ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT AZOJETE June 2023. Vol. 19(2):203-210 Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria. Print ISSN: 1596-2490, Electronic ISSN: 2545-5818 www.azojete.com.ng Corresponding author’s e-mail address: takor@nda.edu.ng 203 ORIGINAL RESEARCH ARTICLE MODEL FOR PREDICTION OF SOME MECHANICAL PROPERTIES OF DUCTILE CAST IRON AUSTEMPERED IN JATROPHA CURCAS SEED OIL A. Terngu, O. F. Agboola and D. K. Garba Department of Mechanical Engineering, Nigerian Defence Academy Kaduna *Corresponding author’s email address: takor@nda.edu.ng 1.0 Introduction Improvements in properties of metals can be achieved by controlling composition and by further processing in mechanical working and heat treatment. The heat treatment principle governs the procedures required to obtain particular microstructure in a given metal to achieve these properties to suit desirable working conditions (Aachary and Venugopalan, 2000). The importance of heat treatment lies in its ability to control a metal’s structure-sensitive properties. Austempering heat treatment is a proven way of obtaining the desired microstructure for improved mechanical properties such as increased strength, toughness, wear resistance, hardness and fatigue strength in ductile iron components (Adewuyi and Afonja, 2002). It is an isothermal heat treatment process in which, depending on the applied austempering conditions, an attractive combination of mechanical properties of austempered ductile iron may be produced (Alp et al., 2005). In many applications, this renders the austempered ductile iron a valuable and an economical substitute for high strength steels (ASM, 1996). The important microstructural features of austempered ductile iron are the morphology of the ferrite, the volume fraction of retained austenite, the carbon content in retained austenite, and the presence or absence of carbide in austenite or ferrite. A mixture of bainitic ferrite retained austenite, and graphite nodules, are the most desirable combination of phases in the cast iron. Thus, the mechanical properties of austempered ductile iron may be related to three microstructural variables: bainite morphology, austenite volume fraction and the formation of martensite (ASM, 1996). Austempered ductile iron components, competes ARTICLE INFORMATION ABSTRACT Austempering heat treatment is a proven way of obtaining the desired microstructure for improved mechanical properties. It is an isothermal heat treatment process in which an attractive combination of mechanical properties of austempered ductile iron (ADI) may be produced. In this paper, a statistical model for the determination of some mechanical properties was developed. The ductile cast iron was annealed after which it was austennitized at 850 and 950 °C. After the austenitizing process, it was then austempered in hot jatropha seed oil. The developed prediction model was then utilized to assess the tensile strength and hardness of the ADI. The result of the austempering process showed appreciable improvement in tensile and hardness values measured. Optimum values of tensile and hardness were 962 kN/mm2 and 405 BHN respectively. Values of 961.4N/mm2 and 340.1BHN were obtained using the developed model. It can therefore be concluded that, the closeness in the values obtained from the experimental measurement and the prediction model is an indication of the effectiveness of the developed model. © 2023 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved. Submitted 12 December, 2022 Revised 18 March, 2023 Accepted 24 March, 2023 Keywords: Austempering, Austempered Ductile Iron (ADI) Prediction Model Tensile Strength Hardness Value http://www.azojete.com.ng/ file:///C:/Users/Engr.%20Samuel/Documents/Engr%20Oyeniyi/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2019%20NO%202/AZOJETE%20VOL%2019%20NO%202/takor@nda.edu.ng takor@nda.edu.ng Arid Zone Journal of Engineering, Technology and Environment, June, 2023; Vol. 19(2):203-210. ISSN 1596-2490; e-ISSN 2545-5818; www.azojete.com.ng Corresponding author’s e-mail address: takor@nda.edu.ng 204 favorably with steel forgings, especially for heavy-duty parts where reliability is paramount. It is used to upgrade from standard ductile irons, and as a substitute for manganese steel and nickel- hard materials. AID is particularly cost-effective when strength is required: tensile and yield values are twice those of standard ductile iron; fatigue strength is 50 % higher. Austempered ductile iron can replace aluminum with its high strength-to-weight ratio when reduced section sizes are the requirement. ADI castings are increasingly displacing steel forgings and castings, welded fabrications and carburized steel, due to superior performance. Because of its equivalent strength, nearly 80 % of all cast and forged steels can be replaced with some grade of ADI (Ayman and Megahead, 2008). An ADI component will be 10 % lighter than steel for a given shape. ADI is three times stronger than the best cast or forged aluminum and weighs only 2.5 times as much. Because it is twice as stiff, an adequately designed ADI part can replace aluminum at a weight saving. ADI's dynamic properties exceed those of forged, cast and micro- alloyed steels. Unlike aluminum, ADI's endurance limit remains nearly constant after tens of millions of cycles. The presence of graphite in the ADI matrix improves noise damping, for quieter and smoother running components. ADI's abrasion resistance exceeds that of conventionally processed steels and irons at a lower 'bulk' hardness level. Unlike carburized steel, which loses wear resistance as the carburized layer is removed, ADI improves in service. Wear resistance is superior to steel at any hardness level, making it ideal for earth moving and high abrasion applications (Metals Handbook, 1981). Austempering is mainly carried out in a nitrate/nitrite salt bath, due to its advantages compared to other hot baths like lead, mineral oils and polymer solutions. However, in recent years attention has been given to vegetable oils by many researchers. A study on quenching properties of sunflower, coconut oil, palm, and groundnut oils by (Canale et al., 2005) compared the quench severities obtained with petroleum oil. They reported that vegetable oils performed better than mineral oils in a decreasing order: Sunflower oil > Coconut oil > Palm oil > Groundnut oil. Sani (2008) investigated the potentials of using hot shear butter and groundnut oils as austempering quenchants for steels and cast iron. His findings indicated that these oils could be used to austemper medium carbon steel and ductile iron. A recent study by Isah (2011) evaluated Kahaya Senegalensis (Mahogany) seed oil as quenching medium in austempering of ductile iron. He reported that the Kahaya Senegalensis seed oil is an effective austempering quenchant for ductile iron. These breakthroughs could eliminate the need for a molten salt bath which has its attendant side effects such as high energy consumption, increased capital equipment cost, and the hazards the workers are exposed to when using molten salt bath. Jatropha curcas seed oil was utilized as austempering medium in this research work. A prediction model was then designed to predict some of the mechanical properties of the austempered cast iron produced from the austempering process. file:///C:/user/Downloads/azojete143/www.azojete.com.ng file:///C:/Users/Engr.%20Samuel/Documents/Engr%20Oyeniyi/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2019%20NO%202/AZOJETE%20VOL%2019%20NO%202/takor@nda.edu.ng Akor et al: Model for Prediction of Some Mechanical Properties of Ductile Cast Iron Austempered in Jatropha Curcas Seed Oil. AZOJETE, 19(2):203-210. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: takor@nda.edu.ng 205 2.0 Materials and Methods: 2.1 Materials The raw materials used for this investigation were high-purity sorrel pig iron obtained from Metallurgical research institute Jos, and ferroalloys of magnesium, silicon, manganese and cast iron to produce ductile iron. 2.2 Equipment The equipment used in casting and production of test samples and mechanical tests include a 250kg rotary furnace at Nasir foundries, Jos; Nobertherm electric furnace, electric oven, Lathe, Milling machine, Pensky Martens Flash point tester and Wolpet Impact testing machine were accessed at the laboratories of the Mechanical Engineering Department, Nigerian Defence Academy, Kaduna. Metal Analyzer at the research and development laboratories of Defence Industries Corporation of Nigeria (DICON) Kaduna was also used in analyzing some of the metallic materials. Jatropha oil used for austempering was produced at NARIT Zaria. 2.3 Methods 2.3.1 Production of ductile iron samples Charges consisted of 50 kg pig iron with composition C=4.17%, Si=1.66%, Mn=0.19%, S=0.01%) and a nodularizing alloy. The 25mm diameter nodularizing alloy had chemical composition (Si=45.5%, Mg= 5.85% Ca=1.08%,). A sandwich treatment technique was used. The ferrosilicon alloy was placed on a pocked in the bottom of an open heated ladle and covered with scrap in this technique. The melt was poured on the other side of the ladle to react with the magnesium alloy effectively. The melt was then cast into ‘Y’ blocks. The pouring temperature was 1380 oC (Metals Hand Book, 1992). The ductile iron produced had the chemical composition: C = 3.42%, Si = 3.1%, Mn = 0.21%, Cr = 0.02%, P = 0.11% and Ni = 0.00004% 2.4. Production of Jatropha seed oil Dry jatropha seeds were collected from Rafin Sewa Gora village of Zango LGA, Kaduna state. The seeds were manually shelled and dried inside the house to prevent exposure to direct sun rays. They were then taken to National Research Institute for Chemical Technology (NARICT) Zaria, Nigeria for oil extraction. The Cold Pressed method was employed to extract oil from the seeds. The mechanically extracted jatropha oil was used in its crude form for austempering ductile iron without further processing. The chemical composition of the jatropha seed oil produced is as follows: flash point = 8.43; Acid value = 4.22; Free fatty acid = 210; Saponification value = 62.12mgKOH; Peroxide value meg/kg = 88.15; Iodine value g/100g = 40; Viscosity at 38 0C mm2/sec = 249 respectively. Test samples were machined from the nodular cast iron. These were subjected to annealing heat treatment after which jatropha seed oil was used for the austempering. 2.5 Mechanical properties determination. Two methods were utilized to determine the mechanical properties of the austempered ductile cast iron; the specimens were physically subjected to mechanical testing and then the developed model. In the experimental testing, the universal testing machine was used. Each of the http://www.azojete.com.ng/ file:///C:/Users/Engr.%20Samuel/Documents/Engr%20Oyeniyi/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2019%20NO%202/AZOJETE%20VOL%2019%20NO%202/takor@nda.edu.ng Arid Zone Journal of Engineering, Technology and Environment, June, 2023; Vol. 19(2):203-210. ISSN 1596-2490; e-ISSN 2545-5818; www.azojete.com.ng Corresponding author’s e-mail address: takor@nda.edu.ng 206 machined samples were fixed in-between the two jaws of the machine and subjected to tensile loading till failure. Readings of extension and load where taken in at intervals. 2.6 Development of the Prediction Model As described earlier in this study, the ductile iron structures where enhanced by austenitizing and austempering at selected temperature levels and times. Data was collected from the ductile iron smaples by running each condition as indicated in Tables 1 and 2 to study the factors influencing the austempering process. Table 1: Test Factors for Austempering Process of Ductile Iron. Factors Low Level High Level Austenitizing temperature (Tϕ) 800 °C 950 °C Austempering temperature (Tϵ) 250 °C 300 °C Austempering time (tϵ ) 1 hr 5 hr In this regard, statistical design and development of a mathematical model for the austempered ductile iron was carried out. A total of 8 runs were performed on the samples, factors of interest and response variables were identified, and appropriate levels for each variable were determined. A complete factorial design was used to test every combination of the factor levels. Mathematical symbols (- and +) called “coded factor levels” representing lows and highs (actual) levels were randomly used as shown in Table 2 6 in order to set off any lurking variables (Stankova, 2015). Table 2: Factorial Design of Austempering Process of Ductile Iron Showing the Combination of Chosen Factors Experiment Number Austenitizing temperature (Tϕ) Austempering temperature (Tϵ) Austempering time (tϵ ) 1 -1 -1 -1 Tϕ +1 -1 -1 Tϵ -1 +1 1 Tϕ +1 +1 -1 tϵ -1 -1 +1 Tϵ tϵ +1 -1 +1 Tϕ tϵ -1 +1 +1 Tϕ Tϵ tϵ +1 +1 +1 The response data (Tensile strength and Hardness values) from running all the combinations of the chosen factors, each at two levels, were combined. A linear mathematical model equation to predict a given response was developed. The model will be derived from the response function expressed according to Stankova (2015) as: Y = β0 + β1 Tϕ+β2Tϵ + β3 Tϕ tϵ + β4 tϵ + β5 Tϵ tϵ + β6 Tϕ tϵ + β7 Tϕ Tϵ tϵ (1) Where Y = the predicted mechanical properties (Tensile Strength and Hardness) β0 = the intercept β1 to β7 = the model coefficient for the input factor Tϕ = Austenitization temperature (Ductile iron and steel samples) file:///C:/user/Downloads/azojete143/www.azojete.com.ng file:///C:/Users/Engr.%20Samuel/Documents/Engr%20Oyeniyi/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2019%20NO%202/AZOJETE%20VOL%2019%20NO%202/takor@nda.edu.ng Akor et al: Model for Prediction of Some Mechanical Properties of Ductile Cast Iron Austempered in Jatropha Curcas Seed Oil. AZOJETE, 19(2):203-210. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: takor@nda.edu.ng 207 Tϵ = Austempering temperature and tϵ = Austempering time 3.0 Results and Discussion 3.1 Experimental measurements The result of the experimental measurement for the tensile strength and hardness test are shown in Tables 3 and 4 respectively. Table 3: Tensile Strength of the Austempered Ductile Iron Tensile Strength (N/mm2) Austenitised at 950 °C Austempering Temperature 250 °C Austempering Tempreture 300 °C Time(hrs) Jatropha Jatropha 1 726 668 2 770 690 3 822 740 4 839 814 5 962 840 Austenitised at 850 °C 1 847 683 2 931 790 3 892 764 4 840 745 5 820 730 Table 4: Hardness strength of the Austempered Ductile Iron Hardness (BHN Austenitised at 950 °C Austempering Temperature 250 °C Austempering Tempreture 300 °C Time (hrs) Jatropha Jatropha 1 331 227 2 325 297 3 346 275 4 305 291 5 340 265 Austenitised at 850 °C 1 287.6 254 2 302.1 279.5 3 291.4 264.1 4 297.8 239.5 5 288 220 3.2 Tensile Strength and Hardness The responses measured from running all the combinations of chosen factors at two levels are shown in Table 5. The factors had impact on the responses obtained. http://www.azojete.com.ng/ file:///C:/Users/Engr.%20Samuel/Documents/Engr%20Oyeniyi/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2019%20NO%202/AZOJETE%20VOL%2019%20NO%202/takor@nda.edu.ng Arid Zone Journal of Engineering, Technology and Environment, June, 2023; Vol. 19(2):203-210. ISSN 1596-2490; e-ISSN 2545-5818; www.azojete.com.ng Corresponding author’s e-mail address: takor@nda.edu.ng 208 Table 5: Complete Matrix Including Interactions with Effects Calculated for Austempered Ductile Iron Run No Main Effects Interaction Effect Response Tϵ Tϕ tϵ TϕTϵ Tϵtϵ Tϕtϵ TϕTϵtϵ TSJ HVJ 1 - - + + - + - 847 287.6 2 + - - - - + + 683 235.4 3 - + - - + - + 726 331 4 + + - + - - - 668 297 5 - - + + - - + 820 288 6 + - + - + - - 730 220 7 - + + - - + - 962 340 8 + + + + + + + 840 265 784.5 283 Effect TSJ -108.5 29 107 18.5 2.5 97 -34.5 EffectHVJ -57.3 50.5 -9.5 2.8 -14.2 -2 -6.3 Where: TSJ = Tensile strength values for samples austempered in jatropha oil. HVJ= Hardness values for samples austempered in jatroph oil. 3.3 Discussion The combination of low levels of austempering temperature, austenitizing temperature and time, produced austempered ductile iron of tensile strength value as high as 847 N/mm2 for jatropha oil. A lower tensile strength values of 840 N/mm2 for jatropha oil at the combination of high austempering temperature, high austenitizing temperature and time. The highest tensile strength values of 962 N/mm2 were achieved at a combination of low austempering temperature with high austenitizing temperature and time. It means a low level of austempering temperature would increase tensile strength. The developed mathematical model equation for the prediction of the tensile strength values with the fitted factors of temperatures and time in coded form for jatropha seed oil is expressed as: T.S =784.5+14.5Tϕ -54Tϵ+9.3TϕTϵ+ 53.5 tϵ +1.3Tϵtϵ + 48.5 Tϕtϵ -17TϕTϵtϵ (2) where: Tϕ = Austenitizing temperature (Ductile iron samples) Tϵ = Austempering temperature and tϵ = Austempering time in all the equations. The value for the intercept of 784.5 represents the average of all the tensile strength values obtained after 8 runs of the test (actual responses). By substituting the values of the main and interactions effects in coded form in Equation (1) for any experimental condition using jatropha seed oil as austempering medium, the tensile strength values for the austempering process of ductile iron were calculated. The predicted values for tensile strength were determined by putting the code factor levels into the coded model in Equation (2). The effect of Tϵ, tϵ and TϕTϵ caused bigger effect on the predicted tensile strength values than other effects. These are in the magnitude of -108.5, 107 and 97 for samples austempered. The comparison of actual and predicted tensile strength of the ADI is presented in Table 6. file:///C:/user/Downloads/azojete143/www.azojete.com.ng file:///C:/Users/Engr.%20Samuel/Documents/Engr%20Oyeniyi/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2019%20NO%202/AZOJETE%20VOL%2019%20NO%202/takor@nda.edu.ng Akor et al: Model for Prediction of Some Mechanical Properties of Ductile Cast Iron Austempered in Jatropha Curcas Seed Oil. AZOJETE, 19(2):203-210. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: takor@nda.edu.ng 209 Table 6: Actual and the Predicted Tensile Strength Values Table 6 compares the predicted values of tensile strength values with the responses obtained under different experimental conditions. The predicted values are very close to the actual values obtained from the experiment utilizing jatropha. The reliability of the model equations predicted well with the studied austempered ductile iron. Responses have been ascertained within the selected temperatures and time. 3.4 Prediction of the hardness of austempered ductile iron A similar statistical design and mathematical model were developed to predict the hardness of the ductile iron austempered in jatropha oil. The responses obtained for hardness values depended on austenitization temperature, austempering temperature and time. Combining a low level of austempering temperature with high austenitizing temperature and austempering time produced the highest hardness of 405BHN for the samples austempered in jatropha seed oil. High levels of austempering temperature and time and low levels of austenitizing temperature produced the most negligible hardness value of 220 BHN. This suggests that high a level of austempering temperature and low levels of austenitizing temperature contribute greatly to the decrease in hardness value. The developed mathematical model equation for the prediction of hardness value (HV) with the fitted factors of temperature and time in coded form for samples austempered in jatropha seed oil can be expressed as: H.V =283 + 25.3Tϕ – 28.7Tϵ + 1.4TϕTϵ - 4.8 tϵ -7.1Tϵtϵ - Tϕtϵ - 3.2TϕTϵtϵ (3) Table 7 presents the predicted hardness values compared with the actual values of responses obtained under different experimental conditions. The predicted values obtained by applying Equation (3) are found to be very close to the actual values obtained. Table 7: Actual and Predicted Hardness Values of ADI at different conditions Hardness Values (BHN) of ADI Jatropha Seed Oil Quenchant Run No Actual Predicted R1 287 287.7 R2 235.4 235.3 R3 331 331.1 R4 297 297.1 R5 288 287.9 R6 220 219.9 R7 340 340.1 R8 265 264.9 Tensile Strength Values (N/mm2) of ADI Jatropha Seed Oil Quenchant Run No Actual Predicted R1 847 849.5 R2 683 683.4 R3 726 726 R4 668 668 R5 820 820 R6 730 730 R7 962 961.4 R8 840 840.6 http://www.azojete.com.ng/ file:///C:/Users/Engr.%20Samuel/Documents/Engr%20Oyeniyi/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2019%20NO%202/AZOJETE%20VOL%2019%20NO%202/takor@nda.edu.ng Arid Zone Journal of Engineering, Technology and Environment, June, 2023; Vol. 19(2):203-210. ISSN 1596-2490; e-ISSN 2545-5818; www.azojete.com.ng Corresponding author’s e-mail address: takor@nda.edu.ng 210 4. Conclusions From the results and analysis of the results obtained, the following conclusions could be drawn. (i) Jatropha, seed oil was able to cause the formation of ‘ausferrite’ and ‘bainite’ structures at 250°C in the ductile cast iron specimens. (ii) There was an appreciable improvement in the mechanical properties of ductile iron when austempered in jatropha seed oil. The as-cast tensile strength, yield strength and hardness values of 560 N/mm2; 266 BHN which increased to optimum values of 1039N/mm2 and 405 BHN for samples austempered in the jatropha seed oil. (iii) The developed statistical model for predicting the tensile and hardness values for the austempered ductile iron compared well with the values obtained using the experimental method of determining mechanical properties. References Aachary, J. and Venugopalan, D. 2000 Microstructural Development and Austempering Kinetics of Ductile Iron during Thermomechanical Processing. Metallurgical and Materials Transaction, 31(A): 2575- 2585. Adewuyi, BO. and Afonja, AA. 2002. Austempered Ductile Iron, a Viable to Steel. Nigerian Journal of Engineering and Management, 1(1): 6-13. Alp, T. Wazzan, AA. and Yilmaz, F. 2005. Microstructure Property Relationships in Cast Irons. The Arabian Journal for Science and Engineering, 2 (B): 163-175. American Society Metals (ASM) 1996. Specialty hand book, cast iron. 1st edition, (Davis, JR. (ed.)). ASM international, Ohio, pp. 356-392. Ayman, H. and Megahed, MM. 2008. Fracture toughness characterization of austempered ductile iron produced using both conventional austempering processes. Materials and Design, 3: 1866-1877. Canale, LCF., Fernandes, MR., Agustinho, SCM., Totten, GE. And Farah, AF. 2005. Oxidation of Vegetable Oils and its Impact on Quenching Performance. International Journal of Materials and Product Technology, 24(1-4): 101-125. Isah, LA. 2011. Evaluation of Khaya Senegalensis (Mahogany) Seed Oil as Quenching Medium in Austempering Process of Ductile Iron. Ph.D thesis. Department of Metallurgical and Materials Engineering, Ahmadu Bello University, Zaria, Nigeria. Metals Handbook, 1992. Heat Treating of Ductile Irons. 9th Edition, Ohio, American Society of Metals Metal Park, USA., 15: 358-488. Sani, S. 2008. Potentials of using some Vegetable Oils as Quenchants for Austempering of steel and Cast Irons. Ph.D thesis. Department of Metallurgical and Materials Engineering, Ahmadu Bell University, Zaria, Nigeria. Stankova, K. 2015. Probability and Statistics for Engineers and Scientists. Prentice Hall India Ltd India. file:///C:/user/Downloads/azojete143/www.azojete.com.ng file:///C:/Users/Engr.%20Samuel/Documents/Engr%20Oyeniyi/azojete/AZOJETE%20ARCHIVE/UPLOAD/VOL%2019%20NO%202/AZOJETE%20VOL%2019%20NO%202/takor@nda.edu.ng