CI · 10 grades
Cast Irons
Damping, wear resistance and machinability that comes from free graphite.
Cast iron is bought for three things: vibration damping, wear resistance and the fact that the graphite flakes make it cut cleanly at high speed. Ductile grades (GGG40, GGG60) give real elongation and impact toughness; grey grades (GJL250, GJL300) are stiffer and damp better but brittle. Both are usually supplied as castings and then machined - often starting from a rough casting rather than bar.
What this family does well, and where it bites
- The graphite acts as an internal lubricant and a built-in chip breaker
- Damping capacity several times steel - the reason for machine beds and bases
- Machined dry or with mist; coolant is used for dust control, not cooling
- Casting skin is abrasive and hard - expect to scrap the first cut
Industries served
- Machine Tools
- Automotive & EV
- Energy & Oil & Gas
- Water Treatment
- Agricultural Machinery
Cast Irons grades we machine
Each grade page carries the properties as supplied, what heat treatment does or does not do to it, the achievable surface finish, starting cutting parameters and the DFM notes that matter for that specific grade.
GJL250 (Grey Iron 250)
7/10180–240 HB · 250 MPa
Grey 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.
GJL200 (Grey Iron 200)
7/10150–210 HB · 200 MPa
The lowest-strength of the common grey irons, and the easiest: more free graphite, softer matrix, and a fast, clean cut.
GJL300 (Grey Iron 300)
6/10200–260 HB · 300 MPa
The 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
6/10160–210 HB · 400 MPa
Ductile 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.
GGG50 / Ductile Iron 500-7
5/10170–230 HB · 500 MPa
A higher-strength ductile iron with less elongation: harder matrix, longer tool life needed, and the cutting speeds step down accordingly.
GGG60 / Ductile Iron 600-3
5/10190–270 HB · 600 MPa
A high-strength ductile iron: 600 MPa with 3% elongation.
GGG70 / Ductile Iron 700-2
5/10240–300 HB · 700 MPa
The top of the standard ductile iron range: 700 MPa with 2% elongation.
CGI (Compacted Graphite Iron)
4/10200–250 HB · 350–450 MPa
The graphite is in worm-like compacted form between grey and ductile, which gives roughly 70% more strength and 45% more stiffness than grey iron - and makes it noticeably harder to machine, especially after the surface has chilled.
ADI (Austempered Ductile Iron)
3/10269–341 HB (30–40 HRC) · 800–1,100 MPa
Ductile iron put through an austempering heat treatment to reach 800–1,100 MPa.
Ni-Resist (Austenitic Iron)
4/10140–190 HB · 370–400 MPa
A nickel-alloyed austenitic iron: it machines more slowly than grey iron, with the gummy chip and work-hardening of an austenitic steel, and it is bought for corrosion and heat resistance.
Questions buyers ask
- Why machine cast iron dry?
- Because the graphite dust makes a coolant sludge that is difficult to handle, and because the heat leaves with the chip. Applying coolant to a grey iron cut turns dust into a grinding paste that wears the ways. Where coolant is used it is for dust suppression and the concentration has to be managed.
- Ductile or grey iron for a machine base?
- Grey iron dampens better and is cheaper, which is why it is the traditional choice for beds and columns. Ductile iron is chosen where the base has to take impact or a bolted joint that would crack a brittle grade. If the design has thin sections or sharp section changes, grey iron will crack there.