Precious Metal B628-H08
Supply condition
GB B628
H08 = spring hard
Standard hard temper for flat springs, brush strips and wear-loaded contact faces.
Values for the H08 condition
Other B628 tempers and conditions
B628 is listed in 9 conditions; see the grade overview at B628.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ODefault Annealed | Choose for maximum ductility: deep-drawn contact rivets, stamped bimetal contacts and braze preform forming. | 130 | 280 | 25 | 62 HB | 87 % IACS |
Quarter hard | Use where slightly better stiffness and cut-edge quality are needed but forming is still severe. | 250 | 330 | 18 | 81 HB | 86 % IACS |
Half hard | Balanced temper for stamped contact blanks that still need moderate bending. | 320 | 390 | 12 | 95 HB | 85.5 % IACS |
Full hard | Most common hard temper for sliding contacts, slip rings and commutator segments requiring wear resistance. | 420 | 460 | 6 | 114 HB | 85 % IACS |
Extra hard | Pick when higher yield strength is required and only gentle forming radii are involved. | 480 | 510 | 4 | 128 HB | 84.5 % IACS |
H08This page Spring hard | Standard hard temper for flat springs, brush strips and wear-loaded contact faces. | 530 | 600 | 3 | 142 HB | 80 % IACS |
Extra spring hard | For thin strip and fine wire where stiffness and dimensional stability outrank any forming ability. | 620 | 680 | 2 | 156 HB | 78 % IACS |
Strain hardened, quarter hard | Contact springs and reed blades needing high elastic limit together with silver-class conductivity. | 640 | 660 | 2 | 170 HB | 83 % IACS |
Strain hardened, half hard | Highest strength temper for fine drawn wire and very thin spring strip; essentially unformable. | 690 | 710 | 1.5 | 180 HB | 83 % IACS |
What is B628-H08?
B628-H08 is B628 supplied in the H08 condition — standard hard temper for flat springs, brush strips and wear-loaded contact faces. B628-H08 has a yield strength of 530 MPa (76.9 ksi) and a tensile strength of 600 MPa (87 ksi) — stronger than 97% of precious metal grades. Elongation at break is 3% and the elastic modulus is 100 GPa (14.5 Msi). B628-H08 has a density of 9.9 g/cm³ (0.358 lb/in³), lighter than 70% of precious metal grades. It melts at 779°C (1,434 °F). O is the default condition FabDigit quotes; H08 is available on request or by drawing note.
Advantages
- High strength — 530 MPa (76.9 ksi), better than 97% of precious metal grades
- Easy to machine — 60/100, better than 97% of precious metal grades
- Conducts heat well — 350 W/m·K (202.2 BTU/hr·ft·°F), better than 89% of precious metal grades
- High electrical conductivity — 80 % IACS, better than 83% of precious metal grades
Limitations
- Limited service temperature — 150°C (302 °F), worse than 100% of precious metal grades
- Limited ductility — 3%, worse than 95% of precious metal grades
- Limited formability — 25/100, worse than 95% of precious metal grades
B628-H08 properties
Typical room-temperature values for B628-H08; 32 are specific to this condition. Other listed values are B628 reference data and may not represent this condition. Bars are the position among precious metal grades.
Physical3
B628-H08 has a density of 9.9 g/cm³ (0.358 lb/in³), lighter than 70% of precious metal grades. It melts at 779°C (1,434 °F).
Mechanical14
B628-H08 has a yield strength of 530 MPa (76.9 ksi) and a tensile strength of 600 MPa (87 ksi) — stronger than 97% of precious metal grades. Elongation at break is 3% and the elastic modulus is 100 GPa (14.5 Msi).
Thermal6
B628-H08 is rated for continuous service to 150°C (302 °F). It conducts heat at 350 W/m·K (202.2 BTU/hr·ft·°F), better than 89% of precious metal grades. Thermal expansion is 19.6 µm/m·K (10.9 µin/in·°F).
Electrical3
B628-H08 conducts electricity at 80 % IACS, better than 83% of precious metal grades.
Chemical & Environmental3
Corrosion resistance is very good (80/100), worse than 52% of precious metal grades.
Sustainability4
Producing a kilogram of B628-H08 takes about 1,100 MJ of energy and emits 105 kg of CO₂ — less than 71% of precious metal grades. Typical recycled content is 55%.
Manufacturability8
B628-H08's machinability is good (60/100, better than 97% of precious metal grades); weldability fair (45/100); formability poor (25/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with B628-H08
Is B628 easy to machine?
Machines like soft copper — gummy in the annealed state; use sharp positive-rake carbide, high speed, light feed and oil mist, and collect all chips for silver recovery.
Can B628 be welded?
Rarely fusion welded; contacts are attached by resistance welding, laser welding or by using the alloy itself as the braze at 780–850 °C in reducing atmosphere or with white flux.
Can B628 be formed, bent or molded?
Annealed strip stamps, coins and deep-draws readily; interanneal at 600–650 °C after roughly 50–60 % cold reduction to restore ductility.
What surface finishes work on B628?
Polishes to a mirror; not anodizable — protect against sulfide tarnish with hard-gold flash, rhodium or an anti-tarnish lacquer for storage.
B628 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 |
|---|---|---|
| Ageutectic silver content | 71.85 – 72.15 | 72 |
| Other (total impurities)Pb, Bi, Fe, O and similar tramp elements held low to protect ductility and arc behaviour | ≤ 0.15 | — |
| Cu | balance | — |
B628-H08 — frequently asked
What is B628-H08 used for?
B628-H08 is typically used for braze-clad contact tips, vacuum brazing of contact assemblies and relay contact overlays. In short: eutectic Ag-Cu braze and contact; lowest-melting Ag-Cu composition; 87 % IACS with 62 HB.
What is the yield strength of B628-H08?
B628-H08 has a typical yield strength of 530 MPa (76.9 ksi) and a tensile strength of 600 MPa (87 ksi) — stronger than 97% of precious metal grades. Strength varies by condition: see the 9 listed tempers.
Is B628-H08 easy to machine?
Reasonably — machinability is rated good (60/100, better than 97% of precious metal grades). Machines like soft copper — gummy in the annealed state; use sharp positive-rake carbide, high speed, light feed and oil mist, and collect all chips for silver recovery.
Can B628-H08 be welded?
With care — weldability is rated fair (45/100). Rarely fusion welded; contacts are attached by resistance welding, laser welding or by using the alloy itself as the braze at 780–850 °C in reducing atmosphere or with white flux.
What surface finishes work on B628-H08?
Polishes to a mirror; not anodizable — protect against sulfide tarnish with hard-gold flash, rhodium or an anti-tarnish lacquer for storage.
Can B628-H08 be formed, bent or molded?
Annealed strip stamps, coins and deep-draws readily; interanneal at 600–650 °C after roughly 50–60 % cold reduction to restore ductility.
What is the maximum service temperature of B628-H08?
B628-H08 is rated for continuous use to about 150°C (302 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between B628-O and B628-H14?
O is the default condition — choose for maximum ductility: deep-drawn contact rivets, stamped bimetal contacts and braze preform forming. H14: highest strength temper for fine drawn wire and very thin spring strip; essentially unformable. Yield strength is 130 MPa in O versus 690 MPa in H14.
Sources
- ASTM B628 Standard Specification for Silver-Copper Eutectic Electrical Contact Alloy — ASTM International (2021)
- AWS A5.8/A5.8M Filler Metals for Brazing (BAg-8) — American Welding Society (2019)
- ASM Handbook Vol. 2: Properties and Selection — Nonferrous Alloys and Special-Purpose Materials (precious metals & electrical contact materials) — ASM International (1990)
- ASM Handbook Vol. 3: Alloy Phase Diagrams (Ag-Cu system) — ASM International (1992)
- Silver-copper braze and contact alloy datasheets — Lucas-Milhaupt / Umicore / Materion (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.