Análise comparativa da resistência à corrosão e propriedades mecânicas de soldas dissimilares entre os aços 20MnMoNi55 e SA312 TP 316L soldadas com Inconel 600 e 690

Abstract

The present work evaluated the corrosion resistance and toughness of dissimilar welds welded with Inconel 600 and Inconel 690. For this study, thermal aging treatments were accomplished at a temperature of 800°C for a period of up to 24 hours. Under these conditions, microstructural characterizations were carried out by optical (OM) and scanning electron microscopy (SEM-EDS). The mechanical properties were evaluated by microhardness and impact toughness tests on the metallic joints, and verified among themselves under the indicated aging conditions. The evaluation of the corrosion resistance was performed using the cyclic potentiodynamic polarization technique. The results obtained show an increase of approximately 10% in the average HV Microhardness of the samples welded with Inconel 690 compared to those welded with Inconel 600. This is justfied by the presence of intermetallic phases such as γ″, carbides or even carbonitrides. On average, the toughness results obtained in samples welded with Inconel 690 were considerably lower than those welded with Inconel 600 due to the formation of intermetallic compounds harmful to toughness verified during the microstructural characterization of the weld metal. In addition, there was a sudden drop in the values of the average energy felt by the impact on the welded Inconel 690 aged for 24 hours. The corrosion resistance of samples welded with Inconel 690 was considerably higher than that of samples welded with Inconel 600 alloy consumable. This difference increased considerably with aging time. The tests and comparative analyzes carried out during this work, therefore, reveal an advantage of the filler metal Inconel 690 in relation to Inconel 600 in terms of corrosion resistance. On the other hand, this advantage is inverted when the focus is toughness. Therefore, for applications where resistance is the main mechanism responsible for introducing damage to nozzles and other components, such as the nozzles of pressurized water nuclear reactors, Inconel alloy 690 filler metal is considered the better option when compared to Inconel alloy 600, but is necessary to observe in the design the important losses of toughness involved in this choice.