Materials / Compare
Plastic HDPE vs. Steel AISI 4340
Compare Plastic HDPE 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 | 24MPasourcetypical, tensile stress at yield 23 °C, 50 mm/min ISO 527 | 1,035MPasourcetypical, transverse |
| Ultimate tensile strength | not sourced | 1,140MPasourcetypical, transverse |
| Elongation at break | not sourced | 18%sourcetypical, transverse |
| Young's modulus (stiffness) | 0.9GPasourcetypical, tensile modulus 23 °C ISO 527 | 200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered) |
| Density | 950kg/m³sourcetypical, ISO 1183 | 7,840kg/m³sourcetypical |
| Strength to weight | 25.3kN·m/kg | 132kN·m/kg5.23x higher |
| Stiffness to weight | 0.947MN·m/kg | 25.5MN·m/kg26.9x higher |
| Poisson's ratio | 0.4–0.45sourcebase material: high-density polyethylene family (INEOS Olefins & Polymers USA, Typical Engineering Properties of HDPE) | 0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered) |
| Shear modulus | 0.316GPa | 75.7GPa240x stiffer in shear |
| Bulk modulus | 2GPa | 185GPa |
| Speed of sound | 973m/s | 5,049m/s |
| Thermal | ||
| Thermal conductivity | 0.4–0.49W/m·Ksourcebase material: high-density polyethylene family (INEOS Olefins & Polymers USA, Typical Engineering Properties of HDPE) | 37.5W/m·Ksourcetypical |
| Thermal expansion | 120µm/m·Ksourcebase material: high-density polyethylene family (INEOS Olefins & Polymers USA, Typical Engineering Properties of HDPE) | 11.3µm/m·Ksourcemean, -18 to 93 °C |
| 100 mm part over a 50 °C swing | 600µm growth | 56.5µm growth10.6x less |
| Specific heat | 2,250J/kg·Ksourcebase material: high-density polyethylene family (INEOS Olefins & Polymers USA, Typical Engineering Properties of HDPE) | 448J/kg·Ksourcetypical |
| Heats up and cools (diffusivity) | 0.208mm²/s | 10.7mm²/s51.3x faster |
| Thermal shock resistance | 56.9W/m | 11,678W/m205x more resistant |
| Values for | LyondellBasell Hostalen 23050 B high density polyethylene, typical ISO values | 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 Plastic HDPE stronger than Steel AISI 4340?
Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 24 MPa for Plastic HDPE (43.1x).
Which is lighter, Plastic HDPE or Steel AISI 4340?
Plastic HDPE is lighter: 950 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.
Which is stiffer, Plastic HDPE or Steel AISI 4340?
Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 0.9 GPa for Plastic HDPE, so the same part in Steel AISI 4340 deflects less under the same load.
Which is lighter for the same job, Plastic HDPE or Steel AISI 4340?
For the same stiffness or strength: Plastic HDPE is lighter for a stiff panel or plate, strong panel or plate; Steel AISI 4340 is lighter for a stiff rod or tie (tension), stiff beam (bending), strong rod or tie, strong beam.
| Part that must be | Plastic HDPE | Steel AISI 4340 |
|---|---|---|
| Stiff rod or tie (tension) | 26.9x heavier | lighter |
| Stiff beam (bending) | 1.81x heavier | lighter |
| Stiff panel or plate | lighter | 36% heavier |
| Strong rod or tie | 5.23x heavier | lighter |
| Strong beam | 49% heavier | lighter |
| Strong panel or plate | lighter | 26% heavier |
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, Plastic HDPE or Steel AISI 4340?
Steel AISI 4340 conducts heat better: 37.5 W/m·K against 0.445 W/m·K for Plastic HDPE.
Which expands less with temperature?
Steel AISI 4340 expands less: 11.3 µm/m·K against 120 µm/m·K for Plastic HDPE.