Atomic scale study of grain boundary segregation before carbide nucleation in Ni–Cr–Fe Alloys

•Impurities segregated at grain boundaries were observed by atom probe tomography.•The comparison of segregation features in two Ni–Cr–Fe alloys was studied by APT.•C and Cr atoms co-segregated at grain boundaries before carbide precipitation. Three dimensional chemical information concerning grain boundary segregation before carbide nucleation was characterized by atom probe tomography in two Ni–Cr–Fe alloys which were aged at 500°C for 0.5h after homogenizing treatment. B, C and Si atoms segregation at grain boundary in Alloy 690 was observed. B, C, N and P atoms segregation at grain boundary in 304 austenitic stainless steel was observed. C atoms co-segregation with Cr atoms at the grain boundaries both in Alloy 690 and 304 austenitic stainless steel was found, and its effect on the carbide nucleation was discussed. The amount of each segregated element at grain boundaries in the two Ni–Cr–Fe alloys were analyzed quantitatively. Comparison of the grain boundary segregation features of the two Ni–Cr–Fe alloys were carried out based on the experimental results.