Effect of microalloying elements on the microstructural evolution and mechanical properties of weld joints of centrifugally cast furnace tubes

Microstructural evolution and mechanical properties of weld joints of centrifugally cast furnace tubes with different contents of Ti and W are investigated via field emission scanning electron microscopy (FESEM) equipped with energy-dispersive X-ray spectroscopy, tensile testing machine and creep testing machine. The results show that high temperature performance of weld joints of 25Cr35NiNb+MA (micro alloy) and 35Cr45NiNb+MA furnace tube with addition of Ti and W is significantly higher than that of the weld joints without Ti and W. Micro alloying element Ti significantly affects the microstructures of weld joints. The microstructure of the original welded joints with high Ti content is NbTiC, and it partially transformed to G phase (Ni16Nb6Si7) during aging, which has poor creep resistance. Both NbTiC and NbC are present in the original welded joints with low Ti content, which totally transformed to G phase after high temperature aging. Micro alloying element W could improve high temperature performance of weld joints by solid solution strengthening.