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Plastic POM/Acetal vs. Steel AISI 4340

Compare Plastic POM/Acetal vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

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Plastic POM/AcetalBulk polymer (molded or machined)
Steel AISI 4340Wrought
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Mechanical
Yield strength69MPasourcetypical (single ASTM D638 tensile strength)1,035MPasourcetypical, transverse
Ultimate tensile strength69MPasourcetypical1,140MPasourcetypical, transverse
Compressive strength124MPasourcecompressive stress at 10% deformationnot sourced
Flexural strength99MPasourceflexural yield strength, typicalnot sourced
Elongation at break75%sourcetypical18%sourcetypical, transverse
Young's modulus (stiffness)2.8GPasourcetypical200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Density1,420kg/m³sourcetypical (DuPont product information for Delrin 100 NC010; 'The data listed here fall within the normal range of product properties')7,840kg/m³sourcetypical
Strength to weight48.6kN·m/kg132kN·m/kg2.72x higher
Stiffness to weight1.97MN·m/kg25.5MN·m/kg12.9x higher
Poisson's ratio0.35sourcetypical0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Shear modulus1.04GPa75.7GPa73x stiffer in shear
Bulk modulus3.11GPa185GPa
Speed of sound1,404m/s5,049m/s
Thermal
Thermal conductivity0.4W/m·Ksourcetypical37.5W/m·Ksourcetypical93.7x more heat through a fin
Thermal expansion122µm/m·Ksourcemean, 29 to 60 °C11.3µm/m·Ksourcemean, -18 to 93 °C
100 mm part over a 50 °C swing610µm growth56.5µm growth10.8x less
Specific heat1,465J/kg·Ksourceaverage -18 to 100 °C, Delrin acetal resins (not grade-specific)448J/kg·Ksourcetypical
Heats up and cools (diffusivity)0.192mm²/s10.7mm²/s55.5x faster
Thermal shock resistance52.5W/m11,678W/m222x more resistant
Melting point175°Csourcecrystalline melting pointnot sourced
Max service temperature125°CsourceHDT 1.8 MPa (annealed)not sourced
Values forDuPont Delrin 100 acetal homopolymer, Table 2 'Typical Properties of Delrin Acetal Resins' (ASTM methods), Delrin Design Guide Module III hosted on delrin.comCarpenter (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 POM/Acetal stronger than Steel AISI 4340?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 69 MPa for Plastic POM/Acetal (15x).

Which is lighter, Plastic POM/Acetal or Steel AISI 4340?

Plastic POM/Acetal is lighter: 1,420 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.

Which is stiffer, Plastic POM/Acetal or Steel AISI 4340?

Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 2.8 GPa for Plastic POM/Acetal, so the same part in Steel AISI 4340 deflects less under the same load.

Which is lighter for the same job, Plastic POM/Acetal or Steel AISI 4340?

For the same stiffness or strength: Plastic POM/Acetal 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 bePlastic POM/AcetalSteel AISI 4340
Stiff rod or tie (tension)12.9x heavierlighter
Stiff beam (bending)1.53x heavierlighter
Stiff panel or platelighter33% heavier
Strong rod or tie2.72x heavierlighter
Strong beam10% heavierlighter
Strong panel or platelighter43% 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 POM/Acetal or Steel AISI 4340?

Steel AISI 4340 conducts heat better: 37.5 W/m·K against 0.4 W/m·K for Plastic POM/Acetal.

Which expands less with temperature?

Steel AISI 4340 expands less: 11.3 µm/m·K against 122 µm/m·K for Plastic POM/Acetal.

Among 59 materials

1k10k0.1110100Density (kg/m³)Young's modulus (GPa)Plastic PLAPlastic PETGPlastic ABSPlastic TPUPlastic NylonAluminumSteelIronTitaniumSteel AISI 1018Stainless 304Stainless 316Aluminum 6061-T6Aluminum 7075-T6Brass C360Copper C110GlassSteel AISI 1045Steel A992Stainless 303Stainless 17-4PHAluminum 2024-T351Aluminum 5052-H32Aluminum 7050-T7451Titanium Ti-6Al-4VBrass C260Nickel Inconel 718Magnesium AZ31B-H24Zinc Zamak 3Plastic ABS (bulk/injection)Plastic PolycarbonatePlastic Nylon PA6Plastic Nylon PA66Plastic PEEKPlastic UHMWPEPlastic HDPEPlastic PolypropylenePlastic PMMAFDM ASAFDM PolycarbonateFDM PAHT-CFFDM HIPSSLA Resin Tough 2000SLS PA12 NylonDMLS AlSi10Mg AluminumDMLS Ti-6Al-4V ELI TitaniumDMLS 316L Stainless SteelDMLS 17-4PH Stainless SteelPlastic POM/AcetalSteel AISI 4340
Stiffness against density
1k10k101001kDensity (kg/m³)Yield strength (MPa)Plastic PLAPlastic PETGPlastic ABSPlastic TPUPlastic NylonRubberAluminumSteelIronTitaniumSteel AISI 1018Stainless 304Stainless 316Aluminum 6061-T6Aluminum 7075-T6Brass C360Copper C110GlassSteel AISI 1045Steel A992Stainless 303Stainless 17-4PHAluminum 2024-T351Aluminum 5052-H32Aluminum 7050-T7451Titanium Ti-6Al-4VBrass C260Nickel Inconel 718Magnesium AZ31B-H24Zinc Zamak 3Plastic ABS (bulk/injection)Plastic PolycarbonatePlastic Nylon PA6Plastic Nylon PA66Plastic PEEKPlastic PTFEPlastic UHMWPEPlastic HDPEPlastic PolypropylenePlastic PMMAFDM ASAFDM PolycarbonateFDM PAHT-CFFDM HIPSSLA Resin Tough 2000SLA Resin Elastic 50ASLS PA12 NylonDMLS AlSi10Mg AluminumDMLS Ti-6Al-4V ELI TitaniumDMLS 316L Stainless SteelDMLS 17-4PH Stainless SteelBrickPlastic POM/AcetalSteel AISI 4340
Strength against density

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