a us tempered ductile iron [adi]-small

8/3/2019 A Us Tempered Ductile Iron [Adi]-Small

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AUSTEMPERED DUCTILE

IRON [ADI]

Rahul Gupta.

ND Gupta Enterprises.S 38, MIDC, Bhosari, Pune. 411026.

Tel.: 91-020-27120398, 91-020-27123850.

Email. [email protected]


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Overview to ADI.

ADI was discovered almost 50 years ago and foundsuccessful commercial application in 1972. TodayADI has become the material of choice for thedesigner, as it offers the best design combinations oflow cost, design flexibility, machinability, highstrength to weight ratio, good toughness, wear

resistance & fatigue strength. ADI is moreenvironment friendly than many competing materials.


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Overview to ADI. Material selection, processing, cost, product design,

ease of availability, environmental impact due to itsuse, & performance of the final product areinseparable. ADI comes out with high scores on allthese counts.


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Making of ADI Molten Cast iron when treated with magnesium

results in nodular iron on freezing.

Graphite is present in a spheroidal form rather thanas flakes.

Ductile iron has superior mechanical properties ascompared to cast iron & is cheaper than malleable

iron. Malleable irons were manufactured by subjecting

white cast irons to very long heat treatment cycles,and hence were very expensive.


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Making of ADI

Ductile iron has replaced malleable irons entirely & steel /cast iron in many applications.

Ductile iron when heated to the austenitic range [900o Capprox] and quenched in the range of 280o C to 500o Cgives us Austemperted Ductile Iron [ADI].

The original inventors called the process incompleteaustemperingas the resultant microstructure contained

large quantities of RETAINED AUSTENITE [RA].Incomplete austempered ductile iron exhibited highelongation values as compared to normalized, hardenedor fully bainitic ductile irons for similar tensile strengthlevels.


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Advantages 0f ADI1. Lower in cost when compared to other competing

manufacturing methods, such as fabrication, wrought/machined, forged / machined.

2. Superior mechanical properties as compared to castiron, weldments, aluminum alloys, normalized or

toughened ductile irons.3. Energy consumption for a finished ADI product is

almost half that of a forged, machined & casecarburised hardened component, for a similarapplication.

4. Ductile irons will exhibit superior damping capacity &machinability as compared to steel.


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Advantages 0f ADI

5. ADI has a very low cost to strength ratio whencompared to other commonly used engineeringmaterials.

Material. Forged

Al.

Cast

Al.

Cast

Steel

Forged

Steel

H&T

Steel

Ductile

Iron

ADI.

Unit Cost /

Unit Y.S.

20 12 6 4 3 2 1


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Advantages 0f ADI

6. ADI exhibits transformation induced plasticity [TRIP].Hence it has superior wear resistance as comparedto irons & steels of equivalent hardness values. An ADIwith a hardness value of 350 BHN (38 HRC) will have

a wear resistance equivalent to a case hardened steelof 60 HRC, making ADI a suitable choice for gears,camshafts, rollers, & other wear parts. Wear resistanceof ADI is further enhanced by shot peening.

7. Due to TRIP, ADI also has higher toughness & fatigue

strength as compared to normalized / toughenedductile iron, nearing those of steel at times, especiallyfor the lower tensile grades.


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Prior Metallurgical Parameters to

Ensure Success with ADI

1. Good foundry practice to ensure a sound casting free fromshrinkage & porosity. The austempering processcannot compensate for foundry defects

2. Maintenance of proper and consistent chemistry.

Recommended limits for chemical composition are asfollows: Carbon: 3.5/3.9%; Silicon: 2.3/2.7%;Manganese: 0.25% max; Copper 0.8% max;Nickel:2.0% max; Molybdenum: 0.25% max onlyfor heavy sectioned castings.

3. Nodularity should be more than 80% & nodulecount should be more than 100/mm2

4. Minimum 50% pearlite in the matrix & less than 1%carbides prior to austempering.


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Heat Treatment of ADI

Selection of time & temperature are decided on the basis of:

1. Section thickness of the component

2. Grade of ADI: Higher the tensile, lower will be thequenching temperature, but never below the Ms

Temperature. Quenching temperatures are normally between250 to 425o C. Quenching time varies between 20 to 150minutes. Normally higher the tensile strength required, lowerwill be the temperature.

3. Pearlite content in the matrix prior to austenitisation.

4.

Higher the austenitisation temperature greater will be theRA, greater will be the austenite carbon content & the ferritewill be coarser. The austenitisation conditions should beselected, with an aim for optimizing the mechanicalproperties.


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Response to Heat Treatment

Unlike for steels, transformation curves for ductile iron gradesare not available easily. Hence one has to use personalexperience & the response of specific grades. The guidingprinciple should be achievement of an ausferrite structure &

correct hardness. Normally one has to establish processparameters, using the limits of tolerance for martensite & bainitein the final structure and the hardness specified.


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Ausferrite.(2% Picral)


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Ausferrite(2% Nital)


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Strain Hardening.


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Bad Nodularity.


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ADIShowing Carbides due to

presence of W 0.2%...


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1. Always look out for an AUSFERRITE structure &correct hardness after austempering. Upto 3%martensite & 10 % bainite may be present with therest being AUSFERRITE. The 750 N/mm2 grademay also have some ferrite.

2. Dont look for BAINITE just becauseaustempering has been done. A bainitic structure

of the same hardness will give lower elongationvalues than an AUSFERRITE structure

3. Tempering or reheating ADI leads to a loss oftoughness. Hence please avoid this practice.


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ADI is used in diverse components operating underextreme engineering conditions. ADI is used formanufacturing crankshafts, camshafts, gears,sprockets, wear parts in earthmovers, breaker body,

suspension/chassis members etc. With the abovementioned advantages many more components are inthe development / change over phase to be convertedto ADI. Many organizations are studying the benefitsof ADI so as to reduce weight & cost of their finished

products. ADI offers a great opportunity for valueaddition & cost reduction to the engineering industry.ADI has very wide spread applications and willdefinitely be a major growth area in the days to come.


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AUSTEMPERED DUCTILE

IRON [ADI]

THANK YOU.Please feel free to call on us @ND Gupta Enterprises.

S 38, MIDC, Bhosari, Pune. 411026.

Tel.: 91-020-27120398, 91-020-27123850.

Email. [email protected]

a us tempered ductile iron [adi]-small

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