SAE-AISI 4340 (SNCM439, G43400) Ni-Cr-Mo Steel
SAE-AISI 4340 steel is an alloy steel formulated for primary forming into wrought products. 4340 is the designation in both the SAE and AISI systems for this material. G43400 is the UNS number.
It can have a moderately high tensile strength among SAE-AISI wrought steels. In addition, it has a moderately high base cost and a moderately high electrical conductivity.
The properties of SAE-AISI 4340 steel include four common variations. This page shows summary ranges across all of them. For more specific values, follow the links immediately below. The graph bars on the material properties cards further below compare SAE-AISI 4340 steel to: SAE-AISI wrought steels (top), all iron alloys (middle), and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.
Mechanical Properties
Brinell Hardness
210 to 360
Elastic (Young's, Tensile) Modulus
190 GPa 27 x 106 psi
Elongation at Break
12 to 22 %
Fatigue Strength
330 to 740 MPa 48 to 110 x 103 psi
Poisson's Ratio
0.29
Shear Modulus
73 GPa 11 x 106 psi
Shear Strength
430 to 770 MPa 62 to 110 x 103 psi
Tensile Strength: Ultimate (UTS)
690 to 1280 MPa 100 to 190 x 103 psi
Tensile Strength: Yield (Proof)
470 to 1150 MPa 68 to 170 x 103 psi
Thermal Properties
Latent Heat of Fusion
250 J/g
Maximum Temperature: Mechanical
430 °C 800 °F
Melting Completion (Liquidus)
1460 °C 2650 °F
Melting Onset (Solidus)
1420 °C 2580 °F
Specific Heat Capacity
470 J/kg-K 0.11 BTU/lb-°F
Thermal Conductivity
44 W/m-K 26 BTU/h-ft-°F
Thermal Expansion
13 µm/m-K
Electrical Properties
Electrical Conductivity: Equal Volume
7.5 % IACS
Electrical Conductivity: Equal Weight (Specific)
8.6 % IACS
Otherwise Unclassified Properties
Base Metal Price
3.5 % relative
Density
7.8 g/cm3 490 lb/ft3
Embodied Carbon
1.7 kg CO2/kg material
Embodied Energy
22 MJ/kg 9.6 x 103 BTU/lb
Embodied Water
53 L/kg 6.4 gal/lb
Common Calculations
Resilience: Ultimate (Unit Rupture Work)
79 to 170 MJ/m3
Resilience: Unit (Modulus of Resilience)
590 to 3490 kJ/m3
Stiffness to Weight: Axial
13 points
Stiffness to Weight: Bending
24 points
Strength to Weight: Axial
24 to 45 points
Strength to Weight: Bending
22 to 33 points
Thermal Diffusivity
12 mm2/s
Thermal Shock Resistance
20 to 38 points
Alloy Composition
Among alloy steels, the composition of SAE-AISI 4340 steel is notable for including nickel (Ni). Nickel is used to improve mechanical properties, and to make the alloy easier to heat treat.
| Fe | 95.1 to 96.3 | |
| Ni | 1.7 to 2.0 | |
| Cr | 0.7 to 0.9 | |
| Mn | 0.6 to 0.8 | |
| C | 0.38 to 0.43 | |
| Si | 0.15 to 0.35 | |
| Mo | 0.2 to 0.3 | |
| S | 0 to 0.040 | |
| P | 0 to 0.035 |
All values are % weight. Ranges represent what is permitted under applicable standards.
Followup Questions
Similar Alloys
Further Reading
ASTM A752: Standard Specification for General Requirements for Wire Rods and Coarse Round Wire, Alloy Steel
Sintering of Advanced Materials: Fundamentals and Processes, Zhigang Zak Fang (editor), 2010
Properties and Selection: Irons, Steels and High Performance Alloys, ASM Handbook vol. 1, ASM International, 1993
ASM Specialty Handbook: Carbon and Alloy Steels, J. R. Davis (editor), 1996
Manufacture and Uses of Alloy Steels, Henry D. Hibbard, 2005
Steels: Processing, Structure, and Performance, 2nd ed., George Krauss, 2015