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SAE-AISI 8655 Steel vs. SAE-AISI 4340 Steel

Both SAE-AISI 8655 steel and SAE-AISI 4340 steel are iron alloys. They have a very high 98% of their average alloy composition in common.

For each property being compared, the top bar is SAE-AISI 8655 steel and the bottom bar is SAE-AISI 4340 steel.

Metric UnitsUS Customary Units

Mechanical Properties

Brinell Hardness 190
210 to 360
Elastic (Young's, Tensile) Modulus, GPa 190
190
Elongation at Break, % 23
12 to 22
Fatigue Strength, MPa 290
330 to 740
Poisson's Ratio 0.29
0.29
Shear Modulus, GPa 73
73
Shear Strength, MPa 390
430 to 770
Tensile Strength: Ultimate (UTS), MPa 620
690 to 1280
Tensile Strength: Yield (Proof), MPa 410
470 to 1150

Thermal Properties

Latent Heat of Fusion, J/g 250
250
Maximum Temperature: Mechanical, °C 410
430
Melting Completion (Liquidus), °C 1460
1460
Melting Onset (Solidus), °C 1410
1420
Specific Heat Capacity, J/kg-K 470
470
Thermal Conductivity, W/m-K 39
44
Thermal Expansion, µm/m-K 13
13

Electrical Properties

Electrical Conductivity: Equal Volume, % IACS 7.3
7.5
Electrical Conductivity: Equal Weight (Specific), % IACS 8.4
8.6

Otherwise Unclassified Properties

Base Metal Price, % relative 2.6
3.5
Density, g/cm3 7.8
7.8
Embodied Carbon, kg CO2/kg material 1.5
1.7
Embodied Energy, MJ/kg 20
22
Embodied Water, L/kg 50
53

Common Calculations

Resilience: Ultimate (Unit Rupture Work), MJ/m3 130
79 to 170
Resilience: Unit (Modulus of Resilience), kJ/m3 440
590 to 3490
Stiffness to Weight: Axial, points 13
13
Stiffness to Weight: Bending, points 24
24
Strength to Weight: Axial, points 22
24 to 45
Strength to Weight: Bending, points 21
22 to 33
Thermal Diffusivity, mm2/s 10
12
Thermal Shock Resistance, points 18
20 to 38

Alloy Composition

Carbon (C), % 0.51 to 0.59
0.38 to 0.43
Chromium (Cr), % 0.4 to 0.6
0.7 to 0.9
Iron (Fe), % 96.4 to 97.6
95.1 to 96.3
Manganese (Mn), % 0.75 to 1.0
0.6 to 0.8
Molybdenum (Mo), % 0.15 to 0.25
0.2 to 0.3
Nickel (Ni), % 0.4 to 0.7
1.7 to 2.0
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