AMS Specification 4130 Alloy Steel Chrome-Molybdenum

AMS-S-6758

4130 Alloy Steel – Chrome-Molybdenum, Aircraft Quality

Steel Bars and Reforging Stock, Aircraft Quality
0.95 Cr – 0.20 Mo | Chrome-Molybdenum (4130)

AS9100D / ISO 9001

Mill Test Reports

2–4 Week Delivery

877-237-6822

Quick Specification Facts

Spec Number AMS-S-6758

Material 4130 Chrome-Molybdenum Alloy Steel

Spec Type AMS (Aerospace Material Specification / MilSpec)

Category 4130 Alloy Steel

Composition 0.95 Cr – 0.20 Mo

Condition Aircraft Quality

Product Forms Bars, Reforging Stock

Certification AS9100D / ISO 9001 with full MTR traceability

Specification Overview

AMS-S-6758 is an SAE International aerospace material specification (also recognized as a military specification) covering chrome-molybdenum (4130) alloy steel bars and reforging stock of aircraft quality. Per the specification: "This specification covers chrome-molybdenum (4130) steel bars and forging stock of aircraft quality." It is widely used in aerospace, defense, and high-performance structural applications where a combination of high strength, good toughness, and excellent weldability is required.

The nominal composition of 0.95% Chromium and 0.20% Molybdenum gives 4130 its characteristic chrome-molybdenum designation. The chromium provides hardenability and oxidation resistance, while the molybdenum enhances strength at elevated temperatures and improves hardenability. The low-to-medium carbon content (0.28–0.33%) makes AMS-S-6758 material readily weldable with proper preheat procedures, making it a preferred choice for welded aircraft structures and forged aerospace components.

Available Product Forms

Bars

Reforging Stock

All product forms are supplied to Aircraft Quality per AMS-S-6758 requirements. Bars are available in round, flat, and hex cross-sections. Reforging stock (forging billets) are available in a range of sizes suitable for custom forging operations. Custom sizes, lengths, and pre-machined forms are available upon request. Contact our materials specialists for non-standard dimensions.

Nominal Chemical Composition

Element	Symbol	Range / Nominal %	Notes
Carbon	C	0.28–0.33%	Provides strength; low enough for good weldability
Chromium	Cr	0.80–1.10% (0.95 nominal)	Hardenability and oxidation resistance
Molybdenum	Mo	0.15–0.25% (0.20 nominal)	Elevated temperature strength and hardenability
Manganese	Mn	0.40–0.60%	Hardenability and deoxidizer
Silicon	Si	0.20–0.35%	Deoxidizer; strength contribution
Iron	Fe	Balance	Base metal

Chemical composition ranges are nominal. Consult the current issue of AMS-S-6758 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-S-6758
Issuing Organization	SAE International (Society of Automotive Engineers)
Material Type	Chrome-Molybdenum Alloy Steel, Aircraft Quality
Steel Grade	4130 (AISI / UNS G41300)
Nominal Composition	0.95 Cr – 0.20 Mo
Condition	Aircraft Quality (Normalized, Annealed, or as specified)
Available Forms	Bars, Reforging Stock
Tensile Strength (normalized)	97,000 psi (670 MPa) min
Yield Strength (normalized)	63,000 psi (434 MPa) min
Weldability	Good – preheat recommended for heavier sections
Machinability	Good – approximately 72% of AISI 1212
Magnetic Properties	Magnetic (ferritic/martensitic alloy steel)
Certification Available	AS9100D / ISO 9001, Certificate of Conformance, MTR

Typical Applications

Aerospace Structures: Aircraft fuselage frames, wing fittings, engine mounts, firewall structures, and welded tubular assemblies requiring high strength-to-weight ratio and reliable weldability.

Landing Gear & Structural Components: Landing gear struts, drag struts, torque links, and structural brackets where fatigue resistance and toughness are critical.

Forged Aerospace Parts: Reforging stock used to produce precision forgings such as fittings, clevises, flanges, and other near-net-shape aerospace components.

Defense & Military: Military aircraft components, ordnance hardware, vehicle structural members, and weapons system parts requiring aircraft-quality alloy steel.

High-Performance Industrial: Hydraulic cylinders, pressure vessels, tooling fixtures, shafts, and mechanical components requiring good strength, toughness, and machinability.

Frequently Asked Questions – AMS-S-6758

What is AMS-S-6758 and what does it cover?

AMS-S-6758 is an SAE International aerospace material specification (also recognized as a military specification) covering chrome-molybdenum (4130) alloy steel bars and reforging 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 provides an excellent balance of strength, toughness, and weldability. It is widely used in aerospace, defense, and high-performance structural applications where reliable mechanical performance is critical.

What is 4130 alloy steel and why is it preferred for aerospace applications?

4130 alloy steel (AISI/UNS G41300) is a chrome-molybdenum steel widely used in aerospace and defense due to its excellent combination of strength, toughness, ductility, and weldability. The chromium content (0.80–1.10%) improves hardenability and oxidation resistance, while molybdenum (0.15–0.25%) enhances elevated-temperature strength and hardenability uniformity. The relatively low carbon content (0.28–0.33%) makes 4130 significantly more weldable than higher-carbon steels, an important characteristic for aircraft structures. When heat treated, 4130 can achieve tensile strengths well above 125,000 psi, making it a cost-effective choice for aircraft frames, engine mounts, landing gear components, and forged fittings.

Does Aero-Vac supply AMS-S-6758 with full mill test reports and certifications?

Yes. All AMS-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, our quality team can coordinate as needed.

What forms and sizes of AMS-S-6758 does Aero-Vac stock?

Aero-Vac maintains inventory of AMS-S-6758 in both bars (round, flat, and hex) and reforging stock (forging billets). We carry a range of standard sizes and can provide custom-cut lengths, discs, and blocks from our in-house processing facility at the Port of Kalama. For reforging stock, we stock a variety of billet sizes suitable for custom forging operations. 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.

What are the typical lead times for AMS-S-6758 material?

In-stock AMS-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 reforging stock or items requiring mill production may require 4–8 weeks depending on quantity and form. 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-S-6758 material?

Yes. Aero-Vac operates a complete in-house processing facility at our Port of Kalama location. For AMS-S-6758 4130 alloy steel, we offer precision saw cutting (including disc and ring cutting), surface grinding, trepanning, turning, milling, and heat treatment (normalizing, annealing, quench and temper). 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 AMS-S-6758 material or a custom quote?

Our alloy steel specialists can provide fast pricing, availability, and technical guidance for your AMS-S-6758 / 4130 alloy steel requirements.