Materials / Compare
Steel AISI 1018 vs. Steel AISI 4340
Compare Steel AISI 1018 vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.
| Try it on a partA bracket to run stress or thermal on, free in your browser | Open in LessCAD | Open in LessCAD |
|---|---|---|
| Mechanical | ||
| Yield strength | 372MPasourceproducer-stated, cold drawn | 1,035MPasourcetypical, transverse |
| Ultimate tensile strength | 441MPasourceproducer-stated, cold drawn | 1,140MPasourcetypical, transverse |
| Elongation at break | 15%sourcein 2 in (50.8 mm) | 18%sourcetypical, transverse |
| Young's modulus (stiffness) | 200GPasourcebase material: AISI 1025 plain carbon steel (MIL-HDBK-5J design value; ASTM A108 bar is the cold-finished carbon-steel bar spec that also covers 1018) | 200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered) |
| Density | 7,861kg/m³sourcebase material: AISI 1025 plain carbon steel (MIL-HDBK-5J design value; ASTM A108 bar is the cold-finished carbon-steel bar spec that also covers 1018) | 7,840kg/m³sourcetypical |
| Strength to weight | 47.3kN·m/kg | 132kN·m/kg2.79x higher |
| Stiffness to weight | 25.4MN·m/kg | 25.5MN·m/kg |
| Poisson's ratio | 0.32sourcebase material: AISI 1025 plain carbon steel (MIL-HDBK-5J design value; ASTM A108 bar is the cold-finished carbon-steel bar spec that also covers 1018) | 0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered) |
| Shear modulus | 75.7GPa | 75.7GPa |
| Bulk modulus | 185GPa | 185GPa |
| Speed of sound | 5,043m/s | 5,049m/s |
| Thermal | ||
| Thermal conductivity | 51.9W/m·Ksourcebase material: AISI 1025 plain carbon steel (MIL-HDBK-5J design value; ASTM A108 bar is the cold-finished carbon-steel bar spec that also covers 1018) | 37.5W/m·Ksourcetypical |
| Thermal expansion | 12µm/m·Ksourcebase material: unalloyed carbon steel, Ovako family table (S275JR, 'none alloyed structural steels', C <= 0.21%); mean 20-300 °C | 11.3µm/m·Ksourcemean, -18 to 93 °C |
| 100 mm part over a 50 °C swing | 60µm growth | 56.5µm growth6% less |
| Specific heat | 486J/kg·Ksourcebase material: AISI 1025 plain carbon steel (MIL-HDBK-5J design value; ASTM A108 bar is the cold-finished carbon-steel bar spec that also covers 1018) | 448J/kg·Ksourcetypical |
| Heats up and cools (diffusivity) | 13.6mm²/s27% faster | 10.7mm²/s |
| Thermal shock resistance | 5,473W/m | 11,678W/m2.13x more resistant |
| Values for | AISI 1018 cold drawn bar (Niagara LaSalle, cold-finished bar producer) | Carpenter (Latrobe) Lescalloy 4340 VAC-ARC datasheet; mechanical row for 1100 °F temper; physical properties grade-level |
Every value links to the document that states it. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.
Questions
Is Steel AISI 1018 stronger than Steel AISI 4340?
Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 372 MPa for Steel AISI 1018 (2.78x).
Which is lighter, Steel AISI 1018 or Steel AISI 4340?
Steel AISI 4340 is lighter: 7,840 kg/m³ against 7,861 kg/m³ for Steel AISI 1018.
Which is stiffer, Steel AISI 1018 or Steel AISI 4340?
Steel AISI 1018 is stiffer: Young's modulus 200 GPa against 200 GPa for Steel AISI 4340, so the same part in Steel AISI 1018 deflects less under the same load.
Which is lighter for the same job, Steel AISI 1018 or Steel AISI 4340?
For the same stiffness or strength: Steel AISI 4340 is lighter for a strong rod or tie, strong beam, strong panel or plate.
| Part that must be | Steel AISI 1018 | Steel AISI 4340 |
|---|---|---|
| Stiff rod or tie (tension) | about equal | about equal |
| Stiff beam (bending) | about equal | about equal |
| Stiff panel or plate | about equal | about equal |
| Strong rod or tie | 2.79x heavier | lighter |
| Strong beam | 1.98x heavier | lighter |
| Strong panel or plate | 1.67x heavier | lighter |
For the same stiffness or strength, mass scales with density over stiffness (or strength) raised to a power set by how the part is loaded: 1 for a rod in tension, 1/2 for a beam in bending, 1/3 for a panel (the standard material-selection indices).
Which conducts heat better, Steel AISI 1018 or Steel AISI 4340?
Steel AISI 1018 conducts heat better: 51.9 W/m·K against 37.5 W/m·K for Steel AISI 4340.
Which expands less with temperature?
Steel AISI 4340 expands less: 11.3 µm/m·K against 12 µm/m·K for Steel AISI 1018.