Plastic PEEK vs. Steel AISI 1045

Q: Is Plastic PEEK stronger than Steel AISI 1045?

Steel AISI 1045 is stronger: its yield strength is 531 MPa against 98 MPa for Plastic PEEK (5.42x).

Q: Which is lighter, Plastic PEEK or Steel AISI 1045?

Plastic PEEK is lighter: 1,300 kg/m³ against 7,800 kg/m³ for Steel AISI 1045.

Q: Which is stiffer, Plastic PEEK or Steel AISI 1045?

Steel AISI 1045 is stiffer: Young's modulus 210 GPa against 4 GPa for Plastic PEEK, so the same part in Steel AISI 1045 deflects less under the same load.

Q: Which is lighter for the same job, Plastic PEEK or Steel AISI 1045?

For the same stiffness or strength: Plastic PEEK is lighter for a stiff panel or plate, strong rod or tie, strong beam, strong panel or plate; Steel AISI 1045 is lighter for a stiff rod or tie (tension), stiff beam (bending).

Q: Which conducts heat better, Plastic PEEK or Steel AISI 1045?

Steel AISI 1045 conducts heat better: 42.5 W/m·K against 0.29 W/m·K for Plastic PEEK.

Q: Which expands less with temperature?

Steel AISI 1045 expands less: 12 µm/m·K against 55 µm/m·K for Plastic PEEK.

Compare Plastic PEEK vs. Steel AISI 1045 strength, stiffness, weight and thermal properties.

Change either side

Plastic PEEKBulk polymer (molded or machined)

Steel AISI 1045Wrought

Mechanical
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Yield strength	98MPasourcetypical, tensile yield	531MPasourceproducer-stated, cold drawn
Ultimate tensile strength	not sourced	627MPasourceproducer-stated, cold drawn
Compressive strength	125MPasourcetypical, 23 C	not sourced
Flexural strength	165MPasourcetypical, flexural stress at yield, 23 C	not sourced
Elongation at break	25%sourcetypical, at break	12%sourcein 2 in (50.8 mm)
Young's modulus (stiffness)	4GPasourcetypical (nominal)	210GPasourcetypical
Density	1,300kg/m³sourcetypical (crystalline)	7,800kg/m³sourcetypical
Strength to weight	75.4kN·m/kg11% higher	68.1kN·m/kg
Stiffness to weight	3.08MN·m/kg	26.9MN·m/kg8.75x higher
Poisson's ratio	0.38sourcetypical	0.3sourcetypical
Shear modulus	1.45GPa	80.8GPa55.7x stiffer in shear
Bulk modulus	5.56GPa	175GPa
Speed of sound	1,754m/s	5,189m/s
Thermal
Thermal conductivity	0.29W/m·Ksourcetypical, average, 23 C	40–45W/m·Ksourcetypical range, ambient
Thermal expansion	55µm/m·Ksourceaverage of flow/cross-flow, below Tg (<143 C)	12µm/m·Ksourcetypical, mean 20-300 °C
100 mm part over a 50 °C swing	275µm growth	60µm growth4.58x less
Specific heat	2,200J/kg·Ksourcetypical, 23 °C, DSC (Victrex PEEK 450G TDS, revision Jul 2012)	460–480J/kg·Ksourcetypical range, 50/100 °C
Heats up and cools (diffusivity)	0.101mm²/s	11.6mm²/s114x faster
Thermal shock resistance	80.1W/m	6,269W/m78.3x more resistant
Melting point	343°Csourcetypical, DSC	not sourced
Glass transition	143°Csourceonset (midpoint 150 C)	not sourced
Max service temperature	240°CsourceUL 746B RTI, mechanical strength (continuous use index)	not sourced
Values for	Victrex PEEK 450G (unreinforced, injection moulded), Victrex TDS rev. March 2026; Poisson from Victrex fluid-management flyer (2020-07)	AISI 1045 cold drawn bar (Niagara LaSalle) for mechanical; Ovako C45 (lists 'SAE 1045' as a similar designation) for physical constants

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 PEEK stronger than Steel AISI 1045?

Steel AISI 1045 is stronger: its yield strength is 531 MPa against 98 MPa for Plastic PEEK (5.42x).

Which is lighter, Plastic PEEK or Steel AISI 1045?

Plastic PEEK is lighter: 1,300 kg/m³ against 7,800 kg/m³ for Steel AISI 1045.

Which is stiffer, Plastic PEEK or Steel AISI 1045?

Steel AISI 1045 is stiffer: Young's modulus 210 GPa against 4 GPa for Plastic PEEK, so the same part in Steel AISI 1045 deflects less under the same load.

Which is lighter for the same job, Plastic PEEK or Steel AISI 1045?

For the same stiffness or strength: Plastic PEEK is lighter for a stiff panel or plate, strong rod or tie, strong beam, strong panel or plate; Steel AISI 1045 is lighter for a stiff rod or tie (tension), stiff beam (bending).

Part that must be	Plastic PEEK	Steel AISI 1045
Stiff rod or tie (tension)	8.75x heavier	lighter
Stiff beam (bending)	21% heavier	lighter
Stiff panel or plate	lighter	1.6x heavier
Strong rod or tie	lighter	11% heavier
Strong beam	lighter	1.94x heavier
Strong panel or plate	lighter	2.58x 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 PEEK or Steel AISI 1045?

Steel AISI 1045 conducts heat better: 42.5 W/m·K against 0.29 W/m·K for Plastic PEEK.

Which expands less with temperature?