Correlation between the degree of sensitization and stress corrosion cracking susceptibility of type 304H stainless steel

Austenitic stainless steel 304H is extensively used in the super heater tubes of power boiler due to its superior mechanical properties at elevated temperatures. However, its relatively high carbon content increases the susceptibility to sensitization and subsequent stress corrosion cracking.This work is concerned with investigation of the sensitization and stress corrosion cracking (SCC) of austenitic stainless steel grade 304H. Electrochemical potentiokinetic reactivation (EPR) test was used to evaluate the degrees of sensitization (DOS) of the studied alloy at various temperatures and periods of time. DOS increased with increasing sensitization time and temperature. This was confirmed by microstructure examination after EPR test. Boiling magnesium chloride (MgCl2) test was used to evaluate the susceptibility of 404H stainless steel to stress corrosion cracking. DOS and test stress level had negative effects on time to failure in boiling MgCl2. The correlation between DOS and SCC was also discussed.