A sealing surface laser cladding layer with thickness of 2.04 mm and cross section of circular arc having a fitting radius of 2.69 mm was prepared on a 0Cr18Ni12Mo3Ti nuclear valve sample surface using FCo-5 fluxed cobalt-base alloy powder as overlaying welding material. The microstructure and phase composition of the cladding layer were analyzed using SEM and XRD. The microhardness of the cladding layer and high temperature hardness at the position with minimum thickness were measured. The results show that the crystal morphology of coating altered in turn as plane crystal cellular dendrites,...