Evaluation microstructure and corrosion behavior of different keyhole TIG welded joints of duplex stainless steel grade 2205 pipe

Abstract

To analyze how the chemical composition and heat input influence the microstructure, mechanical properties, and corrosion resistance of the 2205 Duplex stainless steel (DSS) weld metal, different 2205 DSS pipeline weld joints were fabricated by the K-TIG welding process with and without 2209 filler metal. Subsequently, a comparative analysis on the microstructure evolution and corrosion behavior was systematically conducted. The result show that the microstructure of the weld metal (WM) in different welding joints primarily is consisted of the ferrite matrix, grain boundary austenite (GBA), widmänstten austenite (WA), and intergranular austenite (IGA). The cover weld of K-TIG-Wire joints contains a higher volume of austenite and predominantly IGA, compared to other joints. In addition, from EBSD observations, it was found that the grain size in the root weld of the K-TIG + Wire joint is slightly refined. Meanwhile, the low angle grain boundaries (LAGBs, 2°≤ θ ≤ 5°) increased from 0.02 to 0.24 in the root weld of the K-TIG + Wire joint when compare to that of WM in the K-TIG joint. Besides, the Vickers hardness of the cover weld metal (WM) in K-TIG + Wire joints is significantly higher than that of other specimens, attributed to higher alloy element and austenite phase content. Based on the results obtained from corrosion testing and the subsequent analysis of the corroded morphologies, the corrosion resistance of the samples can be ordered as follows: Cover WM of K-TIG + Wire > Root WM of K-TIG + Wire > WM of K-TIG. These results indicate that the higher alloy content of the filling wire and heat input of the multi-pass welding process exerts a significantly positive effect on the mechanical and corrosion properties of the 2205 DSS WM.