Category: Clay Sand Casting
Zhaoyuqi Machinery manufactures custom ductile iron cast parts for buyers who need strength, toughness and impact resistance in a sand-cast component. With a nodular (spheroidization) rate of at least 90%, our ductile iron delivers far higher tensile strength and shock absorption than ordinary grey iron — making it the right choice for loaded machinery, chassis parts, gears and structural castings.
Ductile iron earns its place where a grey iron part would crack rather than bend. That means loaded brackets, yokes, gear blanks, suspension-type components, high-pressure flanges and valve bodies, and anything that sees vibration, impact or thermal cycling in service. The reason is in the microstructure: graphite in spherical form interrupts the metal matrix far less than the flakes in grey iron, so the material deforms under overload instead of fracturing.
Where it does not pay is just as useful to know. Machine bases, counterweights, covers and vibration-sensitive frames are better in grey iron, because damping and dimensional stability matter more there than elongation, and grey iron costs less per kilo. A part that is stiff by geometry does not need toughness it will never use. In practice most of what we pour in ductile iron goes into machinery and equipment, automotive and transport components, pipe and valve hardware, and structural castings for construction and utility projects.
We routinely pour EN-GJS-400-15, EN-GJS-500-7 and EN-GJS-600-3 equivalents, plus QT450 and QT500 to Chinese standard, all held above 90% spheroidization. Tell us the tensile strength and elongation required on the drawing and the grade follows; the heat and hardness report can travel with the first sample. Where a specification names ASTM A536 rather than an EN grade, say so at inquiry, because the two systems do not map one-to-one on elongation.
Most ductile parts we ship fall in the 0.5 to 50 kg band on the automatic clay sand line. Machinery bases, counterweights and structural brackets above that go to lost foam casting from 50 to 200 kg, which avoids hard tooling cost on medium batches. Cast wall thickness typically runs 5 to 15 mm depending on section and load, and a section below the limit needs a conversation about feeding rather than a promise. Moulding, shot blasting, tapping, drilling and CNC machining for critical bores all sit in one plant, so a part does not travel between suppliers to be finished.
As-cast parts go straight to shot blasting after shake-out. From there we machine critical bores, mounting faces and threads on CNC centres, tap bolt holes to your class, and polish sealing surfaces where a gasket or O-ring has to sit. Finishing coats include primer, top paint to your colour, and epoxy for parts working in humid or corrosive plants.
An order starts with the 3D model or 2D drawing plus the required grade and quantity. Our engineer reviews feeding, venting and draft before quoting, since those are what decide whether the first sample comes out right. A test casting is poured, measured and sent with its material certificate, and after approval mass production runs on the same tooling and parameters. Every shipment carries dimensional, visual and spheroidization records, so the paperwork matches the parts when they land.
Buyers see "ductile iron, spheroidization rate ≥ 90%" in every foundry's brochure, and it is worth understanding what that number does for your part. In ductile iron, graphite forms as spheres instead of the flakes you get in grey iron. Flakes act like internal cracks; spheres do not. The more of the graphite that is fully spherical, the closer the material behaves to steel — bending, absorbing impact, and warning you before it breaks instead of snapping.
At 90% spheroidization and above, EN-GJS-400-15 and ASTM A536 65-45-12 deliver elongation in double digits, which is why brackets, yokes and suspension-type parts survive loads that would crack a grey iron casting. Below about 85%, properties fall off quickly, and a part may pass a hardness check while failing in service — which is why we verify spheroidization metallographically per heat rather than judging from the outside of the casting.
Every melt holds a coupon that goes through chemical analysis and a tensile test; selected coupons are polished and examined for nodularity and nodule count. Results are tied to the heat number cast into or marked on the parts, so any casting in your shipment traces back to its test record. For customers with utility or OEM audits, this heat-to-part chain is documented on the packing paperwork, and 3.1 certificates are available when your spec calls for them.
Ductile iron's advantage is not one number but a family of grades trading strength against elongation. 400-15 gives way before it breaks — the right choice for parts that get dropped, struck or shock-loaded. 500-7 and 600-3 trade some elongation for yield strength, which suits parts that must not deform under steady load. 80-55-06 sits between, common for automotive-class brackets. Choosing wrongly in either direction costs you: too soft and the part deforms, too hard and it cracks at the first impact.
Temperature matters as much as grade. Ferritic ductile iron keeps useful impact toughness at low temperature, which is why cold-climate line hardware and winter-service machinery use it. Above roughly 350 °C, ductile iron's advantage fades and growth becomes a concern; if your part runs hot, say so and we will discuss whether a different material is the honest answer.
Ductile iron forgives more than grey iron, but it is not steel. Three design habits get the most out of it. First, use generous fillets where sections meet — a sharp internal corner becomes the crack origin no matter how good the metallurgy is. Second, avoid abrupt section changes; a gradual transition spreads load and cools more evenly. Third, put machining allowance where the functional surface is, not everywhere, so the casting's skin stays intact on non-functional faces — the skin is often the strongest part of a casting.
These are cheap changes at the drawing stage. They become tooling changes later, which is why we raise them during quotation and in writing rather than leaving them to a first-article surprise.
The common ferritic and pearlitic grades — EN-GJS-400-15, -450-10, -500-7 and the ASTM A536 equivalents 60-40-18, 65-45-12, 80-55-06 — run routinely. Special grades are discussed against your drawing.
No. Grey iron dampens vibration better and machines cheaper, so a housing with no shock loading is often better in grey. Our gray iron casting page covers when grey wins.
Welding is possible with correct filler and preheat, but we design castings to avoid needing it. If your process expects weld rework, tell us now — grade and route change accordingly.
That is usually a design question, not a material one: hole too close to a cast edge, or a section that necks down behind the boss. Our engineering review flags these before tooling.
When a drawing calls for a specific microstructure or stress relief, yes. Normalizing and stress relieving are routine; the treatment is quoted as a line item so you can see it.
Feed design, chill placement and gating are set for the thickest section, since that is where shrinkage appears last. Heavy-section parts are reviewed individually rather than run on standard rigging.
Send your drawing and target quantity — we reply with feasibility, pricing and an approval sample schedule.
Professional technical research and development team to provide customers with the best solution.
Jimo District, Qingdao City, Shandong Province, China
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