Two repair weld metals Inconel 52 and its newer version Inconel 52M were used as materials for development of repair welding method of a VVER 1000 pressure vessel. The properties and microstructure of the trial welds were investigated using light, scanning and transmission electron microscopy. Both modifications of Inconel revealed a structure of elongated grains with clear evidence of dendritic segregation. Fine chromium carbides occurred at wavy grain boundaries and fine cuboidal titanium carbides pinned dislocations within grains. Coarser skeletal titanium carbides and globular oxides were sparsely precipitated in interdendritic spaces. Some small common defects were observed in the weldments. No cracks were detected which could be classified as ductile dip cracking. It was concluded that both Inconel 52 and Inconel 52M are acceptable for repair welding.