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SAE-AISI 4340 Steel vs. SAE-AISI 8637 Steel

Both SAE-AISI 4340 steel and SAE-AISI 8637 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 4340 steel and the bottom bar is SAE-AISI 8637 steel.

Metric UnitsUS Customary Units

Mechanical Properties

Brinell Hardness 210 to 360
160
Elastic (Young's, Tensile) Modulus, GPa 190
190
Elongation at Break, % 12 to 22
23
Fatigue Strength, MPa 330 to 740
260
Poisson's Ratio 0.29
0.29
Shear Modulus, GPa 73
73
Shear Strength, MPa 430 to 770
340
Tensile Strength: Ultimate (UTS), MPa 690 to 1280
540
Tensile Strength: Yield (Proof), MPa 470 to 1150
360

Thermal Properties

Latent Heat of Fusion, J/g 250
250
Maximum Temperature: Mechanical, °C 430
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 44
38
Thermal Expansion, µm/m-K 13
11

Electrical Properties

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

Otherwise Unclassified Properties

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

Common Calculations

Resilience: Ultimate (Unit Rupture Work), MJ/m3 79 to 170
110
Resilience: Unit (Modulus of Resilience), kJ/m3 590 to 3490
340
Stiffness to Weight: Axial, points 13
13
Stiffness to Weight: Bending, points 24
24
Strength to Weight: Axial, points 24 to 45
19
Strength to Weight: Bending, points 22 to 33
19
Thermal Diffusivity, mm2/s 12
10
Thermal Shock Resistance, points 20 to 38
18

Alloy Composition

Carbon (C), % 0.38 to 0.43
0.35 to 0.4
Chromium (Cr), % 0.7 to 0.9
0.4 to 0.6
Iron (Fe), % 95.1 to 96.3
96.6 to 97.8
Manganese (Mn), % 0.6 to 0.8
0.75 to 1.0
Molybdenum (Mo), % 0.2 to 0.3
0.15 to 0.25
Nickel (Ni), % 1.7 to 2.0
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