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Stainless Steel 21-6-9
21-6-9 AMS5561 CL 1&2 | BMS 7-185
Product description
Alloy 21-6-9 AMS 5561 Stainless Steel Tube
High-Strength Austenitic Stainless Steel Tubing for Demanding Aerospace Applications
Alloy 21-6-9 (UNS S21900) to AMS 5561 specification is a nitrogen-strengthened austenitic stainless steel, known for its exceptional mechanical strength, excellent corrosion resistance, and superb weldability. Engineered to meet the stringent requirements of the aerospace industry, this material is ideally suited for high-temperature hydraulic lines, structural tubing, and other critical applications where strength-to-weight ratio and reliability are paramount.
Manufactured to AMS 5561, this seamless or welded and drawn tubing provides a minimum yield strength of 85 ksi, offering enhanced resistance to stress-corrosion cracking and deformation under pressure. Its stable austenitic structure ensures consistent performance across a wide range of operating environments, from cryogenic temperatures to elevated service conditions.
Key Features:
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Specification: AMS 5561
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Material: Stainless Steel Alloy 21-6-9 (UNS S21900)
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Form: Seamless or welded & drawn tubing
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Minimum Yield Strength: 85 ksi
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Temperature Range: Excellent performance from sub-zero to elevated temperatures
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Corrosion Resistance: Superior to standard austenitic grades in oxidizing environments
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Weldability: Readily weldable using standard techniques with minimal risk of hot cracking
Typical Applications:
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Aircraft hydraulic and pneumatic systems
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High-pressure fuel and exhaust systems
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Structural tubing for aerospace and defense
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Engine and afterburner components
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Cryogenic containment systems
The 21-6-9 AMS5561 aerospace tube is a high-strength, corrosion-resistant stainless steel alloy tube primarily used in aircraft and aerospace applications.
21-6-9 refers to its nominal composition: ~21% chromium, ~6% nickel, and ~9% manganese.
AMS5561 is the Aerospace Material Specification that defines its properties, dimensions, and manufacturing standards.
It offers excellent resistance to oxidation, scaling, and corrosion, while maintaining good toughness and strength at both high and low temperatures.
This makes it ideal for aircraft hydraulic systems, engine components, and structural tubing where durability and reliability are critical.
In aerospace, the requirement for a meticulous process ensures the tube meets high strength, toughness, and corrosion resistance requirements for critical applications like hydraulic systems, landing gear, and engine tubing.
The 21-6-9 stainless steel (AMS5561 tube) is sometimes called the “workhorse nitrogen-strengthened alloy” in aerospace because the addition of nitrogen gives it unusually high strength without sacrificing toughness at cryogenic temperatures.
That means the same tubing that handles jet engine heat and stress can also perform reliably in liquid hydrogen or liquid oxygen environments—which is why it has been used not just in aircraft, but also in rocket propulsion systems. 🚀
Technical Specification
| Specification | Material | Publication Date |
|---|---|---|
| AMS5561 | Steel, Corrosion and Heat-Resistant, Welded and Drawn or Seamless and Drawn Tubing | 30/11/1974 |
| BMS 7-185 | Boeing Material Specification – Metallic Tube |
In an attempt to try and unify the designations used, a system called the Unified Numbering System was developed by the American Society for Testing and Materials (ASTM) and Society of Automotive Engineers (SAE) in 1972.
Technical Data
| Specification | Yield Strength | Tensile Strength | Elongation |
|---|---|---|---|
| AMS5561 | 120 ksi Minimum | 142 to 162 ksi | 20% Minimum |
Aerocom Stock List
| OD (Inches) | 0.016 | 0.020 | 0.026 | 0.028 | 0.033 | 0.036 | 0.039 | 0.052 |
|---|---|---|---|---|---|---|---|---|
| 0.250 | STOCK | STOCK | ||||||
| 0.3125 | STOCK | STOCK | STOCK | |||||
| 0.375 | STOCK | |||||||
| 0.500 | STOCK | STOCK | ||||||
| 0.625 | STOCK | |||||||
| 0.750 | STOCK | |||||||
| 1.000 | STOCK |