Products Features
Excellent Thermal Shock and Thermal Fatigue Resistance
The low carbon content of Stellite 21 results in a moderate and uniform distribution of carbides, with a cobalt matrix that offers good ductility. The alloy is resistant to thermal cracking during rapid temperature cycling and can withstand severe thermal shocks. It is especially suitable for applications with frequent temperature fluctuations, such as nuclear power plant valves, gas turbine components, and hot work dies.
Good Balance of Wear Resistance and Toughness
Typical hardness in cast or weld-deposited condition is HRC 28-38 (approximately HV 270-380), offering better wear resistance than ordinary stainless steels while maintaining high impact toughness (Charpy V-notch impact energy of approximately 20-40 J). Compared to high-carbon cobalt-based alloys (e.g., Stellite 1, 6, 20), Stellite 21 exhibits significantly superior toughness, making it suitable for components subjected to both impact and wear.
Superior Corrosion Resistance
With approximately 28% chromium content, Stellite 21 demonstrates good corrosion resistance in oxidizing acids (e.g., nitric acid), moderately concentrated non-oxidizing acids (e.g., ≤50% sulfuric acid), and alkaline solutions. It performs exceptionally well in high-temperature and high-pressure water environments, serving as a classic material for nuclear reactor valve sealing surfaces. In seawater and chloride environments, it primarily exhibits pitting corrosion rather than uniform corrosion.
Good Machinability and Weldability
Stellite 21 is one of the most machinable and weldable grades among cobalt-based alloys. It can be surface-hardened using various weld overlay processes such as PTA, TIG, MIG, and oxy-acetylene welding, with extremely low susceptibility to hot cracking. Preheating to 200-350°C and controlled post-weld cooling are typically sufficient during welding. Limited machining is possible in the annealed condition, with final finishing recommended via grinding or electrical discharge machining (EDM).
Technical Specifications
Chemical Composition
|
Element |
Standard Requirements |
Notes |
|
Co |
Remaining quantity
|
Matrix elements that provide high-temperature strength, thermal stability, toughness, and inherent corrosion resistance |
|
Cr |
26.0 - 30.0% |
Form a dense Cr₂O₃ protective film, providing oxidation and corrosion resistance, and is also a main component of hard carbides |
|
W |
5.0 - 6.0% |
Provide solid solution strengthening, form a moderate amount of carbides with carbon, and improve high-temperature hardness |
|
C |
0.2 - 0.3% |
Low carbon content forms a small amount of carbides, ensuring good toughness while maintaining wear resistance. |
|
Ni |
2.0 - 3.0% |
Add a small amount to stabilize the austenitic structure and improve toughness |
|
Fe |
≤ 3.0% |
Strict control to ensure purity and microstructural stability |
|
Si |
≤ 2.0% |
Deoxidizer |
|
Mn |
≤ 1.0% |
Deoxidizer, improve processing performance |
|
Mo |
≤ 1.0% |
Optional small additions to provide enhanced solid solution strengthening and pitting corrosion resistance |
Physical Properties
|
Property |
Value/Range |
Test Conditions |
|
Density |
8.40 - 8.60 g/cm³ |
Room temperature (20°C) |
|
Melting Point |
1300 - 1370°C |
- |
|
Coefficient of Thermal Expansion (20-100°C) |
12.0 - 13.0 × 10⁻⁶ /K |
- |
|
Elastic modulus (Young's modulus) |
200 - 220 GPa |
Room temperature |
|
Thermal Conductivity (20°C) |
21.8 W/(m·K) |
- |
|
Resistivity |
0.85 - 0.95 μΩ·m |
- |
|
Magnetism |
Non-magnetic (weakly magnetic) |
Cobalt-based alloys are typically non-magnetic or weakly magnetic at room temperature |
Mechanical Properties (Cast/Welded Condition, Typical Values)
|
Property |
Typical Value |
Specification |
|
Hardness (Cast/Weld Overlay Condition) |
28 - 38 HRC(270 - 380 HV) |
AWS A5.21 ECoCr-A |
|
Tensile Strength |
700 - 850 MPa |
- |
|
Yield Strength (0.2% Offset) |
450 - 600 MPa |
- |
|
Elongation |
5 - 10% (good toughness) |
- |
|
Compressive strength at room temperature |
1800 - 2200 MPa |
- |
|
Impact toughness |
Charpy V-notch impact energy of approximately 20 - 40 J |
- |
Note: The toughness of Stellite 21 is relatively high among cobalt-based alloys. Its elongation and impact toughness are significantly better than those of high-carbon grades. However, it still falls within the category of wear-resistant materials and is not recommended for structural components subjected to high tensile loads.
High-temperature performance
Stellite 21 has a moderate ability to maintain hardness at high temperatures. The following are typical reference values for how hardness changes with temperature:
|
Temperature |
Typical hardness |
|
Room Temperature |
28 - 38 HRC |
|
400°C(750°F) |
26 HRC |
|
600°C(1110°F) |
22 HRC |
|
760°C(1400°F) |
18 HRC |
|
870°C(1600°F) |
14 HRC |
Antioxidant Performance:
In high-temperature oxidation environments, Stellite 21 forms a dense Cr₂O₃ oxide film on its surface. After exposure to air at 800°C for 1000 hours, the oxidation weight gain is less than 1 mg/cm², indicating good antioxidant properties.
Long-Term Thermal Stability:
When in service at temperatures above 600°C over extended periods, the alloy exhibits excellent microstructural stability with no significant phase transformations or softening. The allotropic transformation of the cobalt matrix and solid-solution strengthening by tungsten ensure long service life under thermal cycling conditions.
Applicable Media:
1. High-temperature and high-pressure water (primary nuclear reactor circuit)
2. Seawater, saltwater (excellent pitting corrosion resistance)
3. Oxidizing acids: Nitric acid (superior corrosion resistance at room temperature)
4. Non-oxidizing acids: Sulfuric acid (concentration ≤50%), hydrochloric acid (concentration ≤30%) (corrosion rate typically <0.1 mm/a)
5. Alkaline solutions: Sodium hydroxide, potassium hydroxide (resistant to all concentrations)
6. Organic acids: Acetic acid, formic acid, etc.
7. High-temperature oxidizing atmospheres, sulfur/chlorine-containing gases (forms a protective Cr₂O₃ film on the surface)
Note: Stellite 21 has limited corrosion resistance in strongly reducing acids (e.g., concentrated hot hydrochloric acid) and fluorine-containing media.
Stellite 21 is suitable for hot cycling, impact, medium-to-low wear, and corrosive conditions, and is recommended for the following fields:
Application Fields
-
Nuclear Power Industry: Sealing surfaces of nuclear reactor valves (main steam valves, safety valves, isolation valves) and other wear-resistant components within the nuclear island, leveraging its excellent resistance to thermal shock, irradiation, and high-temperature high-pressure water corrosion.
-
Valves and Sealing Industry: Sealing surfaces of medium-to-high pressure valves (valve seats, valve discs, valve stems), particularly suitable for steam valves and feedwater valves with frequent temperature fluctuations, offering superior thermal crack resistance.
-
Aerospace and Energy: Combustion chamber components, guide vanes, and turbine seal rings of gas turbines, which endure severe thermal cycling and oxidation corrosion.
-
Oil and Gas: High-temperature high-pressure valve internals, wellhead equipment, and acid medium processing equipment, with good resistance to H₂S and CO₂ corrosion.
-
Industrial Machinery and Tools: Hot shear blades, hot forging dies, and die-casting molds (gates, plungers) in applications requiring resistance to thermal shock and thermal fatigue.
-
Chemical and Petrochemical: Reactor agitator blades, wear-resistant linings of heat exchanger tube plates, and valve sealing surfaces, which withstand the combined effects of corrosion and wear.
-
Shipbuilding and Offshore Engineering: Wear-resistant surfaces of propeller shafts and valve/pump components, resisting seawater corrosion and mechanical wear.
-
Automotive and Internal Combustion Engines: Engine exhaust valves, rocker arms, and turbocharger seal rings, maintaining wear and seizure resistance under high-temperature cyclic conditions.
-
Steel and Heat Treatment: Hot shear blades, hot saw blades, furnace bottom rolls, and guide rolls, enduring high-temperature oxidation and thermal shock.
-
Glass and Ceramic Forming: Glass molds and hot extrusion molds, due to their good thermal fatigue and corrosion resistance.
Delivery and Customization
We offer flexible and reliable supply chain solutions to ensure you receive Stellite 21 materials that perfectly match your project requirements.
|
Form |
 Sheet/Plate
|
 Bar/Rod
|
 Seamless Pipe
|
 Strip/Sheet Coil
|
 Wire/Wire Rod
|
|---|---|---|---|---|---|
|
Conventional Range |
Thickness: 0.5 - 100 mm |
Diameter Φ6-500mm |
Outer diameter Φ10-300mm |
Thickness: 0.1 – 3.0 mm |
Diameter Φ0.5-10mm |
|
Customization Capability |
Special thick/thin rolling, ultra-wide plates; special surface treatment, fixed-length cutting |
Large-sized forged bars (up to Φ800 mm), special-shaped bars, and various heat treatment conditions |
Large-diameter thick-walled pipes, special alloy composition; Pipe end processing (beveling, fixed length) |
Different hardness conditions, special heat treatments (stabilization treatment, grain size control), acid-washed surfaces, electrolytic polishing, coatings, or special protective films |
Special surface treatment, precision drawing |
Why Choose Us? - Reliable Engineering Technology. Dependable Delivery.
We are not just a supplier, but a trusted materials partner for you in China.
Vertically Integrated Production
Own 20,000㎡ facility with 10+ automated lines (8,000+ tons/year). In-house tooling & die center enables rapid customization and effective cost control - no middleman markup.
Strict Quality Control at Every Stage
Full traceability across key QC checkpoints throughout production. 100% compliant with ASTM/ASME, EN, and GB standards. Material test reports available with every shipment.
Reliable Delivery & Export Packaging
10+ years exporting to Europe, North America, Southeast Asia & Middle East with waterproof and anti-rust protection, combined with flexible shipping options ensures safe and on-time arrival.
Sample Validation Before Mass Production
We provide free samples for quality verification, allowing you to place bulk orders only after approval. We ensure consistency from sample to mass production by accurate dimensional measurement and transparent manufacturing.
FAQ
Q: What are the main advantages of Stellite 21?
Q: What kind of heat treatment does Stellite 21 require?
Q: What is the maximum service temperature?
Q: What is the difference between Stellite 21 and Stellite 6 ?
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