Resistance spot weldability of nuclear ODS steel

For evaluating the resistance spot weldability of oxide dispersion-strengthened alloy (ODS) steel, the microstructure of different regions of 9CrYWT-ODS steel spot weld was observed by optical microscope and scanning electron microscope, and the tensile and shear properties of spot welds were tested. Finally, the appropriate welding current range was confirmed. Results show that the size of the oxides in different areas of the spot weld exhibits obvious differences. The tempered zone in the heat affected zone contains tiny, dispersed oxides due to the low temperature during welding process. The phase transformation zone in the heat affected zone contains less small oxides and more large oxides owing to the higher temperature. The very high temperature in the weld nugget zone results in obvious coarsening of the oxides. As the welding current increases, the increase of the nugget size leads to the increase of tensile and shear force, and the tensile shear failure mode gradually changes from the interfacial mode to the partial interfacial-partial pullout mode, and then further transformed into the fully pullout mode. Continuing to increase the current to the occurrence of splash, the decrease of the nugget size results in the decrease of tensile shear force. The failure mode again changes to the partial interfacial-partial pullout mode and interfacial mode. According to the tensile and shear test results, the appropriate welding current range is 6.6 ~ 7.0 kA.