Corrosion fatigue of spot-welded austenitic stainless steels in 3.5% NaCl solution

Corrosion fatigue and fatigue properties of spot‐welded austenitic stainless steels EN 1.4301 and EN 1.4318 in 2B or 2F and 2H conditions were investigated in 3.5% sodium chloride (NaCl) solution and in air. The shear‐loaded specimens were single spot overlap joints. The effect of steel grade, load, frequency, temperature and type of chloride on fatigue strength of the 1.0 mm thick steel specimens was evaluated by using the Taguchi Method®. Increase of the load, rise of temperature and lowering of the frequency accelerate corrosion fatigue of the spot‐welded steel samples. Type of chloride had only a minor effect on fatigue strength. The 2B grade spot‐welded steel samples exhibited better fatigue strength than the 2H grade samples of the same steels. On the basis of the results obtained by the Taguchi Method® the S‐N curves were defined for the spot‐welded 1.9 mm thick steels in 3.5% sodium chloride solution at 50°C. For reference the fatigue experiments were performed in air at the ambient temperature. Comparison of the results shows that corrosive environment decreases remarkably the fatigue strength of the spot‐welded steels. The EN 1.4301 2H and EN 1.4318 2H steels have no distinctive difference in their corrosion fatigue strength even though they show a different fatigue behaviour in air. The microscopic investigations indicate that the fatigue cracks in the spot welds initiate from either side of the recrystallised area in the HAZ outside the spot‐weld nugget both in air and in the corrosive environments. Pre‐exposure in the corrosive environment seems to have no major influence on the crack initiation, because the cracks do not initiate at the heat‐tinted area of the crevice where the crevice corrosion occurs.