Abstract
The effects of deformation, prior to sensitization, on intergranular stress corrosion cracking (IGSCC) were studied on the AISI 304 (UNS S30400) stainless steel (SS). The degree of sensitization (DOS) was quantified by the double loop electrochemical potentiokinetic reactivation (DL-EPR) method. The susceptibility to IGSCC was investigated by the slow strain rate test (SSRT) carried out in polythionic acid (PTA) solutions. The results were complemented by scanning electron microscopy (SEM) fractographs. Deformation was found to accelerate sensitization, and a peak in sensitization vs. deformation was always observed. This peak was found to shift toward lower deformations with an increase in sensitization temperature. At 700°C, prior deformation is able to desensitize or heal the SS after 24 h. IGSCC was observed in AISI 304 SS after some treatments. No one-to-one correspondence was observed between IGSCC and DOS; this could be explained by the fact that the DOS measured by the DL-EPR indicates the depleted regions below ∼15% Cr, whereas IGSCC depends on the availability of continuous grain boundary paths that are chromium-depleted, along with strain rate and environment (pH, temperature, etc.). Deformation prior to sensitization causes carbide formation and chromium depletion to occur near dislocations within the grain interiors, in addition to along grain boundaries. The DOS does not differentiate between these interior regions and the grain boundary regions, and shows a total value accounted for chromium depletion. However, IGSCC occurs only when there is chromium depletion along grain boundaries and therefore these intragrain regions further reduce the correlation between the DOS and IGSCC susceptibility. Deformation close to or beyond 60% was found to prevent IGSCC of AISI 304 SS, irrespective of the sensitization temperature or DOS value.
