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.

In many industries, safe organic inhibitors that are soluble in corrosive media, environmentally friendly, and effective need to be developed for protection against corrosion during descaling and steel pickling in dilute acids. In this work we describe, for the first time, the effects of 2-(nitromethylene) oxazolidine (OXA) and 2-(nitromethylene) imidazolidine (IMD) as inhibitors of the corrosion of SAE 1020 steel in 0.1 mol L⁻¹ HCl aqueous solution. Electrochemical analyses showed that the IMD inhibitor was most effective, acting as a mixed type inhibitor. SEM analysis confirmed the electrochemical results, clearly showing the excellent corrosion inhibition effect of IMD. The corrosion inhibition was related to the protective film deposited on the surface, forming a layer that reduced the corrosion reactions. DFT calculations showed that donor and acceptor interactions between the heterocyclic nitrogen lone pair electrons and the vacant d orbitals of the metal surface atoms could explain the better corrosion inhibition values obtained for IMD. Finally, in addition to its efficiency, in silico toxicity predictions indicated that IMD could be considered environmentally friendly.

One of the main ways to protect steel against corrosion is by the galvanizing process. This process has been continuously developed and its first optimization was performed by the addition of Aluminum in the coating. As a result, Zn-5wt.%Al and 55wt.%Al-Zn coatings were developed. Recently, the search for increased corrosion resistance led to the development of zinc coating with the addition of magnesium and aluminum. In this work, a comparative study of the corrosion resistance of zinc coated steel and Zn-2wt.%Al-1wt.%Mg alloy coated steel was performed. Samples were exposed to immersion corrosion tests in 0.1 M NaCl electrolyte and were analyzed by using SEM, XDR and EIS. On zinc-coated steel, the steel substrate was attacked after 48 days of immersion, while on Zn-2wt.%Al-1wt.%Mg coated steel, the steel substrate showed corrosive process after 90-day of immersion. The corrosion product formed from Zn-2wt.%Al-1wt.%Mg coated steel is the main cause of its better corrosion resistance compared to zinc coated steel.

The influences of temperature and chloride content on the corrosion resistance of stainless steels (SS) in acid solution were investigated employing polarisation curves (PC) and electrochemical impedance spectroscopy measurements. Although the duplex SS presented a higher pitting resistance equivalent number than that of 316L SS, the PC for the duplex SS in solution containing 250 ppm chloride ions showed a surprisingly large positive hysteresis loop, suggesting that there was damage to the passive film caused by localised intergranular corrosion at 120^oC. In contrast, it was interesting to note that the 316L SS immersed in an acid solution containing 250 ppm chloride did not exhibit pitting corrosion. The oxides naturally formed on both steels at open circuit potential at 120^oC had double layer structures and their thicknesses were obtained from constant phase element calculations.