EFFECT OF COPPER ON THE PROPERTIES OF AUSTEMPERED DUCTILE ... · PDF fileEFFECT OF COPPER ON THE PROPERTIES OF AUSTEMPERED DUCTILE IRON ... Anil Kumar M M, [email protected] ...

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Int. J. Mech. Eng. & Rob. Res. 2012 Anil Kumar M M and R Suresh, 2012

EFFECT OF COPPER ON THE PROPERTIES OFAUSTEMPERED DUCTILE IRON (ADI)

Anil Kumar M M1* and R Suresh1

*Corresponding Author: Anil Kumar M M,[email protected]

ADI refers to heat treated Ductile Iron (DI). Austempering heat treatment is used to bring aboutchanges in microstructure of ductile iron hence enhancement in the properties. ADI has thecombined properties of cast iron and steel. Damping capacity, wear resistance combined withhigh strength are the key features of ADI. Development of ADI is a very challenging process,because lot of process variables are involved in the preparation of ADI. Attempt has been madein this work to evaluate the properties of the ADI and properties of DI are compared before andafter heat treatment with addition of Cu in the range of 0.5 wt%, 1 wt%, 2 wt% in the DI matrix.The ductile iron preparation followed by the preparation of test specimens of each composition.The specimens were subjected to the austenization (900 °C), austempering (300 °C) in engineoil for the holding time of 1 hr. The heat treatment was carried in a conventional resistancefurnace and electric oven. The prepared specimens were tested for tensile strength;microstructural analysis was carried out using optical microscope. Each test and analysis wascarried out to specimen of each composition before and after the treatment for the purpose ofcomparing the properties.

Keywords: ADI, Austempering, Austenization

INTRODUCTIONThe increasing interest in energy saving hasled to the development of lightweight materialsto reduce the weight of existing materialswithout compromising their properties. Forexample, in the automotive industries, attemptshave been made to replace cast iron and steelcomponents with aluminum and austemperedductile iron.

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Int. J. Mech. Eng. & Rob. Res. 2012

1 Department of Mechanical Engineering, SIT, Tumkur, India.

Austempered Ductile Iron (ADI) is a ductileiron that has undergone a special isothermalheat treatment called austempering. Unlikeconventional “as-cast” irons, its properties areachieved by specific heat treatment. Therefore,the only prerequisite for good ADI is a goodquality ductile iron (Olivera et al., 2005).

ADI offers superior combination ofproperties because it can be cast, like any

Research Paper

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Int. J. Mech. Eng. & Rob. Res. 2012 Anil Kumar M M and R Suresh, 2012

other member of the ductile iron family. It offersall production advantages of conventionalductile iron castings. The unique features ofADI are low cost, design flexibility, highstrength to weight ratio, good toughness, wearand fatigue resistance (Najmeddin, 2011).Subsequently it is subjected to theaustempering process to produce mechanicalproperties that are superior to conventionalductile iron, many cast and forged steels. Themechanical properties of ductile iron andAustempered Ductile Iron (ADI) aredetermined by the metal matrix (Myszka,2007). In conventional ductile iron it iscontrolled by the mixture of pearlite and ferrite(Hasan and Almaida, 2009). However theproperties of ADI are due to its unique matrixof acicular ferrite and carbon stabilizedaustenite called aus-ferritic (bainite). In manycases composition of ADI castings differs littlefrom conventional Ductile Iron casting. Whenselecting the composition for both ADI andconventional Ductile Iron, consideration shouldbe given first to limiting elements whichadversely affect the casting quality through theproduction of non-spheroidal graphite, theformation of carbides and inclusions, andpromoting the shrinkage. For this reason it’sknown from the previous research that thepercentages of carbon, silicon and other majorand minor alloying elements that control themechanical properties are important (Anita,2009; Nofal and Jekova, 2009; and Erfanian-Naziftoosi et al., 2011).

In the present work, the effect of Copper withaustempering heat treatment on themechanical properties and hardness of ductileiron were studied. Austenization time,Austempering time (60 minutes) and

temperature (900 °C-Austenization,Austempering-300 °C) are kept constant.Metallographic studies on DI and ADI are alsoconducted.

EXPERIMENTMaterials Selected: CRC scrap, BurntCoconut shell for carbon, Ferro siliconMagnesium, Ferro silicon and pure copper(99%), engine oil as quenching medium.

Equipments Used: Resistance furnace,electric oven, miscellaneous equipments likequenching tube made of mild steel, graphitecrucible etc.

Experimental Procedure

Experiment was conducted in a normal foundrylocated in Bangalore for the preparation of ADI.Melting of scrap was done in a inductionfurnace. Detail steps are explained below.

Material Selection: Cold Rolled Coil (CRC)scrap is used as the raw material for thepreparation ductile iron. Carbon is added inthe form of burnt coconut shell. Magnesium andsilicon is added in the form of Ferro siliconmagnesium and Ferro silicon as inoculantsand graphite promoter respectively.

Melting: Melting was done in a inductionfurnace of capacity of 250 kg and 130 kWpower. After melting the melt was transferredinto the ladle for alloying purpose.

• Melted material was poured into theprepared sand mold and it is allowed forsolidification.

• The specimens for tensile test weremachined from the test bar casted and thenspecimens were subjected toaustempering heat treatment.

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• Two sets of specimens were prepared foreach composition for the purpose ofcomparing the properties between the DIbefore and after heat treatment.

Heat Treatment

The prepared specimen was subjected toaustempering process. Beforeaustempering the specimen was subjectedto austenization in a resistance furnace.Program was done in the furnace in such away that to maintain 900 °C where thespecimen is kept for 1 hour. Then thespecimen is transferred to the oven wherethe quenching media was maintained at300 °C in a cylindrical tube. The ovenchamber was enclosed and specimen keptfor 1hour and it is allowed for cooling slowlyto room temperature. The quenching mediaselected for austempering was engine oil(Servo Max 4T grade). Figure 1 show theheat t reatment cycle used in th isexperiment.

Equipments Used for HeatTreatment

The following are the equipments used for heattreatment cycle:

• Resistance furnace: for Austenization at900 °C.

• Electric oven: for Austempering at 300 °C.

After heat treatment specimens weretested for tensile property, hardness, andmicrostructural study using opticalmicroscopy.

RESULTS AND DISCUSSION

Microstructure of DI and ADI

From all the groups microstructuralexamination specimens were prepared. Thephotographs taken from these specimens aregiven at the Figure 2. The specimens areexamined both before and after the heattreatment. At the microstructural examinationbefore the heat treatment the percent ofspherodisation is controlled. To determine thesuccess of austempering microstructures arechecked after heat treatment.

The microstructure of ductile iron in ascast condition is mostly pearlitic. Afterdifferent heat treatments there is a changein matrix/phase structure, number of nodulesand their spheroidicity. These causechanges in the mechanical properties ofductile iron. The microstructures afterdifferent types of treatments of two differentgrades are shown.

Bainitic matrix structure can be seen atphotographs. The amount of stabilizedaustenite increases with the increasingtemperature. In addition to this by thedecrease of the transformation temperature a

Figure 1: Typical Heat Treatment Cycle

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Int. J. Mech. Eng. & Rob. Res. 2012 Anil Kumar M M and R Suresh, 2012

Effect of Copper on the TensileStrength of Ductile Iron

To find out effect of copper, four samples weremade with 0.0 wt%, 0.5 wt%, 1.0 wt% and 2.0wt%. The tensile samples were machined fromthe castings. The samples were austenitizedin a Resistance furnace at a temperature of900 °C for one hour and austempered in aResistance oven at 300 ºC for one hour. Thenthe tensile test was performed. The results aretabulated in Table 1.

Figure 2: Microstructure of DI Before andAfter Heattreatment

decrease at the grain size is observed. Thisis possibly a cause of increase in hardnessvalues and tensile strength.

Without heattreatment 561.5 696.1 734.3 762.2

With heattreatment 1009.4 1468.1 1523.6 1491.2

Table 1: Effect of Copperon Tensile Strength of Ductile Iron

Ultimate Tensile Strength (N/mm2)Copper

0 wt% 0.5 wt% 1.0 wt% 2.0 wt%

From the Table 1 and Figure 3 it can besaid that addition of Cu in the Ductile Ironincreases the strength of the Ductile Iron. Thisis because of the grain refinement takesplace after the addition of Cu. When it issubjected to austempering process thepresence of retained austenite matrix-ferrite

Figure 3: Comparision of Tensile StrengthBefore and After Heattreatment of DI

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Int. J. Mech. Eng. & Rob. Res. 2012 Anil Kumar M M and R Suresh, 2012

matrix around the graphite nodules increasesthe tensile strength very high. But it is limitedup to 1% of Cu, because after 1% there isdecrease in the amount of retained austenitephase. But compare to Ductile Iron beforeheat treatment, tensile strength of ductile ironafter heat treatment is very high.

CONCLUSIONBased on the experiment carried out andresults obtained the following conclusionswere made.

• Servo engine oil used for the austemperingprocess helps in obtaining the ADI withgood strength and ductility with compare tothat of salt bath quenching from previousliterature.

• The tensile strength of the DI before heattreatment was increased gradually with theaddition of Cu (0.5, 1 and 2 in wt %) withoutdecrease. Therefore the addition of Cuhelps in improving the tensile strength of thematerial. The maximum tensile strengthobtained was 762 N/mm2 at 2 wt%.

• The tensile strength of the DI after heattreatment was increased up to the 1 wt% ofthe Cu addition, after it tends to decrease.The austempering helps in improvement oftensile strength compare to specimens ofwithout heat treatment. The maximumtensile strength obtained was 1523.6N/mm2 at 1 wt%.

REFERENCES1. Anita Bisht (June 2009), “Effect of Heat

Treatment Prodedures on Microstructureand Mechanical Properties of NodularIron”, National Institute of Technology,Rourkela.

2. Erfanian-Naziftoosi H R, Haghdadi N andKiani-Rashid A R (2011), “The Effect ofIsothermal Heat Treatment Time on theMicrostructure and Properties of 2.11%Al Austempered Ductile Iron”, ASMInternational, DOI: 10.1007/s11665-011-0086.

3. Hasan Avdusinovic and AlmaidaGigoviæ-Gekiæ (2009), “Heat Treatmentof Nodular Cast Iron”, Trends in theDevelopment of Machinery andAssociated Technology, October 16-21,TMT, Hammamet, Tunisia.

4. Kiani-Rashid A R and Edmonds D V(2005), “Carbide Precipitation in theMicrostructure of Austemperd Ductile IronContaining 0.48% and 4.88% Aluminium”,International Journal of ISSI, Vol. 2,No. 2, pp. 1-8.

5. Myszka D (2007), “Austenite-MartensiteTransformation in Austempered DuctileIron”, Archives of Metallurgy andMaterials, Vol. 52, No. 3, pp. 475-480.

6. Najmeddin Arab (2011), “Investigation toProduction Machinable AustemperedDuctile Iron (MADI)”, Journal of AmericanScience, Vol. 7, No. 9.

7. Nofal A A and Jekova L (2009), “NovelProcessing Techniques and Applicationsof Austempered Ductile Iron (Review)”,Journal of the University of ChemicalTechnology and Metallurgy, Vol. 44,No. 3, pp. 213-228.

8. Olivera Eri et al. (2005), “AnAustempering Study of Ductile IronAlloyed with Copper”, J. Serb. Chem.Soc., Vol. 70, No. 7, pp. 1015-1022.