Steel AISI 1045 vs. Steel AISI 4340

Compare Steel AISI 1045 vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

Change either side

Mechanical
Try it on a partA bracket to run stress or thermal on, free in your browser	Open in LessCAD	Open in LessCAD
Yield strength	531MPasourceproducer-stated, cold drawn	1,035MPasourcetypical, transverse
Ultimate tensile strength	627MPasourceproducer-stated, cold drawn	1,140MPasourcetypical, transverse
Elongation at break	12%sourcein 2 in (50.8 mm)	18%sourcetypical, transverse
Young's modulus (stiffness)	210GPasourcetypical	200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Density	7,800kg/m³sourcetypical	7,840kg/m³sourcetypical
Strength to weight	68.1kN·m/kg	132kN·m/kg1.94x higher
Stiffness to weight	26.9MN·m/kg6% higher	25.5MN·m/kg
Poisson's ratio	0.3sourcetypical	0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Shear modulus	80.8GPa7% stiffer in shear	75.7GPa
Bulk modulus	175GPa	185GPa
Speed of sound	5,189m/s	5,049m/s
Thermal
Thermal conductivity	40–45W/m·Ksourcetypical range, ambient	37.5W/m·Ksourcetypical
Thermal expansion	12µm/m·Ksourcetypical, mean 20-300 °C	11.3µm/m·Ksourcemean, -18 to 93 °C
100 mm part over a 50 °C swing	60µm growth	56.5µm growth6% less
Specific heat	460–480J/kg·Ksourcetypical range, 50/100 °C	448J/kg·Ksourcetypical
Heats up and cools (diffusivity)	11.6mm²/s9% faster	10.7mm²/s
Thermal shock resistance	6,269W/m	11,678W/m1.86x more resistant
Values for	AISI 1045 cold drawn bar (Niagara LaSalle) for mechanical; Ovako C45 (lists 'SAE 1045' as a similar designation) for physical constants	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 Steel AISI 1045 stronger than Steel AISI 4340?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 531 MPa for Steel AISI 1045 (1.95x).

Which is lighter, Steel AISI 1045 or Steel AISI 4340?

Steel AISI 1045 is lighter: 7,800 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.

Which is stiffer, Steel AISI 1045 or Steel AISI 4340?

Steel AISI 1045 is stiffer: Young's modulus 210 GPa against 200 GPa for Steel AISI 4340, so the same part in Steel AISI 1045 deflects less under the same load.

Which is lighter for the same job, Steel AISI 1045 or Steel AISI 4340?

For the same stiffness or strength: Steel AISI 1045 is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate; Steel AISI 4340 is lighter for a strong rod or tie, strong beam, strong panel or plate.

Part that must be	Steel AISI 1045	Steel AISI 4340
Stiff rod or tie (tension)	lighter	6% heavier
Stiff beam (bending)	lighter	3% heavier
Stiff panel or plate	lighter	2% heavier
Strong rod or tie	1.94x heavier	lighter
Strong beam	1.55x heavier	lighter
Strong panel or plate	39% 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 1045 or Steel AISI 4340?

Steel AISI 1045 conducts heat better: 42.5 W/m·K against 37.5 W/m·K for Steel AISI 4340.

Which expands less with temperature?

Steel AISI 4340 expands less: 11.3 µm/m·K against 12 µm/m·K for Steel AISI 1045.

Among 59 materials

Stiffness against density

Strength against density