Abstract
The corrosion resistance was examined of stainless steel weld metal covering the range 17-28%Cr, 6-60%Ni, 0-9%Mo and 0.037%N, comparison being made with base metal behaviour. Critical pitting temperatures were determined in ferric chloride, with assessment of passive film breakdown potentials from potentioynamic scans in 3%NaCl at 50°C. Potentiodynamic and potentiostatic tests were carried out in 30% sulphuric acid at 25°C as representative of chloride-free acid media of low redox potential. Metallographic examination and microanalysis were carried out on the test welds.
Because of segregation of alloying elements, weld metal pitting resistance was always lower than that of matching composition base steel, the difference increasing at higher Cr, Mo and N contents. Segregation also reduced resistance to general corrosion in sulphuric acid, but the effect relative to the base steel employed was less marked than with chloride pitting.
Segregation of Cr, Mo and N in fully austenitic deposits decreased as the Ni'eq/Cr'eq ratio increased. Over the compositional range studied, weld metal pitting resistance was dependent mainly on the Mo content and segregation, nitrogen having much less effect than in wrought alloys. Both Mo and nitrogen enhanced weld metal corrosion resistance in sulphuric acid.
