Dissimilar Electron Beam Welding of Nickel base Alloy 625 and 9% Cr Steel

Abstract:

To improve the thermal efficiency of fossil running power plants increasing the live steam temperature is essential. In power plant construction, 9-12% chromium martensitic steels are widely used but if steam temperatures rise above 625°C there is no way around nickel base alloys.

The scope of this study was to ascertain the weldability of cast nickel base alloy 625 with cast martensitic 9% chromium steel COST CB2, using electron beam welding (EBW). Similar (A625/A625) and dissimilar joint welding experiments on 50mm thick plates were executed. Microstructure of welded joints was investigated and mechanical-technological tests were carried out. Results show that work pieces were completely welded and the microstructure of the seam shows no problems except some δ ferrite grains near the fusion line on the CB2 side. The joints exhibit good mechanical properties in spite of the presence of a thin layer with very high hardness in the heat affected zone (HAZ) on the CB2 steel side.

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