Banca de QUALIFICAÇÃO: WILLIAM CONSTANTINO DA SILVA

Cladding Welding of C-Mn stainless steel 309L and Inconel 625 alloys deposited by GMAW processes: operational and metallurgical aspects

GMAW, cladding, dilution, partially mixed zones (PMZ), microhardness.

Chromium and nickel-based alloys are widely used in the surface protection of equipment and mechanical parts in the most varied sectors as oil, pharmaceutical, food and power generation industries. All this demand is due to the mechanical, metallurgical and corrosion resistance properties observed in parts coated using filler metals that have anti-corrosion properties, usually deposited on substrates of structural steels. In order to evaluate aspects related to the operability in the cladding processes (geometry, dilution, efficiency and productivity of the process/filler metal), as well to correlate these aspects to the mechanical-metallurgical properties of the parts (microhardness, microconstituents and microstructure), the present study started from an experimental matrix with GMAW processes,with two metallic transfer modes (conventional and pulsed) and two filler metals (Inox 309L and Inconel 625), totaling a universe of 72 specimens, already taking into account the reproducibility and reliability aspects of the tests, in order to avoid/minimize deviations and provide safety in the results demonstration. All of these variables aimed at choosing an appropriate process/material aiming at its application as cladding in industrial parts. For the cladding process, the ratio between the welding speed (Ws) and the feed speed (Fs) was kept constant: k (Ws / Fs) = 20. So that when establishing this parameter, in the preliminary welding procedures, variations in the welding speeds were tested and proportionally compensated with the feed speed, so that the matching in the welding energies (Uw) was maintained and, consequently, the comparison between different processes and materials would make viable and metallurgically acceptable. In the initial stage a preliminary survey of the potential suitable metal transfer processes/modes was carried out, as well as the welding parameters that best suited each case (filler metal/welding/metal transfer). In the preliminary tests in simple deposition on plates, only the best result within a given control factor was selected, in order to make possible its subsequent coating test with the overlapping of passes in linear displacement (monolayer coating), with the overlap of layers (multilayer coating) and, finally, depositions with torch movement. All this framework of techniques, processes and materials in the deposition of welded coatings, aims to subsidize and, through the analysis of its results, converge to a parameter called “optimal”, in a reduced number of welding coating experiments carried out. The parts claded in the preliminary testing stage were evaluated based on their visual characteristics, weld bead geometry and dilution. Concerning the claddings obtained by welding, in addition to the visual aspects, geometric characteristics and dilution, metallurgical characteristics were also evaluated by optical microscopy (OM), field emission gun scanning electron microscopy (FEG-SEM), and energy dispersive spectroscopy (EDS). In order to measure mechanical properties, microhardness and corrosion resistance tests were carried out according to the ASTM G-48 standard. Regarding the results, these are in the survey and investigation stage