Effects of Sensitization on Corrosion Fatigue Crack Growth Behavior of 316NG Austenitic Stainless Steel

In order to investigate the fatigue crack growth behavior of 316 NG austenitic stainless steel unsensitized and sensitized at 725℃,corrosion fatigue crack growth tests were conducted in simulated corrosion environments.SEM and OM were used to observe the microstructure and crack growth paths of the specimen.EDS was also applied to analyze the chemical components of the segregation.The fatigue crack growth rates of the unsensitized specimen decreased from 2.21×10^-4 mm/cycle to 1.02×10^-4 mm/cycle for the specimen sensitized by 10 minutes,which means that the fatigue cracking in the corrosion environment has been remarkably restrained by the sensitization.Being sensitized,the amount of segregation particle and branch crack increase,which results in the reduction of the crack growth rates.However,the sensitizing heat treatment can increase the Cr element content in segregation particles,lead to chromium-depleted zone being formed in the vicinity of particles,electrochemical corrosion being intensified,and crack propagation being enhanced.