Precious Metal B628-H04
Supply condition
GB B628
H04 = full hard
Most common hard temper for sliding contacts, slip rings and commutator segments requiring wear resistance.
Values for the H04 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 |
H04This page 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 |
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-H04?
B628-H04 is B628 supplied in the H04 condition — most common hard temper for sliding contacts, slip rings and commutator segments requiring wear resistance. B628-H04 has a yield strength of 420 MPa (60.9 ksi) and a tensile strength of 460 MPa (66.7 ksi) — stronger than 96% of precious metal grades. Elongation at break is 6% and the elastic modulus is 92 GPa (13.3 Msi). B628-H04 has a density of 10 g/cm³ (0.361 lb/in³), lighter than 65% of precious metal grades. It melts at 779°C (1,434 °F). O is the default condition FabDigit quotes; H04 is available on request or by drawing note.
Advantages
- Easy to machine — 68/100, better than 101% of precious metal grades
- High strength — 420 MPa (60.9 ksi), better than 96% of precious metal grades
- Conducts heat well — 352 W/m·K (203.4 BTU/hr·ft·°F), better than 91% of precious metal grades
- High electrical conductivity — 85 % IACS, better than 88% of precious metal grades
Limitations
- Limited service temperature — 150°C (302 °F), worse than 100% of precious metal grades
- Limited ductility — 6%, worse than 93% of precious metal grades
- Limited formability — 60/100, worse than 87% of precious metal grades
B628-H04 properties
Typical room-temperature values for B628-H04; 14 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-H04 has a density of 10 g/cm³ (0.361 lb/in³), lighter than 65% of precious metal grades. It melts at 779°C (1,434 °F).
Mechanical14
B628-H04 has a yield strength of 420 MPa (60.9 ksi) and a tensile strength of 460 MPa (66.7 ksi) — stronger than 96% of precious metal grades. Elongation at break is 6% and the elastic modulus is 92 GPa (13.3 Msi).
Thermal6
B628-H04 is rated for continuous service to 150°C (302 °F). It conducts heat at 352 W/m·K (203.4 BTU/hr·ft·°F), better than 91% of precious metal grades. Thermal expansion is 18.5 µm/m·K (10.3 µin/in·°F).
Electrical3
B628-H04 conducts electricity at 85 % IACS, better than 88% of precious metal grades.
Chemical & Environmental3
Corrosion resistance is very good (72/100), worse than 66% of precious metal grades.
Sustainability4
Producing a kilogram of B628-H04 takes about 1,100 MJ of energy and emits 105 kg of CO₂ — less than 71% of precious metal grades. Typical recycled content is 60%.
Manufacturability8
B628-H04's machinability is good (68/100, better than 101% of precious metal grades); weldability good (55/100); formability good (60/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with B628-H04
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-H04 — frequently asked
What is B628-H04 used for?
B628-H04 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-H04?
B628-H04 has a typical yield strength of 420 MPa (60.9 ksi) and a tensile strength of 460 MPa (66.7 ksi) — stronger than 96% of precious metal grades. Strength varies by condition: see the 9 listed tempers.
Is B628-H04 easy to machine?
Reasonably — machinability is rated good (68/100, better than 101% 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-H04 be welded?
Yes — weldability is rated good (55/100). 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-H04?
Polishes to a mirror; not anodizable — protect against sulfide tarnish with hard-gold flash, rhodium or an anti-tarnish lacquer for storage.
Can B628-H04 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-H04?
B628-H04 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.