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ASTM B631 Class B Silver-Tungsten Electrical Contact Alloy

ASTM B631 class B is a precious metal alloy formulated for use in electrical contacts.

The properties of ASTM B631 class B 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 B 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

210 GPa 30 x 106 psi

Poisson's Ratio


Rockwell B Hardness

53 to 85

Shear Modulus

78 to 79 GPa 11 x 106 psi

Thermal Properties

Latent Heat of Fusion

150 J/g

Melting Completion (Liquidus)

2460 to 2480 °C 4470 to 4500 °F

Specific Heat Capacity

170 J/kg-K 0.040 to 0.041 BTU/lb-°F

Thermal Conductivity

450 W/m-K 260 BTU/h-ft-°F

Thermal Expansion

12 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

50 to 53 % IACS

Electrical Conductivity: Equal Weight (Specific)

32 to 34 % IACS

Otherwise Unclassified Properties


14 g/cm3 880 lb/ft3

Embodied Carbon

49 kg CO2/kg material

Embodied Energy

760 MJ/kg 330 x 103 BTU/lb

Common Calculations

Stiffness to Weight: Axial

8.1 points

Stiffness to Weight: Bending

14 points

Thermal Diffusivity

190 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