4140 Alloy Steel – Mechanical Tubing
Steel, Mechanical Tubing, 0.95Cr – 0.20Mo (0.38 – 0.43C)
AMS 6381 (also referenced as AMS6381) covers 4140 alloy steel in the form of mechanical tubing. This specification is issued by SAE International and is widely used in aerospace, defense, and high-performance industrial applications requiring high strength, toughness, and good fatigue resistance. The nominal composition of 0.95% Chromium and 0.20% Molybdenum with a carbon range of 0.38–0.43% provides an excellent balance of strength, hardness, and machinability.
The chromium content contributes to hardenability and corrosion resistance, while molybdenum enhances strength at elevated temperatures and improves hardenability. The controlled carbon content in the 0.38–0.43% range places this steel in the medium-carbon category, making it well-suited for heat treatment to achieve a wide range of mechanical properties. AMS 6381 tubing is commonly used in structural, hydraulic, and high-load applications throughout the aerospace and defense industries.
AMS 6381 material is supplied as Mechanical Tubing per specification requirements. Seamless and welded tubing options are available in a range of outside diameters and wall thicknesses. Custom lengths and pre-machined forms are available upon request. Contact our materials specialists for non-standard dimensions.
| Element | Symbol | Nominal % | Notes |
|---|---|---|---|
| Carbon | C | 0.38 – 0.43% | Medium carbon – enables heat treatment to high strength |
| Chromium | Cr | 0.80 – 1.10% (~0.95%) | Improves hardenability and corrosion resistance |
| Molybdenum | Mo | 0.15 – 0.25% (~0.20%) | Enhances hardenability and elevated-temperature strength |
| Manganese | Mn | 0.75 – 1.00% | Deoxidizer; improves hardenability and strength |
| Silicon | Si | 0.15 – 0.35% | Deoxidizer; improves strength |
| Iron | Fe | Balance | Base metal |
| Property / Attribute | Details |
|---|---|
| Specification Number | AMS 6381 (AMS6381) |
| Issuing Organization | SAE International (Society of Automotive Engineers) |
| Material Type | Alloy Steel – Mechanical Tubing |
| Steel Grade | 4140 (AISI / UNS G41400) |
| Nominal Composition | 0.95Cr – 0.20Mo (0.38 – 0.43C) |
| Available Forms | Mechanical Tubing |
| Hardenability | Excellent – responds well to heat treatment over a wide range of section sizes |
| Machinability | Good – approximately 65% of B1112 in annealed condition |
| Weldability | Good – pre- and post-weld heat treatment recommended for heavier sections |
| Fatigue Resistance | High – excellent for cyclically loaded structural applications |
| Magnetic Properties | Magnetic (ferritic/martensitic) |
| Certification Available | AS9100D / ISO 9001, Certificate of Conformance, MTR |
Both AMS 6381 and AMS 6382 cover 4140/4142 alloy steel tubing, but they differ in specific requirements for manufacturing process, heat treatment condition, and mechanical property requirements. AMS 6381 covers mechanical tubing in the 4140 composition range, while AMS 6382 typically addresses seamless tubing with potentially different heat treatment or mechanical property requirements. Your engineering team should review the applicable specification for your specific application. Aero-Vac can supply material to either specification and will help you determine the correct one for your requirements.
Yes. All AMS 6381 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.
Aero-Vac maintains inventory of AMS 6381 mechanical tubing in a range of outside diameters and wall thicknesses. We carry standard sizes and can provide custom-cut lengths from our in-house processing facility at the Port of Kalama. For non-standard dimensions, 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.
In-stock AMS 6381 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 items 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.
Yes. Aero-Vac operates a complete in-house processing facility at our Port of Kalama location. For AMS 6381 alloy steel tubing, 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. 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.
Our alloy steel specialists can provide fast pricing, availability, and technical guidance for your AMS 6381 requirements.
Connect with our materials specialists for custom quotes, technical specifications, and professional guidance on your AMS 6381 / 4140 alloy steel requirements. Fast, honest, and straight-talking.
For immediate assistance, call us toll-free at (877) 237-6822. You can also email us at [email protected]
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2615 N. Hendrickson Dr.
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Call us toll-free at (877) 237-6822 or email [email protected]