Stainless 17-4PH vs. Steel AISI 4340

Compare Stainless 17-4PH vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	1,275MPasourcetypical, transverse, sheet/strip	1,035MPasourcetypical, transverse
Ultimate tensile strength	1,379MPasourcetypical, transverse, sheet/strip	1,140MPasourcetypical, transverse
Elongation at break	9%sourcetypical, transverse, in 2 in. (50.8 mm)	18%sourcetypical, transverse
Young's modulus (stiffness)	197GPasourceH 900	200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Density	7,800kg/m³sourceH 900	7,840kg/m³sourcetypical
Strength to weight	163kN·m/kg24% higher	132kN·m/kg
Stiffness to weight	25.3MN·m/kg	25.5MN·m/kg
Poisson's ratio	0.272sourceH 900 (column)	0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Shear modulus	77.4GPa2% stiffer in shear	75.7GPa
Bulk modulus	144GPa	185GPa
Speed of sound	5,026m/s	5,049m/s
Thermal
Thermal conductivity	17.9W/m·Ksourceat 149 °C (300 °F), H 900	37.5W/m·Ksourcetypical
Thermal expansion	10.8µm/m·Ksourcemean, 21–93 °C (70–200 °F), H 900	11.3µm/m·Ksourcemean, -18 to 93 °C
100 mm part over a 50 °C swing	54µm growth5% less	56.5µm growth
Specific heat	460J/kg·Ksourcemean, 0–100 °C, H 900	448J/kg·Ksourcetypical
Heats up and cools (diffusivity)	4.99mm²/s	10.7mm²/s2.14x faster
Thermal shock resistance	7,809W/m	11,678W/m50% more resistant
Max service temperature	316°Csourcestrength-retention limit (not oxidation)	not sourced
Values for	Cleveland-Cliffs 17-4 PH, Condition H 900, sheet/strip, transverse (Product Data Bulletin, May 2021)	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 Stainless 17-4PH stronger than Steel AISI 4340?

Stainless 17-4PH is stronger: its yield strength is 1,275 MPa against 1,035 MPa for Steel AISI 4340 (23%).

Which is lighter, Stainless 17-4PH or Steel AISI 4340?

Stainless 17-4PH is lighter: 7,800 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.

Which is stiffer, Stainless 17-4PH or Steel AISI 4340?

Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 197 GPa for Stainless 17-4PH, so the same part in Steel AISI 4340 deflects less under the same load.

Which is lighter for the same job, Stainless 17-4PH or Steel AISI 4340?

For the same stiffness or strength: Stainless 17-4PH is lighter for a strong rod or tie, strong beam, strong panel or plate.

Part that must be	Stainless 17-4PH	Steel AISI 4340
Stiff rod or tie (tension)	about equal	about equal
Stiff beam (bending)	about equal	about equal
Stiff panel or plate	about equal	about equal
Strong rod or tie	lighter	24% heavier
Strong beam	lighter	16% heavier
Strong panel or plate	lighter	12% 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, Stainless 17-4PH or Steel AISI 4340?

Steel AISI 4340 conducts heat better: 37.5 W/m·K against 17.9 W/m·K for Stainless 17-4PH.

Which expands less with temperature?

Stainless 17-4PH expands less: 10.8 µm/m·K against 11.3 µm/m·K for Steel AISI 4340.

Among 59 materials

Stiffness against density

Strength against density