Monel400 alloy, UNS N04400, 2.4360 properties, hot and cold processing and welding
Monel400 alloy (UNS N04400, 2.4360) is a single-phase solid solution Ni-Cu alloy. It is a nickel-based alloy that can withstand various corrosive environments and has good ductility.
It has good corrosion resistance in many media environments. It has good corrosion resistance from slightly oxidizing media environment to neutral environment to suitable reducing environment. This alloy has a long history of use as a corrosion-resistant material.
In the early 20th century, people tried to smelt alloys from nickel ores with high copper content. Today's Monel 400 has a nickel-to-copper content ratio similar to that of the original ore.
Compared to metals such as pure nickel, Monel 400 alloy is less strong when annealed, and for this reason, this material often requires tempering to increase its strength.
Monel400 alloy is also used in underwater environments and chloride solutions that cannot be oxidized.
Material standards
Product form Standard ASTM ASME AMS
Sheet and Strip B127 SB127 4544
Seamless pipe B163 SB163 4574 B165 SB165
Bars and forgings B164 SB164 4675 B564 SB564
Silk 4730 4731
ASTM: American Society for Testing and Materials standards; ASME: American Society of Mechanical Engineers standards; AMS: American Military Standards
Physical properties
Density: 8.9g/cm3 Melting point range: 1300~1350℃
Monel 400 General Properties
Monel 400 has excellent corrosion resistance in neutral environments, alkali and salt environments, and has now become a standard application material in salt plants.
This alloy material is one of the few metals that can resist fluorine, hydrofluoric acid, hydrogen fluoride or their derivatives. It is also very corrosion-resistant in caustic soda and has cavitation corrosion resistance similar to copper-based alloys in seawater environments. It has better effects in sulfuric acid, hydrochloric acid and other environments, especially in the absence of air. However, since the material does not contain Cr, the corrosion rate will be greatly increased in an oxidizing environment.
Although Monel 400 is very resistant to chloride ion stress corrosion cracking, it can develop stress corrosion cracking in environments with mercury or moisture exposure to hydrogen fluoride gas. At this time, attention should be paid to stress-relieving heat treatment of the material.
The characteristics can be summarized as follows:
1. Good corrosion resistance in marine and chemical environments;
2. Very insensitive to chloride ion stress corrosion cracking;
3. It has good mechanical properties from below zero to 550℃;
4. It is approved by ASME and can be used as a pressure vessel at -10~425℃;
5. Good processing and welding performance.
Chemical analysis
Anti-corrosion
Monel 400 alloy is more corrosion resistant than commercially available pure nickel (UNS N02200) in attenuated environments and more corrosion resistant than refined copper alloys in oxidizing conditions. In suitably weakened acid, neutral or alkaline solutions, Alloy 400 may be considered for use. The alloy is corrosion resistant to most alkalis, salts, organic compounds, and atmospheric conditions. Although the material has experienced corrosion stress cracking under high temperatures, high stresses and high corrosion concentrations, Alloy 400 can be considered for use under cooler alkali corrosion conditions. The alloy is used in weak acids such as sulfur and hydrogen chloride, especially when there is no ventilation and no oxides.
Alloy 400 is particularly resistant to chloride stress cracking corrosion. Its main application environment is various types of water including seawater and salt water.
Alloy 400 will corrode when sulfur-containing gases exceed 700 degrees Fahrenheit (371 degrees Celsius); melted sulfuric acid will corrode when molten sulfuric acid exceeds approximately 500 degrees Fahrenheit (260 degrees Celsius).
MATERIAL Corrosion Rate, mpy (mm/a)
Alloy 400 22 (0.56)
Nickel 200 >200 (>5.08)b
Alloy 600 150 (3.81)
AISI 304 Stainless Steel >210 (>5.33)b
AISI 316 Stainless Steel >190 (>4.83)b
Mild Steel >170 (4.32)
ALLOY Corrosion/Erosion Rate
mpy mm/a
Alloy 625 Nil Nil
Alloy 825 0.3 0.008
Alloy K-500 0.4 0.01
Alloy 400 0.4 0.001
Alloy 200 40 1.0
processing
heat treatment
The entire annealing sequence for Alloy 400 is conducted over a short period of time in the typical temperature range of 1400 degrees Fahrenheit to 1800 degrees Fahrenheit (760-980 degrees Celsius). The annealing temperature of Monel 400 material is generally 700~900℃, and the best effect is at 825℃. Rapid air cooling after treatment can achieve good corrosion resistance. The purpose of this is to soften the material after forging and forming to keep the material relatively fine particles. Annealing should be performed in an atmosphere as free of sulfides as possible, as increased exposure time within the annealing temperature range will embrittle the material. Cryogenic stress relief can be used on cold-deformed materials by heating them to approximately 575 degrees Fahrenheit (300 degrees Celsius) for one to three hours.
Annealing temperature and annealing time are directly related to the final grain size of the material, so annealing parameters should be carefully considered.
For pipes, the stress relief heat treatment temperature is generally controlled at 550~650℃.
Thermal processing
heating
It is very important to ensure that the surface of Monel 400 is clean before heat treatment. If contaminants such as S, P, Pb or other low melting point metals are present on the surface of Monel 400 during the heating process, the properties of the alloy may be weakened. The main sources of pollutants include marker pen marks, temperature indicating paint, lubricating grease and furnace gas. The sulfur content of the furnace gas must be low.
The furnace gas should be neutral or slightly reducing, and the furnace gas must not be allowed to fluctuate between reducing and oxidizing properties. The flame in the furnace cannot directly impact the material.
Monel 400 can be hot processed in the range of 800~1200℃, but only slight forging can be done below 925℃. Hot bending can be performed between 1025~1200℃. When furnace heat treatment is required for thermal processing, the furnace temperature must first be heated to 1200°C, and then the Monel 400 material is put in for heating.
There is a guideline for material heating: 60 minutes for every 100mm of thickness. Once the heating time is up, take out the material immediately for thermal processing. If the material temperature drops below the minimum thermal processing temperature during thermal processing, it must be reheated.
cold forming
Monel 400 alloy exhibits excellent cold forming properties typically associated with nickel-chromium stainless steels. Compared with 301 or 304 alloy, this alloy has a lower work hardening ratio and can be used in a variety of drawing and forming processes. During this process, relatively large deformation will occur in the tempering gap.
Cold worked Monel 400 materials must be in the annealed state. Because it has a slightly higher work hardening rate than carbon steel, the forming equipment must be appropriately changed. Cold forming requires inter-process annealing.
Cold deformation is sometimes used to improve mechanical properties. If the material is to be used in environments prone to stress corrosion cracking such as mercury, moisture exposure, hydrogen fluoride gas, etc., stress relief heat treatment is recommended.
Descaling
The oxides and stains near the welds of Monel 400 materials are closer than those of stainless steel materials. Before pickling in mixed acid of nitric acid and hydrofluoric acid, they can be polished with a grinding wheel or pretreated in a salt bath.
machining
Monel 400 material should be machined in the annealed condition. Materials after cold forming and stress relief are easier to process. You must have sufficient understanding of the work hardening of this material. For example, the surface cutting speed is smaller than that of carbon steel, and the tool must be continuously operated. In order to avoid the surface hardening layer , the feed amount should be large, etc.
Machining tools should be special tools for nickel-based alloys and high-alloy stainless steel, and stainless steel brushes should be used to brush welds. Manufacturing and processing machinery such as shears, presses, plate rolling machines, etc. must take measures to avoid contamination by iron impurities. The processing area must be clean and separated from the carbon steel processing area.
welding
Monel 400 alloy can be welded by a variety of procedures, including gas tungsten arc, gas metal arc welding, and shielded gas metal arc welding. Before performing all these operations, the parts to be welded must be cleaned to avoid brittle materials such as lubricants and paints. Materials must be kept clean for best welding results.
The welding procedure for Monel400 alloy is similar to that of austenitic stainless steel, and neither preheat treatment nor post-welding heat treatment is required. The welding design is similar to that for austenitic stainless steels with two exceptions. First: The nature of the metal welding solution needs to be adjusted so that the interface part is fully opened and can accommodate the entire filler wire to fill the joint. Second: high heat conduction and material purity result in lower welding penetration compared to austenitic stainless steels.
The welding groove of Monel 400 material is suitable to be completed by mechanical processing. If the groove is polished, local overheating should be avoided. Since nickel alloys and high-alloy stainless steels have obvious differences in physical properties compared to carbon steel, their thermal conductivity coefficients are low and their thermal expansion coefficients are large. For this point, clamping, large welding feet (1-3mm), etc. must be used during welding. method to solve. Because Monel 400 material has poor fluidity when welding molten metal, a design with a large groove angle (60-70°) is required to allow the welding wire to fill the weld.
Clean the groove and welding rod with acetone before welding. Use GTAW as the welding method. Use ERNiCu-7 for the welding wire and ENICU-7 for the welding rod. Monel 400 does not require preheating before welding, and generally does not require post-weld heat treatment, because the strength of the material after welding is improved, which will have certain benefits for future use.
Monel 400 application fields
Marine and Chemical Processing Equipment
Valves, water pumps, propeller shafts
Fasteners for marine fixtures
Gasoline and clean water tanks
Processing vessels and pipes
heat exchanger
Typical engineering applications of Monel 400
1. Water supply and steam generator piping system of the power station;
2. The theme part of heaters and evaporators in salt plants;
3. Alkylation device for sulfuric acid and hydrofluoric acid;
4. Industrial heat exchanger;
5. Composite plates in crude oil distillation units;
6. Wave protection cover for offshore installations;
7. Shafts of propellers and pumps in seawater systems;
8. Uranium and isotope separation systems in nuclear fuel production;
9. Pumps and valves in hydrocarbon chlorination production;
10. MEA reboiler pipeline.
