What Is Austempered Ductile Iron? Properties, Microstructure and Uses

Table of contents

What ADI is (the short answer)

ADI = ductile iron that’s heat-treated to form ausferrite (acicular ferrite + high-carbon stabilized austenite).
The cycle is austenitize → quench to above Ms → isothermal hold until bainitic transformation completes. Result: high strength & fatigue, with useful toughness vs cast steels of similar strength.

Deep-dive intro: Open ADI Guide

Microstructure 101: ausferrite, carbon partitioning & TRIP

• Ausferrite: a needle-like ferrite framework plus retained high-C austenite.
• Carbon partitioning during hold stabilizes austenite; under load, some austenite transforms to martensite (TRIP), boosting work-hardening and fatigue.
• Lower hold temperature (≈260–320 °C / 500–610 °F) → higher strength, lower ductility.
• Higher hold temperature (≈330–380 °C / 625–715 °F) → lower strength, higher ductility.

ASTM A897 – ADI grade requirements

Cycle design details: ADI Process Window

Strength–ductility maps: ADI Grade Selection

Properties by grade (quick table)

Typical ranges: lock acceptances per drawing/PO. Hardness is informational unless specified for acceptance.

Standards & t-band notes: ADI Standards: ASTM A897 vs EN 1564

When ADI wins (and when it doesn’t)

ADI wins when you need high strength/fatigue at a reasonable weight, shock tolerance better than cast steels of similar strength, or gear/sprocket life without through-hardening.
Doesn’t win when you need weldability, very thick sections with long transfers (risk of pearlite), or corrosion resistance without coatings (ADI ≈ ductile iron for corrosion → use coatings or material upgrade as needed).

Corrosion choices: Coatings vs Material

Process notes: austenitize → quench → isothermal hold

• Austenitize ~ 840–920 °C (1545–1690 °F); soak for uniform austenite.
• Fast transfer above Ms into an isothermal bath (≈260–380 °C / 500–715 °F).
• Hold to completion (ausferrite fully formed); wash; optional stabilize/temper.
• Control inoculation and chemistry (Ni/Cu/Mo assists heavy sections).
• Keep pearlite out—transfer time is critical, especially on thick parts.

Cycle guidance & QA: ADI Process Window

Design rules: section size, walls, radii & notches

• Section size matters: properties in EN 1564 depend on t-band; heavy sections need Ni/Cu/Mo and short transfer times.
• Minimum walls: see rules by ductile-iron base → Minimum Wall for Ductile Iron
• Uniform walls + ribs beat slabs; avoid isolated pads (shrinkage risk).
• Generous radii reduce notch sensitivity and boost fatigue; see Fillet & Radius Rules
• Plan feeder/chill strategy for junctions: Fix Shrinkage Porosity
• Keep CT & stock realistic: ISO 8062 CT Grades, Open GD&T Guide

Machining, coating & distortion tips

• Machining: carbide inserts, control heat; ADI is tougher than DI—optimize speeds/feeds and tool edge prep. Reference: Machinability: Gray vs Ductile Iron
• Distortion: fixture for stability; for large housings, see Heat-Treatment Distortion Control
• Coating: ADI ≈ DI for corrosion; pick stack & DFT by environment: Coatings vs Material
• Welding: generally not recommended; if allowed, qualify and consider re-austempering.

Process selection for castings that will become ADI:

• Green vs Resin vs Shell capability: Green Sand, Resin vs Green, Shell Thin-Wall
• Surface finish expectations: Surface Finish by Process

What to put on the drawing

Material & heat treatment:
Material: ASTM A897 Grade 1050-750-07 (or EN-GJS-1050-6, t ≤ 30 mm).
Coupons: [separately cast/attached / from casting] — state in PO.
Austempering: Hold 300–330 °C (572–626 °F) above Ms to full austenite; no pearlite allowed.
Hardness: 302–375 HBW (informational unless used for acceptance).
Impact (if required): Unnotched, room temp; criteria per PO.

Process capability
Casting tolerances per ISO 8062; CT grade by size band.
Maintain machining stock per control plan. Avoid isolated heavy pads; use directional solidification.

QA & docs (PPAP/FAI)
Provide tensile (Rm/Rp0.2/A%), HBW, metallography (nodularity %, ausferrite/pearlite check), and CMM FAI on datum features.

ISO 8062-3 – Casting dimensional & machining allowance tolerances

Templates: PPAP Levels & Docs

Applications & case-style ideas

• Drivetrain: gears, sprockets, differential housings, torque-arm brackets.
• Pumps/Compressors: high-strength covers & mounting ears (pressure verified).
• Ag/Construction: thin but strong arms, clevises, hubs; wear-resistant pads.
• Industrial handling: wheels, sheaves, track shoes, where fatigue + wear matter.

If NVH matters more than strength, prefer gray iron housings: Ductile vs Gray Iron

What YB Metal delivers

YB Metal Solution quotes with an ADI plan attached:

• Grade selection matched to your section size & load case with A897 ⇆ EN 1564 nearest equivalent.
• Heat-treatment window (austenitize temp, isothermal band, transfer-time limit, quench medium).
• Section-size review & alloy nudges (Ni/Cu/Mo) + impact on cost/lead-time.
• Pilot evidence pack: tensile/hardness tables, metallography (nodularity %, ausferrite photos), optional impact, and CMM FAI on criticals.
• Program docs ready for your gate: PPAP/FAI forms and acceptance plan.

Need a plan for your part? Upload your drawing—we’ll return recommendations and a quote.