Materials / Compare
Plastic Polypropylene vs. Steel AISI 4340
Compare Plastic Polypropylene 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 | 33MPasourcetypical, tensile stress at yield 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) | 1.45GPasourcetypical, tensile modulus ISO 527 | 200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered) |
| Density | 900kg/m³sourcetypical, 23 °C ISO 1183-1 | 7,840kg/m³sourcetypical |
| Strength to weight | 36.7kN·m/kg | 132kN·m/kg3.6x higher |
| Stiffness to weight | 1.61MN·m/kg | 25.5MN·m/kg15.8x higher |
| Poisson's ratio | 0.42sourcebase material: polypropylene homopolymer family (INEOS Olefins & Polymers USA, Typical Engineering Properties of Polypropylene) | 0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered) |
| Shear modulus | 0.511GPa | 75.7GPa148x stiffer in shear |
| Bulk modulus | 3.02GPa | 185GPa |
| Speed of sound | 1,269m/s | 5,049m/s |
| Thermal | ||
| Thermal conductivity | 0.17–0.22W/m·Ksourcebase material: polypropylene homopolymer family (INEOS Olefins & Polymers USA, Typical Engineering Properties of Polypropylene) | 37.5W/m·Ksourcetypical |
| Thermal expansion | 80–100µm/m·Ksourcebase material: polypropylene homopolymer family (INEOS Olefins & Polymers USA, Typical Engineering Properties of Polypropylene) | 11.3µm/m·Ksourcemean, -18 to 93 °C |
| 100 mm part over a 50 °C swing | 450µm growth | 56.5µm growth7.96x less |
| Specific heat | not sourced | 448J/kg·Ksourcetypical |
| Heats up and cools (diffusivity) | not sourced | 10.7mm²/s |
| Thermal shock resistance | 28.6W/m | 11,678W/m408x more resistant |
| Max service temperature | 90°CsourceHDT 0.45 MPa (ISO 75B), unannealed | not sourced |
| Values for | LyondellBasell Moplen HP501H polypropylene homopolymer (general purpose), 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 Polypropylene stronger than Steel AISI 4340?
Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 33 MPa for Plastic Polypropylene (31.4x).
Which is lighter, Plastic Polypropylene or Steel AISI 4340?
Plastic Polypropylene is lighter: 900 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.
Which is stiffer, Plastic Polypropylene or Steel AISI 4340?
Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 1.45 GPa for Plastic Polypropylene, so the same part in Steel AISI 4340 deflects less under the same load.
Which is lighter for the same job, Plastic Polypropylene or Steel AISI 4340?
For the same stiffness or strength: Plastic Polypropylene 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 Polypropylene | Steel AISI 4340 |
|---|---|---|
| Stiff rod or tie (tension) | 15.8x heavier | lighter |
| Stiff beam (bending) | 35% heavier | lighter |
| Stiff panel or plate | lighter | 1.69x heavier |
| Strong rod or tie | 3.6x heavier | lighter |
| Strong beam | 14% heavier | lighter |
| Strong panel or plate | lighter | 1.56x 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 Polypropylene or Steel AISI 4340?
Steel AISI 4340 conducts heat better: 37.5 W/m·K against 0.195 W/m·K for Plastic Polypropylene.
Which expands less with temperature?
Steel AISI 4340 expands less: 11.3 µm/m·K against 90 µm/m·K for Plastic Polypropylene.
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