SAE-AISI 8640 (SNCM240, G86400) Ni-Cr-Mo Steel
SAE-AISI 8640 steel is an alloy steel formulated for primary forming into wrought products. Cited properties are appropriate for the annealed condition. 8640 is the designation in both the SAE and AISI systems for this material. G86400 is the UNS number.
The graph bars on the material properties cards below compare SAE-AISI 8640 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
170
Elastic (Young's, Tensile) Modulus
190 GPa 27 x 106 psi
Elongation at Break
23 %
Fatigue Strength
270 MPa 39 x 103 psi
Poisson's Ratio
0.29
Shear Modulus
73 GPa 11 x 106 psi
Shear Strength
360 MPa 53 x 103 psi
Tensile Strength: Ultimate (UTS)
570 MPa 83 x 103 psi
Tensile Strength: Yield (Proof)
380 MPa 55 x 103 psi
Thermal Properties
Latent Heat of Fusion
250 J/g
Maximum Temperature: Mechanical
410 °C 780 °F
Melting Completion (Liquidus)
1460 °C 2660 °F
Melting Onset (Solidus)
1420 °C 2580 °F
Specific Heat Capacity
470 J/kg-K 0.11 BTU/lb-°F
Thermal Conductivity
39 W/m-K 22 BTU/h-ft-°F
Thermal Expansion
13 µm/m-K
Electrical Properties
Electrical Conductivity: Equal Volume
7.3 % IACS
Electrical Conductivity: Equal Weight (Specific)
8.4 % IACS
Otherwise Unclassified Properties
Base Metal Price
2.6 % relative
Density
7.8 g/cm3 490 lb/ft3
Embodied Carbon
1.5 kg CO2/kg material
Embodied Energy
20 MJ/kg 8.7 x 103 BTU/lb
Embodied Water
50 L/kg 6.0 gal/lb
Common Calculations
Resilience: Ultimate (Unit Rupture Work)
120 MJ/m3
Resilience: Unit (Modulus of Resilience)
380 kJ/m3
Stiffness to Weight: Axial
13 points
Stiffness to Weight: Bending
24 points
Strength to Weight: Axial
20 points
Strength to Weight: Bending
20 points
Thermal Diffusivity
10 mm2/s
Thermal Shock Resistance
17 points
Alloy Composition
Among alloy steels, the composition of SAE-AISI 8640 steel is notable for including nickel (Ni). Nickel is used to improve mechanical properties, and to make the alloy easier to heat treat.
| Fe | 96.6 to 97.8 | |
| Mn | 0.75 to 1.0 | |
| Ni | 0.4 to 0.7 | |
| Cr | 0.4 to 0.6 | |
| C | 0.38 to 0.43 | |
| Si | 0.15 to 0.35 | |
| Mo | 0.15 to 0.25 | |
| 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
ASTM A322: Standard Specification for Steel Bars, Alloy, Standard Grades
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