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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.

Iron (Fe) 95.1 to 96.3
Nickel (Ni) 1.7 to 2.0
Chromium (Cr) 0.7 to 0.9
Manganese (Mn) 0.6 to 0.8
Carbon (C) 0.38 to 0.43
Silicon (Si) 0.15 to 0.35
Molybdenum (Mo) 0.2 to 0.3
Sulfur (S) 0 to 0.040
Phosphorus (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