Copper Alloy C12900-OS025
Temper
UNS C12900
OS025 = annealed to 0.025 mm grain size
Fine-grain anneal — forming with better surface finish (less orange peel) than OS050.
Values for the OS025 condition
Other C12900 tempers and conditions
C12900 is listed in 11 conditions; see the grade overview at C12900.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed to 0.050 mm grain size | Softest commercial anneal — pick for deep drawing, severe forming and maximum conductivity. | 69 | 221 | 45 | 42 HB | 101 % IACS |
As hot extruded | As-extruded bar, rod, bus bar and commutator sections before any drawing or annealing. | 69 | 220 | 50 | 42 HB | 100 % IACS |
OS025This page Annealed to 0.025 mm grain size | Fine-grain anneal — forming with better surface finish (less orange peel) than OS050. | 76 | 235 | 42 | 48 HB | 100 % IACS |
As hot rolled | Mill temper for hot-rolled plate and bus plate where soft, formable copper is acceptable. | 76 | 228 | 45 | 45 HB | 100 % IACS |
1/8 hard | Slight stiffening while keeping most forming ductility — good for lightly formed conductive parts. | 190 | 250 | 30 | 60 HB | 100 % IACS |
Quarter hard | Balanced temper for moderate bending with useful spring-back resistance. | 205 | 262 | 25 | 70 HB | 99 % IACS |
Half hard | General-purpose semi-rigid temper for bus bar, gaskets and formed conductive hardware. | 230 | 276 | 14 | 80 HB | 98 % IACS |
H04Default Full hard | Standard stocked hard temper for bus bar, commutator segments and hard-drawn conductor parts. | 280 | 315 | 6 | 95 HB | 98 % IACS |
Extra hard | Between full hard and spring; used where extra stiffness is needed without spring-temper flatness. | 295 | 330 | 5 | 100 HB | 97 % IACS |
Spring hard | Spring-hard strip for contacts, clips and gaskets that must resist set at slightly elevated temperature. | 310 | 345 | 4 | 105 HB | 97 % IACS |
Extra spring hard | Maximum cold-worked strength for thin strip springs; essentially no further forming possible. | 325 | 365 | 4 | 110 HB | 97 % IACS |
What is C12900-OS025?
C12900-OS025 is C12900 in the OS025 temper — fine-grain anneal — forming with better surface finish (less orange peel) than OS050. C12900-OS025 has a yield strength of 76 MPa (11 ksi) and a tensile strength of 235 MPa (34.1 ksi) — weaker than 91% of copper alloy grades. Elongation at break is 42% and the elastic modulus is 120 GPa (17.4 Msi). C12900-OS025 has a density of 8.94 g/cm³ (0.323 lb/in³), heavier than 90% of copper alloy grades. It melts at 1,065°C (1,949 °F). H04 is the default condition FabDigit quotes; OS025 is available on request or by drawing note.
Advantages
- Conducts heat well — 390 W/m·K (225.3 BTU/hr·ft·°F), better than 96% of copper alloy grades
- High electrical conductivity — 100 % IACS, better than 96% of copper alloy grades
- Forms and bends easily — 92/100, better than 91% of copper alloy grades
- Ductile — tolerates forming and impact — 42%, better than 86% of copper alloy grades
Limitations
- Difficult to machine — 18/100, worse than 100% of copper alloy grades
- Low strength — 76 MPa (11 ksi), worse than 91% of copper alloy grades
C12900-OS025 properties
Typical room-temperature values for C12900-OS025; 13 are specific to this condition. Other listed values are C12900 reference data and may not represent this condition. Bars are the position among copper alloy grades.
Physical3
C12900-OS025 has a density of 8.94 g/cm³ (0.323 lb/in³), heavier than 90% of copper alloy grades. It melts at 1,065°C (1,949 °F).
Mechanical13
C12900-OS025 has a yield strength of 76 MPa (11 ksi) and a tensile strength of 235 MPa (34.1 ksi) — weaker than 91% of copper alloy grades. Elongation at break is 42% and the elastic modulus is 120 GPa (17.4 Msi).
Thermal6
C12900-OS025 is rated for continuous service to 250°C (482 °F). It conducts heat at 390 W/m·K (225.3 BTU/hr·ft·°F), better than 96% of copper alloy grades. Thermal expansion is 17 µm/m·K (9.44 µin/in·°F).
Electrical3
C12900-OS025 conducts electricity at 100 % IACS, better than 96% of copper alloy grades.
Chemical & Environmental3
Corrosion resistance is good (60/100), worse than 68% of copper alloy grades.
Sustainability4
Producing a kilogram of C12900-OS025 takes about 57 MJ of energy and emits 3.9 kg of CO₂ — less than 52% of copper alloy grades. Typical recycled content is 50%.
Manufacturability8
C12900-OS025's machinability is poor (18/100, worse than 100% of copper alloy grades); weldability fair (40/100); formability excellent (92/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with C12900-OS025
Is C12900 easy to machine?
Gummy and stringy (rating ≈20 % of free-cutting brass) — use sharp positive-rake carbide, high speed, generous soluble-oil coolant; hard tempers cut cleaner than annealed.
Can C12900 be welded?
Oxygen-bearing tough pitch copper: use GTAW/GMAW with low heat input or resistance welding; avoid oxyacetylene and any hydrogen-containing atmosphere above ~370 °C to prevent hydrogen embrittlement.
Can C12900 be formed, bent or molded?
Excellent cold formability in OS tempers (deep draw, roll form, bend to 0T); hard and spring tempers need generous bend radii and interstage anneals at 375–650 °C.
What surface finishes work on C12900?
Solders and brazes readily; can be tin-, nickel- or silver-plated, mechanically polished to bright lustre, or lacquered/patinated — tarnishes in air if left bare.
C12900 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 |
|---|---|---|
| Ag≈16 troy oz per short ton silver minimum — the defining addition of C12900 | ≥ 0.05 | 0.06 |
| Otough pitch oxygen, typically 0.02–0.05 % as Cu2O; not a specification limit | ≈ 0.03 | 0.03 |
| CuCu + Ag combined, minimum per ASTM B5 / CDA registration for fire-refined tough pitch copper | ≥ 99.88 (balance) | — |
C12900-OS025 — frequently asked
What is C12900-OS025 used for?
C12900-OS025 is typically used for commutator bars and segments, general electrical hardware, busbar and connector stock, brazed electrical assemblies, motor and generator components and formed terminals and lugs. In short: silver-bearing softening resistance; 98 % IACS conductivity; 200 °C service copper.
What is the yield strength of C12900-OS025?
C12900-OS025 has a typical yield strength of 76 MPa (11 ksi) and a tensile strength of 235 MPa (34.1 ksi) — weaker than 91% of copper alloy grades. Strength varies by condition: see the 11 listed tempers.
Is C12900-OS025 easy to machine?
Not especially — machinability is rated poor (18/100, worse than 100% of copper alloy grades). Gummy and stringy (rating ≈20 % of free-cutting brass) — use sharp positive-rake carbide, high speed, generous soluble-oil coolant; hard tempers cut cleaner than annealed.
Can C12900-OS025 be welded?
With care — weldability is rated fair (40/100). Oxygen-bearing tough pitch copper: use GTAW/GMAW with low heat input or resistance welding; avoid oxyacetylene and any hydrogen-containing atmosphere above ~370 °C to prevent hydrogen embrittlement.
What surface finishes work on C12900-OS025?
Solders and brazes readily; can be tin-, nickel- or silver-plated, mechanically polished to bright lustre, or lacquered/patinated — tarnishes in air if left bare.
Can C12900-OS025 be formed, bent or molded?
Excellent cold formability in OS tempers (deep draw, roll form, bend to 0T); hard and spring tempers need generous bend radii and interstage anneals at 375–650 °C.
What is the maximum service temperature of C12900-OS025?
C12900-OS025 is rated for continuous use to about 250°C (482 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between C12900-H04 and C12900-OS050?
H04 is the default condition — standard stocked hard temper for bus bar, commutator segments and hard-drawn conductor parts. OS050: softest commercial anneal — pick for deep drawing, severe forming and maximum conductivity. Yield strength is 280 MPa in H04 versus 69 MPa in OS050.
Sources
- ASTM B5 — Electrolytic Tough Pitch / fire-refined copper refinery shapes — ASTM International (2021)
- CDA Alloy Database — C12900 fire-refined tough pitch copper with silver — Copper Development Association (2023)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys — ASM International (1990)
- ASTM B152/B152M — Copper Sheet, Strip, Plate and Rolled Bar — ASTM International (2019)
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.