A casting is a part made by pouring molten metal into a mould of the shape wanted and letting it solidify. Iron and steel castings — pump and valve bodies, machine frames, gearbox housings, wear parts, manhole covers — are made where a shape is too complex, too large or too costly to machine or forge.
Most iron and steel castings are poured into sand moulds made around a pattern, with cores for the internal passages; the mould is broken away after the metal has cooled. Investment casting, with a ceramic shell built around a wax pattern, gives small parts with fine detail and tolerances. Centrifugal casting spins the mould to make pipes, rings and liners. A casting is then cleaned, fettled, heat-treated and machined where it has to fit.
Cast iron has 2–4% carbon. In grey (lamellar) iron the carbon forms graphite flakes, which make it easy to cast and machine, damp vibration and resist wear but leave it brittle; it is used for machine beds, engine blocks, brake discs and manhole covers. Ductile (spheroidal graphite, SG) iron is treated with magnesium so that the graphite forms spheres, giving strength and elongation close to steel; it is used for ductile iron pipes and fittings, crankshafts, valve and pump bodies.
Cast steel has less than about 0.5% carbon and is chosen where a part must be both shaped and tough or weldable: valve bodies for pressure service (ASTM A216 WCB), heavy machine parts, railway couplers, mining equipment, and wear-resistant manganese and chromium steel castings. It is harder to pour than iron and needs heat treatment after casting.
The GCC has foundries for ductile iron fittings, municipal castings, and wear and spare parts for the cement, mining and steel industries, and imports most complex and pressure castings from India, China, Turkey and Europe. Castings for oil and gas valves are bought to ASTM grades under the owner's specifications, with radiography or other non-destructive testing of critical areas.
A casting is made to a drawing, so it is ordered by drawing number and revision, material grade and standard, heat treatment, the tests required and the casting tolerance grade. See the grey and ductile iron grade equivalents.
Full dimensions: Grey and ductile cast iron grade equivalents (EN 1561 / EN 1563, ISO, ASTM, JIS, GB)
| Region | Standard | What it covers |
|---|---|---|
| Europe | EN 1561 CEN-CENELEC |
Founding — grey cast irons, EN-GJL-100 to EN-GJL-350 |
| Europe | EN 1563 CEN-CENELEC |
Founding — spheroidal graphite cast irons, EN-GJS-350-22 to EN-GJS-900-2 and solution-strengthened ferritic grades |
| Europe | EN 10293 CEN-CENELEC |
Steel castings for general engineering uses (GE200, GE240, GE300, G20Mn5 and alloy grades) |
| Europe | EN 10213 CEN-CENELEC |
Steel castings for pressure purposes (GP240GH, GP280GH and alloy grades) |
| Germany | DIN 1691 / DIN 1693 replaced by EN 1561 / EN 1563 |
Grey cast iron (GG) and ductile cast iron (GGG) |
| International | ISO 185 / ISO 1083 ISO |
Grey cast irons and spheroidal graphite cast irons — classification |
| International | ISO 8062-3 ISO |
General dimensional and geometrical tolerances and machining allowances for castings |
| USA | ASTM A48/A48M ASTM |
Gray iron castings, Classes 20 to 60 (tensile strength in ksi) |
| USA | ASTM A536 ASTM |
Ductile iron castings, grades 60-40-18 to 120-90-02 |
| USA | ASTM A27/A27M ASTM |
Steel castings, carbon, for general application |
| USA | ASTM A216/A216M ASTM |
Carbon steel castings suitable for fusion welding for high-temperature service — WCA, WCB, WCC |
| USA | ASTM A352/A352M ASTM |
Ferritic and martensitic steel castings for pressure parts at low temperature — LCB, LCC |
| Japan | JIS G5501 / G5502 / G5101 JSA |
Grey iron (FC), ductile iron (FCD) and carbon steel (SC) castings |
| China | GB/T 9439 / GB/T 1348 / GB/T 11352 SAC |
Grey iron (HT), ductile iron (QT) and general engineering cast carbon steel (ZG) |
Grade equivalents and the standards bodies: Steel grades & standards
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