Monel 400
Ⅰ. Executive Standards
The main standards for Monel 400 revolve around the ASTM (American Society for Testing and Materials) and ASME (American Society of Mechanical Engineers) systems, covering different forms (plates, bars, pipes, etc.):
- Plates/Strip: ASTM B127, ASME SB127;
- Bars/Forgings: ASTM B164, ASME SB164;
- Seamless Pipes: ASTM B165, ASME SB165;
- Other Extended Standards: ASTM B564 (forgings), ASTM B163 (heat exchanger tubes), as well as international standards (such as British Standard BS 3072/3073, German Standard DIN 17750/17752, U.S. Military Standard QQ-N-281, etc.).
Ⅱ. Names and Codes
Monel 400 has multiple aliases and designations, with the core identifications as follows:
- UNS Number: UNS No4400 (Unified Numbering System of the United States);
- General Designations: Alloy 400, Ni68Cu28Fe (abbreviation based on the proportions of nickel, copper, and iron);
- European Designations: W.Nr 2.4360, NiCu30Fe, etc.
Ⅲ. Chemical Composition (Mass Fraction, %)
Monel 400 is based on nickel – copper, supplemented by a small amount of elements such as iron and manganese. The typical composition ranges are as follows:
| Element | Content Range | Role |
|---|---|---|
| Nickel (Ni) | 63~67 (Balance) | Dominates corrosion resistance, stabilizes the matrix |
| Copper (Cu) | 28~34 | Synergizes corrosion resistance, improves workability |
| Iron (Fe) | ≤2.5 | Strengthens the matrix, reduces cost |
| Manganese (Mn) | ≤2.0 | Improves hot working performance |
| Silicon (Si) | ≤0.5 | Controls impurities, optimizes structure |
| Carbon (C) | ≤0.3 | Prevents embrittlement caused by carbide precipitation |
| Sulfur (S) | ≤0.02 | Inhibits hot cracking tendency during hot workings |
Ⅳ. Mechanical Properties (Room Temperature, Typical Values in Annealed State)
Monel 400 combines high strength and high plasticity, and its properties change with the processing state (cold working/annealing):
- Tensile strength: 480 – 620 MPa (can be increased to a higher value by cold working);
- Yield strength (0.2% offset): 170 – 345 MPa;
- Elongation: ≥35% (excellent formability, easy for rolling and forging);
- Hardness: HB 150 – 300 (relatively soft in annealed state, hardness increases after cold working).
Ⅴ. Heat Treatment Requirements
- Solution Annealing (Core Process, Optimizing Corrosion Resistance and Plasticity):
- Temperature: \(871 – 982^\circ\text{C}\) (common range, can also be extended to \(704 – 982^\circ\text{C}\)). After holding, water quenching or air cooling is performed (rapid cooling ensures a single – phase solid solution and avoids precipitation phases from reducing corrosion resistance).
- Stress Relief Treatment (Eliminating Internal Processing Stress):
- Temperature: \(538 – 566^\circ\text{C}\), holding for 1 – 2 hours, followed by slow cooling (only relieves stress without changing the grain structure).
Ⅵ. Main Application Fields
Monel 400 focuses on the following scenarios due to its advantages of “resistance to reducing corrosion + wide – temperature strength + easy processing”:
- Marine Engineering: Hull structures, propellers, seawater valves, offshore platform fasteners (resistant to seawater/salt spray corrosion, resistant to chloride ion stress corrosion cracking);
- Chemical Industry: Hydrofluoric acid/dilute sulfuric acid equipment (reactors, heat exchangers), concentrated alkali storage tanks (resistant to strong alkali corrosion);
- Oil and Natural Gas: Linings of crude oil distillation towers, oil and gas transmission pipelines (resistant to high temperature, high pressure and corrosive media);
- Heat Exchange Equipment: Boiler feed water heaters, condensers (resistant to high temperature + corrosion, ensuring long – term stable operation);
- Special Fields: High – purity water components in the nuclear industry (resistant to water corrosion), food processing equipment (resistant to organic acids), valves/pump shafts (wear – resistant + corrosion – resistant).
Supplementary Characteristics
- Corrosion Resistance Limitation: Not resistant to strong oxidizing environments (such as concentrated nitric acid, chromic acid, ferric salts), and such media should be avoided;
- Workability: Can be hot – rolled, cold – rolled and forged. ERNiCu – 7 welding wire is commonly used for welding, and it has good weldability;
- High – temperature Performance: Can serve for a long time at ≤ 538°C (the upper temperature limit is higher in an oxygen – free environment), maintaining strength and toughness.
The above content integrates authoritative standards and practical applications, providing references for the material selection and processing of Monel 400.