The corrosion resistance of laser-welded joints made of Ti and Nb stabilized B430LNT ultrapure ferritic stainless-steel sheets

The corrosion resistance of laser-welded joints in ultra-pure B430LNT ferritic stainless-steel sheets stabilized with titanium and niobium was investigated in this study. The pitting resistance of the welded joints was evaluated by conducting immersion and potentiodynamic polarization tests. The intergranular corrosion resistance was assessed by chemical acid etching tests and double-loop electrochemical potentiokinetic reactivation methods. The passive films on the surfaces of welded joints were analyzed by using electrochemical impedance spectroscopy tests. The results indicate that the microstructure of welded joints are as-welded, consists of large columnar and small equiaxed grains. Pitting corrosion occurs in the heat-affected zone and fusion zone, with the majority of pits in the heat-affected zone being parallel to the fusion line. The base metal demonstrates better resistance to intergranular corrosion compared to the fusion zone, and the stability of the passive films at the base metal is greater than that of the welded joint. The Ti and Nb in welded joints do not work as effectively as they do in the base metal. The high content of chromium in the metal matrix and absorption of nitrogen from the shielding gas promote the formation of chromium carbonitrides at grain boundaries, leading to the creation of chromium-depleted zones. The formation of Cr and Ti carbonitrides near the surfaces of welded joints decreases the stability of the passive films and promotes pitting corrosion. The various factors render the welded joint area susceptible to corrosion.