Steel AISI 4340 vs. Titanium Ti-6Al-4V

Compare Steel AISI 4340 vs. Titanium Ti-6Al-4V strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	1,035MPasourcetypical, transverse	885MPasourcetypical, plate (>0.187 in), annealed, 0.2% offset
Ultimate tensile strength	1,140MPasourcetypical, transverse	940MPasourcetypical, plate, annealed
Elongation at break	18%sourcetypical, transverse	16%sourcetypical, in 2 in., plate annealed
Young's modulus (stiffness)	200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)	107–122GPasourcetypical range, 20 °C
Density	7,840kg/m³sourcetypical	4,430kg/m³sourcenominal
Strength to weight	132kN·m/kg	200kN·m/kg1.51x higher
Stiffness to weight	25.5MN·m/kg	25.8MN·m/kg1% higher
Poisson's ratio	0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)	0.342sourcemean of TIMET measurements
Shear modulus	75.7GPa1.77x stiffer in shear	42.7GPa
Bulk modulus	185GPa	121GPa
Speed of sound	5,049m/s	5,084m/s
Thermal
Thermal conductivity	37.5W/m·Ksourcetypical	6.6W/m·Ksourcetypical, 20 °C, mill annealed
Thermal expansion	11.3µm/m·Ksourcemean, -18 to 93 °C	9µm/m·Ksourcetypical, mean 0-100 °C
100 mm part over a 50 °C swing	56.5µm growth	45µm growth26% less
Specific heat	448J/kg·Ksourcetypical	580J/kg·Ksourcetypical, 20 °C
Heats up and cools (diffusivity)	10.7mm²/s4.15x faster	2.57mm²/s
Thermal shock resistance	11,678W/m3.13x more resistant	3,730W/m
Melting point	not sourced	1,630–1,650°Csourcemelting range
Max service temperature	not sourced	400°Csourceupper recommended use temperature
Values for	Carpenter (Latrobe) Lescalloy 4340 VAC-ARC datasheet; mechanical row for 1100 °F temper; physical properties grade-level	TIMETAL 6-4 (Ti-6Al-4V Grade 5) annealed plate typical (TIMET properties manual) + TIMET datasheet TMC-0150 physical properties

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 Steel AISI 4340 stronger than Titanium Ti-6Al-4V?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 885 MPa for Titanium Ti-6Al-4V (17%).

Which is lighter, Steel AISI 4340 or Titanium Ti-6Al-4V?

Titanium Ti-6Al-4V is lighter: 4,430 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.

Which is stiffer, Steel AISI 4340 or Titanium Ti-6Al-4V?

Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 115 GPa for Titanium Ti-6Al-4V, so the same part in Steel AISI 4340 deflects less under the same load.

Which is lighter for the same job, Steel AISI 4340 or Titanium Ti-6Al-4V?

For the same stiffness or strength: Titanium Ti-6Al-4V is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate, strong rod or tie, strong beam, strong panel or plate.

Part that must be	Steel AISI 4340	Titanium Ti-6Al-4V
Stiff rod or tie (tension)	1% heavier	lighter
Stiff beam (bending)	34% heavier	lighter
Stiff panel or plate	47% heavier	lighter
Strong rod or tie	1.51x heavier	lighter
Strong beam	1.59x heavier	lighter
Strong panel or plate	1.64x heavier	lighter

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, Steel AISI 4340 or Titanium Ti-6Al-4V?

Steel AISI 4340 conducts heat better: 37.5 W/m·K against 6.6 W/m·K for Titanium Ti-6Al-4V.

Which expands less with temperature?

Titanium Ti-6Al-4V expands less: 9 µm/m·K against 11.3 µm/m·K for Steel AISI 4340.

Among 59 materials

Stiffness against density

Strength against density