Precious Metal 9K-AC (Spheroidize annealed)
Heat-treated state
GB Au375 · ISO 9202
Condition of lost-wax cast rings and pendants straight from the flask, before work hardening or ageing.
Values for the AC condition
Other 9K tempers and conditions
9K is listed in 8 conditions; see the grade overview at 9K.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ACThis page 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-AC?
9K-AC is 9K heat treated to AC — condition of lost-wax cast rings and pendants straight from the flask, before work hardening or ageing. 9K-AC has a yield strength of 200 MPa (29 ksi) and a tensile strength of 330 MPa (47.9 ksi) — stronger than 51% of precious metal grades. Elongation at break is 18% and the elastic modulus is 90 GPa (13.1 Msi). 9K-AC 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). ANN is the default condition FabDigit quotes; AC is available on request or by drawing note.
Advantages
- Easy to machine — 60/100, better than 97% of precious metal grades
Limitations
- Needs corrosion protection — 50/100, worse than 99% of precious metal grades
- Limited formability — 35/100, worse than 92% of precious metal grades
- Limited ductility — 18%, worse than 83% of precious metal grades
9K-AC properties
Typical room-temperature values for 9K-AC; 20 are specific to this condition. Other listed values are 9K reference data and may not represent this condition. Bars are the position among precious metal grades.
Physical3
9K-AC 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-AC has a yield strength of 200 MPa (29 ksi) and a tensile strength of 330 MPa (47.9 ksi) — stronger than 51% of precious metal grades. Elongation at break is 18% and the elastic modulus is 90 GPa (13.1 Msi).
Thermal6
9K-AC is rated for continuous service to 300°C (572 °F). It conducts heat at 105 W/m·K (60.7 BTU/hr·ft·°F), better than 59% of precious metal grades. Thermal expansion is 17.5 µm/m·K (9.72 µin/in·°F).
Electrical3
9K-AC conducts electricity at 16 % IACS, worse than 60% of precious metal grades.
Chemical & Environmental3
Corrosion resistance is fair (50/100), worse than 99% of precious metal grades.
Sustainability4
Producing a kilogram of 9K-AC 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-AC's machinability is good (60/100, better than 97% of precious metal grades); weldability very good (70/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 9K-AC
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.
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.
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 | — |
9K-AC — frequently asked
What is 9K-AC used for?
9K-AC 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-AC?
9K-AC has a typical yield strength of 200 MPa (29 ksi) and a tensile strength of 330 MPa (47.9 ksi) — stronger than 51% of precious metal grades. Strength varies by condition: see the 8 listed tempers.
Is 9K-AC easy to machine?
Reasonably — machinability is rated good (60/100, better than 97% 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-AC be welded?
Yes — weldability is rated very good (70/100). 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-AC?
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-AC 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-AC?
9K-AC 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.