A quick, practical grade map for gray/grey iron: ASTM A48 vs EN-GJL grades, indicative properties, machinability, and where each grade is used—plus casting/design notes and an RFQ checklist.
Executive summary (what to choose & when)
- Lower classes/grades (A48 20–30 / EN-GJL-150–250) → best damping & machinability, lower strength.
- Mid (A48 35–50 / EN-GJL-250–350) → balanced for housings, machine bases, pump/valve bodies.
- High (A48 60 / EN-GJL-400) → highest strength, less damping, and machinability drops.
- Section size, cooling rate, and pearlite content drive the real properties—sample to lock the window.
Grade cross-reference (indicative)
EN 1561 names EN-GJL-xxx by min tensile MPa on a standard test bar. ASTM A48 uses “Class xx” by min tensile ksi. The mapping below is the nearest typical, not one-to-one.
| ASTM A48 class (min UTS) | Nearest EN-GJL | Indicative UTS (MPa) | Typical HBW | Matrix trend | Typical uses |
|---|---|---|---|---|---|
| 20 (20 ksi) | EN-GJL-150 | 140–170 | 120–170 | Ferritic-leaning | Covers, gearboxes, vibration bases |
| 25 (25 ksi) | EN-GJL-200 | 170–210 | 150–190 | Ferrite + pearlite | Pump/valve bodies, compressor shells |
| 30 (30 ksi) | EN-GJL-200/250 | 200–260 | 170–210 | More pearlite | Engine blocks, machine beds |
| 35 (35 ksi) | EN-GJL-250 | 240–300 | 180–220 | Pearlitic | Housings, flanges, brackets |
| 40 (40 ksi) | EN-GJL-250/300 | 270–320 | 190–240 | Pearlitic↑ | Brake drums, pulleys |
| 45 (45 ksi) | EN-GJL-300 | 300–340 | 200–250 | Pearlitic↑ | Hydraulic bodies, gears (as-cast) |
| 50 (50 ksi) | EN-GJL-350 | 330–370 | 210–260 | Pearlitic-high | High-load housings, rolls (machined) |
| 60 (60 ksi) | EN-GJL-400 | 380–420 | 240–300 | Pearlitic-highest | Thinner sections with higher stress |
Values are typical production windows for guidance only; verify on your section size and cooling conditions.
Design notes (castability, damping, machinability)
- Damping: gray iron’s graphite flakes give superior damping—lower grades damp best.
- Machinability: improves with ferrite; declines as pearlite/HB rise. Carbide-tipped or CBN for high-HB parts.
- Wall thickness: in green sand, ~4–8 mm (0.16–0.31 in) practical minimum depending on envelope/cores; keep uniform walls and add radii.
- Leak-tightness: gray iron is porosity-sensitive in thin sections—pressure parts may need impregnation or choose ductile iron.
- Tolerances & finish (indicative): ISO 8062-3 ~ CT8–CT10 (size-dependent); Ra 6.3–12.5 μm (250–500 μin) after shot-blast.
Selecting by application (what the market really uses)
- Machine bases/beds/frames: EN-GJL-200/250 (A48 30–35) for damping + machinability.
- Pump/valve bodies: EN-GJL-250/300 (A48 35–40) when pressure is moderate; check leak tests.
- Brake drums/pulleys: EN-GJL-300 (A48 45) for wear & thermal stability.
- Engine blocks/compressor housings: EN-GJL-200/250; local higher HB acceptable.
- Thinner high-stress housings: EN-GJL-350/400 (A48 50–60) if you can trade damping for strength.
Chemistry & structure (why grades behave differently)
- Higher strength comes from higher pearlite, finer graphite, adequate Mn/Cu, but HB ↑, machinability ↓, and damping ↓.
- Manage phosphorus (P) and sulfur (S) to avoid steadite/fulgurite and brittleness; typical targets P ≤0.08%, S ≤0.12% (program-dependent).
- Fast-cooling thin walls act as “higher grade” than test bars—don’t over-spec.
YB Metal production snapshot
From recent gray-iron programs:
- Chemistry windows (indicative): C 3.0–3.4%, Si 1.8–2.4%, Mn 0.5–0.9%, P ≤0.08%, S ≤0.12% (grade-dependent).
- Sand KPIs: AFS GFN 55–65, moisture 2.8–3.2%, LOI 3.0–3.8%; shot-blast to Ra 6.3–12.5 μm.
- Dimensional capability: green sand CT8–CT10 (ISO 8062-3), envelope-dependent.
- Verification: Brinell per batch; tensile coupons by heat; FAI + CMM/3D scan on criticals; optional pressure/leak and NDT.
Cost & risk signals (why a grade quote moves)
| Driver | Effect |
|---|---|
| Step-up grade (e.g., 250→300) | More pearlite/HB → tool wear ↑, machining cost ↑ |
| Thinner sections | Scrap/leak risk ↑; gating/feeding complexity ↑ |
| Tight CT/flatness | Pattern & process cost ↑; more inspection |
| Leak/NDT requirements | Extra process & cycle time |
RFQ checklist (send with your drawing)
- Target standard (ASTM A48 class / EN-GJL grade) or performance window (UTS/HB).
- Section map + min walls; pressure/leak requirements; GD&T & critical datums.
- Volume/batch, surface finish/paint; inspection scope (FAI/CMM, hardness, tensile).
- Any field issues to avoid (noise, wear, leaks, distortion).
FAQs
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