Influence of heat input on microstructure, hardness and pitting corrosion of weld metal in duplex stainless steel welded by keyhole-TIG

Abstract

The efficient and accurate welding technologies, including several high-energy density beam welding technologies, are generally used to weld mid-thick duplex stainless steel (DSS). However, there are still some unresolved welding problems, i.e. blowhole, excessive content of ferrite, and coarse columnar grain. Therefore, in the present paper, the keyhole gas tungsten arc (K-TIG) welding technique, a novel process, was used. The microstructural characterization, hardness and pitting corrosion of weld metal (WM) with different heat inputs were investigated in detail. The results show that weld defects in the welded joint could be effectively avoided by appropriate welding parameters. As the heat input is enhanced, Widmanstätten austenite (WA) content increases, while fine-grained intergranular austenite (IGA) content decreases. The hardness of austenite in WM is associated with solution nitrogen and dislocation proliferation caused by deformation. Besides, the PREN of ferrite in the same WM is lower than austenite. The variation of Epit in each WM could be neglected owing to the similar chemical composition. However, the corrosion rate of WM gradually increases with the enhancement of heat input. Meanwhile, the initiation and propagation of pits could be significantly affected by the precipitate Cr2N, PREN as well as Σ3 coincident site lattice (CSL) boundaries. Furthermore, fine-grained IGA could be beneficial to improve the stability and continuity of the passive film.