The welding metallurgical behavior of nickel-based alloys and their welding wires is significantly different from that of carbon steel and stainless steel, which is due to the physical and chemical properties of nickel itself.Nickel-based alloys have a higher melting point and lower thermal conductivity, and the liquid metal has poor fluidity and shallow melting depth.More importantly, nickel is extremely sensitive to impurity elements such as sulfur and phosphorus, and it is easy to form a low melting point eutectic at the grain boundary, which leads to a significant increase in the tendency of welding thermal cracks (such as solidification cracks and liquefaction cracks).Therefore, the formulation design and welding process formulation of nickel-based welding wire must revolve around the two core topics of “crack resistance” and “guaranteed fusion”.

In order to enhance the crack resistance, nickel-based welding wire adopts multiple strategies in the composition design.First of all, it is extremely pure smelting, which controls the sulfur and phosphorus content to a very low level.Secondly, it is to adjust the alloy system, such as adding appropriate amounts of molybdenum, tungsten and other elements to strengthen the matrix, and strictly control the content of silicon, boron and other easily polarized elements.Sometimes trace amounts of rare earth elements such as cerium and lanthanum are added to purify the grain boundary and improve the microstructure.These measures are designed to enhance the plastic reserve of the weld metal at high temperatures and resist the binding stress of welding.

Accordingly, the welding process also needs to be adjusted in a targeted manner.Due to the poor fluidity of liquid nickel-based metals, the bevel design needs to be wider to ensure the fusion of the side walls.Usually a smaller welding line energy, a lower inter-channel temperature, and a short arc operation are used to control the heat input, reduce the brittleness temperature range, and reduce welding stress.Before welding, the bevel and the surface of the welding wire should be thoroughly cleaned of oil and moisture.These strict and even slightly cumbersome process disciplines are the prerequisites for the release of the excellent performance of nickel-based welding wire, highlighting its application characteristics of “material is the foundation, process is the key”.