Precious Metal 9K
GB Au375 · ISO 9202
9K (Au375) is a 37.5% gold karat alloy with the balance mostly copper and silver, the lowest karat legally marketable as gold in the UK and common EU markets.
Reference datasheet — 9K 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 ANN condition
9K tempers and conditions
9K is supplied in 8 conditions, soft to hard. ANN is the default FabDigit quotes; the values on this page are for it.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Condition of lost-wax cast rings and pendants straight from the flask, before work hardening or ageing. | 200 | 330 | 18 | 124 HB | 16 % IACS |
ANNDefault Annealed | Pick for forming, stone setting, bending and chain assembly where maximum ductility is needed. | 210 | 360 | 35 | 115 HB | 17 % IACS |
9K Yellow | Standard yellow colour composition — the default 9K sold for chain, sheet and casting grain. | 210 | 360 | 35 | 115 HB | 17 % IACS |
9K Red / Rose | Copper-rich colour variant for rose-tone jewellery; hardest 9K colour but most tarnish-prone and hot-short. | 250 | 400 | 28 | 133 HB | 20 % IACS |
9K White | Choose for white-metal look at lowest gold cost; harder and stiffer, but check EU nickel-release limits. | 300 | 480 | 22 | 165 HV | 60 W/m·K |
Half hard | General-purpose stock temper for wire, sheet and tube that must hold shape yet still bend. | 400 | 520 | 10 | 157 HB | 16 % IACS |
Age hardened | Optional low-temperature ageing of Au-Cu-Ag compositions to raise hardness and wear life of set pieces. | 480 | 600 | 6 | 190 HB | 19 % IACS |
Full hard | Pick for earring posts, clasp springs, pin stems and thin wire needing maximum stiffness and wear resistance. | 560 | 660 | 3 | 198 HB | 15.5 % IACS |
What is 9K?
9K (Au375) is a 37.5% gold karat alloy with the balance mostly copper and silver, the lowest karat legally marketable as gold in the UK and common EU markets. It is the hardest and most affordable of the standard karats, with 210 MPa yield strength, 360 MPa tensile strength and 35% elongation, supplied as casting stock, sheet, wire and chain in yellow, white and red variants. The copper-rich matrix work-hardens quickly, forms firescale during torch work and tarnishes more readily than higher karats, and white 9K requires rhodium plating. 10K or 14K are the obvious alternatives where higher gold content is specified. 9K has a density of 11.3 g/cm³ (0.408 lb/in³), heavier than 59% of precious metal grades. It melts at 880°C (1,616 °F). 9K has a yield strength of 210 MPa (30.5 ksi) and a tensile strength of 360 MPa (52.2 ksi) — stronger than 61% of precious metal grades. Elongation at break is 35% and the elastic modulus is 92 GPa (13.3 Msi).
What is 9K used for?
- UK and European mass-market rings
- Chains and bracelets
- Budget engagement and eternity rings
- Stamped findings and settings
- Cast pendants and charms
- Earrings and studs
- Hollow-formed chain links
Advantages
- Easy to machine — 55/100, better than 86% of precious metal grades
- Readily welded — 78/100, better than 84% of precious metal grades
- Ductile — tolerates forming and impact — 35%, better than 83% of precious metal grades
Limitations
- Needs corrosion protection — 55/100, worse than 94% of precious metal grades
9K properties
Typical room-temperature values for 9K-ANN; bars are the position among precious metal grades.
Physical3
9K has a density of 11.3 g/cm³ (0.408 lb/in³), heavier than 59% of precious metal grades. It melts at 880°C (1,616 °F).
Mechanical13
9K has a yield strength of 210 MPa (30.5 ksi) and a tensile strength of 360 MPa (52.2 ksi) — stronger than 61% of precious metal grades. Elongation at break is 35% and the elastic modulus is 92 GPa (13.3 Msi).
Thermal6
9K is rated for continuous service to 300°C (572 °F). It conducts heat at 110 W/m·K (63.6 BTU/hr·ft·°F), better than 60% of precious metal grades. Thermal expansion is 17.5 µm/m·K (9.72 µin/in·°F).
Electrical3
9K conducts electricity at 17 % IACS, worse than 56% of precious metal grades.
Chemical & Environmental3
Corrosion resistance is good (55/100), worse than 94% of precious metal grades.
Sustainability4
Producing a kilogram of 9K takes about 95,000 MJ of energy and emits 6,500 kg of CO₂ — more than 68% of precious metal grades. Typical recycled content is 35%.
Manufacturability8
9K's machinability is good (55/100, better than 86% of precious metal grades); weldability very good (78/100); formability excellent (85/100).
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. 9K is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 9K
Is 9K easy to machine?
Turns and mills cleanly with sharp carbide or HSS tools and light cuts; work in the half-hard temper to avoid smearing and always collect swarf for refining.
Can 9K be welded?
Laser and PUK micro-welding with matching 9K filler are standard; torch work needs matching 9K easy/medium/hard solders and borax-type flux to avoid firescale from the high copper.
Can 9K be formed, bent or molded?
Rolls, draws and stamps well when annealed at 600–650 °C with rapid quench; anneal every 40–50 % reduction because the copper-rich matrix work-hardens quickly.
9K 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 |
|---|---|---|
| Au375‰ minimum fineness per ISO 9202 / UK Hallmarking Act | 37.5 – 38.5 | 37.6 |
| Agcolour and ductility control (yellow grades) | 4 – 15 | 10 |
| Zndeoxidiser, lowers melting range | 3 – 12 | 7.5 |
| Niwhite grades only; must meet EN 1811 nickel-release limits | 0 – 15 | |
| Pdnickel-free white grades | 0 – 10 | |
| Cubalance, typically 40–55 % in yellow/red grades | balance |
What surface finishes work on 9K?
Polishes to a high lustre with tripoli then rouge; white 9K is normally rhodium plated, and copper-rich yellow/red benefits from a protective lacquer or e-coat to slow tarnish.
Equivalent designations
Standards and trade names that resolve to Precious Metal 9K in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ISO
- 9202
- GB (China)
- Au375
How much does 9K cost?
9K 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.
9K — frequently asked
What is 9K used for?
9K is typically used for UK and European mass-market rings, chains and bracelets, budget engagement and eternity rings, stamped findings and settings, cast pendants and charms and earrings and studs. In short: lowest legal UK karat; hardest standard karat; most affordable karat gold.
What is the yield strength of 9K?
9K has a typical yield strength of 210 MPa (30.5 ksi) and a tensile strength of 360 MPa (52.2 ksi) — stronger than 61% of precious metal grades. Strength varies by condition: see the 8 listed tempers.
Is 9K easy to machine?
Reasonably — machinability is rated good (55/100, better than 86% of precious metal grades). Turns and mills cleanly with sharp carbide or HSS tools and light cuts; work in the half-hard temper to avoid smearing and always collect swarf for refining.
Can 9K be welded?
Yes — weldability is rated very good (78/100). Laser and PUK micro-welding with matching 9K filler are standard; torch work needs matching 9K easy/medium/hard solders and borax-type flux to avoid firescale from the high copper.
What surface finishes work on 9K?
Polishes to a high lustre with tripoli then rouge; white 9K is normally rhodium plated, and copper-rich yellow/red benefits from a protective lacquer or e-coat to slow tarnish.
Can 9K be formed, bent or molded?
Rolls, draws and stamps well when annealed at 600–650 °C with rapid quench; anneal every 40–50 % reduction because the copper-rich matrix work-hardens quickly.
What is the maximum service temperature of 9K?
9K 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 9K-ANN and 9K-H04?
ANN is the default condition — pick for forming, stone setting, bending and chain assembly where maximum ductility is needed. H04: pick for earring posts, clasp springs, pin stems and thin wire needing maximum stiffness and wear resistance. Yield strength is 210 MPa in ANN versus 560 MPa in H04.
How much does 9K cost?
9K 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 — Fineness of precious metal alloys — ISO (2019)
- Metallurgy of Gold Jewellery Alloys (Grimwade) — World Gold Council (2009)
- ASM Handbook Vol. 2 — Precious Metals and Their Alloys — ASM International (1990)
- Gold Bulletin — mechanical properties of carat golds — Springer / World Gold Council (2005)
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.