Precious Metal 18K-O (Annealed)
Temper · default condition
JIS K18 · GB Au750 · ISO 9202
Standard stock condition for 18K yellow sheet, wire, tube and chain — maximum ductility for forming, drawing and setting.
Values for the O condition
Other 18K tempers and conditions
18K is listed in 10 conditions; see the grade overview at 18K.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
18K Green | Binary Au-Ag greenish-yellow alloy used for colour contrast and enamelling; very soft and not age-hardenable. | 90 | 250 | 45 | 57 HB | 18 % IACS |
As cast | Pick for cast jewelry bodies and settings straight out of the flask, before work-hardening or ageing. | 220 | 380 | 18 | 138 HB | 15.5 % IACS |
ODefaultThis page Annealed | Standard stock condition for 18K yellow sheet, wire, tube and chain — maximum ductility for forming, drawing and setting. | 240 | 450 | 38 | 143 HB | 16 % IACS |
18K Yellow | Classic yellow colour family — the default 18K alloy for chain, sheet and casting worldwide. | 240 | 450 | 38 | 143 HB | 16 % IACS |
18K Red/Rose | Copper-rich pink to red colour; hardest of the Au-Ag-Cu family and strongly age-hardenable, but most prone to fire-scale and tarnish. | 300 | 500 | 30 | 162 HB | 14 % IACS |
18K White, nickel-based | Low-cost, hard and springy white gold for stamped and machined parts; requires rhodium plating for true white and must meet EU nickel-release limits. | 350 | 620 | 25 | 190 HV | 45 W/m·K |
Half hard | Compromise temper for hinges, pin stems and stampings that must hold shape but still bend without cracking. | 480 | 600 | 12 | 176 HB | 15 % IACS |
18K White, palladium-based | Hypoallergenic, naturally grey-white and very ductile — premium white gold for high-end settings, but heavy, expensive and high-melting. | — | 480 | 35 | 130 HV | — |
Full hard | Use for spring clasps, earring posts, watch bracelet links and any part needing wear and dent resistance. | 680 | 760 | 3 | 17 HRC | 14.5 % IACS |
Age-hardened | Highest hardness route for Au-Ag-Cu yellow/rose grades — ordering of AuCu gives wear resistance for rings and watch cases without cold work. | 750 | 880 | 9 | 24 HRC | 15 % IACS |
What is 18K-O?
18K-O is 18K in the O temper — standard stock condition for 18K yellow sheet, wire, tube and chain — maximum ductility for forming, drawing and setting. 18K-O has a yield strength of 240 MPa (34.8 ksi) and a tensile strength of 450 MPa (65.3 ksi) — stronger than 73% of precious metal grades. Elongation at break is 38% and the elastic modulus is 80 GPa (11.6 Msi). 18K-O has a density of 15.5 g/cm³ (0.56 lb/in³), heavier than 77% of precious metal grades. It melts at 885°C (1,625 °F).
Advantages
- Polishes to a fine finish — 98/100, better than 98% of precious metal grades
- Readily welded — 82/100, better than 89% of precious metal grades
- Ductile — tolerates forming and impact — 38%, better than 88% of precious metal grades
- Good corrosion resistance — 93/100, better than 77% of precious metal grades
Limitations
- High embodied carbon — 15,000 kg CO₂/kg, worse than 94% of precious metal grades
- Heavy — 15.5 g/cm³ (0.56 lb/in³), worse than 77% of precious metal grades
18K-O properties
Typical room-temperature values for 18K-O; 22 are specific to this condition. Other listed values are 18K reference data and may not represent this condition. Bars are the position among precious metal grades.
Physical3
18K-O has a density of 15.5 g/cm³ (0.56 lb/in³), heavier than 77% of precious metal grades. It melts at 885°C (1,625 °F).
Mechanical16
18K-O has a yield strength of 240 MPa (34.8 ksi) and a tensile strength of 450 MPa (65.3 ksi) — stronger than 73% of precious metal grades. Elongation at break is 38% and the elastic modulus is 80 GPa (11.6 Msi).
Thermal6
18K-O is rated for continuous service to 300°C (572 °F). It conducts heat at 150 W/m·K (86.7 BTU/hr·ft·°F), better than 65% of precious metal grades. Thermal expansion is 15.5 µm/m·K (8.61 µin/in·°F).
Electrical3
18K-O conducts electricity at 16 % IACS, worse than 60% of precious metal grades.
Chemical & Environmental3
Corrosion resistance is excellent (93/100), better than 77% of precious metal grades.
Sustainability4
Producing a kilogram of 18K-O takes about 190,000 MJ of energy and emits 15,000 kg of CO₂ — more than 81% of precious metal grades. Typical recycled content is 35%.
Manufacturability8
18K-O's machinability is fair (50/100, better than 74% of precious metal grades); weldability very good (82/100); formability excellent (92/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 18K-O
Is 18K easy to machine?
Soft and gummy in the annealed state — use sharp polished carbide or single-crystal diamond, high speed, light feed and oil mist; age-hardened or cold-worked stock chips far more cleanly, and all swarf must be collected for refining.
Can 18K be welded?
Laser and pulse-arc micro-welding are routine with matching 18K filler; torch work uses graded karat solders (easy/medium/hard) with fluoride flux, and boric-acid coating prevents fire-scale on Cu-rich colours.
Can 18K be formed, bent or molded?
Excellent cold formability when annealed (≥60 % reduction between 650 °C anneals); investment cast at 950–1050 °C flask/metal for yellow and rose, higher and under protective atmosphere for Pd whites.
What surface finishes work on 18K?
Takes a mirror polish easily; standard finishing chain is pumice/tripoli/rouge, then optional rhodium or ruthenium plating on white golds and matte/satin or sandblast textures for contrast.
18K 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 |
|---|---|---|
| Au750‰ minimum per ISO 9202 / GB 11887; producers aim 75.2–75.5 for assay margin | 75 – 75.8 | 75 |
| Ag12.5 in classic 3N yellow; 25 in green gold; 5–15 in Pd whites | 0 – 25 | 12.5 |
| Cuup to ~25 in 5N red gold; 0 in green and most Pd whites | 0 – 25 | 12.5 |
| Zndeoxidiser / colour and flow modifier, common in white and solder alloys | 0 – 5 | 0.5 |
| Niwhite-gold whitener; EU REACH nickel-release limit applies to skin contact | 0 – 15 | 0 |
| Pdwhitener in hypoallergenic white golds; also grain refiner at 0.1–1 % | 0 – 16 | 0 |
| Ir/Ru/Co/Sigrain refiners and deoxidisers in casting grain | 0 – 0.2 | 0.05 |
| Ag+Cu+otherbalance to 100 %, 250‰ nominal | balance | — |
18K-O — frequently asked
What is 18K-O used for?
18K-O is typically used for fine jewelry, watch cases, wedding rings and luxury goods. In short: most common international karat; age-hardenable gold alloy; widest colour range.
What is the yield strength of 18K-O?
18K-O has a typical yield strength of 240 MPa (34.8 ksi) and a tensile strength of 450 MPa (65.3 ksi) — stronger than 73% of precious metal grades. Strength varies by condition: see the 10 listed tempers.
Is 18K-O easy to machine?
Reasonably — machinability is rated fair (50/100, better than 74% of precious metal grades). Soft and gummy in the annealed state — use sharp polished carbide or single-crystal diamond, high speed, light feed and oil mist; age-hardened or cold-worked stock chips far more cleanly, and all swarf must be collected for refining.
Can 18K-O be welded?
Yes — weldability is rated very good (82/100). Laser and pulse-arc micro-welding are routine with matching 18K filler; torch work uses graded karat solders (easy/medium/hard) with fluoride flux, and boric-acid coating prevents fire-scale on Cu-rich colours.
What surface finishes work on 18K-O?
Takes a mirror polish easily; standard finishing chain is pumice/tripoli/rouge, then optional rhodium or ruthenium plating on white golds and matte/satin or sandblast textures for contrast.
Can 18K-O be formed, bent or molded?
Excellent cold formability when annealed (≥60 % reduction between 650 °C anneals); investment cast at 950–1050 °C flask/metal for yellow and rose, higher and under protective atmosphere for Pd whites.
What is the maximum service temperature of 18K-O?
18K-O is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 18K-O and 18K-AH?
O is the default condition — standard stock condition for 18K yellow sheet, wire, tube and chain — maximum ductility for forming, drawing and setting. AH: highest hardness route for Au-Ag-Cu yellow/rose grades — ordering of AuCu gives wear resistance for rings and watch cases without cold work. Yield strength is 240 MPa in O versus 750 MPa in AH.
Sources
- ISO 9202 Jewellery and precious metals — Fineness of precious metal alloys — ISO (2019)
- Introduction to Precious Metals: Metallurgy for the Jeweller & Silversmith (M. Grimwade) — Brynmorgen Press (2009)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys (Precious Metals) — ASM International (1990)
- Gold Bulletin / Santa Fe Symposium on Jewelry Manufacturing Technology proceedings — World Gold Council / Met-Chem (2020)
- Karat gold master alloy technical sheets (18K yellow/red/white) — Legor Group / Progold / Hoover & Strong (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.