Irradiation-induced segregation/desegregation at grain boundaries of a ferritic Fe-Mn-Si steel

Abstract

Irradiation-induced segregation of solutes at typical grain boundaries (GBs) i.e. random high-angle, low angle and special Σ3 GBs in an Fe-Mn-Si steel has been investigated by using atom probe tomography. By effectively restraining carbide formation in the steel with carbon as an impurity, this research explores the effect of Mn-Si and Mn-C interactions on irradiation-induced segregation/desegregation and precipitation at GBs with different characteristics. Mn, Si and C segregate at unirradiated GBs, but only Mn's and C's segregations depend on the GBs’ characteristics, with the strongest segregation at the random high-angle GBs and the weakest segregation at the Σ3 GBs. GB dislocations develop Mn segregation above the rest GB. The irradiation enhances the segregation of Mn, but triggers the desegregation of C at the GBs. The irradiation-induced desegregation of C from the GBs, for the first time, is found to be not due to the formation of GB carbide, but likely due to sinking of interstitials at the GBs and enhanced solubility of C in steel under irradiation. With quantitative information unveiled by this research, solute interactions and effective diffusion paths of solutes for the irradiation-induced segregation/depletion are discussed.