Abstract
For the purpose of non-destructive evaluation of the degree of temper-embrittlement in 2.25wt%Cr-1wt%Mo steels, anodic and single loop electrochemical potentiokinetic reactivation (SL-EPR) polarization curves of the embrittled specimens which had been serviced for oil refinery reactor for the maximum 25 years have been measured in 55wt% Ca (NO3)2 solution at 30°C. The characteristic of electrochemical polarization is influenced by fracture appearance transition temperature shift (ΔFATT) of Charpy impact test, P content and X-ray diffraction intensity ratio of M23C6/M6C in temper-embrittled specimens. Difference in current density (IP2-E-Ipass-E) between active second peak and passive in an anodic polarization curve of temper-embrittled specimens increases linearly with increase in ΔFATT in the range of mode transfer over transgranular cleavage to intergranular of Charpy impact fracture. On the other hand, difference in current density (IPA1-E-Ipass-E) between active first peak and passive in a SL-EPR polarization curve of largely temper-embrittled specimens turned up in region of ΔFATT of above 69°C, P content of above 0.01wt% and X-ray diffraction intensity ratio of M23C6/M6C of above 1.38 in the range of intergranular mode of Charpy impact fracture. Therefore, it is possible to evaluate nondestructively the degree of temper-embrittlement in the range of mode transfer over transgranular cleavage to intergranular, in addition to judge transgranular or intergranular mode of Charpy impact fracture which indicate a criterion of intergranular bond deteriorate by measuring IP2-E-Ipass-E and IPAl-E-Ipass-E of temper-embrittled specimens.
