Role of nitrogen shielding environment on microstructure and corrosion behavior of 2205 duplex stainless-steel A-GTA welds

Abstract

The present study aims to understand the role of the shielding environment viz., argon (Ar) and nitrogen (N2) on microstructure, general and pitting corrosion behavior of activated gas tungsten arc (A-GTA) welds of 2205 duplex stainless steel. A-GTA welds made with activated flux SiO2 along with 100% Ar and 95% Ar + 5 % N2 are compared with conventional gas tungsten arc (C-GTA) welds made with 100% Ar. All the metallographic specimens of C-GTA and A-GTA welds are recorded to observe the microstructural changes using an optical microscope connected with image analyser. The basic GillAC electro-chemical system is used to perform potentio-dynamic polarization studies for general and pitting corrosion behavior in a 1 M NaCl solution. From the present study, it is established that activated-GTA welds with SiO2 flux resulted in reduced weld width and enhanced depth of penetrationachieved in a single pass compared to C-GTA welds. The grain morphology of the weld zone (WZ) is observed to be a mixture of austenite and delta ferrite in all the weldments. Secondary austenite is found in the interior of the ferrite whereas at the interfaces of ferrite and primary austenite, various forms of primary austenite are noticed in the weld zone of A-GTA welds. From the corrosion studies, it is found that A-GTA welds made with 95% Ar + 5 % N2 show higher general and pitting corrosion resistance compared to C-GTA and A-GTA welds made with 100% Ar.Improved corrosion behavior may be due to the favourable microstructure and presence of nitrogen as shielding environment, which favors the formation of austenite in the ferrite matrix.