ThePipingMart Blog Grades AISI 4320 Alloy Steel (UNS G43200) – Composition, Properties and Uses

AISI 4320 Alloy Steel (UNS G43200) – Composition, Properties and Uses

SAE/AISI 4320 Steel

If you work in the engineering industry, chances are you’ve encountered AISI 4320 Alloy Steel. 4320 Alloy Steel is a high-carbon, chromium-nickel-molybdenum steel that offers great mechanical properties and excellent corrosion resistance. This blog post will look at the uses of UNS G43200, its corrosion resistance, heat resistance, heat treatment properties, machining capabilities, and welding characteristics.

AISI 4320 Composition

Element Content (%)
Iron, Fe 95.855 – 96.98
Nickel, Ni 1.65 – 2.00
Manganese, Mn 0.450 – 0.650
Chromium, Cr 0.400 – 0.600
Molybdenum, Mo 0.200 – 0.300
Carbon, C 0.170 – 0.220
Silicon, Si 0.150 – 0.300
Sulfur, S  0.0400
Phosphorous, P  0.0350

AISI 4320 Physical Properties

Properties Metric Imperial
Density 7.85 g/cm3 0.284 lb/in³
Melting point 1422°C 2590°F

AISI 4320 Mechanical Properties

Properties Metric Imperial
Tensile strength 580 MPa 84100 psi
Yield strength 425 MPa 61600 psi
Bulk modulus (typical for steel) 140 GPa 20300 ksi
Shear modulus (typical for steel) 80 GPa 11600 ksi
Elastic modulus 190-210 GPa 27557-30458 ksi
Poisson’s ratio 0.27-0.30 0.27-0.30
Elongation at break (in 50 mm) 29% 29%
Reduction of area 58% 58%
Hardness, Brinell 163 163
Hardness, Knoop (converted from Brinell hardness) 184 184
Hardness, Rockwell B (converted from Brinell hardness) 84 84
Hardness, Vickers (converted from Brinell hardness) 170 170
Machinability (annealed and cold drawn. Based on 100 machinability for AISI 1212 steel) 60 60

AISI 4320 Thermal Properties

Properties Metric Imperial
Thermal expansion co-efficient (@ -18-95°C/-0.400-203°F, condition of specimen unknown) 11.3 µm/m°C 6.28 µin/in°F
Thermal conductivity (typical steel) 44.5 W/mK 309 BTU in/hr.ft².°F

AISI 4320 Equivalent

  • ASTM A29 (4320)
  • ASTM A322 (4320)
  • ASTM A331 (4320)
  • ASTM A519 (4320)
  • ASTM A535 (4320)
  • ASTM A752 (4320)
  • SAE J1397 (4320)
  • SAE J404 (4320)
  • SAE J412 (4320)

AISI 4320 Uses

SAE/AISI 4320 is a general-purpose alloy steel that can be used for a variety of applications. This grade of steel is often used in the production of forgings that require high strength and toughness. It is also widely used for applications such as gears and shafts where wear resistance is important. Additionally, this grade of steel has been used for aircraft components such as landing gear parts, bushings, and other parts requiring superior fatigue strength.

Corrosion Resistance

SAE/AISI 4320 exhibits excellent corrosion resistance when exposed to both atmospheric conditions and many corrosive environments or solutions. This grade of steel resists most organic acids as well as chloride solutions such as seawater or brine solutions containing chloride ions. In addition, it has good resistance to reducing agents such as sulphuric acid and nitric acid, provided they are not highly concentrated.

Heat Resistance

SAE/AISI 4320 has excellent heat resistance due to its content of chromium and molybdenum, which provide higher oxidation temperatures compared with carbon steels. The maximum temperature that this grade can be subjected to without suffering permanent damage is around 850°C (1562°F). Additionally, this grade has good scaling resistance at temperatures up to 800°C (1472°F).

Heat Treatment

SAE / AISI 4320 can be hardened by heating it between 820 – 860°C (1508 – 1580°F) followed by oil quenching, resulting in a Rockwell hardness range between HRC 50 – 55 depending on the size and shape being treated.   For best results when hardening this grade, it’s recommended to perform double tempering cycles, each at temperatures below 400°C (752°F).

Following hardening, it should also be tempered between 150 – 370°C (302 – 698°F) depending on desired hardness level before use.


Due to its relatively high Sulphur content, machining operations must be performed with care using sharp tools at slow speeds combined with generous amounts of lubrication if any burrs are to be avoided.   As part of pre-machining operations, it’s also recommended to stress relieve the material prior to machining if possible, especially when components are large or thick-walled, which could otherwise suffer from distortion due to internal stresses caused by machining operations themselves or any other previous treatments applied on material prior machining operations was performed. During post-machining operations, parts should again preferably be stress relieved prior to use if possible, especially when components are relatively large or thick-walled, which could otherwise suffer from distortion due to internal stresses caused by machining operations themselves or any previous treatments applied on material prior to these said machines were performed.


Welding of SAE / AISI 4320 steel is a complicated process, but with the right preparation and safety measures, a skilled welder can produce excellent results. The steel is an alloy containing chromium, nickel, and molybdenum, making it exceptionally strong and heat-resistant – ideal for heavy machinery and transportation applications. In order to join two pieces of 4320 steel securely, welders must use precise techniques that take into consideration the alloys’ higher ductility. Careful weld preparation, correct filler material choice, reducing sulfur content in the welding environment, and application to preheat are just some components essential for a successful welding job on steel. With patience and attention to detail, any weld accomplished on SAE / AISI 4320 materials will be able to withstand even extreme temperatures and pressure.


In conclusion, while SAE/AISI4330 steel alloy offers great mechanical properties making it ideal for a number of engineering applications, there are several factors that need to be taken into consideration before using this alloy in your project. From taking proper care when welding the material together, through preheating and post-heating processes when performing machining operations all way down to selecting the right type of cutting tool according to appropriate speed settings combined with a generous amount of lubrication during operation, all these parameters need careful attention if best possible results are expected from using this particular grade forging materials in your specific application. Good luck!

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AISI 4320 Alloy Steel (UNS G43200) – Composition, Properties and Uses

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