Materials / Compare
Iron vs. Steel AISI 4340
Compare Iron 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 | 186MPasourcetypical (0.2% YS), hot rolled + SRA/recrystallization anneal | 1,035MPasourcetypical, transverse |
| Ultimate tensile strength | 290MPasourcetypical, SRA/recrystallization anneal | 1,140MPasourcetypical, transverse |
| Elongation at break | 38%sourcetypical, gauge 4D0 | 18%sourcetypical, transverse |
| Young's modulus (stiffness) | 207GPasourcetypical, after SRA/recrystallization anneal | 200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered) |
| Density | 7,860kg/m³sourcetypical | 7,840kg/m³sourcetypical |
| Strength to weight | 23.7kN·m/kg | 132kN·m/kg5.58x higher |
| Stiffness to weight | 26.3MN·m/kg3% higher | 25.5MN·m/kg |
| Poisson's ratio | 0.282sourceNIST critically evaluated best value (polycrystalline iron) | 0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered) |
| Shear modulus | 80.7GPa7% stiffer in shear | 75.7GPa |
| Bulk modulus | 158GPa | 185GPa |
| Speed of sound | 5,132m/s | 5,049m/s |
| Thermal | ||
| Thermal conductivity | 73.2W/m·Ksourcetypical at 20 °C | 37.5W/m·Ksourcetypical |
| Thermal expansion | 13.7µm/m·Ksourcemean, 20-399 °C | 11.3µm/m·Ksourcemean, -18 to 93 °C |
| 100 mm part over a 50 °C swing | 68.5µm growth | 56.5µm growth21% less |
| Specific heat | 450J/kg·Ksourcetypical | 448J/kg·Ksourcetypical |
| Heats up and cools (diffusivity) | 20.7mm²/s1.94x faster | 10.7mm²/s |
| Thermal shock resistance | 3,447W/m | 11,678W/m3.39x more resistant |
| Melting point | 1,532°Csourcetypical | not sourced |
| Values for | Cleveland-Cliffs / AK Steel ARMCO Pure Iron Product Data Bulletin (07/2022): Table 1 typical physical properties, Table 2 typical mechanical properties after SRA/recrystallization anneal. | 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 Iron stronger than Steel AISI 4340?
Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 186 MPa for Iron (5.56x).
Which is lighter, Iron or Steel AISI 4340?
Steel AISI 4340 is lighter: 7,840 kg/m³ against 7,860 kg/m³ for Iron.
Which is stiffer, Iron or Steel AISI 4340?
Iron is stiffer: Young's modulus 207 GPa against 200 GPa for Steel AISI 4340, so the same part in Iron deflects less under the same load.
Which is lighter for the same job, Iron or Steel AISI 4340?
For the same stiffness or strength: Iron is lighter for a stiff rod or tie (tension), stiff beam (bending); Steel AISI 4340 is lighter for a strong rod or tie, strong beam, strong panel or plate.
| Part that must be | Iron | Steel AISI 4340 |
|---|---|---|
| Stiff rod or tie (tension) | lighter | 3% heavier |
| Stiff beam (bending) | lighter | 2% heavier |
| Stiff panel or plate | about equal | about equal |
| Strong rod or tie | 5.58x heavier | lighter |
| Strong beam | 3.15x heavier | lighter |
| Strong panel or plate | 2.36x 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, Iron or Steel AISI 4340?
Iron conducts heat better: 73.2 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 13.7 µm/m·K for Iron.