Simulação física da ZTA de aços inoxidáveis lean duplex 2101 e 2404 em sistema Gleeble®: evolução microestrutural e resistência à corrosão

Abstract

In this study, physical simulations of welding thermal cycles were performed to evaluate the microstructural evolution and corrosion resistance of the heat-affected zones (ZTAs) of lean duplex stainless steels (LDSSs) 2101 and 2404 using the Gleeble® thermomechanical system. The simulations were performed under two conditions: i) peak temperature of 1350 °C, dwell time of 3 seconds, cooling rates of 200, 100, 50, 20 and 10 °C/s up to 800 °C and subsequent cooling to room temperature; and ii) peak temperature of 1050 °C, dwell time of 120 seconds and cooling rates of 5 and 1 °C/s with cooling to room temperature. The results obtained show that the cooling rates of 200 to 10 °C/s caused microstructural changes with the formation of different austenite morphologies, while for the rates of 5 and 1 °C/s the microstructures were composed of ferrite and austenite phases. The cooling rates of 200 and 100 °C/s were the conditions where both materials showed the highest presence of Cr nitrides and carbides. Although the precipitation of deleterious phases occurred, the degree of Cr depletion remained below 1%, except for the 200 °C/s cooling rate of LDSS 2404. For LDSS 2101, the resistance to pitting corrosion was lower, with a narrow passive range, while LDSS 2404 showed resistance to pitting corrosion with a passive range greater than 1000 mVAg/AgCl. The results obtained for both materials showed that the precipitation of Cr nitrides and carbides did not cause significant changes in the localized corrosion behavior.