What are the properties and characteristics of Monel 400 alloy

 　　What are the structural characteristics of Monel 400 alloy?

　　Monel 400 alloy, also known as Ni68Cu28Fe alloy in China. The chemical composition of this alloy is mainly composed of 30% Cu and 65% Ni with a small amount of Fe (1-2%) added. The microstructure is a typical single-phase austenitic structure. Due to the compatibility of nickel and copper in any ratio, there is generally no precipitation of intermetallic phases.

　　How about the corrosion resistance of Monel 400 alloy steel?

　　Nickel copper alloys are more resistant to corrosion in reducing media than pure nickel, while they are more resistant to corrosion in oxidizing media than pure copper. Due to the single-phase austenite structure of Monel 400 alloy, there is no corrosion caused by the electric couple reaction between different phases in the multiphase alloy.

　　In the atmosphere, Monel 400 alloy has extremely high corrosion resistance and belongs to the category of extremely corrosion-resistant alloys.

　　In water corrosion, Monel 400 alloy not only has excellent corrosion resistance in most water corrosion cases, but also has little discovery of pitting corrosion, stress corrosion, etc. In natural water and distilled water, this alloy is extremely corrosion-resistant, with a corrosion rate generally ≤ 0.025mm/a, including many harsh conditions at different temperatures, flow rates, and air filling. In acidic slurry water containing oxidizing salts, the corrosion of Ni688Cu28Fe alloy will worsen, but it still belongs to the category of corrosion-resistant materials. Monel 400 alloy has excellent corrosion resistance in both natural and artificial seawater. One important use of Monel 400 in seawater is to manufacture structural components for preventing seawater corrosion in the splash zone of procurement platforms. In still seawater, this alloy steel is prone to pitting corrosion, but the expansion of such pitting corrosion is slow.

　　Experiments in air and oxygen at high temperatures have shown that the oxidation resistance of Monel 400 alloy is lower than that of pure nickel. The outer layer of the oxide film on the alloy surface contains CuO and Cu ₂ O, while the inner layer is rich in nickel, which is basically pure nickel oxide. The maximum temperature for continuous operation of Monel 400 alloy in air is generally considered to be around 600 ℃. In high-temperature steam, whether dry or wet, the service temperature of Monel 400 alloy should be ≤ 485 ℃. In high flow rate steam, this alloy also has good erosion resistance.

　　In ammonia containing media, due to the high nickel content of Monel 400 alloy, it can withstand corrosion under anhydrous ammonia and nitrogen conditions below 588 ℃.

　　In sulfur containing media, similar to nickel, Monel 400 alloy is corroded due to the formation of low melting point nickel sulfide in molten sulfur and sulfur containing media. Its operating temperature is generally not higher than 320 ℃ and 370 ℃. The former is Monel 400 alloy for reducing sulfur and sulfides, while the latter is Monel 400 alloy for oxidizing sulfides.

　　What other media are there?

　　In chlorine and hydrogen chloride media, Monel 400 alloy corrodes more severely in hydrogen chloride than in chlorine gas.

　　In fluorine and hydrogen fluoride media, Monel 400 undergoes intergranular corrosion in fluorine gas at 400 ℃ during long-term experiments, and intergranular fracture occurs after cold bending. Hydrogen fluoride corrodes Monel 400 alloy much less than fluorine gas, but its corrosion resistance decreases when oxygen is present. In high-temperature HF gas, when there is oxygen or condensation conditions, Monel 400 alloy should generally not be used.

　　What is the corrosion resistance in acidic media?

　　In sulfuric acid, Monel400 alloy is corrosion-resistant in H ₂ SO4 at a concentration of ≤ 85% at 30 ℃ without air. If the concentration is higher than 85%, the corrosion resistance of Monel 400 alloy will decrease due to the oxidizing nature of H ₂ SO4. Similarly, in the presence of air in H ₂ SO4, the corrosion rate of this alloy needs to be increased. And the maximum value occurs when the concentration of H ₂ SO4 is 5%.

　　In sulfite, Monel 400 alloy is prone to corrosion, so it cannot be used to treat sulfite solutions and calcium sulfite in the paper industry. However, in dilute sulfuric acid and other media, the corrosion resistance of this alloy is relatively good, so it can be used as a structural material for some purposes in the paper industry.

　　In hydrofluoric acid, Monel 400 alloy is one of the few important metal materials that can withstand hydrofluoric acid.