Influence of welding parameters on pit initiation and pit growth in welded joints of X5CrNi18-10 stainless steel

Abstract

The influence of welding parameters on the resistance to pitting corrosion in welded joints of X5CrNi18-10 stainless steel was studied. Welding was performed by a TIG procedure in a shielding gas containing different amounts of nitrogen. The welding speed, the deposition rate of the filler wire, and the shielding gas flow rate were constant, which allowed the nitrogen content in the weld metal to be directly dependent on the nitrogen content in the shielding gas. It was shown that welding current and arc energy had a significantly lower influence on the resistance to pit formation and pit growth, than the nitrogen content in the shielding gas. Pitting corrosion testing was conducted using the potentiodynamic polarization method. The resistance to pit formation increases with the increase in nitrogen content in the weld metal, while the resistance to pit growth decreases. The microstructure of the weld metal becomes more homogeneous in the presence of nitrogen and the distribution of chromium more uniform, which leads to the increased resistance to pit formation. Also, due to the formation of ammonia ions, the pH value of the solution within the pit is higher than in the bulk solution, which also increases the resistance to pit formation.