Low temperature embrittlement of duplex stainless steel: Correlation between mechanical and electrochemical behavior

The low temperature embrittlement behavior of duplex stainless steel 2205 was investigated on the basis of changes in mechanical and electrochemical properties after aging for 5000 h at 335, 365 and 400 °C. Aging leads to increase in the hardness of δ-ferrite phase. The ferrite hardening was very rapid in the initial stages of aging; thereafter the hardness increase was more gradual at all the aging temperatures. Charpy impact test of the aged samples showed drastic decrease in impact toughness. The value of Charpy impact energy saturated after aging to 5000 h at all the aging temperatures. The embrittlement in the material is known to be caused by spinodal decomposition reaction in which the δ-ferrite decomposes into iron-rich α and chromium-enriched α′. For the purpose of non-destructive evaluation of thermal aging embrittlement, double loop electrochemical potentiokinetic reactivation (DL-EPR) test and anodic polarizations in acetic acid and HCl solution were carried out. The peak current density during the anodic scan in DL-EPR test and the peak anodic current density for secondary passivation during polarization in acetic acid increased with increase in aging time. A good linear correlation was observed between the peak anodic current density for secondary passivation during polarization in acetic acid and the microhardness of δ-ferrite phase.