There is no single ASTM standard for cast iron. ASTM publishes a family of separate iron-casting specifications under Committee A04, and for machinery castings the two that get cited are A48/A48M for gray iron and A536 for ductile iron.
Both of those grade the iron on the minimum tensile strength of a separately cast test bar and subordinate chemical composition to that strength.
Which ASTM Standards Cover Cast Iron
ASTM’s cast iron catalog runs to 56 designations, and they sort into three groups: general specifications by iron type, application-specific specifications written around a service condition, and supporting documents.
| Standard | What it covers |
|---|---|
| A48/A48M-22 | Gray iron castings for general engineering use |
| A536-26a | Ductile iron castings |
| A842-11A(2022)e1 | Compacted graphite iron castings |
| A47/A47M, A220/A220M, A197/A197M | Malleable iron — ferritic, pearlitic, cupola |
| A532/A532M-10(2023) | Abrasion-resistant white cast irons |
| A126-04(2023) | Gray iron for valves, flanges and pipe fittings |
| A278/A278M-01(2024) | Gray iron pressure-containing parts to 650 °F [350 °C] |
| A319-71(2024) | Gray iron at elevated temperature, non-pressure-containing |
| A395/A395M-99(2022) | Ferritic ductile iron, pressure-retaining, elevated temperature |
| A874/A874M-98(2022) | Ferritic ductile iron for low-temperature service |
| A436-24, A439/A439M-18(2022) | Austenitic gray iron and austenitic ductile iron |
| A897/A897M-22 | Austempered ductile iron castings |
| A644-24 | Terminology relating to iron castings |
| A834-24 | Common requirements for iron castings, general industrial use |
| A247-24, A327/A327M-22, A367-22 | Graphite evaluation, impact testing, chill testing |
| E351 | Chemical analysis, referee methods for Committee A04 materials |
ASTM also publishes a cast iron pipe branch — soil pipe A74 and A888, ductile iron gravity sewer pipe A746, utility poles A1133. They do not govern machinery castings.
Which Specification Fits Which Part
The specification follows from the part and its service condition: a general engineering part takes A48 or A536, while pressure, temperature and abrasion each have a dedicated spec.
- General gray iron part(housing, bracket, counterweight): A48/A48M.
- General ductile iron part: A536.
- Gray iron valve body, flange or pipe fitting: A126.
- Gray iron pressure-containing part at temperature: A278. All classes are suitable to 450 °F [230 °C]; above that, only Classes 40 through 60, to a ceiling of 650 °F [350 °C].
- Ductile iron pressure-retaining part at temperature: A395. All grades are suitable to 450 °F; above that, only Grade 60-40-18, to the same 650 °F ceiling.
- Ductile iron for service down to −40 °F: A874.
- Wear part for mining, milling or earth-handling: A532.
- Austempered ductile iron: A897.
ASTM A48: Gray Iron Castings
A48/A48M covers gray iron castings for general engineering use and classifies them by the minimum tensile strength of a separately cast test bar. Class 30 means 30 ksi minimum on that bar; the inch-pound series runs through nine classes from 20 to 60 ksi.
The letter after the class number — S, A, B or C — is the size of the test bar. It is chosen to match the wall thickness of the casting’s controlling section.
| Controlling section thickness | Test bar |
|---|---|
| Under 0.25 in. [under 5 mm] | S |
| 0.25 to 0.50 in. [5 to 14 mm] | A |
| 0.51 to 1.00 in. [15 to 25 mm] | B |
| 1.01 to 2 in. [26 to 50 mm] | C |
| Over 2 in. [over 50 mm] | S |
Bar S is sized by agreement between foundry and purchaser. A48 also carries a separate metric class series in which the class number is the MPa value, so Class No. 200 means 200 MPa. The standard treats the two systems as independent and warns that combining values from them may result in nonconformance, so a ksi class does not get converted into MPa on a drawing.
ASTM A536: Ductile Iron Castings
Yes, A536 is a cast iron specification: it covers ductile iron, which the standard describes as cast iron with the graphite substantially spheroidal in shape and essentially free of other forms of graphite.
The grade is three numbers — minimum tensile strength in ksi, minimum yield strength in ksi, minimum elongation in percent. Grade 65-45-12 is 65,000 psi tensile, 45,000 psi yield at 0.2 % offset, and 12 % elongation in a 2-in. gage length.
Table 1 holds the five general-use grades, 60-40-18 through 120-90-02; Table 2 adds three more for special applications such as pipe and fittings — 60-42-10, 70-50-05 and 80-60-03.
Heat treatment follows from the grade. 60-40-18 normally requires a full ferritizing anneal, and 100-70-03 and 120-90-02 require a quench and temper, a normalize and temper, or an isothermal heat treatment. The two middle grades, 65-45-12 and 80-55-06, can be met as-cast.
What an ASTM Cast Iron Spec Does Not Control
Neither A48 nor A536 controls chemistry, and neither promises that the casting has the properties its test bar showed. Both leave those to the purchase order.
On the test bar, A536 states it outright: no precise quantitative relationship can be stated between the properties of the iron in different locations of one casting, or between a casting and a test specimen poured from the same iron. The purchaser chooses the coupon size; if the order is silent, the foundry chooses it, and bars cut from castings need their location agreed and marked on the drawing.
Everything else a machinery buyer cares about — hardness, microstructure, pressure tightness, radiographic soundness, magnetic-particle inspection, dimensions, surface finish — applies only when the contract or purchase order calls for it. The certification and the report of test results are furnished when the order asks for them.
How to Cite an ASTM Cast Iron Grade on a Drawing
A complete call-out carries five things: the full designation with its year date, the class or grade, the test bar or coupon, any supplementary requirement by clause number, and the inspection document you want back. “A48/A48M-22 Class 30 B, inch-pound units, manufacturer’s certification with test report” is a call-out a foundry can quote without a phone call.
Cite both halves of a combined designation and name the unit system. A48 is combined. A536 is not combined: there is no A536M.
The year date is part of the designation. The two digits after the hyphen are the year of last revision, a trailing letter marks a second revision in the same year (A536-26a), and a year in parentheses is a reapproval (A126-04(2023)).
On a legacy drawing, an old number still identifies a real document, since ASTM never reassigns a discontinued designation. Which edition governs is a contract question, and ASTM’s own guidance is to state the year date in the order. Most of the withdrawn cast iron designations are the old all-metric twins — A48M, A278M, A897M — absorbed into today’s combined standards, so a print calling out “ASTM A48M” is usually pointing at the metric half of A48/A48M.