Nickel and Copper in Monel 400 alloy

Monel 400, designated as UNS N04400 and W.Nr. 2.4360, is a classic nickel‑copper solid‑solution alloy, and its chemical composition is uniformly specified by authoritative international standards including ASTM B127, ASTM B164, ASTM B564, EN standards and ISO standards. For the two core elements, nickel and copper, the standard content ranges are clearly defined. The total content of nickel plus cobalt (Ni+Co) shall be no less than 63.0% and no more than 70.0% by weight. Cobalt is not a separately added element but an associated impurity, so it is calculated together with nickel in the standard specification. Copper, as the second major constituent element, has a standard mass fraction ranging from a minimum of 28.0% to a maximum of 34.0%. This fixed proportion of nickel and copper endows the alloy with excellent corrosion resistance in reducing environments, seawater and alkaline media, as well as stable mechanical properties at room and medium temperatures.

To ensure the mechanical properties, corrosion resistance and processing performance of Monel 400, strict upper limits are set for all residual trace and impurity elements in relevant material standards. Iron is allowed at a maximum content of 2.5% by weight; a proper small amount can improve the alloy's strength and wear resistance, while excessive iron will impair its overall corrosion resistance. Manganese, which functions as a deoxidizer in smelting and improves hot workability, has a maximum permissible limit of 2.0%. The maximum carbon content is controlled at 0.3%: although carbon can increase the hardness of the alloy, excessive carbon will lead to the precipitation of carbides at grain boundaries, reducing the ductility and toughness of the material. Silicon, which helps improve casting fluidity, is restricted to a maximum of 0.5%, because an overly high silicon content will increase brittleness and negatively affect plastic processing.