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SAE-AISI 8645 Steel vs. SAE-AISI 4340M Steel

Both SAE-AISI 8645 steel and SAE-AISI 4340M steel are iron alloys. They have a very high 97% of their average alloy composition in common. There are 31 material properties with values for both materials. Properties with values for just one material (4, in this case) are not shown.

For each property being compared, the top bar is SAE-AISI 8645 steel and the bottom bar is SAE-AISI 4340M steel.

Metric UnitsUS Customary Units

Mechanical Properties

Brinell Hardness 180 to 200
710
Elastic (Young's, Tensile) Modulus, GPa 190
190
Elongation at Break, % 12 to 23
6.0
Fatigue Strength, MPa 280 to 350
690
Poisson's Ratio 0.29
0.29
Shear Modulus, GPa 73
72
Shear Strength, MPa 380 to 400
1360
Tensile Strength: Ultimate (UTS), MPa 600 to 670
2340
Tensile Strength: Yield (Proof), MPa 390 to 560
1240

Thermal Properties

Latent Heat of Fusion, J/g 250
280
Maximum Temperature: Mechanical, °C 410
430
Melting Completion (Liquidus), °C 1460
1440
Melting Onset (Solidus), °C 1420
1400
Specific Heat Capacity, J/kg-K 470
480
Thermal Conductivity, W/m-K 39
38
Thermal Expansion, µm/m-K 13
13

Electrical Properties

Electrical Conductivity: Equal Volume, % IACS 7.3
7.8
Electrical Conductivity: Equal Weight (Specific), % IACS 8.4
9.1

Otherwise Unclassified Properties

Base Metal Price, % relative 2.6
3.9
Density, g/cm3 7.8
7.8
Embodied Carbon, kg CO2/kg material 1.5
1.9
Embodied Energy, MJ/kg 20
26
Embodied Water, L/kg 50
55

Common Calculations

Resilience: Ultimate (Unit Rupture Work), MJ/m3 77 to 120
120
Resilience: Unit (Modulus of Resilience), kJ/m3 420 to 840
4120
Stiffness to Weight: Axial, points 13
13
Stiffness to Weight: Bending, points 24
25
Strength to Weight: Axial, points 21 to 24
84
Strength to Weight: Bending, points 20 to 22
51
Thermal Diffusivity, mm2/s 10
10
Thermal Shock Resistance, points 18 to 20
70

Alloy Composition

Carbon (C), % 0.43 to 0.48
0.38 to 0.43
Chromium (Cr), % 0.4 to 0.6
0.7 to 1.0
Iron (Fe), % 96.5 to 97.7
93.3 to 94.8
Manganese (Mn), % 0.75 to 1.0
0.65 to 0.9
Molybdenum (Mo), % 0.15 to 0.25
0.35 to 0.45
Nickel (Ni), % 0.4 to 0.7
1.7 to 2.0
Phosphorus (P), % 0 to 0.035
0 to 0.012
Silicon (Si), % 0.15 to 0.35
1.5 to 1.8
Sulfur (S), % 0 to 0.040
0 to 0.012
Vanadium (V), % 0
0.050 to 0.1