MIL Specification 4340 High Tensile Steel Alloy Steel

MIL-S-5000

4340 High Tensile Steel – Chrome-Nickel-Molybdenum

Steel, Chrome-Nickel-Molybdenum (4340) Bars, and Forging Stock
Military (Department of Defense) Specification | Superseded by SAE-AMS-S-5000

AS9100D / ISO 9001

Mill Test Reports

2–4 Week Delivery

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Quick Specification Facts

Spec Number MIL-S-5000 (MIL-S5000)

Material 4340 High Tensile Steel

Spec Type MIL (Military / Department of Defense Specification)

Category 4340V High Tensile Steel / Alloy Steel

Composition Chrome-Nickel-Molybdenum (4340)

Superseded By SAE-AMS-S-5000

Product Forms Bars, Forging Stock

Certification AS9100D / ISO 9001 with full MTR traceability

Specification Overview

MIL-S-5000 (also referenced as MIL-S5000) is a Military (Department of Defense) specification covering Chrome-Nickel-Molybdenum (4340) high tensile steel in the form of bars and forging stock. This specification has been superseded by SAE-AMS-S-5000 but remains widely referenced in legacy aerospace, defense, and military procurement documents. It specifies requirements for one of the most widely used high-strength alloy steels in the world.

4340 steel per MIL-S-5000 is a nickel-chromium-molybdenum alloy steel known for its exceptional strength, toughness, and hardenability. The combination of chromium, nickel, and molybdenum provides deep hardenability, allowing large cross-sections to be heat treated to high strength levels while retaining excellent toughness and fatigue resistance. This makes it a premier choice for highly stressed structural components in aerospace, defense, and industrial applications.

Available Product Forms

Bars

Forging Stock

All product forms are supplied per MIL-S-5000 / SAE-AMS-S-5000 requirements. Bars are available in round, flat, and hex profiles. Custom sizes, lengths, and pre-machined forms are available upon request. Contact our materials specialists for non-standard dimensions or special processing requirements.

Nominal Chemical Composition

Element	Symbol	Range %	Notes
Carbon	C	0.38–0.43%	Primary hardening element
Manganese	Mn	0.65–0.85%	Hardenability and strength
Silicon	Si	0.15–0.35%	Deoxidizer
Chromium	Cr	0.70–0.90%	Hardenability and wear resistance
Nickel	Ni	1.65–2.00%	Toughness and deep hardenability
Molybdenum	Mo	0.20–0.30%	Hardenability and high-temperature strength
Iron	Fe	Balance	Base metal

Chemical composition ranges are nominal. Consult the current issue of MIL-S-5000 or its superseding document SAE-AMS-S-5000 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	MIL-S-5000 (MIL-S5000)
Issuing Organization	U.S. Department of Defense (Military Specification)
Superseded By	SAE-AMS-S-5000
Material Type	Chrome-Nickel-Molybdenum High Tensile Alloy Steel
Steel Grade	4340 (AISI / UNS G43400)
Nominal Composition	Cr-Ni-Mo (4340)
Available Forms	Bars, Forging Stock
Tensile Strength (typical)	Up to 280 ksi (1930 MPa) depending on heat treatment condition
Hardenability	Excellent – deep hardenability suitable for large cross-sections
Toughness	Very good impact toughness even at high strength levels
Weldability	Fair – pre-heat and post-weld heat treatment recommended
Certification Available	AS9100D / ISO 9001, Certificate of Conformance, MTR

Typical Applications

Aerospace & Defense: Aircraft structural components, landing gear components, airframe fittings, wing spars, and highly stressed structural members requiring exceptional strength-to-weight ratio and fatigue resistance.

Power Transmission: Gears, shafts, axles, crankshafts, and drive components where high tensile strength, toughness, and wear resistance are critical under cyclic loading conditions.

Military & Ordnance: Weapon system components, armor fittings, gun barrels, and military vehicle components requiring superior strength and impact resistance per Department of Defense requirements.

Tooling & Dies: Heavy-duty tooling, forging dies, press tools, and large structural components requiring through-hardening and dimensional stability at elevated hardness levels.

Industrial & Oil & Gas: High-pressure vessels, drilling equipment components, subsea hardware, and industrial machinery parts subjected to extreme stress, pressure, and fatigue loading.

Frequently Asked Questions – MIL-S-5000

What is MIL-S-5000 and what does it cover?

MIL-S-5000 (also written MIL-S5000) is a Military (Department of Defense) specification covering Chrome-Nickel-Molybdenum (4340) high tensile steel in the form of bars and forging stock. This specification has been superseded by SAE-AMS-S-5000 but remains widely referenced in legacy defense and aerospace procurement documents. 4340 steel per this specification is renowned for its exceptional combination of high tensile strength, deep hardenability, and excellent toughness, making it one of the most widely used high-strength alloy steels in aerospace and defense applications.

What is the difference between MIL-S-5000 and AMS 6414?

Both MIL-S-5000 and AMS 6414 cover 4340 alloy steel, but they differ in origin and scope. MIL-S-5000 is a Department of Defense (military) specification, while AMS 6414 is issued by SAE International as an Aerospace Material Specification. MIL-S-5000 has been superseded by SAE-AMS-S-5000. AMS 6414 covers a broader range of product forms including bars, forgings, tubing, and rings, while MIL-S-5000 specifically addresses bars and forging stock. For current procurements, AMS 6414 or AMS-S-5000 are typically specified, but MIL-S-5000 material remains acceptable where legacy contracts reference it. Our team can advise on the most appropriate specification for your application.

Does Aero-Vac supply MIL-S-5000 material with full mill test reports and certifications?

Yes. All MIL-S-5000 / 4340 alloy steel 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 or Defense Contract Audit Agency (DCAA) compliance documentation, our quality team can coordinate as needed.

What forms and sizes of MIL-S-5000 / 4340 steel does Aero-Vac stock?

Aero-Vac maintains inventory of MIL-S-5000 / 4340 high tensile steel in multiple product forms including round bars, flat bars, hex bars, and forging stock (billets and blocks). We carry a range of standard sizes from small diameter rounds to large cross-section billets and can provide custom-cut lengths, discs, and blocks from our in-house processing facility at the Port of Kalama. For non-standard dimensions or very large forgings, our team can source from our global supplier network. Contact us with your specific size requirements and we will provide a prompt quote with availability and lead time.

What are the typical lead times for MIL-S-5000 material?

In-stock MIL-S-5000 / 4340 alloy steel 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 forging stock or items requiring mill production may require 4–8 weeks depending on quantity and size. 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 MIL-S-5000 / 4340 material?

Yes. Aero-Vac operates a complete in-house processing facility at our Port of Kalama location. For MIL-S-5000 / 4340 alloy steel, we offer precision saw cutting (including disc and ring cutting), surface grinding, trepanning, turning, milling, and heat treatment including annealing, normalizing, and quench-and-temper cycles. We also provide comprehensive mechanical and non-destructive testing services in-house. 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 MIL-S-5000 material or a custom quote?

Our alloy steel specialists can provide fast pricing, availability, and technical guidance for your MIL-S-5000 / 4340 high tensile steel requirements.