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SAE-AISI 4718 Steel vs. SAE-AISI 8642 Steel

Both SAE-AISI 4718 steel and SAE-AISI 8642 steel are iron alloys. Both are furnished in the annealed condition. Their average alloy composition is basically identical.

For each property being compared, the top bar is SAE-AISI 4718 steel and the bottom bar is SAE-AISI 8642 steel.

Metric UnitsUS Customary Units

Mechanical Properties

Brinell Hardness 150
170
Elastic (Young's, Tensile) Modulus, GPa 190
190
Elongation at Break, % 24
23
Fatigue Strength, MPa 270
270
Poisson's Ratio 0.29
0.29
Shear Modulus, GPa 73
73
Shear Strength, MPa 330
370
Tensile Strength: Ultimate (UTS), MPa 510
580
Tensile Strength: Yield (Proof), MPa 370
380

Thermal Properties

Latent Heat of Fusion, J/g 250
250
Maximum Temperature: Mechanical, °C 420
410
Melting Completion (Liquidus), °C 1460
1460
Melting Onset (Solidus), °C 1420
1420
Specific Heat Capacity, J/kg-K 470
470
Thermal Conductivity, W/m-K 39
39
Thermal Expansion, µm/m-K 11
13

Electrical Properties

Electrical Conductivity: Equal Volume, % IACS 7.3
7.3
Electrical Conductivity: Equal Weight (Specific), % IACS 8.4
8.4

Otherwise Unclassified Properties

Base Metal Price, % relative 3.0
2.6
Density, g/cm3 7.9
7.8
Embodied Carbon, kg CO2/kg material 1.6
1.5
Embodied Energy, MJ/kg 21
20
Embodied Water, L/kg 51
50

Common Calculations

Resilience: Ultimate (Unit Rupture Work), MJ/m3 110
120
Resilience: Unit (Modulus of Resilience), kJ/m3 360
390
Stiffness to Weight: Axial, points 13
13
Stiffness to Weight: Bending, points 24
24
Strength to Weight: Axial, points 18
20
Strength to Weight: Bending, points 18
20
Thermal Diffusivity, mm2/s 10
10
Thermal Shock Resistance, points 17
17

Alloy Composition

Carbon (C), % 0.16 to 0.21
0.4 to 0.45
Chromium (Cr), % 0.35 to 0.55
0.4 to 0.6
Iron (Fe), % 96.3 to 97.4
96.6 to 97.8
Manganese (Mn), % 0.7 to 0.9
0.75 to 1.0
Molybdenum (Mo), % 0.3 to 0.4
0.15 to 0.25
Nickel (Ni), % 0.9 to 1.2
0.4 to 0.7
Phosphorus (P), % 0 to 0.035
0 to 0.035
Silicon (Si), % 0.15 to 0.35
0.15 to 0.35
Sulfur (S), % 0 to 0.040
0 to 0.040