Casting is the way to make parts with complex shapes in one go, with far less material loss than machining. But “a casting” can mean very different materials. The right choice depends on the load the part carries, the impacts it sees, whether its environment is corrosive and the wear conditions.
Grey iron castings (lamellar graphite cast iron)
Also known as grey cast iron; it contains about 2.5–4% carbon and 1–3% silicon. Part of the carbon is present in the structure as flake (lamellar) graphite.
- Strengths: Very good vibration damping, high compressive strength, easy machining, economical production.
- Limitation: Because the graphite flakes act like notches, tensile strength and ductility are low; it is brittle under impact.
- Grades: Such as EN-GJL-200 and EN-GJL-250; the number is the minimum tensile strength (MPa).
- Typical parts: Machine-tool and machine housings, covers, tables, brake discs.
Ductile iron castings (spheroidal graphite cast iron)
The molten metal is treated with magnesium so that the graphite forms as spheroids. Spheroidal graphite does not act as a notch, so the material is much stronger and more ductile than grey iron.
- Strengths: High tensile strength, ductility and impact resistance; strength close to steel, with the shape freedom of casting.
- Grades: Such as EN-GJS-400-15, EN-GJS-500-7 and EN-GJS-600-3; the first number is the minimum tensile strength (MPa), the second the minimum elongation (%).
- Typical parts: Gearbox housings, hubs, brackets, pipe fittings and machine parts under dynamic load.
Steel castings
Made by pouring carbon or alloy steel into a mould. The carbon content is lower than in cast irons and there is no graphite in the structure.
- Strengths: Combines high strength and toughness; weldable, and its properties can be adjusted by heat treatment.
- Standards: EN 10293 for general engineering and EN 10213 for pressure equipment are common references.
- Typical parts: Heavy-duty machine and equipment parts, construction-machinery parts, housings.
Stainless steel castings
Castings of stainless steels with at least 10.5% chromium; a thin chromium oxide layer on the surface protects the material against corrosion. The most common grades are CF8 (1.4308), the cast equivalent of 304 stainless, and CF8M (1.4408), the equivalent of molybdenum-bearing 316.
- Strengths: Corrosion and chemical resistance, hygienic surface.
- Typical parts: Pump casings, impellers, valves and fittings in chemical, food and fluid-handling applications.
Abrasion-resistant (Ni-Hard) castings
Ni-Hard is a white cast iron alloyed with nickel and chromium. The carbon is present as hard carbides instead of graphite, while the nickel keeps the matrix in a hard martensitic structure. Ni-Hard 1 and 2 contain about 3–5% nickel and 1.5–2.5% chromium; Ni-Hard 4 contains about 5–7% nickel and 8–10% chromium.
- Strengths: Very high wear resistance; hardness is typically above 550 HB.
- Limitation: Brittle and sensitive to impact; its hardness makes conventional machining difficult, so it is usually finished by grinding.
- Typical parts: Mill liners, crusher parts and parts of slurry pumps in mining, cement and metallurgy.
Comparison table
| Casting type | Key property | Weakness | Typical use |
|---|---|---|---|
| Grey iron | Vibration damping, machinability | Brittle, low tensile strength | Machine housings, tables |
| Ductile iron | Strength and ductility | Costs more than grey iron | Hubs, brackets, gearboxes |
| Steel | Toughness, weldability | Harder to cast | Heavy-duty parts |
| Stainless | Corrosion resistance | High material cost | Pumps, valves, food and chemicals |
| Ni-Hard | Wear resistance | Brittle, hard to machine | Mill liners, crushers |
What to prepare for a casting quote
- A technical drawing of the part (PDF, DWG, STEP) or details of a sample part
- The casting type and grade/standard required (e.g. EN-GJS-500-7, Ni-Hard 4)
- Order quantity, how often it repeats and the approximate weight per part
- Whether the part is delivered as-cast or machined