The nuclear power plants in Eastern Europe face problems with supplies of spare parts manufactured according to the same Russian standards as the originals. Therefore, the dissimilar welds of original Russian steel 08Ch18N10T and substitutive 1.4541 were made and analyzed to consider the possibility of original steel replacement during the repairs. Two different filler wires were applied. The welds were subjected to cyclic thermal loading corresponding to the actual operating conditions of a nuclear unit, and their microstructure and mechanical properties were compared to the as-welded joints. An increase in weld metal microhardness induced by aging was found when the filler with higher C and Cr content was used. Although this could indicate possible ferrite decomposition, the detected changes in mechanical properties corresponded to the changes in homogeneous welds of the original steel. The strength requirements for the steel used in nuclear power plant devices were still matched.
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