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AISI 4340 Steel: Properties, Products And Uses
- John
4340 alloy steel is known for its versatility and strength, making it an ideal choice for high-performance components like gears and shafts. At SteelPro Group, we’ve spent decades refining our manufacturing process to unlock the full potential of 4340 steel.
In the upcoming sections, we will delve into what sets 4340 steel apart. From its distinctive characteristics to its broad spectrum of uses, you’ll learn why this material is relied upon by industries across the globe.
What Is 4340 Steel?
4340 steel is a high-strength, low-alloy metal recognized for its durability, fatigue resistance, and ability to withstand wear. It’s a medium-carbon steel, typically containing 0.40% to 0.42% carbon, along with nickel, chromium, and molybdenum, which give it exceptional strength and wear resistance. This makes it perfect for demanding applications in sectors such as aerospace, automotive, and heavy equipment manufacturing.
In the annealed state, 4340 steel is easy to machine and cold work, offering flexibility in manufacturing. It also offers excellent weldability, ideal for intricate welded components. After oil quenching and tempering, it achieves a strong combination of strength and ductility. It can also be further hardened through flame or induction hardening and nitriding, enhancing its durability for demanding uses.
What Is 4340 Steel Used For?
- Aerospace: Military aircraft components, turbine shafts, wing spars
- Automotive: Crankshafts, axle shafts, camshafts, differential gears
- Marine: Propeller shafts, rudder stocks, winch gears
- Wind Power: Pitch and yaw bearings, gear rings for gearboxes
- Heavy Machinery: Hydraulic cylinders, bulldozer tracks, mining equipment gears
- Oil and Gas: Drilling collars, pump shafts, valve bodies, wellhead equipment
4340 Steel Equivalent Grades
The following table outlines the equivalent grades and standards for 4340 steel across different global systems. At SteelPro Group, we provide high-quality 4340 steel that complies with these recognized standards.
| Country/Region | Standard | Grade |
| China | GB | 40CrNiMo |
| USA | ASTM | 4340 |
| UNS | G43400 | |
| EU | EN | 34CrNiMo6 |
| Germany | DIN | 1.6582 |
| W-Nr. | 1.6511 | |
| Japan | JIS | SNCM447 |
| France | NF EN/NF | 35NCD6 |
| England | BS EN/BS | 817M40 |
4340 Steel Chemical Composition
| Element | Content |
| Carbon (C) | 0.38 – 0.43% |
| Silicon (Si) | 0.15 – 0.35% |
| Manganese (Mn) | 0.60 – 0.80% |
| Phosphorus (P) | ≤ 0.035% |
| Sulfur (S) | ≤ 0.04% |
| Chromium (Cr) | 0.70 – 0.90% |
| Nickel (Ni) | 1.62 – 2.00% |
| Copper (Cu) | ≤ 0.35% |
| Molybdenum (Mo) | 0.20 – 0.30% |
4340 Steel Mechanical Properties
| Property | Value (Metric) | Value (Imperial) |
| Yield Strength | 740 – 1860 MPa | 107 – 270 ksi |
| Ultimate Tensile Strength | 860 – 1980 MPa | 125 – 287 ksi |
| Elongation | 11 – 23% | 11 – 23% |
| Plane Strain Fracture Toughness | 53 – 110 MPa√m | 47 – 100 ksi√in |
| Bulk Modulus | 159 GPa | 23100 ksi |
| Poisson’s Ratio | 0.29 | 0.29 |
| Machinability | 57% (Annealed) | 57% (Annealed) |
| Shear Modulus | 78.0 GPa | 11300 ksi |
- Machinability Note: This data is based on 100% machinability for AISI 1212 steel. After annealing and cold drawing, the machinability of 4340 steel is rated at 50%.
4340 Steel Physical Properties
| Property | Value (Metric) | Value (Imperial) |
| Density | 7.85 g/cm³ | 0.284 lb/in³ |
| Melting Point | 1425°C | 2597°F |
| Thermal Conductivity | 46 W/m·K | 32 BTU/h·ft·°F |
| Specific Heat Capacity | 460 J/kg·K | 0.11 BTU/lb·°F |
4340 Steel Thermal Properties
| Thermal Property | Metric | Imperial | Comments |
| Coefficient of Thermal Expansion (CTE) | 12.3 µm/m-°C @ 20°C | 6.83 µin/in-°F @ 68°F | Oil hardened, 600°C (1110°F) temper |
| 12.6 µm/m-°C @ 21-260°C | 7.00 µin/in-°F @ 69.8-500°F | 1.88% Ni, normalized and tempered | |
| 12.7 µm/m-°C @ 20°C | 7.06 µin/in-°F @ 68°F | Oil hardened, 600°C (1110°F) temper | |
| 13.7 µm/m-°C @ 250°C | 7.61 µin/in-°F @ 482°F | Oil hardened, 600°C (1110°F) temper | |
| 13.7 µm/m-°C @ 21-540°C | 7.61 µin/in-°F @ 69.8-1000°F | 1.88% Ni, normalized and tempered | |
| 13.9 µm/m-°C @ 21-540°C | 7.72 µin/in-°F @ 69.8-1000°F | 1.90% Ni, quenched, tempered | |
| Specific Heat Capacity | 0.475 J/g-°C | 0.114 BTU/lb-°F | Typical 4000 series steel |
| Thermal Conductivity | 44.5 W/m-K | 309 BTU-in/hr-ft²-°F | – |
4340 Alloy Steel Advantages and Disadvantages
| Advantages | Disadvantages |
| Good shock and impact resistance. | Risk of quench cracking. |
| High wear and abrasion resistance. | Requires precise, specialized processing. |
| High strength and toughness. | Susceptible to corrosion. |
| Excellent fatigue resistance. |
How 4340 Alloy Steel Is Made？
- Melting and Refining
The process begins by melting iron, carbon, and alloying elements in an electric arc furnace at 1,400°C (2,550°F). This step creates a homogeneous molten alloy. Refining methods, such as vacuum degassing are essential for effective hardening.
- Casting and Shaping
After the steel is cast into billets or ingots, it undergoes forging at temperatures ranging from 427-1,233°C (800-2,250°F). Forging shapes the steel and refines its internal grain structure, boosting its strength.
Cooling must be controlled during this phase to prevent cracking and slow cooling in sand or dry lime is recommended.
- Heat Treatment – Quenching and Tempering
First, the steel is heated to 830-860°C (1,525-1,580°F) and rapidly quenched in oil. This creates a martensitic structure. Afterward, the steel is tempered at 400-600°C (750-1,100°F) to improve its toughness while maintaining strength.
- Annealing (Optional)
4340 steel is heated to 844°C (1,550°F) and cooled slowly in a furnace. This process refines the steel’s structure, making it easier to machine and shape during later stages.
- Final Machining and Surface Finishing
Once the steel has gone through heat treatment and any necessary surface hardening, it is ready for final machining. Precision processes like turning, milling, and grinding are used to achieve the required dimensions and surface finish, ensuring that the steel meets the specific demands of its application.
At SteelPro Group, we focus on delivering top-grade 4340 steel bars, plates, and rods. Our experts guarantee that each batch adheres to the strict standards.
4340 Steel Product Specifications
| Product Type | Diameter/Thickness | Length/Width |
| Bars | 0.5″ to 12″ (12.7 mm to 304.8 mm) in diameter | Up to 20′ (6.1 m) in length |
| Rounds | 0.5″ to 12″ (12.7 mm to 304.8 mm) in diameter | Up to 20′ (6.1 m) in length |
| Plates | 0.5″ to 6″ (12.7 mm to 152.4 mm) in thickness | Up to 120″ (3.05 m) in width |
| Sheets | 0.5″ to 2″ (12.7 mm to 50.8 mm) in thickness | Up to 120″ (3.05 m) in width |
| Rods | 0.5″ to 6″ (12.7 mm to 152.4 mm) in diameter | Up to 20′ (6.1 m) in length |
| Rounds (Machined) | 0.5″ to 10″ (12.7 mm to 254 mm) in diameter | Up to 20′ (6.1 m) in length |
| Bars (Cold Drawn) | 0.5″ to 6″ (12.7 mm to 152.4 mm) in diameter | Up to 20′ (6.1 m) in length |
We offer customized dimensions for 4340 alloy steel to meet your specific needs. Whether you require hot-rolled, annealed, or cold-drawn steel, we can provide the form that suits your application best.
- Hot-Rolled: Steel is processed at high temperatures for improved toughness and strength, ideal for large, high-stress components.
- Annealed: The steel is heated and slowly cooled to refine its structure, making it easier to machine and shape.
- Cold-Drawn: The steel is pulled through a die at ambient temperature, enhancing its strength, precision, and surface quality.
FAQs About 4340 Alloy Steel
Is 4340 Steel Stainless?
No, 4340 steel is not stainless steel. It does not contain a high level of chromium or other elements that would make it resistant to corrosion like stainless steel.
What Is the Difference between 4340 and 4140 Steel?
4340 steel contains higher amounts of nickel, chromium, and molybdenum, making it stronger and more ductile than 4140 steel.
4340 steel is ideal for high-stress, heavy-duty applications, such as in aerospace, automotive, and military components. In contrast, 4140 steel, with its lower alloy content, is used for parts that require moderate strength, such as shafts, gears, and bolts.
Discover 4340 Alloy Steel Strength for Your Next Project
SteelPro Group specializes in providing tailored 4340 steel solutions that meet the unique needs of your industry. Whether you’re looking for expert advice, precise product recommendations, or a seamless ordering process, our team is here to help. Reach out today to discover how 4340 alloy steel can enhance your project’s performance and drive your success.
