronoamperometry, open circuit potentials, and reconstruction rates) showed that phosphate incorporation into the matrix of oxide films grown in H3PO4 make them unstable, bringing a greater dissolution compared to the ones grown in CH3SO3H, H2SO4, and HNO3. The electrochemical impedance spectroscopy measurements showed that the phosphate incorporation into the oxide films grown on the Ti-50Zr at.% alloy by different methods and thickenesses lead to high values of electrical resistance when compared with the ones of films grown in CH3SO3H, H2SO4, and HNO3. The nature of the growth electrolyte was observed to also affect the semiconducting properties of the different oxide films grown on the alloy, leading to different voltammetric profiles of these films when illuminated with radiation of energy greater than that of the band gap. The studies on the effect of the exchange of the electrolyte solution in the galvanostatic growth of anodic films in two steps showed that the breakdown potentials are dependent on the nature of the electrolyte. On the other hand, these measurements also revealed that the initial electrical breakdown of the film or the nature of the electrolyte in which it was initially grown do not alter the film growth kinetics during the second step, carried out in another electrolyte.Universidade Federal de Minas GeraisForam realizados estudos da influência da natureza do eletrólito de crescimento nas propriedades de filmes de óxido crescidos sobre a liga Ti-50Zr at.%. Os resultados obtidos por meio das diferentes medidas realizadas (cronoamperometria, potencial de circuito aberto e taxas de reconstrução) mostraram que a incorporação de fosfato na matriz dos filmes de óxido crescidos em H3PO4 provoca instabilidade dos mesmos, fazendo com que haja maior dissolução em relação aos crescidos em CH3SO3H, H2SO4 e HNO3. As medidas de espectroscopia de impedância eletroquímica mostraram que a incorporação de fosfato na matriz dos filmes de óxido crescidos sobre a liga Ti- 50Zr at.% por diferentes métodos e espessuras proporciona elevados valores de resistência elétrica quando comparados com os de filmes crescidos em CH3SO3H, H2SO4 e HNO3. Foi observado que a natureza do eletrólito de crescimento afeta também as propriedades semicondutoras dos diferentes filmes de óxido crescidos sobre a liga, proporcionando diferentes perfis voltamétricos destes filmes quando iluminados com radiação de energia maior que a da banda proibida. Os estudos do efeito da troca da solução eletrolítica no crescimento por via galvanostática de filmes anódicos em duas etapas mostraram que os potenciais de ruptura são dependentes da natureza do eletrólito. Por outro lado, estas medidas também revelaram que a ruptura elétrica inicial do filme de óxido ou a natureza do eletrólito em que ele foi inicialmente crescido não alteraram a cinética de crescimento durante a segunda etapa, feita em um outro eletrólito

Construction of a cell-autoclave for electrochemical measurements at high temperatures

Measurements at high temperature using liquid solutions require special cells and materials which are able to support the temperature and pressure developed inside. The constructed cell was designed to support pressures up to 20 bar, temperatures relatively high up to around 200 ºC, depending on the pressure developed inside the system. It also supports aggressive solutions since its inner wall is made of Teflon. The electrolyte has no contact with the metallic body of the cell. Then, it is supposed that this work represents a great contribution to the electrochemical studies of materials in solutions at high pressure and temperatur

Microstructural, Mechanical, and Electrochemical Analysis of Duplex and Superduplex Stainless Steels Welded with the Autogenous TIG Process Using Different Heat Input

Duplex Stainless Steels (DSS) and Superduplex Stainless Steels (SDSS) have a strong appeal in the petrochemical industry. These steels have excellent properties, such as corrosion resistance and good toughness besides good weldability. Welding techniques take into account the loss of alloying elements during the process, so this loss is usually compensated by the addition of a filler metal rich in alloying elements. A possible problem would be during the welding of these materials in adverse conditions in service, where the operator could have difficulties in welding with the filler metal. Therefore, in this work, two DSS and one SDSS were welded, by autogenous Tungsten Inert Gas (TIG), i.e., without addition of a filler metal, by three different heat inputs. After welding, microstructural, mechanical, and electrochemical analysis was performed. The microstructures were characterized for each welding condition, with the aid of optical microscopy (OM). Vickers hardness, Charpy-V, and cyclic polarization tests were also performed. After the electrochemical tests, the samples were analyzed by scanning electron microscopy (SEM). The SDSS welded with high heat input kept the balance of the austenite and ferrite, and toughness above the limit value. The hardness values remain constant in the weld regions and SDSS is the most resistant to corrosion