AISI 4340 Forging Steel
AISI 4340 (UNS G43400) is a high-strength Ni-Cr-Mo alloy forging steel with exceptional toughness and deep hardenability. After Q+T, tensile strength reaches 900-1400 MPa with excellent fatigue resistance. Available as forged round bars (80-1500mm), blocks up to 30 tons, and rings up to 5m OD for aerospace, oil & gas, and heavy machinery components.
| Material | Alloy Steel (Ni-Cr-Mo, High Strength) |
|---|---|
| Grade / Standard | AISI 4340 / SAE 4340 (UNS G43400) |
| Diameter | Round Bar: 80mm - 1500mm / Block: up to 30 Tons / Ring: up to 5000mm OD |
| Length | Up to 12m (Round Bar) / Custom (Forged Block & Ring) |
| Delivery Condition | hot_rolled / normalized / quenched_tempered / annealed |
| Surface Treatment | painting / polished / coated |
| MOQ | 1 Piece (Custom Forging) / 1 Ton (Standard Bar) |
| Delivery Time | 30-60 Days (Custom Forging) / 15-25 Days (Stock Bar) |
| Loading Port | Tianjin / Shanghai / Qingdao |
Overview of AISI 4340 Forging Steel
AISI 4340 is a high-strength, medium-carbon nickel-chromium-molybdenum low-alloy forging steel, specified under ASTM A29/A29M with UNS G43400 designation. It contains approximately 0.40% carbon, 1.8% nickel, 0.8% chromium, and 0.25% molybdenum, offering an exceptional combination of very high tensile strength, outstanding toughness, and deep hardenability even in large cross-sections. AISI 4340 is renowned for its superior fatigue resistance and shock-load absorption capability, making it the premier choice for the most demanding forged components in aerospace, defense, oil & gas, and heavy machinery industries.
The high nickel content imparts deep through-hardening characteristics and maintains excellent notch toughness at low temperatures, while chromium and molybdenum provide wear resistance and high-temperature strength. After quenching and tempering (Q+T), AISI 4340 can achieve tensile strengths ranging from 900 MPa to over 1400 MPa, with corresponding yield strengths above 800 MPa and impact energies exceeding 40 Joules at room temperature. The grade is typically supplied in forged round bar, forged block, forged ring, and forged shaft configurations, manufactured through open-die or closed-die forging processes, and is also available to aerospace material specifications such as AMS 6415.
Key Features and Forging Manufacturing
AISI 4340 forging steel is produced through electric arc furnace (EAF) melting followed by vacuum degassing (VD) or electroslag remelting (ESR) for premium quality, low-inclusion content applications. The refined ingot or bloom is hot forged using hydraulic presses or hammers at temperatures between 1100-1200°C, with careful temperature control to prevent grain coarsening. A forging reduction ratio of at least 4:1 is standard to homogenize the microstructure and ensure isotropic mechanical properties throughout the component cross-section.
For critical applications such as aircraft landing gear or rotating shafts, AISI 4340 forgings undergo rigorous heat treatment including normalizing, austenitizing, oil or polymer quenching, and double tempering to optimize strength and toughness. Ultrasonic testing (UT) per ASTM A388 or AMS-STD-2154 is mandatory for forgings in cross-sections over 50mm, ensuring detection of any internal discontinuities. The forging is supplied in dimensions from 80mm to 1500mm diameter for round bars, forged blocks up to 30 tons, and forged rings up to 5 meters outer diameter. Custom machining, including rough turning, semi-finishing, and finish machining to tight tolerances, is available to support final component fabrication.
Main Applications of AISI 4340 Forging Steel
AISI 4340 is the material of choice for aerospace structural forging components, including landing gear struts, cylinders, and trunnions for commercial and military aircraft, helicopter rotor shafts, and critical wing/fuselage attachment fittings subjected to high cyclic loads and fatigue. The defense industry uses AISI 4340 for cannon barrels, armored vehicle drivetrain components, missile bodies, and submarine structural forgings requiring ballistic toughness and strength.
The oil and gas industry extensively employs AISI 4340 for subsea wellhead components, blowout preventer (BOP) bodies, drill stem subs and crossovers, and high-pressure valve bodies operating in deepwater and sour service environments. Power generation applications include high-speed turbine and compressor shafts, generator rotor end rings, and hydroelectric turbine shafting. Other major applications encompass heavy gears and pinions for mining and cement mills, marine propulsion shafting and rudder stocks, railway locomotive axles, and large industrial press rams and columns requiring maximum reliability under extreme stress conditions.
Why Choose Us for AISI 4340 Forging Steel
Shandong Tanglu Metal Material Co., Ltd. supplies premium AISI 4340 forging steel produced by major, internationally accredited Chinese forging mills with AS9100, ISO 9001, and NADCAP certifications for aerospace-grade materials. Every AISI 4340 forging undergoes mandatory chemical composition verification per ASTM A29, comprehensive mechanical property testing including tensile, yield, elongation, reduction of area, and Charpy V-notch impact at specified temperatures, ultrasonic testing (UT) per ASTM A388, and dimensional/layout inspection per customer or standard specifications.
We offer the full spectrum of AISI 4340 forging services: open-die forging for prototypes and large one-off components, closed-die forging for high-volume production runs, seamless ring rolling up to 5 meters diameter, and custom forging-to-print with options for rough, semi-finished, or finished machining. Our supply capacity of 3,000 tons of alloy steel forgings per month and proven export experience to aerospace, oil & gas, and heavy machinery sectors in over 40 countries ensure reliable delivery of consistent, high-quality products. Each shipment is accompanied by an EN 10204 3.1 Mill Test Certificate, with EN 10204 3.2 inspection and third-party certification (SGS, BV, ABS, DNV, LR) available for critical applications requiring enhanced traceability and independent validation.
📐 Dimension & Size Table
| Diameter (mm) | Length (m) | Weight (kg/m) | Forging Process |
|---|---|---|---|
| 80 | 1.0 - 6.0 | 39.46 | Open-die / Hammer |
| 100 | 1.0 - 6.0 | 61.65 | Open-die / Hammer |
| 150 | 1.0 - 6.0 | 138.72 | Open-die / Hydraulic Press |
| 200 | 1.0 - 6.0 | 246.62 | Open-die / Hydraulic Press |
| 250 | 1.0 - 5.0 | 385.34 | Hydraulic Press |
| 300 | 1.0 - 5.0 | 554.89 | Hydraulic Press |
| 400 | 1.0 - 4.0 | 986.47 | Hydraulic Press |
| 500 | 1.0 - 4.0 | 1541.35 | Hydraulic Press |
| 600 | 1.0 - 3.5 | 2219.55 | Heavy Hydraulic Press |
| 800 | 1.0 - 3.0 | 3945.86 | Heavy Hydraulic Press |
| 1000 | 1.0 - 2.5 | 6165.40 | Heavy Hydraulic Press |
| 1200 | 1.0 - 2.0 | 8878.18 | Heavy Hydraulic Press |
| 1500 | 1.0 - 2.0 | 13872.16 | Heavy Hydraulic Press |
* Custom sizes available upon request. Tolerances per relevant international standards.
🔬 Chemical Composition
| Element | Min | Max | Display Value | Note |
|---|---|---|---|---|
| C | 0.38 | 0.43 | 0.38-0.43 | Per ASTM A29 AISI 4340 |
| Si | 0.15 | 0.35 | 0.15-0.35 | |
| Mn | 0.60 | 0.80 | 0.60-0.80 | |
| P | - | 0.035 | ≤0.035 | Per ASTM A29; lower on request for aerospace |
| S | - | 0.040 | ≤0.040 | Per ASTM A29; lower S achievable |
| Cr | 0.70 | 0.90 | 0.70-0.90 | Hardenability & wear resistance |
| Ni | 1.65 | 2.00 | 1.65-2.00 | Toughness & deep hardenability |
| Mo | 0.20 | 0.30 | 0.20-0.30 | High-temperature strength & hardenability |
| Cu | - | 0.35 | ≤0.35 | Residual element |
* Chemical composition may vary by heat, thickness and specification. Please refer to the actual mill test certificate.
⚙️ Mechanical Properties
| Property | Value | Unit | Test Condition |
|---|---|---|---|
| Tensile Strength (Q+T, d≤16mm) | 1200-1400 | MPa | Quenched & Tempered (typical) |
| Tensile Strength (Q+T, 16<d≤40mm) | 1100-1300 | MPa | Quenched & Tempered (typical) |
| Tensile Strength (Q+T, 40<d≤100mm) | 1000-1200 | MPa | Quenched & Tempered (typical) |
| Tensile Strength (Q+T, 100<d≤250mm) | 900-1100 | MPa | Quenched & Tempered (typical) |
| Yield Strength (Q+T, d≤16mm) | ≥1000 | MPa | 0.2% proof stress (typical) |
| Yield Strength (Q+T, 40<d≤100mm) | ≥750 | MPa | 0.2% proof stress (typical) |
| Elongation (A5) | ≥10-12 | % | Depending on thickness |
| Reduction of Area (Z) | ≥45-50 | % | Depending on thickness |
| Impact Energy (KV2) | ≥40-55 | J | Charpy V-notch at +20°C (typical) |
| Brinell Hardness (Annealed) | ≤269 | HBW | Soft annealed condition for machining |
| Brinell Hardness (Q+T) | 300-380 | HBW | Quenched & Tempered (typical) |
* Values shown are minimum requirements unless otherwise stated.
📦 Commercial Information
| Packaging | Standard seaworthy export packing for forging components. Forged round bars are bundled with heavy-duty steel strapping (3-5 wraps per bundle), bundle weight typically 2-5 tons. Large forgings (>500mm diameter or >5 tons single piece) are packed individually with secured wooden cradles, steel angle edge protection, and waterproof film wrapping or VCI paper. Custom packaging including fumigated wooden crates and vacuum-sealed barrier film is available for premium machined components. Each forging is permanently marked with heat number, grade designation (AISI 4340 / SAE 4340), dimensions, weight, and heat treatment condition, ensuring full traceability. |
|---|---|
| Payment Terms | T/T (Telegraphic Transfer),L/C (Letter of Credit),D/P (Documents against Payment),Western Union,PayPal |
| Price Term | FOB,CFR,CIF,EXW |
| Supply Capacity | 3,000 Tons/Month (Alloy Steel Forgings) |
| Loading Port | Tianjin / Shanghai / Qingdao |
Why Choose Our AISI 4340 Forging Steel?
Aerospace & Defense Grade Quality
AISI 4340 forgings supplied with original mill test certificate EN 10204 3.1/3.2, meeting ASTM A29 and AMS 6415 requirements. Full chemical analysis, mechanical properties from Q+T test samples, ultrasonic testing per ASTM A388/AMS-STD-2154, and complete metallurgical traceability from heat to finished forging ensure the highest quality for critical applications.
Capability for Large, Complex Forgings
Round bars from 80mm to 1500mm diameter, forged blocks up to 30 tons, and seamless rolled rings up to 5000mm OD. Custom open-die and closed-die forging services per customer drawings are available, with options for rough, semi-finished, and finish machining to support complete component manufacturing.
Exceptional Strength & Toughness Combination
The high nickel content (1.65-2.00%) provides unmatched toughness and fatigue resistance for highly stressed components. After Q+T, 4340 achieves tensile strengths from 900 to 1400 MPa while maintaining Charpy impact energies above 40J at room temperature, making it ideal for aerospace landing gear, shafts, and heavy machinery.
Multi-Industry & Class Approvals
Our supply chain is supported by ISO 9001, AS9100, and NADCAP certified mills. We can provide forgings with additional material certifications including ABS, DNV, LR, BV, SGS, and PED/CE marking for pressure equipment, ensuring compliance with the most stringent project specifications.
Reliable Project Supply & Logistics
Standard round bar delivery is 15-25 days from stock. Custom forging production takes 30-60 days depending on complexity. We have extensive experience in global logistics, safely shipping forgings up to 30 tons single piece via FCL, break-bulk, or open-top containers with full export documentation and packing security.
🏭 Applications of AISI 4340 Forging Steel
AISI 4340 forging steel is the definitive material for aerospace structural components including landing gear struts, cylinders, and trunnions for commercial and military aircraft, helicopter rotor shafts, and critical wing/fuselage fittings. The defense industry uses AISI 4340 for cannon barrels, armored vehicle drivetrain components, and submarine structural parts. The oil and gas sector relies on 4340 for subsea wellhead bodies, BOP forgings, high-pressure valve bodies, and downhole tool components operating in deepwater and sour service conditions. Power generation applications include high-speed turbine shafts, gas turbine compressor disks, and generator rotor forgings. Other major applications encompass heavy gears and pinions for mining and cement mills, marine propeller and intermediate shafts, railway locomotive axles, and large industrial press rams and columns requiring maximum strength and reliability under extreme cyclic and shock loading conditions.
📋 Quality & Certification
Our Certifications
- ✅ ISO 9001:2015
- ✅ ABS
- ✅ DNV GL
- ✅ Bureau Veritas (BV)
- ✅ SGS Certified
- ✅ RINA
Mill Certificate Type
- 📋 EN 10204 3.1
- 📋 EN 10204 3.2
- 📋 Third Party Inspection Available
- 📋 Certificate of Origin
❓ Frequently Asked Questions
What is AISI 4340 forging steel?
AISI 4340 is a high-strength, medium-carbon Ni-Cr-Mo alloy steel specified under ASTM A29/A29M with UNS G43400 designation. It contains approximately 0.40% carbon, 1.8% nickel, 0.8% chromium, and 0.25% molybdenum. This composition delivers an outstanding combination of very high tensile strength (900-1400 MPa after Q+T), excellent toughness at room and low temperatures, deep hardenability in large sections, and superior fatigue resistance. It is the material of choice for the most demanding forged components in aerospace, defense, oil & gas, and heavy machinery where reliability under extreme stress is paramount.
What are the equivalent grades of AISI 4340?
AISI 4340 has several closely related international equivalents: EN 36CrNiMo4 (1.6511) is the European standard equivalent with similar chemistry; DIN 36CrNiMo4 is the German designation; JIS SNCM439 is the Japanese equivalent; GB 40CrNiMoA is the Chinese standard counterpart; and AFNOR 35NCD6 is the French equivalent. While there may be minor differences in allowed chemical ranges (e.g., 36CrNiMo4 has a slightly lower carbon range of 0.32-0.40%), these grades are considered interchangeable for most engineering applications. AISI 4340 is also available to specific aerospace material specifications like AMS 6415.
What are the key differences between AISI 4340 and AISI 4140?
The key difference is the high nickel content in AISI 4340 (1.65-2.00%) compared to AISI 4140 (≤0.25%). Nickel profoundly improves through-hardenability and, most importantly, low-temperature notch toughness. This makes 4340 capable of achieving significantly higher strength and toughness combinations in very thick sections (over 100mm) where 4140 may lose toughness. Consequently, 4340 is preferred for critical, highly stressed components such as aircraft landing gear, while 4140 is a more economical choice for general-purpose high-strength applications in smaller to medium cross-sections. 4340 also generally commands a higher cost due to its nickel content.
What heat treatments are recommended for AISI 4340 forgings?
The standard heat treatment for AISI 4340 to achieve optimum mechanical properties is quenching and tempering (Q+T). The process involves: (1) normalizing at 870-900°C to refine the grain structure; (2) austenitizing at 815-845°C followed by an oil or polymer quench to form martensite; (3) immediate tempering in the range of 540-650°C to obtain the desired tensile strength (higher tempering temperature yields lower strength but higher toughness); (4) for critical applications, a double tempering process is often employed. A stress relieve treatment at 15-30°C below the final tempering temperature is recommended after rough machining. Annealing (heat to 830°C, slow cool) softens the steel to ≤269 HBW for improved machinability.
Can you provide ultrasonic testing for AISI 4340 forgings?
Yes, ultrasonic testing (UT) is a mandatory and standard process for all AISI 4340 forgings, especially given their use in critical applications. We perform UT in accordance with ASTM A388, EN 10228-3, or the more stringent aerospace standard AMS-STD-2154. Acceptance criteria can be defined per customer specification, ranging from tight grades (e.g., Class A per AMS-STD-2154) for rotating aerospace components to commercial quality classes for general machinery. Each shipment includes a detailed UT test report with scan plans, indication analysis, and pass/fail certification as a core part of the EN 10204 3.1 or 3.2 mill test certificate package.
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