EFFECT OF COMPOSITION ON CORROSION-RESISTANCE OF HIGH-ALLOY AUSTENITIC STAINLESS-STEEL WELD METALS

The corrosion resistance of stainless steel weld metal in the ranges o f 17 to 28% chromium (Cr), 6 to 60% nickel (Ni), 0 to 9% molybdenum (M o), and 0.0 to 0.37% nitrogen (N) was examined. Critical pitting tempe ratures were determined in ferric chloride (FeCl3). Passive film break down potentials were assessed from potentiodynamic scans in 3% sodium chloride (NaCl) at 50-degrees-C. Potentiodynamic and potentiostatic te sts were carried out in 30% sulfuric acid (H2SO4) at 25-degrees-C, whi ch was representative of chloride-free acid media of low redox potenti al. Metallographic examination and microanalysis were conducted on the test welds. Because of segregation of alloying elements, weld metal p itting resistance always was lower than that of matching composition b ase steel The difference increased with higher Cr, Mo, and N contents. Segregation also reduced resistance to general corrosion in H2SO4, bu t the effect relative to the base steel was less marked than with chlo ride pitting. Segregation of Cr, Mo, and N in fully austenitic deposit s decreased as the Ni(eq-)'Cr(eq)' ratio increased. Over the compositi onal range studied, weld metal pitting resistance was dependent mainly on Mo content and segregation. N had less effect than in wrought allo ys. Both Mo and N enhanced weld metal corrosion resistance in H2SO4.