Monel K500
Ⅰ. Executive Standards
The core technical specifications of Monel K500 revolve around ASTM (American Society for Testing and Materials) and aerospace industry standards, covering different product forms:
- Bars, forgings, wires: ASTM B865 (Specification for Precipitation-Hardened Nickel-Copper-Aluminum Alloy (UNS No5500) Bars, Wires, Forgings, and Forging Stock), which defines chemical composition, heat treatment, and mechanical properties;
- Aerospace applications: AMS 4676 (aerospace material specification, specifying performance requirements for aerospace-grade bars and forgings);
- Extended reference: Some forgings can refer to ASTM B564, but ASTM B865 is the most direct product standard.
Ⅱ. Names and Codes
- General names: Monel K500, Monel K – 500, Alloy K500;
- Authoritative identification: UNS No5500 (Unified Numbering System of the United States, distinguished from UNS No4400 of Monel 400, the latter without Al/Ti strengthening).
Ⅲ. Chemical Composition (Mass Fraction, %)
Based on Monel 400 (Ni – Cu base), Monel K500 achieves precipitation hardening by adding Al and Ti. The typical composition ranges are as follows:
| Element | Content Range | Core Role |
|---|---|---|
| Nickel (Ni) | 63.0~70.0 | Matrix, ensuring corrosion resistance |
| Copper (Cu) | Balance (approx. 27~33) | Synergizes corrosion resistance, improves plasticity |
| Aluminum (Al) | 2.3~3.15 | Forms Ni₃(Al, Ti) strengthening phase with Ti |
| Titanium (Ti) | 0.35~0.85 | Promotes precipitation strengthening, refines structure |
| Iron (Fe) | ≤2.0 | Assists in strengthening, controls cost |
| Manganese (Mn) | ≤1.5 | Improves hot working fluidity |
| Carbon (C) | ≤0.25 | Prevents embrittlement caused by carbide precipitation |
| Silicon (Si) | ≤0.5 | Optimizes casting/forging structure |
| Sulfur (S) | ≤0.01 | Inhibits hot working hot cracking tendency |
Ⅳ. Mechanical Properties (Distinguishing Between Solution Annealed State and Aged State)
Monel K500 regulates its properties through “solution treatment + age hardening”, and the strength increases significantly after aging (about 2 – 3 times that of Monel 400):
| State | Tensile Strength (MPa) | Yield Strength (0.2% Offset, MPa) | Elongation (%) | Hardness (HB) |
|---|---|---|---|---|
| Solution Annealed State | ~650 | ~300 | ~40 | ~150 (Soft State) |
| Aged State | 1000~1200 | 800~1000 | 15~25 | 200~350 |
Note: Aging processes (such as 510°C × 4h or 593°C × 2h) directly affect the properties, and the above are typical values; cold working can further increase the strength.
Ⅴ. Heat Treatment Requirements
1. Solution Treatment (Preparing a Uniform Matrix):
- Temperature: 820−900∘C (commonly 870∘C), holding for 1 – 2 hours;
- Cooling: Water quenching (rapid cooling to fully dissolve Al and Ti and obtain a uniform austenitic matrix).
2. Age Hardening (Core Strengthening Step):
- Temperature: 480−593∘C (commonly 510−593∘C; the higher the temperature, the faster the strengthening phase precipitates, but grain coarsening needs to be balanced);
- Holding: 2 – 16 hours (the larger the part size, the longer the holding time);
- Cooling: Air cooling (to precipitate dispersed Ni3(Al,Ti) phases, significantly increasing strength and hardness).
3. Hot Working Recommendations:
- Temperature: 980−1150∘C (avoid being lower than 870∘C to prevent hot brittleness);
- Principle: Process rapidly to reduce high – temperature residence time (prevent premature precipitation of strengthening phases and reduce workability).
Ⅵ. Main Application Fields
Monel K500 combines “the corrosion resistance of Monel 400 + higher strength” and focuses on high – stress + corrosive environments:
- Marine Engineering: Seawater pump shafts/impellers, offshore platform fasteners, seawater valves (resistant to seawater corrosion + fatigue resistance, with a longer service life than Monel 400);
- Petroleum and Petrochemical Industry: Oil well drill collars (resistant to downhole corrosion + high pressure), high – temperature and high – pressure pipelines, oil and gas separation equipment (resistant to H₂S/CO₂ corrosion);
- Aerospace: Engine turbine disks, elastic components of landing gear, fasteners (excellent high – temperature strength, reducing structural weight);
- Chemical Industry: Corrosion – resistant pumps/valves, reactor linings (resistant to strong alkalis, seawater, and weak acid media, replacing Monel 400 in high – stress scenarios);
- Special Fields:
- Medical: Heart valves, orthopedic implants (resistant to body fluid corrosion + high strength, compatible with the human body environment);
- Papermaking: Pulp scraping blades (wear – resistant + corrosion – resistant, resisting pulp corrosion);
- Nuclear Power: Control rod assemblies (radiation – resistant + corrosion – resistant, with good long – term stability).
Supplementary Characteristics
- Corrosion Resistance Limitation: Comparable to Monel 400 (resistant to seawater, dilute acids, and strong alkalis), but slightly higher susceptibility to stress corrosion after aging (strict control of heat treatment and processing stress is required);
- Workability: Easy to cold work in the solution – annealed state (rolling, forging, welding; ERNiCu – 7 welding wire is recommended). After aging, the hardness is high, so cutting parameters need to be optimized;
- Magnetism: Non – magnetic (austenitic matrix, no ferromagnetism in both solution – annealed and aged states);
- Upper Temperature Limit: Long – term service temperature of the aged state ≤ 480°C (exceeding this temperature will cause coarsening of the strengthening phase and a decrease in strength).
Monel K500 achieves a breakthrough in “corrosion resistance + high strength” through precipitation hardening and is an upgraded solution of Monel 400 in high – stress scenarios. When selecting materials, a comprehensive evaluation should be made considering the heat treatment state and stress environment.