Variation of Slow Strain Rate Test Fracture Mode of Type 304L Stainless Steel in 288°C Water

Potentiostatic slow strain rate tests (SSRT) were performed to investigate the susceptibility to intergranular stress corrosion cracking (IGSCC) of type 304L (UNS S30403) stainless steel (SS) in 288°C water, focusing on corrosion potential and the degree of sensitization. The degree of sensitization was examined by means of metallographic observation, double-loop electrochemical potentiokinetic reactivation (DL-EPR) technique, and grain boundary analysis with a transmission electron microscope. The SSRT fracture mode changed from ductile → transgranular stress corrosion cracking (TGSCC) →TGSCC (granulated) → IGSCC, with increasing corrosion potential, water conductivity, and the electrochemical potentiokinetic reactivation (EPR) value. The IGSCC onset occurred at 375 mV vs standard hydrogen electrode (SHE) of corrosion potential for type 304L SS with the EPR value > 3%, but it did not occur when the EPR value < 1%. Even though the microstructure exhibited a step structure, slight chromium depletion and the precipitation of Cr23C6 were observed at grain boundaries after sensitization heat treatment. The variation of minimum corrosion potential for IGSCC onset is presented semi-quantitatively, considering the effects of aqueous impurity and degree of sensitization.