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ASTM B631 Class C Silver-Tungsten Electrical Contact Alloy

ASTM B631 class C is a precious metal alloy formulated for use in electrical contacts. It can have the highest thermal conductivity among the precious metal electrical contact alloys in the database.

The properties of ASTM B631 class C include three common variations. This page shows summary ranges across all of them. For more specific values, follow the links immediately below. The graph bars on the material properties cards further below compare ASTM B631 class C to: precious metal electrical contact alloys (top), all alloys in the same category (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

180 to 190 GPa 26 to 27 x 106 psi

Poisson's Ratio


Rockwell B Hardness

43 to 68

Shear Modulus

66 to 71 GPa 9.6 to 10 x 106 psi

Thermal Properties

Latent Heat of Fusion

140 to 150 J/g

Melting Completion (Liquidus)

2090 to 2230 °C 3800 to 4050 °F

Specific Heat Capacity

180 J/kg-K 0.043 to 0.044 BTU/lb-°F

Thermal Conductivity

450 to 490 W/m-K 260 to 290 BTU/h-ft-°F

Thermal Expansion

14 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

55 to 63 % IACS

Electrical Conductivity: Equal Weight (Specific)

36 to 43 % IACS

Otherwise Unclassified Properties


13 to 14 g/cm3 830 to 850 lb/ft3

Embodied Carbon

55 to 59 kg CO2/kg material

Embodied Energy

860 to 920 MJ/kg 370 to 400 x 103 BTU/lb

Common Calculations

Stiffness to Weight: Axial

7.4 to 7.6 points

Stiffness to Weight: Bending

14 points

Thermal Diffusivity

180 to 200 mm2/s

Followup Questions

Further Reading

ASTM B631: Standard Specification for Silver-Tungsten Electrical Contact Materials

Tungsten: Properties, Chemistry, Technology of the Element, Alloys, and Chemical Compounds, Erik Lassner and Wolf-Dieter Schubert, 1999