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Plastic PETG vs. Steel AISI 4340

Compare Plastic PETG vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

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Plastic PETG3D printed (FDM)
Steel AISI 4340Wrought
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Mechanical
Yield strength46.2MPasourcetypical1,035MPasourcetypical, transverse
Ultimate tensile strength46.2MPasourcetypical, peak stress (= stress at yield)1,140MPasourcetypical, transverse
Flexural strength78.9MPasourcetypicalnot sourced
Elongation at break7.6%sourcetypical18%sourcetypical, transverse
Young's modulus (stiffness)1.94GPasourcetypical200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Density1,270kg/m³sourcetypical6.17x lighter7,840kg/m³sourcetypical
Strength to weight36.4kN·m/kg132kN·m/kg3.63x higher
Stiffness to weight1.53MN·m/kg25.5MN·m/kg16.7x higher
Poisson's rationot sourced0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Shear modulusnot sourced75.7GPa
Bulk modulusnot sourced185GPa
Speed of sound1,236m/s5,049m/s
Thermal
Thermal conductivity0.21W/m·Ksourcebase material: Eastman Eastar Copolyester 6763 (PETG), typical37.5W/m·Ksourcetypical
Thermal expansion51µm/m·Ksourcebase material: Eastman Eastar Copolyester 6763 (PETG), typical11.3µm/m·Ksourcemean, -18 to 93 °C
100 mm part over a 50 °C swing255µm growth56.5µm growth4.51x less
Specific heat1,300J/kg·Ksourcebase material: Eastman Eastar Copolyester 6763 (PETG), DSC at 60 °C (lowest temperature listed)448J/kg·Ksourcetypical
Heats up and cools (diffusivity)0.127mm²/s10.7mm²/s83.9x faster
Thermal shock resistancenot sourced11,678W/m
Glass transition77.4°Csourcetypicalnot sourced
Max service temperature76.2°CsourceHDT 0.455 MPa (printed specimens)not sourced
Values forUltimaker PETG, 3D-printed specimens, XY (flat); Ultimaker S5 Pro, engineering intent profile, 0.15 mm layer height, AA 0.4 print core, 100% infill, Cura 4.9, printed one-at-a-time, conditioned >=24 h at room temperature. TDS v1.00, April 29, 2022.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.

Plastic PETG is 3D printed: its properties depend on build direction and print settings; these are typical values.

Questions

Is Plastic PETG stronger than Steel AISI 4340?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 46.2 MPa for Plastic PETG (22.4x).

Which is lighter, Plastic PETG or Steel AISI 4340?

Plastic PETG is lighter: 1,270 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.

Which is stiffer, Plastic PETG or Steel AISI 4340?

Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 1.94 GPa for Plastic PETG, so the same part in Steel AISI 4340 deflects less under the same load.

Which is lighter for the same job, Plastic PETG or Steel AISI 4340?

For the same stiffness or strength: Plastic PETG 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 PETGSteel AISI 4340
Stiff rod or tie (tension)16.7x heavierlighter
Stiff beam (bending)1.64x heavierlighter
Stiff panel or platelighter32% heavier
Strong rod or tie3.63x heavierlighter
Strong beam29% heavierlighter
Strong panel or platelighter30% 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 PETG or Steel AISI 4340?

Steel AISI 4340 conducts heat better: 37.5 W/m·K against 0.21 W/m·K for Plastic PETG.

Which expands less with temperature?

Steel AISI 4340 expands less: 11.3 µm/m·K against 51 µm/m·K for Plastic PETG.

Among 59 materials

1k10k0.1110100Density (kg/m³)Young's modulus (GPa)Plastic PLAPlastic 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 POM/AcetalPlastic 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 PETGSteel AISI 4340
Stiffness against density
1k10k101001kDensity (kg/m³)Yield strength (MPa)Plastic PLAPlastic 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 POM/AcetalPlastic 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 PETGSteel AISI 4340
Strength against density

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