Copper C12200 vs. Steel AISI 4340

Compare Copper C12200 vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

Mechanical	Copper C12200	Steel AISI 4340
Yield strength	69MPa1	1,035MPa215x stronger
Ultimate tensile strength	221MPa1	1,140MPa25.16x stronger
Elongation at break	45%12.5x more ductile	18%2
Young's modulus (stiffness)	117GPa1	200GPa3
Density	8,941kg/m³1	7,840kg/m³214% lighter
Strength to weight	7.72kN·m/kg	132kN·m/kg17.1x higher
Stiffness to weight	13.1MN·m/kg	25.5MN·m/kg1.95x higher
Poisson's ratio	0.344	0.323
Shear modulus	43.7GPa	75.7GPa1.73x stiffer in shear
Bulk modulus	122GPa	185GPa1.52x higher
Speed of sound	3,621m/s	5,049m/s39% faster

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	Copper C12200	Steel AISI 4340
Thermal conductivity	339W/m·K19.05x more heat through a fin	37.5W/m·K2
Thermal expansion	16.9µm/m·K1	mean11.3µm/m·K250% less
100 mm part over a 50 °C swing	84.5µm growth	56.5µm growth50% less
Specific heat	385J/kg·K1	448J/kg·K216% higher
Heats up and cools (diffusivity)	98.5mm²/s9.23x faster	10.7mm²/s
Thermal shock resistance	7,799W/m	11,678W/m50% more resistant
Melting point	liquidus1,083°C1	not sourced

Thermal conductivity against densityHigher and further left: spreads more heat for its weight

Thermal expansion against thermal conductivityLower and further right: warps less when heated

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Sources4 documents: Copper Development Association, Carpenter Technology, U.S. Department of Defense, Wieland

Copper C12200: C12200 phosphorus-deoxidized copper (DHP, the air-conditioning and refrigeration tube copper), tube annealed to 0.050 mm grain size (OS050), 0.065 in. wall, copper.org typical values
Steel AISI 4340: Carpenter (Latrobe) Lescalloy 4340 VAC-ARC datasheet; mechanical row for 1100 °F temper; physical properties grade-level

1
C12200 Alloy (copper.org)Copper Development Associationarchived copyCopper C12200 · Yield strength: typical, 0.5% extension under load, 0.065 in. tubeCopper C12200 · Ultimate tensile strength: typical, 0.065 in. tubeCopper C12200 · Elongation at break: typical, 0.065 in. tubeCopper C12200 · Young's modulus (stiffness): typicalCopper C12200 · Density: nominalCopper C12200 · Thermal conductivity: typical, 20 °CCopper C12200 · Thermal expansion: typical, mean 20-100 °CCopper C12200 · Specific heat: typical, 20 °CCopper C12200 · Melting point: liquidus
2
Lescalloy 4340 VAC-ARC Data SheetCarpenter Technologyarchived copySteel AISI 4340 · Yield strength: typical, transverseSteel AISI 4340 · Ultimate tensile strength: typical, transverseSteel AISI 4340 · Elongation at break: typical, transverseSteel AISI 4340 · Density: typicalSteel AISI 4340 · Thermal conductivity: typicalSteel AISI 4340 · Thermal expansion: mean, -18 to 93 °CSteel AISI 4340 · Specific heat: typical
3
MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures (2003)U.S. Department of DefenseSteel AISI 4340 · Young's modulus (stiffness): MIL-HDBK-5J design value (AISI 4340, quenched and tempered)Steel AISI 4340 · Poisson's ratio: MIL-HDBK-5J design value (AISI 4340, quenched and tempered)
4
Wieland-K19 (Cu-DHP, C12200) Data SheetWielandarchived copyCopper C12200 · Poisson's ratio: reference value at room temperature (Wieland-K19 = Cu-DHP = C12200, rolled products)

Each number points to the document that states it, with the exact basis. Values without a number are computed from the sourced ones. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.

Questions

Mechanical

Is Copper C12200 stronger than Steel AISI 4340?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 69 MPa for Copper C12200 (15x).

Which is lighter, Copper C12200 or Steel AISI 4340?

Steel AISI 4340 is lighter: 7,840 kg/m³ against 8,941 kg/m³ for Copper C12200.

Which is stiffer, Copper C12200 or Steel AISI 4340?

Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 117 GPa for Copper C12200, so the same part in Steel AISI 4340 deflects less under the same load.

Which is lighter for the same job, Copper C12200 or Steel AISI 4340?

For the same stiffness or strength: Steel AISI 4340 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	Copper C12200	Steel AISI 4340
Stiff rod or tie (tension)	1.95x heavier	lighter
Stiff beam (bending)	49% heavier	lighter
Stiff panel or plate	36% heavier	lighter
Strong rod or tie	17.1x heavier	lighter
Strong beam	6.94x heavier	lighter
Strong panel or plate	4.42x 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 is more ductile, Copper C12200 or Steel AISI 4340?

Copper C12200 stretches further before it breaks: 45% elongation at break against 18% for Steel AISI 4340.

Thermal

Which conducts heat better, Copper C12200 or Steel AISI 4340?

Copper C12200 conducts heat better: 339 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 16.9 µm/m·K for Copper C12200.