Microstructural assessment of ferrite-austenite ratio and its influence on corrosion and mechanical performance of DSS 2205 welds under H2S-rich real environment

Duplex stainless steels (DSS) are used in the oil and gas industry due to their excellent corrosion resistance. Nevertheless, their susceptibility to metallurgical changes during welding can compromise their performance in aggressive environments. The effect of heat input (QE) on the ferrite–austenite ratio, microstructural evolution, mechanical local behavior and corrosion performance of 2205 DSS welds was evaluated in this work. Welds were produced by Robotic Gas Metal Arc Welding (GMAW) with varying QE, and their behavior in a simulated H2S- rich service environment was assessed. The study revealed that higher QE increased the austenite fraction in the Weld Zone (WZ), while lower QE resulted in a higher ferrite content in the Heat-Affected Zone (HAZ) and WZ. Exposure to a corrosive environment involving synthetic seawater solution with H2S injection demonstrated that the pitting of the ferrite was the dominant degradation mechanism, particularly in the HAZ with high ferrite fractions (>70 % - low QE). Sulfide Stress Cracking was more severe in the welds with higher austenite content. Nanoindentation test indicated that variations in ferrite-austenite ratio influenced elastic modulus (E), plasticity index (ηP) and contact stiffness (S). Higher austenite content led to an improvement in the mechanical local behavior of WZ due to a low solidification rate, while the increase in ferrite in HAZ leads to a reduction in the plastic deformation capability. The findings highlight the significant impact of QE on the performance of DSS welds. Higher QE reduces the amount of ferrite in the HAZ, positively impacting corrosion and mechanical properties.