Welding and welding overlay are two different technologies, and there is no relationship between them.
Welding: Welding is a manufacturing process and technique of joining metals or other thermoplastic materials such as plastics using heat, high temperature, or high pressure.
hardfacing: hardfacing, as an economical and rapid process method for surface modification of materials, is becoming more and more widely used in the manufacturing and repairing parts in various industrial sectors. It can make the most effective use of the hardfacing layer. It is desirable to use hardfacing methods with less dilution of the base material, higher deposition rates, and excellent hardfacing layer properties. i.e., high quality, efficient and low dilution rate hardfacing techniques.