International Journal of Engineering Technology Science and Research IJETSR www.ijetsr.com ISSN 2394 – 3386 Volume 5, Issue 3 March 2018

Effect of Austempering on Microstructure and Mechanical Properties of Ductile Cast

*V. P. Patel1 *A. V. Patel2 1. Department of Mechanical Engineering, 2. Department of Mechanical Engineering, U.V.Patel College of Engineering, Kherva, India U.V.Patel College of Engineering, Kherva, India

Abstract-The effects of austempering onmechanical (enables ductility) together with oneof two Bainitic properties and microstructure of ductile with morphologies; namely carbide-free Bainitic ferrite and without different temperature and time has been or Bainitic ferrite, in which carbides are distributed study in this paper. The different time and temperature in the ferrite (affects strength).For many years, the duration selected for this purpose were aaustenisation at ADI has been considered an alternative material, 850 °C for 1 hour and then transferred quickly to a salt substitute for in several mechanical bath maintained at different temperature as 350°C, components, because it offers the possibility of 300°C and 250°C and also for different time duration as obtaining a broad range of mechanical properties 90 minute, 60 minute, and 30 minute. Experiments were carried out in a medium-frequency starting from a generic spheroidal graphite cast iron with 500 kg capacity crucible. Metallic charges were melt and applying specific heat treatments[3-4]. The composed of , scrap, commercially Ferro- austempering process was first developed by silicon, Ferro-manganese, and Sulphur. Metallic charge Davenport and Bain and applied to steels in the material is heated up to 1530˚C. The flux is adding in to 1930s.The austempering process in the metallic charge material and to remove the slag from involves austenitising, and isothermally metallic charge material. The different condition of transforming a specimen or component at a austempering use on test bar casting is generated after temperature in the Bainitic region for an appropriate shot blasting and cleaning. Finally the results of of time. Austenitization and austempering are often examinations allow us to be of opinion that an increase conducted in molten salt baths to avoid surface of austempering time up to one hour resulted in an increase in tensile strength; however, it decreased when oxidation of the specimens or components after the time was increased. which they can either be air or water cooled. The structure and mechanical properties of ADI depend Keywords: Gray cast iron; ductile cast iron; heat treatment; Austempering; Microstructure and strongly on the kinetics of phase transformation and mechanical properties. mechanism that occurs during austempering. In the present investigation, efforts have been made to

improve the mechanical properties and effect of I. INTRODUCTION processing parameters (austempering time and Austempered ductile iron (ADI) is considered to be temperature) on the mechanical properties of ADI an important engineering material because of its has been studied [5-7]. attractive properties such as good ductility, high strength, good wear resistance and fatigue strength II. EXPERIMENTAL PROCEDURE and fracture toughness. Because of these combinations of properties, ADI is now used A. Melting & Casting extensively in many structural applications in The experiments were carried out in a medium automotive industry, defense and earth moving frequency induction furnace with 500 Kg capacity machineries[1-2].The optimum mechanical crucible furnace. Metallic charges were composed properties of ADI i.e. the adequate combination of of pig iron, commercially Ferro silicon, steel scrap, strength, toughness, and fatigue strength and wear and magnesium treatment carried out. Nominal resistance could be achieved if the microstructure composition of the experimental alloys is given in consists of retained carbon-enriched stable Table 1. Metallic charge material heated up to 1530 1123 V. P. Patel, A. V. Patel

International Journal of Engineering Technology Science and Research IJETSR www.ijetsr.com ISSN 2394 – 3386 Volume 5, Issue 3 March 2018

°C. The flux is adding in the metallic charge measurement and Tensile test were carried out material for remove the slag of metallic charge according to ASTM (A370-2002). material. The were treated in a preheated tea Before and after heat treatment, the samples were pot ladle containing 12 kg of 4.5% ferrosilicon prepared for micro structural analysis as shown in magnesium and 2.5 kg of 75% foundry grade fig1, 2, 3 and 4. From each specimen a slice of 4 ferrosilicon (size 2-3 mm). Another 2.5 kg of mm is cut to determine the microstructure. These ferrosilicon was added during tapping. Treatment slices are firstly mounted by using Bakelite powder temperature was 1450-1460˚C. Argon gas purging then polished in SiC paper of different grades (or was carried out during treatment of the for emery papers) then in 1μm cloth coated with proper mixing. At this time sample was taken for diamond paste with use of polishing machine. The chemical analysis. The treated iron was poured into samples were etched using 2 % nital (2 % conc. a dry sand mold bonded with furan resin and Nitric acid in methanol solution). Then the catalyst to cast Y block as per ASTM specification. microstructures were taken for different heat treated The iron was properly post inoculated by adding 1.5 specimen by using Image analyzer microscope and kg of 75% foundry grade ferrosilicon (size 0.3- determine % and % nodularity. 0.4mm) to the stream during pouring.

III. RESULTS AND DISCUSSION TABLE 1: THE CHEMICAL COMPOSITION OF

CAST ALLOY A. Effect of Austempering time on hardness

Material C Si Mn P S Mg 400

300

3.68 2.03 0.03 0.03 0.01 0.03 S.G.I 250°C 0 0 8 0 4 8 200

300°C 100 B. Austempering Process 350°C Hardness in BHN Hardnessin Nine samples were taken in a group. To 0 homogenize the samples kept them in a muffle 30 60 90 furnace for one hour at 850⁰C, some samples were conventionally treated and some were Austempered Time in minute for different times with constant temperature. Fig 5: Hardness Vs. different austempering For austempering process, the samples were heated condition. at 850°C for 1hr. for austenisation and then transferred quickly to a salt bath (salt combination The value of hardness is increase at 250°C with was 50 wt. % NaNO3 and 50 wt. % NaNO2) different time duration as compare to temperature maintained at 250°C. 300°C and 350°C with different time duration. As The samples were kept in the salt bath for different shown in fig. 5 obtain thehardness of casting at a times as 30 minutes, 1hr. and 1.5 hrs. After which given temperature is decrease with increase in time they were allowed to cool in still air. and further increase in time gives increasing in The heat treated samples of dimension 8×8×3 mm hardness value but less than first condition. The were polished in emery papers (or SiC papers) of value of pearlite is maximum at 250 °C and 30 different grades for Brinell hardness number minute due to this maximum hardness is 347 BHN obtained as compare to at 300°C and 350°C.

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International Journal of Engineering Technology Science and Research IJETSR www.ijetsr.com ISSN 2394 – 3386 Volume 5, Issue 3 March 2018

1200

1000 250°C The value of UTS is increase at 250°C with 300°C 800 different time duration as compare to temperature 350°C 300°C and 350°C with different time duration. As

in N/mm² in 600 shown in fig. 6 obtain Ultimate Tensile Strength of Tensile Strength Strength Tensile casting at a given temperature is increase with 30 Time 60 in minute90 increase in time and further increase in time gives Fig.6:Ultimate Tensile Strength Vs. different decreasing in Ultimate Tensile Strength value but austempering condition.

(a) (b) (c) Fig 1: Microstructure of casting at Austempered at 250 °C for 30(a), 60(b), 90(c) min. respectively.

(a) (b) (c) Fig 2: Microstructure of casting at Austempered at 300 °C for 30(a), 60(b), 90(c) min. respectively.

(a) (b) (c) Fig 3: Microstructure of casting at Austempered at 350 °C for 30(a), 60(b), 90(c) min. respectively.

1125 V. P. Patel, A. V. Patel

International Journal of Engineering Technology Science and Research IJETSR www.ijetsr.com ISSN 2394 – 3386 Volume 5, Issue 3 March 2018

Fig 4: Microstructure without heat treatment More than first condition. The value of pearlite is maximum at 250°C and 60 minute due to this The value of pearlite is increase at 250°C with maximum Ultimate Tensile Strength is 1169.38 different time duration as compare to temperature N/mm² obtained as compare to at 300°C and 300°C and 350°C with different time duration. As 350°C. shown in fig. 7 pearlite is maximum at 250 °C and 60 minute. The value nodularity percentage at 100 250°C, 300°C, 350°C with different time duration 98 as shown in figure 8.

96 94 IV. CONCLUSIONS 92 250°C The effect of austempering on the mechanical 90 300°C properties of SG iron Austempered at three 88 different temperatures with varying austempering Pearlite % inPearlite 350°C 86 time has been investigated in the present 84 investigation. The following conclusions are made: 82 1. An increase of austempering time up to one 30 60 90 Time in minute hour resulted in an increase in tensile strength; however, it decreased when the time was Fig. 7: Pearlite vs. different austempering increased. condition. 2. The maximum pearlite percentage achieved was 97.95 and 97.89 by austenizing at 850˚C 90 and Austempered at 250˚C at 60 minute and 90 minute respectively.

85 3. The maximum value of tensile strength achieved was 1169.38 N/mm2 and 1137.98 2 250°C N/mm by austenizing at 850˚C and 80 Austempered at 250˚C at 60 minute and 90 300°C minute respectively. 4. Austempering at 250˚C produced higher 350°C 75 tensile strength as compare to austempering at

300˚C and 350°C which resulted in lower Nodularity in count% Nodularityin 70 tensile strength in all samples. 30 60 90 5. The maximum value of hardness achieved was Time in minute 347 BHN and 341BHN by austenizing at

850˚C and Austempered at 250˚C at 30 minute Fig. 8: Nodularity Vs. different austempering and 90 minute respectively. condition.

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International Journal of Engineering Technology Science and Research IJETSR www.ijetsr.com ISSN 2394 – 3386 Volume 5, Issue 3 March 2018

6. With the application of austempering process, [2] Muhammad Ashraf Seikh, “Effect of heat the tensile strength was doubled. The value of treatment and alloying element on tensile strength without any heat treatment was characteristics of ADI” University of 495.2 N/mm2and when the samples were engineering and technology, Lahore, 2008. subjected to austempering heat treatment at [3] “A journal of kastwel foundry”, 3rd Edition, 250˚C for one hour; it was increased to a value January 2010. www.kastwel.com 1169.38 N/mm2. [4] Susanta Kumar Swain and SudiptaSen, “Effect 7. There was almost no effect of heat treatment of austempering variables on mechanical on nodularity of the ductile iron. Good properties of spheroidal graphite iron” nodularity i.e. 81% to 88% was achieved with international journal of current research, a good selection of charge and careful melting volume 4, issue 06, pp072-076, June 2012. techniques. [5] Ranjan Mittal and Sunit Nanda, “Property 8. With the application of austempering process, enhancement of spheroidal graphite cast iron the hardness was increase. The value of by heat treatment” Department of hardness without any heat treatment was 166 Metallurgical and Materials Engineering, BHN and when the samples were subjected to National Institute of Technology Rourkela, austempering heat treatment at 250˚C for half India, 2010. hour; it was increased to a value 347 BHN. [6] D. S. Padan, “Micro-alloying in Austempered ductile iron” American Foundry Society, paper REFERENCES 12-019, 2012. [1] T.V. Rajan, C.P. Sharma; Heat Treatment [7] Alan Vasko” Microstructure and Mechanical Principles and Techniques, Second Edition, properties of austemperd ductile iron” Delhi (2011) 255-276. ANNALS of faculty engineering Hunedoara, international Journal of engineering, 2012, volume 1, ISSN1584-2665.

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