A complete SG iron specification states the grade and standard, how and where properties are tested, the microstructure you need, dimensional tolerances, inspection and repair rules, and the certificates, finish and packing you expect. Each of these belongs on the drawing or in a short specification attached to the order.
A drawing that just says "SG iron" invites the foundry to fill the gaps in its own favour. The checklist below closes them. If the grade names are unfamiliar, start with FG 260, SG 500/7 and EN-GJS grades.
Material and mechanical properties
- State the full grade and standard, for example EN-GJS-500-7 to EN 1563, SG 500/7 to IS 1865, or the ASTM A536 grade if you work to American standards.
- Say which test piece applies: separately cast, cast-on or cut from the casting, and its size for your wall thickness.
- List the required tensile strength, 0.2% proof strength and elongation if the standard grade is not enough on its own.
- Add impact test requirements and temperature if the part works in cold conditions, using a low-temperature grade where one exists.
- Give a hardness range, the method and the test location.
Microstructure and chemistry
- Set a minimum nodularity, as a percentage, and the method for assessing it, such as comparison charts in ISO 945-1.
- State the matrix you need, for example mainly ferritic or ferritic-pearlitic, if it matters for machining or toughness.
- Set limits on carbides and on any elements that matter for your use, if they are not fixed by the standard.
- Say how often microstructure is checked: per heat, per batch or on samples only.
Dimensions, defects and repair
- Give general casting tolerances to ISO 8062-3 with a DCTG grade and machining allowance grade, as explained in casting tolerances.
- Mark datum surfaces, critical dimensions and surfaces that must be free of defects.
- State NDT requirements by zone, with method, standard and acceptance level.
- Say whether pressure or leak testing is required, with pressure, medium and hold time.
- State whether repair welding is permitted, with what approval, and whether repaired parts must be retested or heat treated.
Documents, finish and packing
- Require an EN 10204 3.1 certificate per heat, or 3.2 if your customer needs third-party verification, as described in material test certificates.
- Require a dimensional report on first samples and on an agreed sample from each batch.
- State marking: part number, heat number, foundry mark and date code, with method and position.
- Specify surface preparation, primer or paint, film thickness and masked areas.
- Specify rust protection for machined faces and the packing standard.
Agree it before samples
Send the specification with the request for quote, not after the first samples. Ask the foundry to confirm each point in writing or list exceptions. Exceptions raised at quotation are cheap to settle, while exceptions found at inspection cost time and money. The same discipline applies to the whole order, as set out in what an engineering purchase contract should include.
Next step
We review specifications with foundries, confirm exceptions before you order, and inspect against the specification before loading. To work through your SG iron part, book a free sourcing review.