ThePipingMart Blog Grades SAE/AISI 4340 Alloy Steel (UNS G43400) – Composition, Properties and Uses

SAE/AISI 4340 Alloy Steel (UNS G43400) – Composition, Properties and Uses

SAE / AISI 4340 Steel

SAE/AISI 4340 (UNS G43400) steel is an ultra-high strength low-alloy steel containing chromium and molybdenum. AISI 4340 Alloy Steel has good strength and toughness and exhibits excellent corrosion resistance in a wide range of environments. SAE/AISI 4340 Alloy Steel, also known as UNS G43400, is a versatile and durable material developed for various applications. Its composition is designed to provide excellent hardness, toughness, and strength, making it ideal for aircraft landing gear, high-strength bolts, and crankshafts. The AISI 4340 steel has greater strength and hardness than other types of steel, making it a popular choice among manufacturers in various industries. Furthermore, the properties of the AISI 4340 alloy steel can be modified through heat treatment, allowing engineers and designers to tailor it for specific uses. Overall, the versatility and strength of AISI 4340 make it a top choice for many critical applications. This guide will cover the various properties of UNS G43400, its uses, heat treatment options, machining & welding capabilities, and much more. Let’s get started!

What Forms of AISI 4340 is Available at Piping Mart?

  • Nut
  • Bar
  • Bolt
  • Pipe
  • Screw
  • Tubing
  • Valves
  • Washers
  • Flanges
  • Fasteners
  • Electrodes
  • Stud Bolts
  • Sheet Plates
  • Pipe Fittings
  • Forged Fitting
  • Instrumentation Fittings

AISI 4340 Composition

Element Content (%)
Iron, Fe 95.195 – 96.33
Nickel, Ni 1.65 – 2.00
Chromium, Cr 0.700 – 0.900
Manganese, Mn 0.600 – 0.800
Carbon, C 0.370 – 0.430
Molybdenum, Mo 0.200 – 0.300
Silicon, Si 0.150 – 0.300
Sulfur, S  0.0400
Phosphorous, P  0.0350

AISI 4340 Physical Properties

Properties Metric Imperial
Density 7.85 g/cm3 0.284 lb/in³
Melting point 1427°C 2600°F

AISI 4340 Mechanical Properties

Properties Metric Imperial
Tensile strength 745 MPa 108000 psi
Yield strength 470 MPa 68200 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 22% 22%
Reduction of area 50% 50%
Hardness, Brinell 217 217
Hardness, Knoop (converted from Brinell hardness) 240 240
Hardness, Rockwell B (converted from Brinell hardness) 95 95
Hardness, Rockwell C (converted from Brinell hardness. Value below normal HRC range, for comparison purposes only) 17 17
Hardness, Vickers (converted from Brinell hardness) 228 228
Machinability (annealed and cold drawn. Based on 100 machinability for AISI 1212 steel.) 50 50

AISI 4340 Thermal Properties

Properties Metric Imperial
Thermal expansion co-efficient (20°C/68°F, specimen oil hardened, 600°C (1110°F) temper 12.3 µm/m°C 6.83 µin/in°F
Thermal conductivity (typical steel) 44.5 W/mK 309 BTU in/hr.ft².°F

AISI 4340 Equivalent

AMS 6359 AMS 6454 ASTM A331 (4340) ASTM A711 SAE J1397 (4340)
AMS 6409 ASTM A29 (4340) ASTM A506 (4340) ASTM A752 (4340) SAE J404 (4340)
AMS 6414 ASTM A320 (L43) ASTM A519 (4340) ASTM A829 SAE J412 (4340)
AMS 6415 ASTM A322 (4340) ASTM A646 (4340-7) MIL S-5000

AISI 4340 Uses

SAE/AISI 4340 steel is used for various applications, including manufacturing aircraft parts such as gears, shafts, bolts, etc., engine components such as crankshafts and valves, and fasteners like screws and nuts. It is also commonly used for tools such as drill collars in the oil industry.

AISI 4340 Uses in Industries

Aerospace Industry

AISI 4340 is commonly used in the aerospace industry due to its high strength and toughness. It is often used in aircraft and spacecraft components such as landing gear, engine parts, and structural components. The steel’s ability to withstand high stress and fatigue makes it a valuable material for these applications.

Automotive Industry

The automotive industry also utilizes AISI 4340 for its high strength and durability. It is commonly used in parts such as crankshafts, gears, and axles, which require strong and tough materials to withstand the stresses of driving. The steel’s ability to be heat treated also allows for customization to meet specific performance requirements.

Oil and Gas Industry

In the oil and gas industry, AISI 4340 is often used for drilling equipment, including drill collars, drill bits, and drill pipes. These components are subjected to extreme pressure, temperature, and wear during drilling operations, making the high strength and toughness of AISI 4340 essential for their performance.

Defence Industry

Due to its excellent mechanical properties, AISI 4340 is also widely used in the defence industry for various applications such as weapons systems, armoured vehicles, and military aircraft components. Its ability to withstand impact forces makes it an ideal material for these critical defence applications.

Tooling Industry

AISI 4340 is popular in the tooling industry due to its excellent machinability and wear resistance properties. It is commonly used in manufacturing tools such as punches, dies, molds, and cutting tools that require high strength and durability.

AISI 4340 Corrosion Resistance

SAE/AISI 4340 steel offers excellent corrosion resistance in a wide range of environments. In fact, it can withstand temperatures ranging from -100F to +450F without any significant degradation or loss of corrosion resistance. This makes it an ideal choice for applications where corrosion resistance is essential.

AISI 4340 Heat Resistance

In addition to its corrosion resistance properties, SAE/AISI 4340 steel also offers excellent heat resistance. It has been tested at temperatures up to 1000°F with no adverse effects on its mechanical properties or microstructure. This makes it suitable for high-temperature applications such as automotive exhaust systems or industrial furnaces where heat resistance is essential.

AISI 4340 Heat Treatment

SAE/AISI 4340 steel can be easily heat treated using both conventional hardening methods, such as quenching and tempering (Q&T), or by using cryogenic treatments, such as liquid nitrogen cooling (LNC). Depending on the desired application and end-use requirements, the proper type of heat treatment should be selected. For example, Q&T treatments are typically used for applications that require improved wear resistance, while LNC treatments are often used for improved fatigue strength or increased dimensional stability during machining operations.

AISI 4340 Machining

SAE/AISI 4340 steel is an excellent choice for machining operations due to its high strength-to-weight ratio and superior wear resistance properties. It can be machined using conventional cutting tools with good results; however, its high hardness may require specialized tooling or cutting fluids to achieve the best results possible when machining this material.

AISI 4340 Welding

SAE/AISI43 40steel can be welded using all conventional welding methods with good results; however, due to its high hardness, it may require pre-heating prior to welding in order to minimize cracking or distortion during cooling after welding operations have been completed. Additionally, post-weld stress relief may also be required depending on the application and end-user requirements in order to ensure optimal performance from the finished weldment once fabrication has been completed.


From aircraft components to automotive exhaust systems—and everything in between—SAE/AISI43 40steel offers superior performance across a wide range of industries thanks to its combination of exceptional strength-to-weight ratio coupled with excellent corrosion and heat resistance properties. The material also offers good machinability and weldability, making it suitable for just about any application you can think of, requiring superior performance under challenging conditions. If your project requires superior performance under extreme conditions, then look no further than SAE/AISI43 40steel!

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