Copper Alloy C50700-HR08
Heat-treated state
UNS C50700 · ASTM B103
HR08 = spring temper, stress-relieved
Best combination of elastic limit and low stress relaxation for long-life electrical contact springs.
Values for the HR08 condition
Other C50700 tempers and conditions
C50700 is listed in 9 conditions; see the grade overview at C50700.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Soft annealed | Pick for deep drawing, severe forming or coining before a final age/stress-relief. | 105 | 290 | 48 | 65 HB | 34 % IACS |
Quarter hard | Use when moderate strength must be combined with continued bending/forming. | 270 | 350 | 25 | 103 HB | 32 % IACS |
Half hard | General-purpose stocked temper for stamped contacts, washers and bushings. | 340 | 405 | 14 | 120 HB | 31 % IACS |
Half hard, cold worked and stress-relieved | Pick when formed parts need improved elastic limit and reduced stress-relaxation/SCC risk after stamping. | 385 | 430 | 12 | 130 HB | 32 % IACS |
Full hard | Choose for wear surfaces, bushings and flat parts needing high strength with light forming only. | 425 | 475 | 7 | 145 HB | 31 % IACS |
Extra hard | Intermediate step between hard and spring temper for stiff flat springs. | 475 | 520 | 5 | 158 HB | 30 % IACS |
H08Default Spring hard | Standard stocked spring temper for connector contacts, clips and flat springs; stress-relieve after forming. | 505 | 550 | 4 | 170 HB | 30 % IACS |
HR08This page Spring temper, stress-relieved | Best combination of elastic limit and low stress relaxation for long-life electrical contact springs. | 530 | 570 | 4 | 175 HB | 32 % IACS |
Extra spring hard | Highest strength strip temper — for very high contact force springs with minimal bending. | 540 | 585 | 3 | 185 HB | 30 % IACS |
What is C50700-HR08?
C50700-HR08 is C50700 heat treated to HR08 — best combination of elastic limit and low stress relaxation for long-life electrical contact springs. C50700-HR08 has a yield strength of 530 MPa (76.9 ksi) and a tensile strength of 570 MPa (82.7 ksi) — stronger than 91% of copper alloy grades. Elongation at break is 4% and the elastic modulus is 117 GPa (17 Msi). C50700-HR08 has a density of 8.89 g/cm³ (0.321 lb/in³), heavier than 72% of copper alloy grades. It melts at 1,025°C (1,877 °F). H08 is the default condition FabDigit quotes; HR08 is available on request or by drawing note.
Advantages
- High strength — 530 MPa (76.9 ksi), better than 91% of copper alloy grades
Limitations
- Limited ductility — 4%, worse than 96% of copper alloy grades
- Limited service temperature — 175°C (347 °F), worse than 92% of copper alloy grades
C50700-HR08 properties
Typical room-temperature values for C50700-HR08; 18 are specific to this condition. Other listed values are C50700 reference data and may not represent this condition. Bars are the position among copper alloy grades.
Physical3
C50700-HR08 has a density of 8.89 g/cm³ (0.321 lb/in³), heavier than 72% of copper alloy grades. It melts at 1,025°C (1,877 °F).
Mechanical15
C50700-HR08 has a yield strength of 530 MPa (76.9 ksi) and a tensile strength of 570 MPa (82.7 ksi) — stronger than 91% of copper alloy grades. Elongation at break is 4% and the elastic modulus is 117 GPa (17 Msi).
Thermal6
C50700-HR08 is rated for continuous service to 175°C (347 °F). It conducts heat at 130 W/m·K (75.1 BTU/hr·ft·°F), better than 71% of copper alloy grades. Thermal expansion is 17.8 µm/m·K (9.89 µin/in·°F).
Electrical3
C50700-HR08 conducts electricity at 32 % IACS, better than 72% of copper alloy grades.
Chemical & Environmental3
Corrosion resistance is good (65/100), better than 58% of copper alloy grades.
Sustainability4
Producing a kilogram of C50700-HR08 takes about 55 MJ of energy and emits 3.6 kg of CO₂ — less than 72% of copper alloy grades. Typical recycled content is 35%.
Manufacturability7
C50700-HR08's machinability is poor (32/100, worse than 57% of copper alloy grades); weldability poor (30/100); formability poor (25/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with C50700-HR08
Is C50700 easy to machine?
Machines like other low-lead phosphor bronzes — gummy, long chips; use sharp positive-rake carbide, high speed, generous coolant; rating ≈20% of free-cutting brass.
Can C50700 be welded?
Fusion welding is poor to fair (hot-short, P loss); prefer resistance spot/seam welding, soldering or silver brazing with low heat input.
Can C50700 be formed, bent or molded?
Excellent cold formability in O60/H01; in spring tempers keep bend radii ≥2t and bend with grain, then stress-relieve 175–230 °C to restore elastic limit.
What surface finishes work on C50700?
Takes bright polishing and tin, silver or nickel plating well; not anodizable — protect from tarnish with benzotriazole or lacquer, and avoid ammonia exposure on hard tempers.
C50700 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 |
|---|---|---|
| Snsolid-solution strengthener | 1.5 – 2 | 1.8 |
| Pdeoxidizer, raises strength and wear resistance | 0.1 – 0.35 | 0.2 |
| Fe | ≤ 0.1 | — |
| Pb | ≤ 0.05 | — |
| Zn | ≤ 0.3 | — |
| CuCu + named elements 99.5 min (Ag countable as Cu) | balance | — |
C50700-HR08 — frequently asked
What is C50700-HR08 used for?
C50700-HR08 is typically used for heavy springs, bushings, bearing bronze strip and diaphragms. In short: strongest phosphor bronze here; spring and bearing temper; wear-resistant strip stock.
What is the yield strength of C50700-HR08?
C50700-HR08 has a typical yield strength of 530 MPa (76.9 ksi) and a tensile strength of 570 MPa (82.7 ksi) — stronger than 91% of copper alloy grades. Strength varies by condition: see the 9 listed tempers.
Is C50700-HR08 easy to machine?
Not especially — machinability is rated poor (32/100, worse than 57% of copper alloy grades). Machines like other low-lead phosphor bronzes — gummy, long chips; use sharp positive-rake carbide, high speed, generous coolant; rating ≈20% of free-cutting brass.
Can C50700-HR08 be welded?
Not readily — weldability is rated poor (30/100). Fusion welding is poor to fair (hot-short, P loss); prefer resistance spot/seam welding, soldering or silver brazing with low heat input.
What surface finishes work on C50700-HR08?
Takes bright polishing and tin, silver or nickel plating well; not anodizable — protect from tarnish with benzotriazole or lacquer, and avoid ammonia exposure on hard tempers.
Can C50700-HR08 be formed, bent or molded?
Excellent cold formability in O60/H01; in spring tempers keep bend radii ≥2t and bend with grain, then stress-relieve 175–230 °C to restore elastic limit.
What is the maximum service temperature of C50700-HR08?
C50700-HR08 is rated for continuous use to about 175°C (347 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between C50700-H08 and C50700-O60?
H08 is the default condition — standard stocked spring temper for connector contacts, clips and flat springs; stress-relieve after forming. O60: pick for deep drawing, severe forming or coining before a final age/stress-relief. Yield strength is 505 MPa in H08 versus 105 MPa in O60.
Sources
- ASTM B103/B103M — Phosphor Bronze Plate, Sheet, Strip and Rolled Bar — ASTM International (2019)
- CDA/UNS alloy data sheet, C50700 phosphor bronze — Copper Development Association (2023)
- ASM Handbook Vol. 2 — Properties of Nonferrous Alloys (Copper and Copper Alloys) — ASM International (1990)
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.