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.
| Cu | 82 to 85 | |
| Sn | 15 to 17 | |
| P | 0 to 1.0 | |
| Ni | 0 to 0.5 | |
| Fe | 0 to 0.25 | |
| Pb | 0 to 0.25 | |
| Zn | 0 to 0.25 | |
| Sb | 0 to 0.2 | |
| S | 0 to 0.050 | |
| Si | 0 to 0.0050 | |
| 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