The graphite flakes act as built-in chip breakers and as a lubricant at the cutting edge, so chips fracture into short pieces instead of forming long strings, cutting forces are lower and no built-up edge forms on the tool. The result is high metal removal rates, long tool life and a good finish, generally without cutting fluid.

It is cast through a water-cooled die as a continuous length and then cut to size, which gives a dense, uniform structure with no sand inclusions, no gas porosity and no hard chill spots. Sand castings vary through the section and can contain inclusions that destroy tooling, which is why continuous cast stock is used where the part will be machined.

Vibration damping and dimensional stability. Grey iron absorbs far more vibrational energy than steel, so chatter is suppressed and surface finish improves, and continuous cast stock carries low residual stress so a machined base holds its geometry over time. Surface plates, gauge bodies and machine frames all rely on both properties.

It is brittle. Tensile strength is modest, elongation is effectively zero and impact resistance is poor, so it fails without warning under shock or when loaded in tension. It performs well in compression. Where some toughness is needed, ductile iron trades away part of the machinability and damping to get it.

The shape of the graphite. Grey iron contains flakes, which give the best machinability and damping but act as internal crack initiators. Ductile iron contains spheroidal nodules, produced by a magnesium treatment, which do not concentrate stress in the same way and give substantially higher strength and real elongation.

It performs unusually well without it. The graphite at the surface acts as a solid lubricant reservoir, so cast iron ways, gibs, wear plates and bushings tolerate dry running and marginal lubrication far better than steel. This is why machine tool slideways were traditionally cast iron running against cast iron.

A range of thicknesses and widths intended to leave a modest machining allowance on each face, cut to length from continuous cast lengths. Because the stock is dimensionally stable and clean, allowances can be smaller than for sand castings, and it is generally more economical to select a stocked section close to the finished part than to machine down a larger one.