In addition to electromagnetic attraction between the arcs in Tandem Pulsed gas metal arc welding (GMAW), arc interruptions, mostly in the trailing arc at low mean current levels, may also occur, which is a phenomenon not widely discussed in the welding field. These arc interruptions must be avoided, since they also represent interruptions in metal fusion and deposition during the welding process, leading to lack of fusion/penetration and/or deposition flaws, adding cost for repairing operations. To improve the understanding on arc interruptions in Tandem Pulsed GMAW and how the current pulsing synchronism between the arcs relates to this phenomenon, this work proposes to evaluate the influence of parameters of adjacent arcs (Tandem Pulsed GMAW) and also of a single arc (GTAW—gas tungsten arc welding), but similarly subjected to magnetic deflection, on the occurrence of arc interruptions/extinctions. High-speed filming was used to help understand the interruption/extinction mechanism. In the case of Tandem Pulsed GMAW, the pulses of current of the leading and trailing arcs need to be almost-in-phase to prevent interruptions in the trailing arc. The distance of 10 mm between the adjacent arcs helped reduce the incidence of trailing arc interruptions, yet keeping a sound weld visual quality. In the case of GTAW, the higher the electrical current flowing through the arcs and the shorter their lengths, the more they resist to the extinction. The trailing arc interruptions in Tandem Pulsed GMAW seem to be determined by the deflection and heat in this arc, and their prevention can be achieved by a balance between these two factors, which is reached by synchronized pulsing currents.

This study investigates the microstructure and tribological behavior of Inconel 625 overlays applied via GMAW (Gas Metal Arc Welding) with and without a 316LSi stainless-steel intermediate layer on top of A36 steel. The microstructural characterization was conducted via FESEM with EDS. The tribological behavior was evaluated using a tribometer in a reciprocating configuration. The results showed that the wear rate of the Inconel 625 weld overlay with the 316LSi intermediate layer was higher than without it. However, no variations were observed in terms of hardness and the friction coefficient of the Inconel 625 weld overlays. The difference in the behavior of the two coatings was justified due to the microstructure morphology found in each case and chemical composition. When applied without the intermediate layer, Inconel 625 coating’s structure was dendritic, whereas it was cellular otherwise. An increase in the amount of Nb was observed in the layer deposited over 316LSi. This rise likely led to an increase in the number of precipitates and/or Laves phase formation. Thus, the results indicated that the difference in thermal conductivity and dilution between the stainless and carbon steels modifies the morphology of the microstructure of the Inconel 625 weld overlay, decreasing wear resistance when deposited on top of the stainless steel.

Ferritic stainless steels are not characterized by good weldability. Wires made of austenitic stainless steels are usually applied to join ferritic materials because of the good mechanical resistance, tenacity, and ductility reached by austenitic weld metal. However, novel ferritic stainless steel wires, stabilized with niobium and titanium, have been developed to tackle the target of matching the required mechanical properties and keeping the costs lower by using ferritic stainless steels. The characterization of these wires concerning weldability aspects (operational and metallurgical) has not been accomplished yet. The aim of the present study was to investigate the influence of the shielding gas composition (pure argon and mixtures with O₂ or CO₂) on the chemical composition and microstructure of weld deposits obtained with gas metal arc welding using stabilized ferritic wires (ER430Ti and ER430LNb). The study was made comparatively to a non-stabilized wire (ER430). For each combination gas/wire, three layers of beads were deposited. To prevent interference from base metal dilution, a UNS 43932 was used as support for the layers and only the last layer was analysed. A special experimental approach was applied to permit more reliable comparison among different combinations of wire-shielding gas. Predicted equations for the demanded level of stabilizers in the wire were successfully applied. The results showed that the shielding gas composition played an important role in determining the final chemical composition and microstructure of the deposits, but its effect was dependent on the chemical composition of the deposit as a rule. In general, it was confirmed that the increase in CO₂ in the shielding gas augmented the carbon content (and martensite formation) in the weld metal, but wire stabilized with niobium could prevent this detrimental effect but was not able to arrest grain coarsening. There were always losses of alloying elements due to the presence of O₂/CO₂, but the intensity depended on the amount of titanium/niobium.

Friction, wear, and corrosion of engineering components operating in harsh environments can be substantially improved by applying hard, corrosion-resistant coatings to prolong their useful lives. Nickel superalloys are particularly relevant due to their excellent mechanical properties and corrosion resistance at elevated temperatures. Among the various coating techniques, arc welding processes are suitable due to their good deposition rate and reliability. This work aimed to evaluate the effect of the shielding gas and after-deposition heat treatment on the microstructure and mechanical properties of Inconel 625 coatings deposited by the GMAW process. The coatings were deposited onto carbon steel plates using two mixtures of shielding gases (Ar+25%CO₂ and Ar+25%He) without interpass temperature control. The specimens were analyzed both as welded and after heat treatment (heating for 1 h at 1000 °C and air cooling) using Vickers hardness tests, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), and wavelength dispersion spectrometry (WDS). The coatings that used Ar+25%He-shielding gas were harder and showed more precipitate formation, which was associated with the higher cooling rates involved. As for the heat treatment, it led to a reduction in the segregation of the alloying elements in the interdendritic region via diffusion and a reduction in surface hardness.

RESUMO Um novo tratamento térmico tem sido pesquisado recentemente, cuja denominação é têmpera e partição (T&P), com o intuito de criar aços com austenita estável em sua microestrutura. Inicialmente, esse tratamento foi realizado em aços de alto silício, não obstante, seu potencial alcança outros diversos materiais como os de baixa liga contendo níquel ou manganês. O mesmo consiste em realizar a têmpera entre temperaturas inicial (Ms) e final (Mf) da transformação martensítica, seguidos por um reaquecimento a um estágio isotérmico durante um certo período. Neste trabalho, foi realizado a T&P no aço SAE 4340, austenitizados a 870 °C durante 30 min, então temperado em polímero ao patamar de 240 °C e por fim, particionado em três tempos distintos: 10 s, 30 s, e 90 s. Ainda, foi feito a têmpera e revenimento (TR) no mesmo material para comparações entre as microestruturas e propriedades mecânicas, através de microscopia óptica, microscopia eletrônica de varredura, difração de raios-x (DRX), além de ensaios de microdureza Vickers. Observou-se uma microestrutura complexa nas amostras oriundas da T&P, diferentemente dos corpos de prova da TR. A partir do DRX, obteve-se indícios de que o tempo de 30 s para o processo de partição foi o mais efetivo em estabilizar a austenita retida. Soma-se a isso, a alta dureza alcançada, chegando ao nível de 696HV1.