AISI 4320 Alloy Steel | UNS G43200 Bar Manufacturer

Looking for a high-performance alloy steel that combines toughness, weldability, and wear resistance? AISI 4320 alloy steel stands out as the top answer. 

At SteelPro Group, we specialize in delivering precision-engineered 4320 steel products tailored to meet rigorous industry standards. 

In this article, you’ll discover the science behind this versatile material, its critical applications, and how our advanced manufacturing capabilities ensure superior quality for your projects—from heavy machinery to aerospace components. 

What Is AISI 4320 Steel?

AISI 4320 is a low-alloy steel known for its strength, toughness, and wear resistance, thanks to its mix of nickel, chromium, and molybdenum. Its low carbon content (0.17-0.22%) ensures good weldability. The steel’s surface hardening property forms a durable, abrasion-resistant outer layer over a resilient core. This makes it perfect for components subjected to intense friction or force, such as gears and shafts. 4320 steel is also used in automotive, aerospace, and heavy machinery.

4320 Steel Chemical Composition

4320 Steel Mechanical Properties

4320 Steel Physical Properties

4320 Steel Thermal Properties

4320 Alloy Steel Benefits

AISI 4320 alloy steel excels in environments demanding both surface hardness and core toughness. Its standout features include:

• Case Hardening Capability: Achieves a wear-resistant surface (via carburizing or nitriding) while retaining a ductile, shock-absorbing core.
• High Fatigue Strength: Resists cyclic stress failure, critical for gears and rotating components.
• Superior Weldability: Low carbon content minimizes pre-/post-weld treatments, reducing fabrication costs.
• Термическая стабильность: Maintains mechanical properties up to 425°C (797°F), suitable for high-temperature applications.
• Adaptability to Heat Treatment: Responds predictably to quenching, tempering, and annealing for tailored hardness (typically 55-62 HRC after case hardening).

Limitations to Consider

• Умеренная коррозионная стойкость: Requires protective coatings or plating for use in humid or corrosive environments.
• Cost of Alloying Elements: Higher nickel and chromium content increases material costs compared to carbon steels.
• Limited High-Temperature Performance: Degrades significantly above 500°C (932°F), restricting use in extreme thermal conditions.

At SteelPro Group, we address these challenges through tailored heat treatment protocols and surface finishing options, ensuring 4320 steel meets your specific operational demands.

4320 Steel Applications

• Automotive Systems: Transmission gears, camshafts, and differential components due to their fatigue resistance and ability to withstand cyclic loads.
• Аэрокосмические компоненты: Landing gear parts, actuator systems, and engine mounts where lightweight durability is critical.
• Тяжелая техника: Mining equipment gears, hydraulic piston rods, and crane shafts exposed to abrasive conditions.
• Oil & Gas Drilling: Drill collars, valve bodies, and high-stress fasteners require corrosion resistance (with coatings).
• Power Transmission: Industrial gearboxes, sprockets, and drive shafts in wind turbines or manufacturing equipment.

4320 Steel Product Specifications and Sizes

At SteelPro Group, we supply AISI 4320 alloy steel in the following specifications and sizes:

Key Specifications:

• Термическая обработка: Supplied in annealed, normalized, or pre-hardened conditions (SAE J1397).
• Сертификаты: Compliant with ASTM, SAE, and ISO standards for quality control.

SteelPro Group offers custom machining, cutting, and surface finishing (e.g., grinding, polishing) to deliver ready-to-install 4320 steel components tailored to your exact requirements.

4320 Steel Forging Process

AISI 4320 alloy steel is forged at temperatures between 1038°C and 1205°C (1900°F–2200°F) to optimize grain structure and mechanical properties. 

Our advanced forging lines support custom geometries up to 3 tons, with tight dimensional tolerances (±1.5mm). Combined with in-process ultrasonic testing, we guarantee defect-free 4320 steel forgings ready for machining or heat treatment.

4320 Steel Heat Treatment

1. Normalizing

At 872°C (1600°F), 4320 steel undergoes normalizing—a process that refines its grain structure and eliminates internal stresses from prior machining or forging. This creates a uniform foundation for subsequent hardening.

2. Annealing

To enhance machinability and relieve internal stresses, AISI 4320 is annealed at 872°C (1600°F) in controlled-atmosphere furnaces. The steel is then cooled at a gradual rate of ≤22°C/hour (40°F/hour) to prevent warping, achieving a soft, workable state ideal for complex machining.

3. Hardening

Critical for wear resistance, hardening involves:

• Austenitizing: Heating to 816–843°C (1500–1550°F) to dissolve carbides.
• Quenching: Rapid oil cooling at 40–80°C (104–176°F) to achieve a martensitic structure with surface hardness up to 62 HRC.

4. Tempering

Post-quenching brittleness is mitigated by tempering at 205–650°C (400–1200°F). Lower temperatures (205–425°C/400–800°F) prioritize hardness for gears, while higher ranges (480–650°C/900–1200°F) optimize toughness for shock-loaded components like axles.

4320 Steel Hot Work

AISI 4320 alloy steel is optimally shaped at elevated temperatures (900–1200°C / 1650–2200°F) to enhance ductility and reduce forming resistance. SteelPro Group utilizes:

• Горячая ковка: High-tonnage hydraulic presses (up to 12,000 tons) mold preheated billets into complex geometries like crankshafts or flanges.
• Горячая прокатка: Convert blooms into bars or plates at 1050–1150°C (1922–2102°F), achieving thickness tolerances of ±1.5mm (±0.06″).
• Термическая стабильность: Post-hot work, parts undergo controlled cooling in inert gas chambers to minimize decarburization.

4320 Steel Cold Work

Cold-forming processes refine dimensions and improve surface finish without heat:

• Холодное волочение: Reduces rod/wire diameters by 15–30% at room temperature, enhancing tensile strength by 10–15%.
• Cold Heading: Produces bolts, screws, and rivets with precision (±0.05mm) and minimal material waste.
• Снятие стресса: Post-cold work annealing at 540–650°C (1004–1202°F) restores ductility for critical applications.

4320 Steel Machine

AISI 4320 steel is easy to machine, making it suitable for precision processes like turning, milling, drilling, and grinding. Its low carbon content ensures good surface finish and dimensional accuracy when machined in annealed or normalized conditions.

4320 Steel Welding

AISI 4320 steel welds well, especially when preheated to 150-300°C (302-572°F). Preheating aids in preventing fractures, and post-weld heat treatment might be required to alleviate stress and decrease hardness in the affected zone.

Elevate Your Engineering with Our 4320 Steel 

At SteelPro Group, we turn AISI 4320 alloy steel’s outstanding properties into practical solutions that move your projects forward. Our vertically integrated capabilities ensure:

• Гарантия качества: ISO 9001-certified production with full traceability, from raw materials to final inspection.
• Tailored Services: On-demand heat treatment (carburizing, nitriding), CNC machining (±0.005mm tolerance), and surface finishing (grinding, polishing).

Contact SteelPro Group today for a free material consultation or to request a customized quote. Let’s work together to engineer lasting durability.