Grain boundary phosphorus and molybdenum segregation under irradiation and thermal conditions in a 2.25Cr1Mo steel

Segregation of P and Mo to prior austenite grain boundaries in a 2.25Cr1Mo steel subjected to neutron irradiation and ageing is examined using field emission gun scanning transmission electron microscopy (FEGSTEM) with energy dispersive X-ray microanalysis. The steel samples are irradiated and aged at around 270 and 400°C, respectively. The irradiation dose rate and dose are about 1.05×10−8 dpa s−1 and 0.042 dpa for 270°C-irradiation, and 1.75×10−8 dpa s−1 and 0.13 dpa for 400°C-irradiation. The FEGSTEM results indicate that, during 270°C-irradiation, there is no irradiation effect for P segregation and some effect for Mo segregation with the Mo boundary concentration decreasing. During 400°C-irradiation, there is a slight irradiation effect for P segregation with the P boundary concentration increasing and some irradiation effect for Mo segregation with the Mo boundary concentration decreasing. The 400°C-ageing does not enhance Mo segregation as compared with the 270°C-ageing, but it enhances P segregation.