Gas tungsten arc welding with the TiNi intermetallic filler material was used to weld overlays onto the SUS 304 stainless steel and AISI 1045 medium carbon steel. The composition, hardness and cavitation erosion resistance of overlays on both kinds of steel was compared. The microstructure analysis results show that the elements from substrate materials diluted the overlay and caused the formation of dendrite structures in overlays. The crystalline phases in overlays on SUS 304 are TiNi-B2, TiNi-B19’, TiNi3 and Ti3Ni4, while those in overlay on AISI 1045 are TiNi-B2 and TiNi3. The multiple phase structures, precipitation of hard carbides and oxides formed in the overlays increases the hardness of the overlays 3-fold over the TiNi filler rod and steel substrate. This significantly increases the cavitation erosion resistance of substrate steels. The corrosion resistant overlays also enhance the cavitation erosion corrosion resistance of substrates in corrosive 3.5 wt% NaCl solution.