This article describes the overlay welding of a cobalt alloy. This overlay is made by the plasma transfer arc (PTA) welding technology. Cobalt alloy is overlaid on a creep resistant steel as the seat of a high-pressure steam valve. High-pressure steam valves are used in the energy, nuclear, petrochemical, oil, gas and pharmaceutical industries. Creep resistant high alloy steels are weldable with proper welding conditions, including stress-relieving. Cobalt alloys, on the other hand, have worse weldability. Overlay welding of these heterogeneous materials is possible as well with meeting specific conditions especially proper welding parameters. In this article, the whole experiment is described, including the design of the part that is overlaid by plasma arc welding. The technological procedure of overlay welding is described, including a description of the welding equipment, subsequent evaluation and all standards and specified inspections needed for welding procedure qualification (WPQR). WPQR qualification of overlay welding was also done and finished with Notify Body.