In this study, the effects of different welding filler materials were examined in the case of repair welding of pressure infiltration casting tool made out of Böhler W350 ISOBLOC hot forming tool steel. Three additional welding filler materials were used: Böhler W350 ISOBLOC (same as the raw material), Böhler W300 ISOBLOC and Anviloy® 1150 tungsten alloy. The welds were created with TIG welding method. The used welding filler material has an impact on the mechanical and corrosive properties of the tool. The hardness of the weld was measured to determine its resistance against mechanical stress. The corrosion rate was measured because molten aluminium corrodes workpieces due to its high chemical activity. It was concluded that a single-pass weld corrosion speed is 0.142 ± 0.010 mm/year while a weld containing multiple layers and passes has the corrosion speed of 0.069 ± 0.005 mm/year which is approximately 48% of the corrosion speed of the single-pass weld. Furthermore, the hardness of a weld made with W350 welding filler material significantly drops in the upper layers of the weld, down to 273 HV1 while the hardness of the base material is 495 ± 8 HV1. The results show that the multiple layers and passes welds have better corrosion resistance and less hardness than the single-pass weld.