Effect of environments, mechanical conditions, and materials characteristics on AE behavior during corrosion fatigue processes of austenitic stainless steel

Acoustic emission (AE) behavior during corrosion fatigue (CF) processes has been studied in a commercial grade 304 austenitic stainless steel with special attention to the effect of environments, mechanical conditions, and materials characteristics. CT specimens precracked were tested under cyclic tension-tension load, polarized potentiostatically in 0.5 kmol/m3 H2SO4 + 0.5 kmol/m3 NaCl or 0.5 kmol/m3 H2SO4 solutions at room temperature. Valuable AE signals discriminated from environmental and mechanical noises by source location were monitored at the loading phase near the maximum load. The experimental results showed that the AE activity observed in corrosive environments increased significantly with the acceleration of crack growth rates, compared with that observed in air (inert enviromment). Detailed SEM observations found cleavagelike cracking, intergranularlike cracking, separations, etc. on the crack surfaces. The AE sources which provided the high AE activity during CF crack growth were shown to be such microcracking processes as cleavagelike cracking, intergranularlike cracking, and separations caused by the cooperation of environments (intergranular corrosion or hydrogen), mechanical conditions (triaxial stress), and materials characteristics (non-metallic inclusions or carbides precipitated at grain boundaries by sensitization). The effect of these three factors on the AE behavior and cracking mechanisms is discussed in detail. (author)