Precious Metal 18K
JIS K18 · GB Au750 · ISO 9202
18K (Au750, K18) is 75 % gold alloyed with silver, copper or palladium, the most widely used jewelry karat internationally and available in yellow, white, rose and green colour variants.
Reference datasheet — 18K is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the O condition
18K tempers and conditions
18K is supplied in 10 conditions, soft to hard. O is the default FabDigit quotes; the values on this page are for it.
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 |
ODefault 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?
18K (Au750, K18) is 75 % gold alloyed with silver, copper or palladium, the most widely used jewelry karat internationally and available in yellow, white, rose and green colour variants. The alloying raises strength to 240 MPa yield and 450 MPa tensile at 38 % elongation, with a 300 °C maximum service temperature, and it is supplied as castings, sheet, wire, tube and age-hardenable stock. Copper-rich colours form fire-scale and require pickling; where a whiter, harder surface is needed, 18K white gold with rhodium plating is the usual alternative. 18K 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). 18K 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).
What is 18K used for?
- fine jewelry
- watch cases
- wedding rings
- luxury goods
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 properties
Typical room-temperature values for 18K-O; bars are the position among precious metal grades.
Physical3
18K 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 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 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 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 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'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. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the precious metal family
Yield strength against density for every precious metal grade FabDigit runs. 18K is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 18K
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.
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 |
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.
Equivalent designations
Standards and trade names that resolve to Precious Metal 18K in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ISO
- 9202
- GB (China)
- Au750
- JIS
- K18
How much does 18K cost?
18K is a high-cost precious metal ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
18K — frequently asked
What is 18K used for?
18K 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?
18K 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 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 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?
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 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?
18K 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.
How much does 18K cost?
18K is a high-cost precious metal ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.