CI · cast iron
Grey Cast Iron GJL200 (Grade 200)
The lowest-strength of the common grey irons, and the easiest: more free graphite, softer matrix, and a fast, clean cut. The usual choice for a big, non-critical housing or base.
Quoting this material
- Typical lead time
- 15–25 working days
- Condition
- As cast
- Achievable finish
- Ra 3.2 µm typical · Ra 1.6 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.
The lowest-strength of the common grey irons, and the easiest: more free graphite, softer matrix, and a fast, clean cut. The usual choice for a big, non-critical housing or base.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Tensile strength | 200 | MPa |
| Compressive strength | ~720 | MPa |
| Hardness | 150–210 | HB |
| Damping capacity | Very high | - |
| Thermal conductivity | 47 | W/m·K |
| Modulus of elasticity | 100 | GPa |
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
As cast
Heat treatment
Stress relief is a machining prerequisite on a large casting, not an option. There is no hardening treatment - grey iron is used for its damping and its cost, not for strength.
Achievable surface finish
Ra 3.2 µm
Ra 1.6 µm
Takes a decent machined finish but is rarely specified for appearance; functional faces are the machining scope.
Tooling and cutting parameters
Cutting speed
- 150–300 m/min (carbide)
Feed
- 0.15–0.40 mm/rev turning · 0.10–0.30 mm/tooth milling
Tooling
- Coated carbide
Coolant
- Dry or mist, with dust extraction
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
- Large machine bases and plinths
- Counterweights and ballast
- Drain covers and access frames
- Pump and valve bodies for low pressure
- General purpose housings
DFM notes for this grade
- It is the cost-driven grey iron: use it for a big, lightly loaded casting where damping and mass matter more than strength
- Wall thickness consistency matters more than the grade on a large casting - thick-to-thin transitions cause porosity and cracking in the foundry
- Any pressure-containing part should be specified at a higher grade or a different material, because grey iron porosity is difficult to avoid at scale
Questions buyers ask
- When is GJL200 the right choice?
- When the part is large, lightly loaded and mainly there to provide mass and damping: a bed, a plinth, a counterweight, a cover frame. Moving up a grade buys strength you will not use and costs more in the foundry.
- Does the grade affect the machined finish?
- A little. The lower grades have more free graphite and a softer matrix, which cuts faster but gives a duller surface. Where the finish is functional - a sliding surface, a seal face - the part is usually specified a grade higher or the surface is ground.
Grades we would quote instead
GJL250 (Grey Iron 250)
7/10Grey iron cuts cleanly and dry: the graphite flakes act as a built-in chip breaker and lubricant, so it machines fast, throws dust instead of chips, and wears the ways if the dust is not contained.
GJL300 (Grey Iron 300)
6/10The strongest of the standard grey irons: harder matrix, slightly tougher on the tool and still cutting clean and dry like its family.
GGG40 / Ductile Iron 400-15
6/10Ductile iron with the graphite in nodules rather than flakes: it has real elongation, it takes impact, and it machines like a soft steel with better chip control than grey iron.