Plastic ABS (bulk/injection) vs. Steel AISI 4340

Compare Plastic ABS (bulk/injection) vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

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Plastic ABS (bulk/injection)Bulk polymer (molded or machined)

Mechanical
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Yield strength	45MPasourcetypical, tensile stress at yield 23 °C	1,035MPasourcetypical, transverse
Ultimate tensile strength	not sourced	1,140MPasourcetypical, transverse
Flexural strength	65MPasourcetypical, 23 °C	not sourced
Elongation at break	10%sourcenominal strain at break, 23 °C	18%sourcetypical, transverse
Young's modulus (stiffness)	2.3GPasourcetypical	200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Density	1,040kg/m³sourcetypical7.54x lighter	7,840kg/m³sourcetypical
Strength to weight	43.3kN·m/kg	132kN·m/kg3.05x higher
Stiffness to weight	2.21MN·m/kg	25.5MN·m/kg11.5x higher
Poisson's ratio	0.39sourcetypical, ABS family (Covestro Part and Mold Design guide, Table 3-1)	0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Shear modulus	0.827GPa	75.7GPa91.5x stiffer in shear
Bulk modulus	3.48GPa	185GPa
Speed of sound	1,487m/s	5,049m/s
Thermal
Thermal conductivity	0.17W/m·Ksourcetypical	37.5W/m·Ksourcetypical220x more heat through a fin
Thermal expansion	80–110µm/m·Ksourcerange	11.3µm/m·Ksourcemean, -18 to 93 °C
100 mm part over a 50 °C swing	475µm growth	56.5µm growth8.41x less
Specific heat	not sourced	448J/kg·Ksourcetypical
Heats up and cools (diffusivity)	not sourced	10.7mm²/s
Thermal shock resistance	21.4W/m	11,678W/m547x more resistant
Max service temperature	94°CsourceHDT 1.8 MPa (annealed 4 h/80 °C)	not sourced
Values for	INEOS Styrolution Terluran GP-22 general-purpose injection-molding ABS, ISO typical values (TDS revision 08/01/2022)	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.

Questions

Is Plastic ABS (bulk/injection) stronger than Steel AISI 4340?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 45 MPa for Plastic ABS (bulk/injection) (23x).

Which is lighter, Plastic ABS (bulk/injection) or Steel AISI 4340?

Plastic ABS (bulk/injection) is lighter: 1,040 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.

Which is stiffer, Plastic ABS (bulk/injection) or Steel AISI 4340?

Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 2.3 GPa for Plastic ABS (bulk/injection), so the same part in Steel AISI 4340 deflects less under the same load.

Which is lighter for the same job, Plastic ABS (bulk/injection) or Steel AISI 4340?

For the same stiffness or strength: Plastic ABS (bulk/injection) 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 ABS (bulk/injection)	Steel AISI 4340
Stiff rod or tie (tension)	11.5x heavier	lighter
Stiff beam (bending)	24% heavier	lighter
Stiff panel or plate	lighter	1.7x heavier
Strong rod or tie	3.05x heavier	lighter
Strong beam	7% heavier	lighter
Strong panel or plate	lighter	1.57x 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 ABS (bulk/injection) or Steel AISI 4340?

Steel AISI 4340 conducts heat better: 37.5 W/m·K against 0.17 W/m·K for Plastic ABS (bulk/injection).

Which expands less with temperature?

Steel AISI 4340 expands less: 11.3 µm/m·K against 95 µm/m·K for Plastic ABS (bulk/injection).

Among 59 materials

Stiffness against density

Strength against density