How to Choose ADI Grades(800–1400 MPa): Quick Strength–Ductility Map

Table of contents

What defines an ADI grade

• ADI starts as sound ductile (nodular/SG) iron, then is austenitized and austempered to form ausferrite (acicular ferrite + high-carbon austenite).
• Grade naming typically reflects UTS–Elongation (e.g., 900-8) under ASTM A897 / EN 1564.
• Properties depend on: nodule quality, section size/hardenability, austemper temperature & time, and chemistry (Si, Cu, Ni, Mo as needed).

Strength–ductility map (800–1400 MPa) with use cases

Indicative windows at room temp for design screening. Confirm with coupons from your section sizes.

Rule of thumb: higher strength grades (↑UTS, ↑HBW) trade off elongation, impact and machinability. Pick the lowest strength that meets requirements for a more robust window.

How to pick a grade by design driver

Helpful deep dives on your site:

• ADI Process Window & Grades
• Ductile Iron Grades (base metal)

Section size, chemistry & hardenability

ADI needs the casting to fully austenitize and transform uniformly during austempering:

• Section size effect: thicker sections cool slower from austenitize → risk of pearlite/martensite islands if hardenability is low.
• Chemistry: raise hardenability with Cu/Ni/Mo (within spec) for medium/large sections; keep Si high (typically ~2.3–2.8%) to stabilize ausferrite and suppress carbides.
• Nodule quality: aim ≥ 80% nodularity, adequate nodule count; avoid carbides/chill in thin walls.
• Process choice: shell/resin sand help section control; uniform walls (ratio 0.7–1.3) simplify heat treat.

Related reads:

• Minimum Wall for Ductile Iron
• Solidification & Modulus

Heat-treat window & quality gates

Typical route (tune to section & grade):

• Austenitize ~840–930 °C to dissolve carbides and homogenize carbon.
• Austemper in salt/oil bath ~250–400 °C for time t_A set by section & target grade.
• Hold to form ausferrite; control retained austenite (RA) fraction (often ~10–35% depending grade).
• No tempering after austemper; tempering degrades ausferrite.

Quality gates (acceptance evidence):

• Hardness map (HBW) by zone;
• Tensile on cast coupons / attached Y-blocks;
• Microstructure: ausferrite, RA %, no martensite;
• Impact where required;
• Dimensional layouts (pre/post HT on datum scheme).

Dimensional change, tolerances & machining

Directional solidification needs a monotonic rise in M toward the riser.

• Growth allowance: ADI shows small positive dimensional change; budget ~+0.02–0.06% after austemper (verify on pilots).
• Stock/tolerances: call realistic ISO 8062 CT; leave stock only where needed.
• Machining:
• Prefer pre-machining datums/roughing before austemper; finish critical faces after HT.
• Use coated carbides, modest cutting speeds, strong fixturing; consider thread milling/form taps.
• Manage coolant & filtration; HBW 320–380 chips demand clean systems.

Drawing notes you can copy

• Material & HT call-out (example):
• “ADI 900-8 per ASTM A897 / EN 1564. Base iron to meet ductile iron quality requirements prior to HT.”
• Properties (verify on pilots):
• “Tensile UTS ≥ 900 MPa; elongation ≥ 8%; HBW 280–330; RA target 15–25%; no martensite.”
• Testing:
• “Hardness map by zone; tensile on cast coupons from similar section; microstructure photos; impact on request.”
• Dimensions:
• “Supplier to manage +0.02–0.06% ADI growth; final inspection on datum scheme after HT.”
• Process notes:
• “Heat-treat records (austenitize & austemper temps/times) to be included in PPAP/FAI.”

What YBmetal delivers

YB Metal Solution provides end-to-end ADI execution:

• DFM & grade pick: we map loads/fatigue and propose 800–1400 MPa grade by section & risk.
• Hardenability plan: alloy windows (Cu/Ni/Mo as needed) + section-based austemper cycles.
• Pilot proof: hardness/tensile/microstructure pack; dimensional layouts pre/post HT.
• Production control: bath calibration, coupons per batch, and full traceability.