Electrochemical monitoring of aging embrittlement of steel for gas-cooled reactor pressure boundary components

The nondestructive testing technique is applied to evaluate the temper embrittlement of normalized and tempered steel; it is based on the anodic polarization behavior in calcium nitrate solution. The steel specimen is aged at a stress of 210 MPa at 450°C for up to 8800 h in order to examine the effect of applied stress on the enhancement of intergranular segregation of phosphorus. The secondary peak observed in the polarization curve for the material aged under stress was compared with that for the non-stressed. It can be quantified with the degree of intergranular segregation of phosphorus. The data suggest that the enhancement of phosphorus segregation due to the applied stress is only recognized after 3000 h of aging. This effect diminishes with increasing aging time.