Corrosion Fatigue of Type 304 Stainless Steel and Inconel™ 600 in a Boiling (140 °C) Concentrated Caustic Solution

Corrosion fatigue crack growth rate tests using compact tension specimens of Type 304 stainless steel and smooth bar corrosion fatigue tests of Inconel Alloy 600 were run in boiling (140 °C) 17.5M NaOH solution. Contrary to earlier results from smooth bar Type 304 specimens, the measured crack growth rates of Type 304 did not show a high accelerative environmental effect; there was also no significant effect of cyclic frequency (0.1 to 10 Hz),R ratio, or electrochemical potential. For Inconel 600 the boiling caustic solution increased fatigue life relative to life in air, and anodic passivation was beneficial. Sensitization, found beneficial in sodium hydroxide, was detrimental in air in spite of similar failure morphologies. A delay of crack initiation is proposed as primarily responsible for the effects of the solution and sensitization.