Refusão superficial a laser de filme fino de nióbio em aço ABNT 1020: análise da taxa de corrosão

Abstract

Although ABNT 1020 steel is widely used in industry due to its excellent balance of low cost, good toughness, and machinability, it has low corrosion resistance, requiring surface treatments to extend its service life in environments such as: marine atmospheres, saline solutions, and humid industrial settings. In this work, the effects of a hybrid treatment—deposition of a niobium (Nb) thin film via Plasma Magnetron Sputtering (PMS) followed by laser surface remelting—on the corrosion resistance of this steel were evaluated. To promote the metallurgical incorporation of the coating into the substrate, the samples were subjected to autogenous remelting with a ytterbium laser, evaluating different combinations of power (50% to 70%) and scanning speed (6 to 11 mm/min). The electrochemical behavior was analyzed in an aerated 3.5% NaCl solution through Open Circuit Potential (OCP) tests, linear polarization resistance, and Tafel extrapolation to obtain current density and corrosion rate, combined with microstructural characterization using optical microscopy. The results showed that all remelting parameters promoted a shift of the corrosion potential to more noble (anodic) values and significantly reduced the corrosion currents compared to the pure base metal. The treatment performed with 50% power (750 W) and a speed of 11 mm/min showed the best performance, resulting in a 98.5% reduction in the corrosion rate. It is concluded that the laser remelting process was highly effective in consolidating the niobium film, promoting the formation of a homogeneous remelted layer that acts as an excellent protective barrier for carbon steel. Consequently, the material exhibits high hot and cold formability, excellent machinability, and great weldability, properties that justify its widespread application in the manufacturing of gears, shafts, pins, screws, and various structural components.