Silicon vs. Steel AISI 4340

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

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SiliconGrown single crystal

Mechanical
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Yield strength	not given (tensile used)	1,035MPasourcetypical, transverse
Ultimate tensile strength	130MPasourcemodulus of rupture (bending fracture stress); brittle, no yield point	1,140MPasourcetypical, transverse
Flexural strength	130MPasourcemodulus of rupture	not sourced
Elongation at break	not sourced	18%sourcetypical, transverse
Young's modulus (stiffness)	131GPasourcetypical (single quoted value of an anisotropic crystal)	200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Density	2,329kg/m³sourcetypical3.37x lighter	7,840kg/m³sourcetypical
Strength to weight	55.8kN·m/kg	132kN·m/kg2.37x higher
Stiffness to weight	56.2MN·m/kg2.21x higher	25.5MN·m/kg
Poisson's ratio	0.221sourcetypical	0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Shear modulus	53.6GPa	75.7GPa41% stiffer in shear
Bulk modulus	78.3GPa	185GPa
Speed of sound	7,500m/s	5,049m/s
Thermal
Thermal conductivity	163W/m·Ksourcetypical at 313 K (40 °C)	37.5W/m·Ksourcetypical
Thermal expansion	2.62µm/m·Ksourcetypical at 300 K	11.3µm/m·Ksourcemean, -18 to 93 °C
100 mm part over a 50 °C swing	13.1µm growth4.31x less	56.5µm growth
Specific heat	732J/kg·Ksourcetypical	448J/kg·Ksourcetypical
Heats up and cools (diffusivity)	95.6mm²/s8.96x faster	10.7mm²/s
Thermal shock resistance	48,095W/m4.12x more resistant	11,678W/m
Melting point	1,412°Csourcetypical	not sourced
Max service temperature	300°Csourceproducer's maximum application temperature (optical components)	not sourced
Values for	Synthetic single-crystal silicon (cubic, diamond structure), Korth Kristalle (crystal grower) material data; Korth usually supplies Floating Zone (FZ) material, Czochralski (Cz) also offered. Silicon is elastically anisotropic; the producer quotes one modulus and the solver is isotropic.	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 Silicon stronger than Steel AISI 4340?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against tensile strength 130 MPa for Silicon (7.96x).

Which is lighter, Silicon or Steel AISI 4340?

Silicon is lighter: 2,329 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.

Which is stiffer, Silicon or Steel AISI 4340?

Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 131 GPa for Silicon, so the same part in Steel AISI 4340 deflects less under the same load.

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

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

Part that must be	Silicon	Steel AISI 4340
Stiff rod or tie (tension)	lighter	2.21x heavier
Stiff beam (bending)	lighter	2.72x heavier
Stiff panel or plate	lighter	2.92x heavier
Strong rod or tie	2.37x heavier	lighter
Strong beam	18% heavier	lighter
Strong panel or plate	lighter	19% 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, Silicon or Steel AISI 4340?

Silicon conducts heat better: 163 W/m·K against 37.5 W/m·K for Steel AISI 4340.

Which expands less with temperature?

Silicon expands less: 2.62 µm/m·K against 11.3 µm/m·K for Steel AISI 4340.

Among 72 materials

Stiffness against density

Strength against density