CI · cast iron
Austempered Ductile Iron (EN-GJS-800-8 through 1100-3)
Ductile iron put through an austempering heat treatment to reach 800–1,100 MPa. It machines like a hardened alloy steel - CBN or ceramic for the final passes, and all the sequence planning that implies.
Quoting this material
- Typical lead time
- 20–35 working days
- Condition
- Austempered (austenitise, quench to a bainitic transformation temperature, hold)
- Achievable finish
- Ra 1.6 µm typical · Ra 0.4 µm best
Machined in-house to your drawing: see the precision CNC machining service and the machine and inspection capability it runs on.
Machinability
Our own 1–10 shop ranking, not a published index: 10 is free-cutting brass C360, 1 is Inconel 718. It ranks how a material behaves on the floor - cycle time, chip control and tool life together. Where a published index exists it is quoted in the note.
Ductile iron put through an austempering heat treatment to reach 800–1,100 MPa. It machines like a hardened alloy steel - CBN or ceramic for the final passes, and all the sequence planning that implies.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Tensile strength | 800–1,100 | MPa |
| Yield strength (0.2%) | 550–750 | MPa |
| Elongation | 3–8 | % |
| Hardness | 269–341 | HB |
| Wear resistance | Approaching a hardened steel | - |
| Weight vs steel part | ~10% lighter | - |
Hardness, tensile and thermal figures are typical published values for the condition stated. Actual mill certificates govern; send the specification with the drawing and we confirm against the certificate before the material is cut.
Condition
Austempered (austenitise, quench to a bainitic transformation temperature, hold)
Heat treatment
The process is the material. Ductile iron is austenitised, quenched into a salt bath at 250–400 °C and held so the matrix transforms to ausferrite. The hold temperature sets the balance of strength and toughness - lower for strength, higher for toughness. Distortion is modest but real, so finishing stock is planned.
Achievable surface finish
Ra 1.6 µm
Ra 0.4 µm
Ground or hard turned after austempering for any tolerance-critical or sliding surface.
Tooling and cutting parameters
Cutting speed
- 60–150 m/min (carbide, roughing before treatment) · 40–90 m/min after treatment (CBN/ceramic)
Feed
- 0.10–0.25 mm/rev turning · 0.06–0.15 mm/tooth milling
Tooling
- Coated carbide before treatment; CBN or ceramic afterwards
Coolant
- Flood; heat at the edge decides the surface integrity
Starting points for carbide on a rigid setup, not a guarantee. The right numbers depend on the machine, the toolholder and the fixturing - ask and we will say what we would actually run.
Typical applications
- Automotive gears and differential parts
- Crankshafts and camshafts
- Rail and heavy vehicle wheels
- Mining wear parts
- Gearbox and drive components
DFM notes for this grade
- The whole advantage over a steel is cast-to-near-net-shape plus strength: the gear teeth are cast and then only the bores and faces are machined, which is why the process competes with forging
- Sequence is critical: rough machine, austemper, then finish. Trying to finish before the treatment means the part moves and the hardness is not there yet
- Machining after austempering is genuinely difficult: at 40 HRC the tooling is CBN or ceramic and the feeds are slow, so keep the post-treatment stock minimal
Questions buyers ask
- Why use ADI instead of a hardened steel?
- Cost and shape. ADI is cast to near net shape, so a gear can be produced with the teeth cast rather than cut, and a 10% weight saving comes with the lower density. Where the shape suits casting, ADI undercuts a forged and case-hardened steel part significantly.
- How much machining is left after austempering?
- As little as possible. The finishing stock is deliberately small - a few tenths of a millimetre on the bores, faces and any ground surface - because the machining rate after treatment is a fraction of the pre-treatment rate.