4130 Alloy Steel – Bars & Reforging Stock
Steel Bars, Steel Reforging Stock, 0.95Cr – 0.20Mo (Aircraft Quality)
MIL-S-6758 is a Department of Defense Military Specification covering chrome-molybdenum (4130) steel bars and forging stock of aircraft quality. Per the specification: "This specification covers chrome-molybdenum (4130) steel bars and forging stock of aircraft quality." The nominal composition of 0.95% Chromium and 0.20% Molybdenum with a carbon range of 0.28–0.33% delivers an excellent combination of strength, toughness, weldability, and hardenability well suited for demanding aerospace and defense applications.
The chromium content contributes to hardenability and corrosion resistance, while molybdenum enhances strength at elevated temperatures and improves hardenability. The lower carbon content of 0.28–0.33% (compared to 4140) places 4130 in the medium-low carbon category, providing excellent weldability while still enabling heat treatment to achieve a wide range of mechanical properties. MIL-S-6758 bars and reforging stock are widely used in structural, hydraulic, and high-load aerospace and defense applications requiring proven aircraft-quality material.
MIL-S-6758 material is supplied as Steel Bars and Steel Reforging Stock per specification requirements. Round, square, flat, and hexagonal bar forms are available in a range of sizes. Custom lengths and pre-machined forms are available upon request. Contact our materials specialists for non-standard dimensions or specific forging stock requirements.
| Element | Symbol | Nominal % | Notes |
|---|---|---|---|
| Carbon | C | 0.28 – 0.33% | Medium-low carbon – excellent weldability with heat treatable 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 | 0.40 – 0.60% | Deoxidizer; improves hardenability and strength |
| Silicon | Si | 0.15 – 0.35% | Deoxidizer; improves strength |
| Iron | Fe | Balance | Base metal |
| Property / Attribute | Details |
|---|---|
| Specification Number | MIL-S-6758 |
| Issuing Organization | Department of Defense (DoD) – Military Specification |
| Material Type | Alloy Steel – Bars and Reforging Stock |
| Steel Grade | 4130 (AISI / UNS G41300) |
| Nominal Composition | 0.95Cr – 0.20Mo (0.28 – 0.33C) |
| Quality Level | Aircraft Quality |
| Available Forms | Bars, Reforging Stock |
| Hardenability | Good – responds well to heat treatment; suited for through-hardening in moderate section sizes |
| Machinability | Good – approximately 70% of B1112 in annealed condition |
| Weldability | Excellent – one of the best weldable alloy steels; pre-heat recommended for heavier sections |
| Fatigue Resistance | High – excellent for cyclically loaded structural and aircraft applications |
| Magnetic Properties | Magnetic (ferritic/martensitic) |
| Certification Available | AS9100D / ISO 9001, Certificate of Conformance, MTR |
Both MIL-S-6758 and AMS 6345 cover 4130 alloy steel in bar and forging stock forms, but they differ in the issuing authority, specific testing requirements, and documentation standards. MIL-S-6758 is a Department of Defense military specification, while AMS 6345 is issued by SAE International. Both are widely accepted for aerospace and defense applications. Your engineering team or procurement documentation should specify which standard applies to your program. Aero-Vac can supply material to either specification and will help you determine the correct one for your requirements.
Yes. All MIL-S-6758 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 government source inspection, our quality team can coordinate as needed.
Aero-Vac maintains inventory of MIL-S-6758 4130 alloy steel in round bar, square bar, flat bar, and reforging stock forms across a range of standard sizes. We carry standard stock and can provide custom-cut lengths from our in-house processing facility at the Port of Kalama. For non-standard dimensions or large-quantity forging stock requirements, our team can source from our global supplier network. Contact us with your specific size and quantity requirements and we will provide a prompt quote with availability and lead time.
In-stock MIL-S-6758 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 or large-quantity reforging stock 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 MIL-S-6758 4130 alloy steel bars and reforging stock, 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 MIL-S-6758 4130 alloy steel requirements.
Connect with our materials specialists for custom quotes, technical specifications, and professional guidance on your MIL-S-6758 / 4130 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]