A feature of fusion welding is melting of the base metal or of the base and filler metals and producing a welded joint without application of external pressure. Fusion welding also includes surfacing, which is a technology, involving application of a layer of molten metal on the surface, of an item effecting either restoration of the initial dimensions of the worn out part, or imparting specially required properties to the surface of a new item. In fusion welding, melting of just the base metal and of the base and additional metals may take place simultaneously. In fusion welding, the liquid metal dissolves a certain amount of gases from the air and the gaseous products of decomposition of the components of the electrode coating or flux. A significant influence on the properties of the welded joint is produced also by the physicochemical processes in the boundary between the solid and molten metals.