Drawing No. EH–MT–003 // Engineering Materials
AISI 4340 Alloy Steel Properties
Reviewed August 2026
AISI 4340 is a nickel-chromium-molybdenum steel valued for high hardenability, toughness and fatigue resistance. The reference is explicitly tied to an oil-quenched, 650°C-tempered condition.
Representative properties
The stated basis, temperature and direction are part of the value. Switch units without changing the physical reference.
What changes these properties?
Engineering variability
- Lower tempering temperatures can raise strength substantially while reducing ductility/toughness balance.
- Low-temperature mechanical properties can differ strongly from room-temperature behavior.
- CTE and thermal values in compiled datasets may represent nearby heat-treatment conditions or typical 4000-series values.
- Use specification-specific fracture toughness, fatigue and cleanliness requirements for critical aerospace/pressure applications.
Selection note
Common for highly loaded gears, shafts, landing-gear components, pressure parts and fatigue-critical machinery where high hardenability and toughness are required.
Where a property is shown as qualitative rather than numeric, that is intentional: the selected source or the material physics does not justify a single comparable scalar.
How to interpret this material
Stiffness
Young’s modulus describes elastic stiffness. For crystals and composites, orientation can make one scalar modulus only a directional reference.
Strength / failure
Ductile metals can use yield and tensile strength. Brittle ceramics/semiconductors and anisotropic composites require fracture, flexural or directional strength descriptions instead.
Thermal response
Conductivity, heat capacity and expansion are temperature dependent. The last column is a melting or transition descriptor only where that physical concept is appropriate.
Technical sources
The database favors manufacturer, industry, government or academic technical references and labels secondary condition-specific datasets when a primary source does not expose a complete property set.