Effect of environmental condition on corrosion susceptibility of GTA welded AISI 202 austenitic stainless steel

Abstract

Austenitic stainless steels with low nickel content or nickel-free content are currently considered structural materials for nuclear fusion reactor applications. Even though the base metal achieves excellent performance, welding may result in premature failures due to morphological and compositional heterogeneities. The presence of pollutants in the environment results in environmental acidification, which influences the corrosion susceptibility of the weldment. This paper it is aimed to examine the influence of the gas tungsten arc welding (GTAW) process on localized corrosion and the degree of sensitization (DOS) of AISI 202 austenitic stainless steel (ASS) butt joints in three distinct regions: base-zone (BZ), heat-affected zone (HAZ), and weld-zone (WZ) in 3.5% NaCl under pH-5 environmental conditions. The localized corrosion behavior of the weldment was studied using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and degree of sensitization (DOS) using the double loop electro-chemical potentiokinetic reactivation (DL-EPR) technique. Optical microscopy (OM) is used to understand the microstructural features of weldments and pit morphologies before and after polarisation studies. The present study establishes that the heat-affected zone (HAZ) has low corrosion resistance, high DOS%, and low intergranular corrosion (IGC) resistance compared to the base and weld zones. This could be due to the thermal cycles involved in HAZ during welding, resulting in chromium depletion and the formation of chromium carbide precipitation.