: Silicon is a strong deoxidizer. In the welding process, it can react with oxygen in the molten pool to form SiO₂ slag, which floats to the surface of the weld metal and removes oxygen impurities. This reduces the risk of porosity and oxide inclusions in the weld, improving the purity and compactness of the weld joint.
: Proper low silicon content can improve the conductivity of the molten pool and stabilize the welding arc, making the welding process more stable and reducing splashing, which is conducive to obtaining a well-formed weld bead.
: Excessive silicon will reduce the melting point of the grain boundary eutectic phase in the weld metal and increase the liquid phase fraction at the grain boundary during the solidification process. Under the action of welding thermal stress, the grain boundary is prone to cracking, thus significantly increasing the hot cracking tendency of the weld joint.
: High silicon content will promote the precipitation of brittle phases (such as silicides) in the weld structure, especially in the heat-affected zone (HAZ). This will reduce the impact toughness and ductility of the weld joint, making it prone to brittle fracture under low-temperature or dynamic load conditions.
: Although silicon has a deoxidizing effect, excessive silicon will react with nitrogen in the welding atmosphere to form silicon nitride (Si₃N₄) gas. If the gas cannot escape from the molten pool in time, it will form porosity in the weld, affecting the mechanical properties and sealing performance of the joint.
: Excessive silicon will increase the viscosity of the molten pool metal, reduce the fluidity of the weld, and easily lead to welding defects such as incomplete penetration and incomplete fusion, especially in complex joint forms or high-current welding processes.
For most nickel-based alloys used in welding applications (such as Inconel 625, Hastelloy C276), the optimal silicon content is usually controlled within 0.1–0.5 wt%. This range can balance the deoxidation effect and welding stability while minimizing the risk of hot cracking and toughness degradation.
