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UNS C94300 (Alloy 3E) Soft Bronze

C94300 bronze is a bronze formulated for casting. Cited properties are appropriate for the as-fabricated (no temper or treatment) condition. C94300 is the UNS number for this material. Additionally, the common industry name is 71-5-24. Older literature may refer to this material as ASTM Alloy 3E, but this is now discouraged.

It has a very low melting temperature among cast bronzes. In addition, it has the lowest heat capacity and a very low tensile strength.

The graph bars on the material properties cards below compare C94300 bronze to: cast bronzes (top), all copper alloys (middle), and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.

Mechanical Properties

Elastic (Young's, Tensile) Modulus

87 GPa 13 x 106 psi

Elongation at Break

9.7 %

Poisson's Ratio


Shear Modulus

32 GPa 4.6 x 106 psi

Tensile Strength: Ultimate (UTS)

180 MPa 25 x 103 psi

Tensile Strength: Yield (Proof)

120 MPa 17 x 103 psi

Thermal Properties

Latent Heat of Fusion

150 J/g

Maximum Temperature: Mechanical

110 °C 240 °F

Melting Completion (Liquidus)

820 °C 1520 °F

Melting Onset (Solidus)

760 °C 1390 °F

Specific Heat Capacity

320 J/kg-K 0.075 BTU/lb-°F

Thermal Conductivity

63 W/m-K 36 BTU/h-ft-°F

Thermal Expansion

20 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

9.0 % IACS

Electrical Conductivity: Equal Weight (Specific)

8.7 % IACS

Otherwise Unclassified Properties

Base Metal Price

28 % relative


9.3 g/cm3 580 lb/ft3

Embodied Carbon

2.9 kg CO2/kg material

Embodied Energy

47 MJ/kg 20 x 103 BTU/lb

Embodied Water

370 L/kg 44 gal/lb

Common Calculations

Resilience: Ultimate (Unit Rupture Work)

15 MJ/m3

Resilience: Unit (Modulus of Resilience)

77 kJ/m3

Stiffness to Weight: Axial

5.2 points

Stiffness to Weight: Bending

16 points

Strength to Weight: Axial

5.2 points

Strength to Weight: Bending

7.4 points

Thermal Diffusivity

21 mm2/s

Thermal Shock Resistance

7.1 points

Alloy Composition

Among cast copper alloys, the composition of C94300 bronze is notable for containing a comparatively high amount of lead (Pb). Lead is used to improve machinability and bearing properties, at the cost of toxicity. It also adds pressure tightness to castings.

Copper (Cu)Cu 67 to 72
Lead (Pb)Pb 23 to 27
Tin (Sn)Sn 4.5 to 6.0
Phosphorus (P)P 0 to 1.5
Nickel (Ni)Ni 0 to 1.0
Zinc (Zn)Zn 0 to 0.8
Antimony (Sb)Sb 0 to 0.8
Iron (Fe)Fe 0 to 0.15
Sulfur (S)S 0 to 0.080
Silicon (Si)Si 0 to 0.0050
Aluminum (Al)Al 0 to 0.0050
Residualsres. 0 to 1.0

All values are % weight. Ranges represent what is permitted under applicable standards.

Followup Questions

Similar Alloys

Further Reading

ASTM B271: Standard Specification for Copper-Base Alloy Centrifugal Castings

ASTM B505: Standard Specification for Copper Alloy Continuous Castings

ASM Specialty Handbook: Copper and Copper Alloys, J. R. Davis (editor), 2001

CRC Materials Science and Engineering Handbook, 4th ed., James F. Shackelford et al. (editors), 2015