Nickel Inconel 718 vs. Steel AISI 4340

Compare Nickel Inconel 718 vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	1,207MPasourcetypical, 1.0 in. hot-rolled bar, 0.2% offset	1,035MPasourcetypical, transverse
Ultimate tensile strength	1,389MPasourcetypical, 1.0 in. bar	1,140MPasourcetypical, transverse
Elongation at break	20%sourcetypical, 1.0 in. bar	18%sourcetypical, transverse
Young's modulus (stiffness)	200GPasourcetypical, 21 °C, annealed + aged	200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Density	8,221kg/m³sourcenominal, annealed and aged	7,840kg/m³sourcetypical
Strength to weight	147kN·m/kg11% higher	132kN·m/kg
Stiffness to weight	24.3MN·m/kg	25.5MN·m/kg5% higher
Poisson's ratio	0.294sourcetypical, 21 °C, annealed + aged	0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Shear modulus	77.3GPa2% stiffer in shear	75.7GPa
Bulk modulus	162GPa	185GPa
Speed of sound	4,932m/s	5,049m/s
Thermal
Thermal conductivity	11.4W/m·Ksourcetypical, 21 °C, annealed + aged (calculated from resistivity per footnote a)	37.5W/m·Ksourcetypical
Thermal expansion	13.2µm/m·Ksourcetypical, mean 21-93 °C, annealed + aged	11.3µm/m·Ksourcemean, -18 to 93 °C
100 mm part over a 50 °C swing	66µm growth	56.5µm growth17% less
Specific heat	435J/kg·Ksourcetypical, 21 °C	448J/kg·Ksourcetypical
Heats up and cools (diffusivity)	3.19mm²/s	10.7mm²/s3.35x faster
Thermal shock resistance	3,680W/m	11,678W/m3.17x more resistant
Melting point	1,260–1,336°Csourcemelting range	not sourced
Max service temperature	704°Csourceupper use temperature stated by producer	not sourced
Values for	INCONEL alloy 718, standard grade, 1750 °F/1 hr anneal + 1325 °F/8 hr F.C. to 1150 °F aged; Special Metals bulletin SMC-045 typical 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 Nickel Inconel 718 stronger than Steel AISI 4340?

Nickel Inconel 718 is stronger: its yield strength is 1,207 MPa against 1,035 MPa for Steel AISI 4340 (17%).

Which is lighter, Nickel Inconel 718 or Steel AISI 4340?

Steel AISI 4340 is lighter: 7,840 kg/m³ against 8,221 kg/m³ for Nickel Inconel 718.

Which is stiffer, Nickel Inconel 718 or Steel AISI 4340?

Nickel Inconel 718 is stiffer: Young's modulus 200 GPa against 200 GPa for Steel AISI 4340, so the same part in Nickel Inconel 718 deflects less under the same load.

Which is lighter for the same job, Nickel Inconel 718 or Steel AISI 4340?

For the same stiffness or strength: Nickel Inconel 718 is lighter for a strong rod or tie, strong beam, strong panel or plate; Steel AISI 4340 is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate.

Part that must be	Nickel Inconel 718	Steel AISI 4340
Stiff rod or tie (tension)	5% heavier	lighter
Stiff beam (bending)	5% heavier	lighter
Stiff panel or plate	5% heavier	lighter
Strong rod or tie	lighter	11% heavier
Strong beam	lighter	6% heavier
Strong panel or plate	lighter	3% 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, Nickel Inconel 718 or Steel AISI 4340?

Steel AISI 4340 conducts heat better: 37.5 W/m·K against 11.4 W/m·K for Nickel Inconel 718.

Which expands less with temperature?

Steel AISI 4340 expands less: 11.3 µm/m·K against 13.2 µm/m·K for Nickel Inconel 718.

Among 59 materials

Stiffness against density

Strength against density