Why Monel 400 is So Damn Expensive
Monel alloy was first developed by Robert Crookes Stanley of the International Nickel Company and patented in 1906. The new invention is named after the company's president. Over time, various alloys in the Monel family were developed for different applications.
Monel alloy composition
Monel is the name given to a group of alloys (401, R405, K-500, 400, 404, and 402) that contain nickel and copper and sometimes iron, silicon, manganese, and titanium. Although all of these alloys are generally known for their good corrosion resistance, each alloy has some unique properties and uses.
For example, Monel 404 has a low nickel content (52%), a high aluminum content (0.05%), and a copper content (47%). Monel R405 is very similar in content to Monel 400, but without the titanium.
Monel K500 contains aluminum (0.3%) and titanium (0.35% to 0.85%). This alloy has a lower coefficient of friction and higher wear resistance than other Monel alloys. It also has excellent mechanical properties, such as strength and hardness at temperatures up to 600°C (1,112°F).
Monel 400 contains copper and nickel in the same proportions as naturally occur in nickel ore from the Sudbury mine in Ontario, Canada. Because this alloy is much more expensive than stainless steel, it is only used in critical applications where cheaper materials cannot be substituted.
Monel 400 contains 28 to 34 percent copper and at least 63 percent nickel. It also typically contains iron, manganese, silicon, carbon, and trace amounts of sulfur and titanium.
Characteristics of Monel Alloy 400
Monel is stronger than nickel or copper alone. Monel 400 contains nickel and copper as well as carbon, iron, manganese, silicon and titanium. This composition helps Monel maintain its excellent corrosion resistance as well as toughness and mechanical strength over a wide temperature range, typically up to 400°C (752°F). This characteristic is a key requirement in aerospace applications where operating temperatures vary widely. Monel 400 is used to make rivets for aluminum-hulled aircraft.
At low temperatures, Monel 400 retains mechanical properties such as hardness and strength, but its ductility is slightly reduced. (For more information on material strength, read the tensile strength in-depth study.)
Monel 400 has excellent corrosion resistance in high temperature steam and high velocity flowing hot brine. It protects against stress corrosion cracking (SCC) in fresh water, and its durability in turbulent seawater justifies its cost. Its resistance to hydrofluoric acid and hydrochloric acid requires degassing. It is generally resistant to acidic foods; however, it is not resistant to nitric acid, which has oxidizing effects.
Monel 400 is not easy to machine because it undergoes work hardening during machining. Therefore, it is best to cut and turn alloys at slower speeds and very low feed rates. This inevitably leads to higher processing costs.
Monel 400 has a conductivity of 34% IACS (International Annealed Copper Standard). Even when frozen to liquid hydrogen temperatures, it retains some ductility. It is also weakly magnetic.
Monel 400 has good welding performance and can be welded by submerged arc welding, gas metal arc welding and gas tungsten arc welding. Monel 60 filler metal used for welding can ensure that the welded joint has the same hardness, mechanical strength and anti-corrosion properties as the base metal. (Related reading: Causes and prevention of corrosion of welded joints.)
In addition to welded connections, Monel 400 can also be connected by soldering or brazing.
Limitations of Monel 400
Monel 400 is not resistant to hypochlorite, sulfur dioxide, nitric acid or nitric oxide. It is also prone to galvanic corrosion.
