C-Cr segregation at grain boundary before the carbide nucleation in Alloy 690

► Grain boundary segregation in Alloy 690 was investigated by atom probe tomography. ► B, C and Si segregate at the grain boundary. ► Concentration of segregated atoms periodicity fluctuated in the grain boundary plane. ► C and Cr co-segregate on one side of the grain boundary before carbide nucleation.