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UNS C91100 (Alloy B) Gear Bronze

C91100 bronze is a bronze formulated for casting. Cited properties are appropriate for the as-fabricated (no temper or treatment) condition. C91100 is the UNS number for this material. Additionally, the common industry name is 84-16 Tin Bronze. Older literature may refer to this material as ASTM Alloy B, but this is now discouraged.

It has a very high embodied energy among cast bronzes. In addition, it has a very high base cost and a very low ductility.

The graph bars on the material properties cards below compare C91100 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

Compressive (Crushing) Strength

140 MPa 20 x 103 psi

Elastic (Young's, Tensile) Modulus

100 GPa 15 x 106 psi

Elongation at Break

2.0 %

Poisson's Ratio

0.34

Shear Modulus

39 GPa 5.7 x 106 psi

Tensile Strength: Ultimate (UTS)

240 MPa 35 x 103 psi

Tensile Strength: Yield (Proof)

170 MPa 25 x 103 psi

Thermal Properties

Latent Heat of Fusion

180 J/g

Maximum Temperature: Mechanical

160 °C 310 °F

Melting Completion (Liquidus)

950 °C 1740 °F

Melting Onset (Solidus)

820 °C 1500 °F

Specific Heat Capacity

360 J/kg-K 0.086 BTU/lb-°F

Thermal Conductivity

63 W/m-K 36 BTU/h-ft-°F

Thermal Expansion

18 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

8.0 % IACS

Electrical Conductivity: Equal Weight (Specific)

8.3 % IACS

Otherwise Unclassified Properties

Base Metal Price

38 % relative

Density

8.7 g/cm3 540 lb/ft3

Embodied Carbon

4.2 kg CO2/kg material

Embodied Energy

69 MJ/kg 30 x 103 BTU/lb

Embodied Water

440 L/kg 52 gal/lb

Common Calculations

Resilience: Ultimate (Unit Rupture Work)

4.4 MJ/m3

Resilience: Unit (Modulus of Resilience)

140 kJ/m3

Stiffness to Weight: Axial

6.7 points

Stiffness to Weight: Bending

18 points

Strength to Weight: Axial

7.7 points

Strength to Weight: Bending

9.9 points

Thermal Diffusivity

20 mm2/s

Thermal Shock Resistance

9.1 points

Alloy Composition

Among cast copper alloys, the composition of C91100 bronze is notable for containing a comparatively high amount of tin (Sn) and including sulfur (S). Tin is used to improve strength, bearing properties, and corrosion resistance against certain types of media. It also places certain constraints on cast part design, so as to avoid porosity problems. Sulfur is used to improve machinability at the cost of a decrease in electrical conductivity.

Copper (Cu) 82 to 85
Tin (Sn) 15 to 17
Phosphorus (P) 0 to 1.0
Nickel (Ni) 0 to 0.5
Iron (Fe) 0 to 0.25
Lead (Pb) 0 to 0.25
Zinc (Zn) 0 to 0.25
Antimony (Sb) 0 to 0.2
Sulfur (S) 0 to 0.050
Silicon (Si) 0 to 0.0050
Aluminum (Al) 0 to 0.0050

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

Followup Questions

Similar Alloys

Further Reading

ASTM B22: Standard Specification for Bronze Castings for Bridges and Turntables

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