AMS Specification 21-6-9 (NIT 40) Stainless Steel

AMS 5656

21-6-9 (NIT 40) Stainless Steel – Bars, Wire, Forgings, Extrusions & Rings

Steel, Corrosion Resistant, Bars, Wire, Forgings, Extrusions, and Rings – 9.0Mn 20Cr 6.5Ni 0.27N Solution Heat Treated

AS9100D / ISO 9001

Mill Test Reports

2–4 Week Delivery

877-237-6822

Quick Specification Facts

Spec Number AMS 5656 (AMS5656)

Material 21-6-9 (NIT 40) Stainless Steel

Spec Type AMS (Aerospace Material Specification)

Category Stainless Steels / 21-6-9

Composition 9.0Mn 20Cr 6.5Ni 0.27N

Condition Solution Heat Treated

Product Forms Bars, Wire, Forgings, Extrusions, and Rings

Certification AS9100D / ISO 9001 with full MTR traceability

Specification Overview

AMS 5656 (also referenced as AMS5656) covers 21-6-9 stainless steel, also known as NIT 40, in the form of bars, wire, forgings, extrusions, and rings. This specification is issued by SAE International and is widely used in aerospace, defense, and cryogenic applications requiring high strength, excellent corrosion resistance, and non-magnetic properties. The alloy's nominal composition of 9.0% Manganese, 20% Chromium, 6.5% Nickel, and 0.27% Nitrogen provides an outstanding combination of mechanical strength, toughness, and resistance to corrosion across a broad temperature range.

AMS 5656 material is supplied in the Solution Heat Treated condition, which dissolves alloying elements into a uniform austenitic matrix, optimizing corrosion resistance and mechanical properties. The high manganese content partially replaces nickel as an austenite stabilizer, while the elevated nitrogen content acts as a potent solid-solution strengthener—significantly increasing yield and tensile strength compared to conventional 300-series austenitic stainless steels. The combination of high strength, non-magnetic character, and outstanding performance at both ambient and cryogenic temperatures makes 21-6-9 (NIT 40) one of the most important stainless steels for critical aerospace structural and pressure-containing components.

Available Product Forms

Bars

Wire

Forgings

Extrusions

Rings

AMS 5656 material is supplied as Bars, Wire, Forgings, Extrusions, and Rings per specification requirements. Round bar, hex bar, wire, and forged ring forms are available in a range of diameters and cross-sections. Custom forgings, near-net-shape forgings, and extruded profiles are available upon request. Contact our materials specialists for non-standard dimensions or custom processing requirements.

Nominal Chemical Composition

Element	Symbol	Nominal %	Notes
Iron	Fe	Balance	Base metal – provides structural integrity and toughness
Chromium	Cr	20%	Primary corrosion and oxidation resistance; austenite stabilizer
Manganese	Mn	9.0%	Austenite stabilizer; partially replaces nickel; improves nitrogen solubility
Nickel	Ni	6.5%	Austenite stabilizer; improves toughness and corrosion resistance
Nitrogen	N	0.27%	Potent solid-solution strengthener; stabilizes austenite; improves pitting resistance

Chemical composition ranges are nominal. Consult the current issue of AMS 5656 for precise minimum/maximum requirements. Aero-Vac provides full mill test reports (MTRs) with certified chemistry for every order.

Key Properties & Specification Details

Property / Attribute	Details
Specification Number	AMS 5656 (AMS5656)
Issuing Organization	SAE International (Society of Automotive Engineers)
Material Type	Steel – Corrosion Resistant, Bars, Wire, Forgings, Extrusions, and Rings
Alloy Name	21-6-9 Stainless Steel (NIT 40)
Nominal Composition	9.0Mn 20Cr 6.5Ni 0.27N
Heat Treatment Condition	Solution Heat Treated
Available Forms	Bars, Wire, Forgings, Extrusions, and Rings
Strength	High – significantly stronger than conventional 304/316 austenitic stainless steels due to nitrogen strengthening
Corrosion Resistance	Very Good – excellent resistance to corrosion in a wide variety of environments due to high chromium content
Cryogenic Performance	Excellent – maintains toughness and ductility at cryogenic temperatures; suitable for liquid nitrogen/oxygen service
Machinability	Moderate – similar to other high-manganese austenitic stainless steels; work hardening tendency requires appropriate tooling
Weldability	Good – can be welded using standard austenitic stainless steel procedures; low carbon minimizes sensitization risk
Magnetic Properties	Non-magnetic (austenitic)
Certification Available	AS9100D / ISO 9001, Certificate of Conformance, MTR

Typical Applications

Aerospace Structural Components: High-strength fasteners, bolts, nuts, shafts, and structural forgings for aerospace applications requiring superior strength combined with non-magnetic properties and excellent corrosion resistance.

Cryogenic Applications: Pressure vessels, piping, valves, and fittings for liquid nitrogen, liquid oxygen, and other cryogenic fluid systems where excellent low-temperature toughness and non-magnetic properties are essential.

Rocket & Space Systems: Rocket engine components, propellant lines, storage tanks, and structural members for launch vehicles and spacecraft requiring high strength-to-weight ratio and cryogenic performance.

Defense Applications: Missile airframes, ordnance components, and military systems requiring high strength, non-magnetic character, and reliable performance across a wide temperature range.

Hydraulic & Pressure Systems: Actuator housings, hydraulic fittings, rings, and extruded profiles for aerospace hydraulic and pneumatic systems where high pressure capacity and corrosion resistance are required.

Frequently Asked Questions – AMS 5656

What is AMS 5656 and what does it cover?

AMS 5656 (also written AMS5656) is an SAE International aerospace material specification covering 21-6-9 stainless steel, also known as NIT 40, in the form of bars, wire, forgings, extrusions, and rings. The nominal chemistry of 9.0Mn 20Cr 6.5Ni 0.27N delivers high strength, excellent corrosion resistance, and non-magnetic properties across a wide temperature range including cryogenic service. The material is supplied in the Solution Heat Treated condition. It is widely used in aerospace structures, cryogenic systems, rocket propulsion, and defense applications where high strength combined with corrosion resistance and non-magnetic character are critical requirements.

What is 21-6-9 (NIT 40) stainless steel and what makes it unique?

21-6-9 stainless steel, sometimes called NIT 40, is a high-nitrogen, high-manganese austenitic stainless steel. The designation "21-6-9" refers to its approximate chromium (21%), nickel (6%), and manganese (9%) contents. Its high nitrogen content (approximately 0.27%) is the key feature that distinguishes it from conventional 300-series stainless steels—nitrogen acts as a potent solid-solution strengthener, providing yield and tensile strengths significantly higher than standard 304 or 316 grades. The high manganese content partially replaces nickel as an austenite stabilizer while improving nitrogen solubility in the melt. The result is a fully austenitic, non-magnetic alloy with excellent strength, toughness, corrosion resistance, and outstanding cryogenic performance, making it ideal for aerospace fasteners, pressure vessels, and structural components.

Does Aero-Vac supply AMS 5656 with full mill test reports and certifications?

Yes. All AMS 5656 material supplied by Aero-Vac is fully traceable to mill test reports (MTRs) confirming chemical composition and mechanical properties per the specification. We are AS9100D/ISO 9001 certified with a 99.6% quality rating. Every order ships with certificates of conformance, material certifications, and chemical/mechanical test reports. Electronic delivery of all documentation is available for fast turnaround. If your program requires additional special process certifications, our quality team can coordinate as needed.

What sizes of AMS 5656 bars, wire, and forgings does Aero-Vac stock?

Aero-Vac maintains inventory of AMS 5656 21-6-9 stainless steel in round bar, wire, and forging forms across a range of diameters and sizes. We carry standard bar diameters and can provide custom-cut lengths from our in-house processing facility at the Port of Kalama. For custom forgings, extrusions, rings, or near-net-shape requirements, our team can source from our global supplier network. Contact us with your specific size, form, and quantity requirements and we will provide a prompt quote with availability and lead time.

What are the typical lead times for AMS 5656 material?

In-stock AMS 5656 material is typically available for same-day or next-day shipment. For custom-cut or specially processed orders, our standard lead time is 2–4 weeks—significantly faster than the industry average of 8–12 weeks. Specialty forgings, extrusions, or rings requiring mill production may require 4–8 weeks depending on quantity and dimensions. We prioritize urgent aerospace and defense requirements and will always provide honest, upfront delivery estimates. Rush processing is available on select items.

Can Aero-Vac provide value-added processing for AMS 5656 21-6-9 stainless steel material?

Yes. Aero-Vac operates a complete in-house processing facility at our Port of Kalama location. For AMS 5656 21-6-9 stainless steel bars, wire, forgings, extrusions, and rings, we offer precision saw cutting, surface grinding, turning, milling, and heat treatment services. We also provide comprehensive mechanical and non-destructive testing services in-house. 21-6-9's work-hardening characteristics require appropriate machining practices, and our experienced team is equipped to handle this demanding high-nitrogen stainless steel. Having all capabilities under one roof allows for faster turnaround, tighter quality control, and reduced overall cost compared to using multiple vendors. Contact us to discuss your specific processing requirements.

Need AMS 5656 material or a custom quote?

Our stainless steel specialists can provide fast pricing, availability, and technical guidance for your AMS 5656 21-6-9 (NIT 40) stainless steel requirements.