SAE-AISI 4340 Steel vs. SAE-AISI 8645 Steel
Both SAE-AISI 4340 steel and SAE-AISI 8645 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 8645 steel.
Metric UnitsUS Customary Units
Mechanical Properties
| Brinell Hardness | 210 to 360 | |
| 180 to 200 |
| Elastic (Young's, Tensile) Modulus, GPa | 190 | |
| 190 |
| Elongation at Break, % | 12 to 22 | |
| 12 to 23 |
| Fatigue Strength, MPa | 330 to 740 | |
| 280 to 350 |
| Poisson's Ratio | 0.29 | |
| 0.29 |
| Shear Modulus, GPa | 73 | |
| 73 |
| Shear Strength, MPa | 430 to 770 | |
| 380 to 400 |
| Tensile Strength: Ultimate (UTS), MPa | 690 to 1280 | |
| 600 to 670 |
| Tensile Strength: Yield (Proof), MPa | 470 to 1150 | |
| 390 to 560 |
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 | |
| 39 |
| Thermal Expansion, µm/m-K | 13 | |
| 13 |
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 | |
| 77 to 120 |
| Resilience: Unit (Modulus of Resilience), kJ/m3 | 590 to 3490 | |
| 420 to 840 |
| Stiffness to Weight: Axial, points | 13 | |
| 13 |
| Stiffness to Weight: Bending, points | 24 | |
| 24 |
| Strength to Weight: Axial, points | 24 to 45 | |
| 21 to 24 |
| Strength to Weight: Bending, points | 22 to 33 | |
| 20 to 22 |
| Thermal Diffusivity, mm2/s | 12 | |
| 10 |
| Thermal Shock Resistance, points | 20 to 38 | |
| 18 to 20 |
Alloy Composition
| Carbon (C), % | 0.38 to 0.43 | |
| 0.43 to 0.48 |
| Chromium (Cr), % | 0.7 to 0.9 | |
| 0.4 to 0.6 |
| Iron (Fe), % | 95.1 to 96.3 | |
| 96.5 to 97.7 |
| 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 |