Precious Metal B631 Class C
ASTM B631 Class C
ASTM B631 Class C is the highest tungsten-content grade of the B631 silver-tungsten series, supplied in infiltrated and pressed-sintered conditions (PSI, PSR-HD, PS-LD, PSI-AgBK, PSI-GRD).
Reference datasheet — B631 Class C is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
What is B631 Class C?
ASTM B631 Class C is the highest tungsten-content grade of the B631 silver-tungsten series, supplied in infiltrated and pressed-sintered conditions (PSI, PSR-HD, PS-LD, PSI-AgBK, PSI-GRD). It is used for severe-duty interrupting contacts where arc erosion and contact-welding resistance matter more than conductivity: 205 HB and 550 MPa tensile at 34% IACS and 180 W/m·K, with service to 400 °C. Elongation is 1.2%, so parts are finished by grinding and EDM and brazed to copper carriers rather than formed or fusion welded. Class B gives higher conductivity for medium duty. B631 Class C has a density of 16.4 g/cm³ (0.592 lb/in³), heavier than 85% of precious metal grades. It melts at 961°C (1,762 °F). B631 Class C has a yield strength of 420 MPa (60.9 ksi) and a tensile strength of 550 MPa (79.8 ksi) — stronger than 96% of precious metal grades. Elongation at break is 1.2% and the elastic modulus is 260 GPa (37.7 Msi).
What is B631 Class C used for?
- high-current circuit breaker contacts
- disconnect switch contacts
- arcing tip inserts
Advantages
- Stiff — 260 GPa (37.7 Msi), better than 100% of precious metal grades
- High strength — 420 MPa (60.9 ksi), better than 96% of precious metal grades
- Low embodied carbon — 42 kg CO₂/kg, better than 94% of precious metal grades
Limitations
- Limited ductility — 1.2%, worse than 100% of precious metal grades
- Limited formability — 8/100, worse than 99% of precious metal grades
- Difficult to machine — 22/100, worse than 98% of precious metal grades
- Hard to polish — 55/100, worse than 97% of precious metal grades
- Difficult to weld — 15/100, worse than 96% of precious metal grades
B631 Class C properties
Typical room-temperature values; bars are the position among precious metal grades.
Physical3
B631 Class C has a density of 16.4 g/cm³ (0.592 lb/in³), heavier than 85% of precious metal grades. It melts at 961°C (1,762 °F).
Mechanical10
B631 Class C has a yield strength of 420 MPa (60.9 ksi) and a tensile strength of 550 MPa (79.8 ksi) — stronger than 96% of precious metal grades. Elongation at break is 1.2% and the elastic modulus is 260 GPa (37.7 Msi).
Thermal5
B631 Class C is rated for continuous service to 400°C (752 °F). It conducts heat at 175 W/m·K (101.1 BTU/hr·ft·°F), better than 67% of precious metal grades. Thermal expansion is 6.8 µm/m·K (3.78 µin/in·°F).
Electrical3
B631 Class C conducts electricity at 33 % IACS, better than 67% of precious metal grades.
Chemical & Environmental3
Corrosion resistance is good (68/100), worse than 74% of precious metal grades.
Sustainability4
Producing a kilogram of B631 Class C takes about 620 MJ of energy and emits 42 kg of CO₂ — less than 91% of precious metal grades. Typical recycled content is 30%.
Manufacturability7
B631 Class C's machinability is poor (22/100, worse than 98% of precious metal grades); weldability poor (15/100); formability not recommended (8/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the precious metal family
Yield strength against density for every precious metal grade FabDigit runs. B631 Class C is highlighted; hover a dot for its name, or open the interactive family chart.
Working with B631 Class C
Is B631 Class C easy to machine?
Grinding with diamond or CBN wheels, wire EDM and sinker EDM are the primary routes; carbide turning tool life is very short, so use low speeds with high-volume coolant and watch for smearing of the silver phase.
Can B631 Class C be welded?
Not fusion weldable: braze with BAg-series filler in a vacuum or hydrogen furnace, or resistance-braze to a copper or copper-alloy carrier, preferably using a silver backing layer to ensure wetting.
Can B631 Class C be formed, bent or molded?
Near-net shape is achieved by powder pressing and sintering/infiltration. The finished material has almost no ductility, so cold bending and cold riveting are not possible; only light flattening is acceptable.
B631 Class C chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Agsilver phase, introduced by infiltration or powder blending | 19 – 21 | 20 |
| Nioptional activated-sintering/wetting addition (Ni or Co) | ≤ 0.5 | — |
| Other (total)maximum total of impurities and residual elements | ≤ 0.5 | — |
| Wtungsten skeleton phase | balance | — |
What surface finishes work on B631 Class C?
The contact face normally needs only grinding, degreasing and passivation; local silver plating can be applied to lower contact resistance. Protect against sulfide tarnishing during long storage; anodizing is not applicable.
How much does B631 Class C cost?
B631 Class C is a high-cost precious metal ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
B631 Class C — frequently asked
What is B631 Class C used for?
B631 Class C is typically used for high-current circuit breaker contacts, disconnect switch contacts and arcing tip inserts. In short: highest-tungsten B631 grade; best arc erosion resistance; lowest conductivity in family.
What is the yield strength of B631 Class C?
B631 Class C has a typical yield strength of 420 MPa (60.9 ksi) and a tensile strength of 550 MPa (79.8 ksi) — stronger than 96% of precious metal grades.
Is B631 Class C easy to machine?
Not especially — machinability is rated poor (22/100, worse than 98% of precious metal grades). Grinding with diamond or CBN wheels, wire EDM and sinker EDM are the primary routes; carbide turning tool life is very short, so use low speeds with high-volume coolant and watch for smearing of the silver phase.
Can B631 Class C be welded?
Not readily — weldability is rated poor (15/100). Not fusion weldable: braze with BAg-series filler in a vacuum or hydrogen furnace, or resistance-braze to a copper or copper-alloy carrier, preferably using a silver backing layer to ensure wetting.
What surface finishes work on B631 Class C?
The contact face normally needs only grinding, degreasing and passivation; local silver plating can be applied to lower contact resistance. Protect against sulfide tarnishing during long storage; anodizing is not applicable.
Can B631 Class C be formed, bent or molded?
Near-net shape is achieved by powder pressing and sintering/infiltration. The finished material has almost no ductility, so cold bending and cold riveting are not possible; only light flattening is acceptable.
What is the maximum service temperature of B631 Class C?
B631 Class C is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does B631 Class C cost?
B631 Class C is a high-cost precious metal ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM B631 Standard Specification for Silver-Tungsten Electrical Contact Material — ASTM International (2018)
- ASM Handbook Vol. 2 — Electrical Contact Materials (Ag-W, Ag-WC, Ag-Mo) — ASM International (1990)
- Electrical Contacts: Principles and Applications (Slade) — CRC Press (2014)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.