The nanohardness values and modulus of the prior delta phase in both direct current (DC) and vibration-assisted (VIB) weld metal were higher than those of the base metal. The dislocation density in the delta phase matrix was the highest in the VIB weld metal, followed by the DC weld metal and the base metal. Therefore, the higher nanohardness value in the delta phase, especially for the VIB welding, was attributed to the existence of a higher dislocation density. By contrast, the nanohardness values of the gamma phase in both weld metals were not affected by the welding process. The predicted nanohardness value of the composite phase with the rule-of-mixture was consistent with the result of nanoindentation measurements. The deformation induced a V-shaped double twin was revealed by the effect of nanoindentation on the austenite grain of the VIB weld metal.