digest3 adi

8/10/2019 Digest3 ADI

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The remarkable properties of ADI are developedby a closely controlled heat treatment operation(austempering) which develops a unique matrixstructure of bainitic ferrite (60%) and retained (highcarbon) austenite.

The retained (H.C.) austenite is thermally stable toextremely low temperatures but is work hardenableand will locally transform to martensite under suitableconditions of stress. Advantage of this feature of ADIis taken by allowing the service loading stresses towork harden the load bearing services. Alternatively,surface stresses can be deliberately imposed prior toservice, e.g. by shot peening of gears or fillet rolling

of crankshafts in order to achieve significantimprovements in wear resistance and fatigue life.

Presently there are no accepted standard specifi-cations for ADI, but proposals for five grades of ADIhave been made which form the basis for discussionand material selection between designers andfoundrymen.

Current ASTM A897ADA Specifications

Tensile Yield Percent Charpy BHN HardnessStrength Strength Elongation (unnotched) Range*

(KSI) (MPa) (KSI) (MPa) (ft. lb.) (J )

125 0850 080 0550 10 75 100 269 - 321

150 1050 100 0700 07 60 080 302 - 363

175 1200 125 0850 04 45 060 341 - 444

200 1400 155 1100 01 25 035 388 - 477

230 1600 185 1300 0- - 0- 444 - 555

*not part of specification

The heat treatment necessary to produce ADI isessentially a two-stage operation:

Stage 1

Austenitizing in the range 1500-1700F (815-920C). The specific austenitizing temperatureselected is related to the subsequent austemperingtemperature and the grade of ADI required. Onceselected, the austenitizing temperature must beclosely controlled (10F).

2000

1600

1200

800

400

00 1 2 3 4 5 6 7 8

Typical Austenitizing & Austempering Cycles

Temperature(F)

Time (h)

1,700F (930C)

1,500F (815C)

Grade 125ADI

Grade 200ADI

750F (400C)(250-320 Bhn)

450F (230C)21/2h max(400-500 Bhn)


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Courtesy: General Motors Corp., Central Foundry Division,Saginaw, Michigan, USA

Austempered Ductile Iron Hypoid Axle Gears:Conversion to Cast Ductile Iron from Forged Steel gavemajor production cost saving, better machinability, quieteroperation, reduced weight.

ADI Timing Gears for Cummins B-Series dieselengines. Replaced forged and case carburised 1022 steel

with 30% cost saving.

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Stage 2

Rapid transfer of the castings to the austemperingfurnace (usually a salt bath) where the castings areheld isothermally at the selected austempering tem-perature. Austempering temperatures are in therange 450-750F (230-400C) according to the prop-erties required in the castings (ADI grade). Closecontrol over temperature and time of austempering isessential.

ADI is well established as a gear material replac-ing forged steel with major production cost savings,quieter operation and reduced weight. By machiningthe gears before the austempering heat treatment,

major savings in machining costs are achieved.

Austempering TemperatureF450 500 550 600 650 700

220 260 300 340 380

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8

4

0

1600

1400

1200

1000

900C(1650F) Austenitizing

250

200

150

Austempering TemperatureC

Elongation%

TensileStrength,M

Pa

TensileStrength,k

si


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Courtesy: Hogfors Industries Ltd., Finland

Austempered Ductile Iron gears to patented specifica-tions K9805.

Other examples of the use of ADI castings include

truck spring supports, railroad axle-box spring adap-tors, crankshafts, connecting rods, agriculturalplough shares, etc.

ADI Crankshaft for Ford turbo-charged engineADIcapable of meeting fatigue strength requirements at muchlower cost than forged steel.

Success in consistently achieving the optimumproperties and performance of ADI requires highquality, careful selection and control over the baseDuctile Iron, and heat treatment parameters. Thisnecessitates material of high nodule count which is

free from carbides, inclusions and shrinkage and of acomposition which minimizes the dangers of alloysegregation.

This brief summary about the DUCTILE IRONFAMILY is based on metallurgy, rather than on stan-dard specifications. A chart showing the properties ofmost of the Ductile Iron grades is enclosed on theinside back cover of this publication. All propertiesare primarily determined by chemical composition,cooling (solidification and solid cooling rate) andmatrix structure.


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DUCTILE IRONMORE STRENGTH FORLESS EXPENSE

Ductile Iron appears to have been invented (1948)

with the designer in mind. The tensile strength, proofstress, and elongation combinations obtainable inDuctile Iron exceed those for ANY OTHER cast fer-rous alloy, including steel and malleable iron.

Since its introduction, the growth of Ductile Ironapplications has exceeded all expectations. World-wide production is approximately 12 million tons andis expected to reach 20 million tons by the turn of thecentury. The application of Ductile Iron is a notable

engineering achievement of our age.DISK BREAK CALIPER

Whether in an automobile component, as shownabove, a water pipe, plow, or a robbery-proof park-ing meter box, Ductile Iron has made major inroadsto the casting market in every industrially developedcountry. There can be little doubt, that the major moti-vating factor for this was MORE STRENGTH FOR

LESS EXPENSE compared to just about every othercast alloy. The lesser expense comes not only fromthe readily available raw materials and the efficienciesof the foundry operation, but also from reduced clean-ing and machining costs of Ductile Iron castings.

The following pages present a variety of DuctileIron case histories from around the world. Manymore examples could have been added. The DuctileIron alloys are versatile and appear to find unlimited

applications.

WORLDPRODUCTIONOF

DUCTILEIRON(Including Pipe)

1950 1960 1970 1980 1990 2000

3-5%Growth

20

16

12

8

4

0

MILLIONTONNES


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The original design of the 1,000 H.P. pump framewas a steel fabrication. Converting to Ductile Ironachieved more uniform stress distribution, lower pro-duction cost and improved strength-to-weight ratio.The weight was reduced by 46 percent, which is par-

ticularly important for remote installations where theparts must be airlifted.

Courtesy: Gardner Denver Co., USA

A camshaft thrust plate is exposed to severeabrasive wear. The reason for selecting Ductile Ironwas to combine wear resistance with machinability.

For break-in, this casting is phosphate-coated.

Courtesy: Fichtel & Sachs, Germany

Ductile Iron can readily by surface hardened to 55Rc, which provides for the superior performance of

this catch-sleeve.

Courtesy: Dana Corp., USA

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