Grey and ductile cast irons are not primary airframe materials, but they keep showing up in auxiliary aerospace hardware where density, cost, and damping matter more than strength-to-weight: pump bodies, valve bodies, gear housings, brackets, counterweights, and ground-support fixtures. The applicable specification set is EN 1561 for grey iron, SAE J431 / SAE J434 for automotive-grade grey and ductile iron, and a narrow slice of SAE AMS specifications (AMS 5310, 5315, 5316, plus the now-replaced 5392 / 5393 / 5394 family) for iron castings [S2][S3].
Specifying engineers should treat the aerospace alloy handbooks (NASA-issued material chapters, MMPDS, AMS for stainless/corrosion-resistant steels) as a negative reference: iron is covered there as "iron alloys (steels)", not as a structural cast-metal family, which is exactly why cast iron ends up in brackets, housings, and cast fittings rather than in primary structure [S1].
Where cast iron actually fits in an aerospace bill of materials
Ferrous castings show up in three slots: non-flight-certified ground equipment, secondary airborne accessories (electrical housing, accessory gearbox covers, hydraulic reservoirs), and static structural fittings where the part is protected from fatigue-critical loading by a redundant load path. Grey iron's flake graphite gives it damping capacity an order of magnitude above steel, which is the engineering reason it still shows up next to rotating machinery on engine test stands and airborne APUs [S5][S6].
Ductile (nodular) iron, with graphite in spheroidal form, raises tensile strength from roughly 150–300 MPa (grey iron EN-GJL-150 through EN-GJL-300) into the 350–550 MPa band covered by SAE AMS 5315 (415 MPa min, ferritize-annealed) and SAE AMS 5316 (550 MPa min, as-cast), and is the cast-iron grade that can credibly replace a cast steel in a structural bracket [S2][S3]. For comparison, the grey iron EN-GJL-250 grade (5.1301) specifies 250–350 MPa tensile on a 30 mm separately cast sample at 10–20 mm wall, dropping to 160–190 MPa at 150–300 mm wall thickness [S2].
Standards that actually govern the call-out
EN 1561 is the cleanest reference for grey iron. It defines five tensile grades (EN-GJL-100, -150, -200, -250, -300, material numbers 5.1100 through 5.1302) and six Brinell hardness grades (EN-GJL-HB155, -HB175, -HB195, -HB215, -HB235, -HB255). Both families are wall-thickness-sensitive: the EN-GJL-HB175 grade (5.1201) specifies 100–175 HBW on a 40–80 mm wall but 170–260 HBW on a 2.5–5 mm wall, which is why the same nominal grade can show very different hardness across a real casting [S2].
For aerospace specifically, the SAE AMS iron-casting set is small and partly historical. AMS 5310 covers pearlitic malleable iron castings, AMS 5315 covers ferritize-annealed ductile iron at 415 MPa minimum tensile, AMS 5316 covers ductile iron at 550 MPa minimum tensile in the as-cast condition, and the AMS 5392 / 5393 / 5394 family (austenitic Ni-Resist type grades with 15–20 % Ni and up to 6.5 % Cu) was replaced by ASTM A 439. On the automotive side, which the aerospace MRO base borrows heavily, SAE J431 (2000) covers grey iron and SAE J434 (2004) covers ductile iron [S3].
Decision map: grey vs ductile vs austempered vs austenitic
The call-out is driven by four gates, in this order: required tensile strength, operating temperature, corrosion/oxidation exposure, and damping or machinability demand. Grey iron wins only when strength is below ~300 MPa and damping or vibration-damping is the lead requirement. Ductile iron is the default for any aerospace bracket above that threshold, with the 415 MPa and 550 MPa AMS grades (5315, 5316) the most commonly called-out specifications [S3][S5].
Austempered ductile iron (ADI) and the austenitic Ni-Resist family are the two high-end options. ADI pushes tensile past 800 MPa with retained ductility and is increasingly used for aerospace gearbox components and landing-gear sub-assemblies, though it requires tight control of austempering bath temperature. Austenitic Ni-Resist (the replaced AMS 5392 / 5393 / 5394 grades, now under ASTM A 439) trades strength for corrosion and heat resistance in the 2.0 Cr / 15–20 Ni / up to 6.5 Cu chemistry window, with 2.4–3.0 % C, and is the cast-iron grade most often approved for hot-side or mildly corrosive aerospace environments [S3].
Hardness, section sensitivity, and what the call-out must include
Section sensitivity is the most under-specified property on aerospace cast-iron drawings. EN 1561 grades are designated on a 30 mm separately cast sample, but real castings routinely run 5–80 mm wall, and the same grade will drop from 250 MPa minimum tensile at 10–20 mm wall (EN-GJL-250, 5.1301) to 160 MPa minimum at 150–300 mm wall. Drawings that call out "EN-GJL-250" without naming the wall-thickness class invite either over- or under-spec'ing the part, and the Brinell hardness table shows the same effect: EN-GJL-HB195 specifies 150–230 HBW at 10–20 mm wall but 120–195 HBW at 40–80 mm [S2].
EN 1561 also gives the buyer five characterization options: tensile on separately cast or side-by-side samples (Option A), tensile on cast-on samples (Option B), tensile on samples cut from the casting (Option C, designation suffix "C"), Brinell hardness on the casting (Option D), or a combination of tensile and hardness by agreement (Option E). For aerospace safety-of-flight parts, Option C (sample cut from a representative area of the actual casting) is the only option that proves the real section properties; cast-on samples cool faster than the casting and report higher values than the casting will actually achieve [S2].
Limits, failure modes, and where cast iron is the wrong call
Cast iron is the wrong material when any of three conditions apply: the part is on a fatigue-critical load path, the part sees below-freezing service with impact loading, or the part must be welded into a larger assembly. Grey iron is essentially unweldable; ductile iron can be welded with preheat and nickel filler but the HAZ loses the nodular graphite structure and the joint becomes a maintenance liability. Below about -20 °C, grey iron's brittle flake-graphite matrix delivers near-zero fracture toughness, which rules it out for any unpressurized exterior bracket on a high-altitude airframe [S5][S6].
Weight is the other disqualifier. Grey iron sits near 7.1 g/cm³ and ductile iron near 7.2 g/cm³, roughly 2.4× the density of 7075-T6 aluminum (2.81 g/cm³) and 1.7× the density of Ti-6Al-4V (4.43 g/cm³). For a primary structural fitting, that mass penalty wipes out the cost advantage of cast iron on any airborne part, and the material gets pushed into cast iron reference data for non-flight or sheltered-secondary use only [S5][S6]. On the comparison axis that aerospace buyers actually use, ductile iron's specific strength (tensile/density) lands around 55–76 kNm/kg for the 415–550 MPa grades, versus roughly 200 kNm/kg for 7075-T6 and 240 kNm/kg for Ti-6Al-4V at typical temper conditions; cast iron only wins on damping and on raw cost per kg of finished part.
Cross-references to other industrial spec maps
For shops that also build ground-support tooling and dies, the same EN 1561 / SAE J431 / J434 / AMS 5315 / 5316 call-outs pair with the tool-steel and bearing spec maps used on the manufacturing side. The tool and die steel selection map for mold and die making covers the AISI D2 / S7 / H13 / P20 side, while the tool and die steel grades mapped to energy equipment covers the same grades under energy-sector duty. For the rotating-equipment side that often shares grey iron housings with aerospace accessory gearboxes, the tapered roller bearing vs ball bearing selection map gives the matching bearing spec gates for those housings. [S3]
Trackable signals for the next review: any update to the ASTM A 439 lineage that the replaced AMS 5392 / 5393 / 5394 grades now point to, and any new ADI specification under SAE AMS (the AMS 5310 / 5315 / 5316 set has not been refreshed since the 1990s for ductile and 2001 for pearlitic malleable, per the public Total Materia index) [S3]. Also watch for revisions to EN 1561 on the Brinell-only grade family (EN-GJL-HB155 through -HB255), which is the more common call-out path for thin-wall aerospace castings where hardness is easier to verify on a finished part than tensile on a cut sample [S2].
Spec-level background on the components involved: pressure transmitter, and flow meter.