Corrosion fatigue and stress corrosion cracking of type 304 stainless steel in boiling NaOH solution

Results are reported for corrosion fatigue of Type 304 stainless steel in boiling (140 C) 17.5M NaOH (46 wt pct) solution. Specimens, of the smooth round bar type, were cycled sinusoidally at 1.0 Hz in tension-tension about mean stresses of 248 MPa (36 ksi) and 124 MPa (18 ksi). Both solution annealed and sensitized specimens cracked readily in a transgranular mode. Sensitization did not increase the environmental effect. The caustic solution drastically shortened cyclic life and eliminated the endurance limit observed in air. Cyclic stress was a more important variable than mean stress as the lower mean stress did not significantly improve life. Anodic passivation did not increase cyclic life as it did for constant load SCC. Comparison of the SCC tests results with those of corrosion fatigue indicates that cyclic stresses, even when confined to the elastic region, accelerate failure more than sustained loads in the plastic region; this accelerative effect was most intense under anodic passivation.