An iron casting is proved on five things: chemical composition, mechanical properties from a test bar, microstructure, internal and surface soundness, and dimensions with surface finish. Which of the five your part gets, and to what level, is set by your drawing and purchase order — ASTM A48 and A536 treat almost everything beyond one tension test per lot as a special requirement that applies only when you ask for it.
Only the tension bar is destroyed; every other test on this list leaves the casting shippable.
Chemical Composition
Chemistry is read on a spark spectrometer, first from a chill coupon poured before the heat is tapped and corrected if it comes back out of range, then from the heat sample that goes on the certificate. The spectrometer reads carbon, silicon, manganese, phosphorus and sulfur — the elements ASTM E1999 covers for cast iron — and, on ductile iron, residual magnesium and cerium.
Write the window into the order — element and range — wherever composition drives something downstream such as weldability, machinability or a heat treatment.
Mechanical Properties
Tensile strength, yield and elongation come from a separately cast test bar pulled to ASTM E8, one test per lot, and in A48 and A536 that single test is the entire mandatory mechanical program. The bar is sized to the controlling section of your casting: A48 classifies bars by letter (S, A, B and C) against wall thickness, and A536 uses a 1-inch Y-block or keel block.
Both standards state outright that no precise quantitative relationship can be stated between the properties of a casting and those of a bar poured from the same iron. For thick-section and safety-critical work, specify a bar cut from the casting at a location marked on the drawing.
Brinell hardness on the casting itself is the per-piece check that the matrix matches the bar’s result. Neither specification lists a hardness value for any grade, so your order has to state the range and the surface it is read on. Impact testing runs to A327 on three specimens, and only when the order calls for it.
Nodularity Check for Ductile Iron
Nodularity is checked only when your order names it — A536 grades ductile iron castings on tensile properties alone. Name the rating method in the order too: A247 is a visual comparison against reference photomicrographs; E2567 computes the percentage by image analysis and repeats far better between operators.
Full-lot screening is done on whole castings by ultrasonic velocity or resonant frequency. Treat either as a calibrated gauge: the limits have to be set against cut-up parts from the same process and section size.
Soundness
Magnetic particle testing finds surface and near-surface cracks, and radiography finds internal shrinkage in the sections your drawing marks as critical. The other methods each catch a different defect family, so match the method to the defect you expect before you write either into the order.
ASTM E802, the gray iron reference radiographs, illustrates one discontinuity: centerline shrinkage, in five severity levels. Ductile iron has no reference set of its own, and E689 uses the steel casting radiographs, which do cover gas porosity, inclusions and hot tears.
Ultrasonic testing is a thick-section ductile iron tool. ASTM never wrote a UT practice for iron castings at all — A609 covers steel — and flake graphite scatters the beam. Where gray iron soundness matters, specify radiography.
Pump and valve bodies take a pressure or proof test as well, and MSS SP-61 is the practice to name. Whichever method you call out, the acceptance criteria have to be named with it — the zone, the indication size and the severity level — because none of the NDT standards supplies one.
Dimensions and Surface
Dimensions are checked with gauges and, on critical features, a CMM against the tolerance grade on the drawing; production iron sand castings are normally held to ISO 8062 grades DCTG 8 to 12. Read that grade correctly, because the table value is a total band disposed symmetrically about the nominal dimension: DCTG 11 on a 500 mm dimension is 7 mm total, or ±3.5 mm.
On a raw casting, check whether the machining allowance is present and even all the way round. ISO 8062 treats required machining allowance as its own quantity, agreed and shown on the drawing separately from the tolerance.
Surface is judged against graded reference photographs at a level named in the order. MSS SP-55, whose 2025 edition was widened to cover iron as well as steel pressure castings, is the comparator standard for valve, flange and fitting work. Sand holes and inclusions need a written acceptance level: size, number and where on the part they are tolerated.
Which Tests Your Casting Actually Needs
Start from what the base specification already buys you: chemistry, one tension test, conformance to the dimensions on your drawing, and a visual check for adhering sand, scale, cracks and hot tears. Everything beyond that is a supplementary requirement that applies only when you name it individually in the order.
| Part class | Tests to put on the order |
|---|---|
| Gray iron counterweight or non-load-bearing part | Chemistry, Brinell hardness, visual, dimensional |
| Ductile iron load-bearing housing or bracket | Add tension test on a named coupon, plus nodularity with its rating method |
| Pressure-containing pump or valve body | Add pressure test to MSS SP-61, plus RT or MT in the zones the drawing marks |
| Thick-section or safety-critical casting | Add a tension bar cut from the casting at a marked location |
Then require the report to show it. A certificate covering the actual castings shipped is a specific inspection document under EN 10204, and for each test you ordered it should carry the heat or lot number, the chemistry, the bar results, the hardness readings, the NDT results with the acceptance level that was applied, and the dimensional report.
A failing lot is segregated at the foundry, and whether it is retested, heat treated as a lot or scrapped is decided by the order; A48’s own path is two retests on the tension bar, and rejection if either one misses.