13 ijaers feb 2016 28 review of enhancement in mechanical properties using austempered ductile iron

International Journal of Advanced Engineering Research and Science (IJAERS)

[Vol-3, Issue-2, Feb- 2016] ISSN: 2349-6495

Review of Enhancement in Mechanical Properties using Austempered Ductile Iron (ADI) C S Wadageri1, R V Kurahatti2 1

Department of Mechanical Engineering, MMEC, Belagavi, Karnataka, India 2 Department of Mechanical Engineering, BEC, Bagalkot, Karnataka, India

Abstract— Austempered ductile cast iron (ADI) has arisen as significant engineering material in recent years.

It has exhibited outstanding mechanical properties from perspective of structural applications. These include high strength with good ductility, good wear resistance, fatigue strength and fracture toughness. Hence its vast usage as an economical substitute for conventional materials in several structural applications especially in the automotive industry has drawn attention of researchers. Lot of research is been reported in this area.

Brief review on the same is presented in this paper.

Keywords— ADI, Fatigue properties, Strain hardening, Stepped Austempering I. INTRODUCTION When ductile iron is subjected to an austempering treatment, a range of microstructures is obtained depending on heat treatment parameters such as austenitizing time and temperature and austempering time and temperature [1-5]. This results in austempered ductile iron (ADIs) of different grades ranging from high strength-low ductility types, to low strength-high ductility ones, which have been found to be economical substitutes for high strength steels in several applications. Besides, it has the advantage of strength-to-weight ratio, toughness, wear resistance, fatigue resistance, lower material cost, lower production cost, better machinability, and higher damping capacity. ADI is considered a very promising engineering material, and is an economical substitute for wrought or forged steel in several structural applications in the automotive industry like crankshaft, transmission gears, connecting rods and in defense like cannon shells, aircraft landing gears, etc. The influence of heat treatment parameters on the microstructure has been extensively studied using optical microscopy, electron microscopy, and X-ray diffraction.

Austempering treatment generally consists of (a) fully austenitizing the iron at suitable austenitizing temperature, (b) quenching to an austempering temperature and holding it for an appropriate length of www.ijaers.com

time for the isothermal transformation, and (c) air cooling to room temperature. Quenching from austenitizing temperature to austempering temperature should be rapid enough to avoid the formation of ferrite and pearlite in order to maximize toughness and ductility. The austempering reaction in ADI occurs in two stages. In the first stage, austenite matrix transforms to a mixture of acicular ferrite and carbon-enriched stabilized austenite, termed appropriately as ausferrite. The second stage consists of decomposition of the carbon-enriched austenite to a ferrite-carbide aggregate. The best combination of properties in ADI is obtained when austempering treatment is stopped when the first stage is nearly complete, but the transformation has not progressed well into the second stage. The austempering transformation in ADI differs from the analogous reaction in steels where austenite decomposes uniformly into the ferrite carbide aggregate called bainite in a relatively shorter period of time [6].

If the austempering time is too short, the first stage of the austempering reaction will be incomplete and the unreacted parent austenite will transform to martensite, resulting in poor toughness and ductility. Conversely, prolonged holding at austempering temperature will result in austenite enrichment to the point where it becomes less stable, and the second stage of the reaction occurs, resulting in more stable ferrite and carbide phases. This results in loss of toughness and ductility. The optimum austempering time is, therefore, the period between the end of stage I and the beginning of stage II. This is called the processing window. The processing window can be enlarged by adding alloying elements, such as nickel, molybdenum, or copper. Proper austempering thus produces a unique bainitic structure in ADI that consist of high carbon or transformed austenite and acicular ferrite with graphite nodules dispersed in it. Higher austempering temperature produces a coarser ferrite but a lower volume fraction of ferrite. This accompanied by a lower yield strength. Lower austempering temperatures Page | 61

International Journal of Advanced Engineering Research and Science (IJAERS) produce finer and greater volume fractions of ferrite, and a higher yield strength [7-10].

The enhancement of mechanical properties are the important aspect from structural point of view.

Austempered ductile cast iron (ADI) has become an significant engineering material due to improved mechanical viz. good ductility, good wear resistance, fatigue strength and fracture toughness [13]. Lot of research is been reported in this area. Brief review on the same is presented in the following sections. A new processing method was investigated for improving the strength and elongation of austempered ductile iron (ADI) by grain refinement of parent austenite using thermomechanical treatment [11]. Also the effects of the amount of deformation, austenitization temperature, austempering temperatures, reaustenitization, and secondary deformation on the tensile properties were studied and compared with those of the ASTM standards and resulted in increase in tensile strength/yield strength/elongation values. Hafiz [12] studied the mechanical properties of spheroidal graphite (SG)-iron subjected to variable and isothermal austempering temperatures heat treatment and showed that the elongation of specimens austempered under variable austempering temperature are significantly improved. In [13] the investigation is carried out on a nodular or ductile cast iron with predominantly pearlitic as-cast structure which was processed by a novel two-step austempering process and influence of the two-step austempering process on microstructure and mechanical properties of ADI was examined. Test results showed that the two-step austempering process has resulted in significant improvement in yield and tensile strengths and fracture toughness of the material over the conventional single-step austempering process.

In [14] the machinability of ADI was evaluated by comparing tool life, tool wear rate, cutting forces, and surface finish produced on a job as general criteria. The cutting force data used in the analyses were gathered by a tool breakage detection system that detects the variations of the cutting forces measured by a three-dimensional force dynamometer and improvement is observed in the mechanical properties. Kim et al. [15] examined the mechanical properties of an austempered ductile cast iron (ADI) using samples alloyed with copper and molybdenum to obtain favorable mechanical properties such as tensile strength, elongation, and fracture toughness and also the comparison the theose properties with various austempering heat treatments was carried out. Also in [16] the investigation on a new low alloy and low carbon steel with exceptionally high strength and high fracture toughness was been developed. The effect of austempering temperature on the microstructure and mechanical properties of this new steel was examined. www.ijaers.com

[Vol-3, Issue-2, Feb- 2016] ISSN: 2349-6495

There were significant improvement in mechanical properties and fracture toughness as a result of austempering heat treatments. The mechanical properties as well as the fracture toughness were found to decrease as the austempering temperature increases and on the other hand, the strain hardening rate of steel increases at higher austempering temperature.

In [17] the comparison of Conventional Austempering (CA) and Stepped Austempering (SA) heat treatments for microstructural and mechanical response of a non-alloyed ductile iron (DI) presented when subjected to X-ray Diffraction (XRD). The mechanical properties values obtained from tensile and impact tests confirmed that for all times used, SA was superior to the CA. Dierk et al.

[18] studied the the effects of the austempering temperature and of Si and Al on the compositional gradients across the phase boundaries between retained austenite and bainitic ferrite. Also the observation is made in controlling the parameters (i.e. Si, Al content and austempering temperature) which can be used to tune the stability of the retained austenite and hence the mechanical behavior of these steels. In [19] investigation was carried out to examine the influence of austempering holding time on the microstructure and mechanical properties of low carbon, high silicon cast steels and is observed that ultimate tensile strength (UTS) increased but percentage of elongation (%El) decreased with increasing austempering time. Also the formation of carbide due to increase in austempering time resulted in decrease in ductility but increase in strength. In [20] the contribution of multi-phase microstructure and retained austenite on mechanical properties of austempered and intercritical annealed Fe–0.23C–1.8Mn–1.35Si (wt%) steel was studied. The work hardening behavior of retained austenite exhibited a three-stage process such that necking was delayed. The increased work hardening rate is attributed to the multi-phase microstructure and TRIP effect.

In [21] the transformation behavior, mechanical properties and stretch-flangeability of an ultra-highstrength TRIP-assisted bainitic–ferritic sheet steel 0.2C– 2Si–1.8Mn were investigated at different austempering temperatures for automotive applications. Increasing the austempering temperature was found to partially transform the uniform fine lath structure matrix and filmtype metastable retained austenite into blocky martensite or austenite. Guerra et al. [22] analyzed the effect of boron addition to an Austempered Ductile Iron, in amounts from zero to 120 ppm and is found that boron has a strong effect on the equivalent carbon content, resulting in an increase on the precipitated graphite volume and a decrease in the dissolved carbon content in the matrix. The increase in hardness and strength, typical Page | 62

International Journal of Advanced Engineering Research and Science (IJAERS) for the start of bainite formation, were not observed in the boron added irons, but just in the base alloy. A novel heat-treatment process, below-Ms austempering, was performed on two low-C high-Si/Al steels, and accordingly the resultant microstructures and mechanical properties were investigated and the results showed that bainitic transformation occurs at isothermal temperatures below Ms and unexpectedly, the transformation process is accelerated significantly by the prior formation of martensite [23].

In [24] an investigation was carried out to examine the influence of a novel two-step austempering process on the strain-hardening behavior of austempered ductile cast iron (ADI) in which test results show that this novel two-step process has resulted in improved microstructural variables in the ADI matrix, and higher hardness, yield strength and tensile strengths, but lower ductility and strain-hardening exponent values compared to the conventional single-step austempering process. Kilicil and Erdogan [ 25 ] studied, an unalloyed ductile iron containing 3.50 C wt.%, 2.63 Si wt.%, 0.318 Mn wt.%, and 0.047 Mg wt.% which was intercritically austenitized (partially austenitized) in twophase regions and results exhibited the best combination of high strength and ductility compared to the pearlitic grades, but their ductility is slightly lower than the ferritic grades. These materials also satisfy the requirements for the strength of the quenched and tempered grades and their ductility is superior to this grade. In [26] “disturbed” bainitic austempering process was employed in a Mn–Si– Cr–C low-alloyed steel to reduce the fraction and size of the blocky martensite/austenite (M/A) islands resulted in remarkable improvement in strain hardening capacity of the steel and hence leading to an excellent combination of strength and ductility. Yang and Patatunda [27] studied the influence of a novel two-step austempering process on the microstructure and the near threshold fatigue crack growth behavior of austempered ductile cast iron (ADI).

And tests results indicated this two-step austempering process’s capability on improvement of hardness, yield and tensile strengths for ADI but higher near threshold fatigue crack growth rate and lower fatigue threshold, as compared to the conventional single-step austempering process.

In [28] ductile iron specimens were applied to various austempering temperatures and interpreted fatigue properties. In this test, Denison 7615 fatigue machine was used for doing double sided bending stresses. The iron was austenitized at 900 °C and then austempered at 235, 300 and 370 °C for 2 h within a salt bath to obtain various austempered microstructures. Also, the fatigue properties of the bainitic structures which occurred by austempering are examined by scanning electron microscope. Jahangiri et al. [29] studied and evaluated the effects of www.ijaers.com

[Vol-3, Issue-2, Feb- 2016] ISSN: 2349-6495

austempering heat treatment on the microstructure, mechanical properties, and bending fatigue behavior of an alloyed ductile iron with chemical composition of 1.6 wt.% Ni, 0.47 wt.% manganese and 0.6 wt.% copper.

From the results of tensile and impact tests, as well as metallographic studies, optimum heat-treating cycles were determined and applied on the standard fatigue specimens. The results showed that the fatigue strength of specimens are considerably greater than those austempered at low temperatures compared to high temperatures. In [30] the rolling contact fatigue (RCF) behavior of PVD CrN and TiN coated ADI samples were studied. The effect of the substrate surface finishing method and coating material on RCF life along with deposition times were adjusted to obtain similar coating thicknesses in both coating materials is evaluated. The maximum contact pressure (p0) was set at 1000 and 1400 MPa. The results obtained indicate that the RCF tests performed at p0=1000 MPa cause no failures and while those performed at p0=1400 MPa cause failures in both uncoated and coated samples. Graphite nodules present on the substrate surface act as preferential sites for coating fracture and subsequent delamination and surface hardening produced by the abrasive cutting of grinding improves the RCF resistance of the uncoated and coated samples.

Aslantas et al. [31] studied the effect of austempering process on pitting formation in spur gears made of ductile iron. Gear test specimens were first austenitized in a salt bath at 900 °C for 90 min after which they were tempered in a salt bath at 250, 325, 375 and 425 °C for 60 and 90 min duration using FZG test machine. From the analysis it is concluded that austempering contributes to the increase of pitting formation life. Yang et al. [32] carried out an investigation to examine the influence of a novel two-step austempering process on microstructural parameters and the abrasion wear resistance of austempered ductile cast iron (ADI). An alloyed nodular ductile cast iron were initially austenitized by single-step austempering process to first batch and two-step austempering process to the second batch. The test results show that this two-step austempering process has resulted in significant improvement in microstructural parameters and has also resulted in significant improvement in abrasion wear resistance in ADI, compared to the conventional single-step austempering process.

Wanga et al. [33] investigated the extremely fine α singlephase nanocrystalline microstructure induced in the dry sliding friction surface layer of 9SiCr steel austempered at low temperature. It was found that the grains in the near surface layers coarsen linearly with increasing depth from the top surface. The retained austenite in the surface layer of the austempered sample was decomposed into α phase Page | 63

International Journal of Advanced Engineering Research and Science (IJAERS) owing to the action of the shear strain during the dry sliding friction. Batra et al. [34] investigated to examine the influence of structural and mechanical properties on wear behavior of austempered ductile iron (ADI) in which Ductile iron (DI) samples which were austenitized at 900 °C for 60 min and subsequently austempered for 60 min at three temperatures: 270, 330, and 380 °C. The structural parameters, volume fraction of austenite, carbon content of austenite, and ferrite particle size were determined using x-ray diffraction technique which showed improvement in the wear resistance through stress-induced martensitic transformation, and strain hardening of austenite [34]. In [35] and investigation was carried out on, a low-manganese nodular cast iron with a predominantly pearlitic as-cast structure was processed by a novel two-step austempering process. The effect of this two-step austempering heat treatment on the microstructure and mechanical properties of the material was examined and compared with the samples processed by conventional single step austempering process. Test results show a significant improvement in mechanical properties and fracture toughness of the material as a result of the two-step austempering process.

Also the work carried by Patatunda [36] out to examine the influence of austempering temperature on the microstructure and mechanical properties of a highcarbon (1.00%), high-silicon (3.00%) and highmanganese (2.00%) cast steel indicated that maximum fracture toughness is obtained in this steel when the microstructure contains very high austenitic carbon (XγCγ). In [37] the work was focused to characterize mainly fracture toughness as well as the other mechanical properties of austempered ductile iron produced using both single-step and two-step austempering processes and was found that two-step austempering process resulted in improving the fracture toughness of the material, while maintaining reasonable levels of strength. Alloyed samples showed higher fracture toughness than unalloyed ones. Also in [38] Austempered ductile iron (ADI) proved to be an excellent material as it possesses attractive properties: high strength, ductility and toughness are combined with good wear resistance and machinability. These properties can be achieved upon adequate heat treatment which yields optimum microstructure for a given chemical composition. In this paper an investigation has been conducted on ADI alloyed with 0.45%Cu and austempered in a range of times and temperatures.

Boronizing and austempering were successively applied to a GGG-40 grade ductile iron in order to combine the advantages of both process in a single treatment as shown in [39]. This new procedure formed a 30 μm thick boride layer on the surface with subsurface matrix structure www.ijaers.com

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consisted of acicular ferrite and retained austenite. The presence of retained austenite gives rise to deterioration of the wear resistance and fracture strength of Cr-Mo steels in many cases [40]. Thus, the effects of heat treatments including direct quenching, martempering, and austempering on the retained austenite existing in the microstructure of these steels were investigated [40]. The results showed that the lowest amount of retained austenite in the microstructure was obtained in the specimens quenched isothermally at 300 °C for 120 min.

In [41] the changes of enthalpy were observed to increase with decreasing temperature of the isothermal transformation during austempering and the results of the present work did not allow revealing the influence of alloying elements, i.e. Cu and Ni, on the heat of isothermal transformation.The effects of the mold preheating and the silicon content of ductile iron on the percentage of carbides, graphite nodule counts and shrinkage volume were investigated by Jafara and Behnamb [42] and the results showed that the percentage of carbides and the shrinkage volume decreased when the mold preheating increased. In [43] an in-depth study and description of cavitation damage and microstructural changes in two types of unalloyed austempered ductile iron (ADI) is carried out. The results proved that the microcracking and ferrite/retained austenite morphology were proved to be of great importance for cavitation resistance. The kinetics of reaction occurring during the austempering treatment of ductile iron (DI) containing different additions of Cu and Ni was investigated in [44].

The outcome of this work indicates that during the first stage of austempering, nucleation of the ferrite plates occurs via a diffusionless mechanism while their growth is diffusion controlled.

Investigation on a comprehensive study was carried out to examine both the thermal and mechanical stability of austenite in the upper and lower austempering (or bainitic) temperature ranges [45] in which test results also showed that cryogenic treatment can improve the mechanical properties without compromising the fracture resistance of the ADI. In [46] ductile iron with austeniticferritic matrix (ADI), due to the specific heat treatment, showed an advantageous combination of engineering properties. The superior wear resistance and strength-toweight ratio, together with high stress resistance and good ductility, make such material suitable for cost- and weight-efficient automotive structural applications.

This article attempts a reasonably comprehensive review of representative journal publications covering improvements in mechanical properties of ADI over conventional materials used for structural applications.

Most of the articles have appeared since 2000, and many Page | 64

International Journal of Advanced Engineering Research and Science (IJAERS) involve the mechanical properties improvement using stepped austempering processes.

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[12] Mahmoud Hafiz,”Mechanical properties of SG-iron subjected to variable and isothermal austempering temperatures heat treatment”, Materials Science and Engineering: A, Volume 340, Issues 1–2, 15 January 2003, Pages 1–7.

[13] Jianghuai Yang, Susil K. Putatunda,” Improvement in strength and toughness of austempered ductile cast iron by a novel two-step austempering process”, Materials & Design, Volume 25, Issue 3, May 2004, Pages 219–230. www.ijaers.com

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[14] Ali Bayrama, Yahya Isikb, Baris Salara,” The effects of austempering temperature and time onto the machinability of austempered ductile iron”, Materials Science and Engineering, Volume 407, Issues 1–2, 25 October 2005, Pages 147–153.

[15] Yoon-Jun Kim, , Hocheol Shin, Hyounsoo Park, Jong Dae Lim,” Investigation into mechanical properties of austempered ductile cast iron (ADI) in accordance with austempering temperature”, Materials Letters, Volume 62, Issue 3, 15 February 2008, Pages 357– 360.

[16] Susil K. Putatundaa, ,Codrick Martisa, James Boileaub,” Influence of austempering temperature on the mechanical properties of a low carbon low alloy steel”, Materials Science and Engineering, Volume 528, Issue 15, 15 June 2011, Pages 5053–5059.

[17] J.L. Hernández-Rivera, R.E. Campos Cambranis, A. de la Garza,” Study of microstructural evolution and mechanical properties exhibited by non alloyed ductile iron during conventional and stepped austempering heat treatment”, Materials & Design, Volume 32, Issue 10, December 2011, Pages 4756– 4762.

[18] Dierk Raabea, Puck-Pa Choia, Yung-Rok Imb, ChanGyung Parkc,” Atomic scale effects of alloying, partitioning, solute drag and austempering on the mechanical properties of high-carbon bainitic– austenitic TRIP steels”, Acta Materialia, Volume 60, Issue 17, October 2012, Pages 6183–6199.

[19] Durbadal Mandal , M. Ghosh, J. Pal, S. Ghosh Chowdhury, G. Das, S.K. Das, Sukomal Ghosh,” Evolution of microstructure and mechanical properties under different austempering holding time of cast Fe–1.5Si–1.5Mn–V steels”, Materials & Design, Volume 54, February 2014, Pages 831–837.

[20] Z.J. Xiea, Y.Q. Rena, W.H. Zhoua, J.R. Yangb, C.J. Shanga, , , R.D.K. Misrac,” Stability of retained austenite in multi-phase microstructure during austempering and its effect on the ductility of a low carbon steel”, Materials Science and Engineering, Volume 603, 6 May 2014, Pages 69–75.

[21] Z.Z. Zhaoa, H.X. Yina, A.M. Zhaoa, Z.Q. Gongc, J.G. Hea, T.T. Tonga, b, H.J. Hua, ” The influence of the austempering temperature on the transformation behavior and properties of ultra-high-strength TRIPaided bainitic–ferritic sheet steel,” Materials Science and Engineering, Volume 613, 8 September 2014, Pages 8–16.

[22] F.V. Guerra La, A. Bedolla-Jacuindea,I. Mejíaa, J. Zunob, C. Maldonadoa,” Effects of boron addition and austempering time on microstructure, hardness and tensile properties of ductile irons”, Materials Page | 65

International Journal of Advanced Engineering Research and Science (IJAERS) Science and Engineering, Volume 648, 11 November 2015, Pages 193–201.

[23] Leijie Zhaoa, Lihe Qiana, Jiangying Menga, Qian Zhoua,Fucheng Zhanga, b,” Below-Ms austempering to obtain refined bainitic structure and enhanced mechanical properties in low-C high-Si/Al steels”, Scripta Materialia, Volume 112, February 2016, Pages 96–100.

[24] Jianghuai Yang, Susil K. Putatunda,” Influence of a novel two-step austempering process on the strainhardening behavior of austempered ductile cast iron (ADI),” Materials Science and Engineering: A, Volume 382, Issues 1–2, 25 September 2004, Pages 265–279.

[25] Volkan Kilicli, Mehmet Erdogan,” The StrainHardening Behavior of Partially Austenitized and the Austempered Ductile Irons with Dual Matrix Structures”, Journal of Materials Engineering and Performance, April 2008, Volume 17, Issue 2, pp 240-249.

[26] Guhui Gaoa, Han Zhanga, Xiaolu Guia, Zhunli Tana, Bingzhe Baia, Yuqing Wenga,” Enhanced strain hardening capacity in a lean alloy steel treated by a “disturbed” bainitic austempering process”, Acta Materialia, Volume 101, December 2015, Pages 31– 39.

[27] Jianghuai Yang, Susil K. Putatunda,” Near threshold fatigue crack growth behavior of austempered ductile cast iron (ADI) processed by a novel two-step austempering process”, Materials Science and Engineering: A, Volume 393, Issues 1–2, 25 February 2005, Pages 254–268.

[28] S. Salmana, F. Fındıkb, P. Topuzc,” Effects of various austempering temperatures on fatigue properties in ductile iron”, Materials & Design, Volume 28, Issue 7, 2007, Pages 2210–2214.

[29] M. R. Jahangiri, M. Nili Ahmadabadi, H. Farhangi,” Enhancement of Fatigue Properties of Ductile Irons

by Successive Austempering Heat Treatment”, Journal of Materials Engineering and Performance, December 2011, Volume 20, Issue 9, pp 1642-1647.

[30] Diego Alejandro Colomboa, María Dolores Echeverríaa, Sebastián Lainob, Ricardo Cesar Dommarcob, Juan Miguel Massoneb,” Rolling contact fatigue resistance of PVD CrN and TiN coated austempered ductile iron”, Wear, Volume 308, Issues 1–2, 30 November 2013, Pages 35–45.

[31] K. Aslantaş, , S. Taşgetiren, Y. Yalçın,” Austempering retards pitting failure in ductile iron spur gears”, Engineering Failure Analysis, Volume 11, Issue 6, December 2004, Pages 935–941.

[32] Jianghuai Yang1, Susil K. Putatunda,” Effect of microstructure on abrasion wear behavior of www.ijaers.com

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austempered ductile cast iron (ADI) processed by a novel two-step austempering process”, Materials Science and Engineering: A, Volume 406, Issues 1– 2, 15 October 2005, Pages 217–228.

[33] T.S. Wanga, J. Yanga, C.J. Shangb, X.Y. Lia, B. Lva, M. Zhanga, F.C. Zhanga,” Sliding friction surface microstructure and wear resistance of 9SiCr steel with low-temperature austempering treatment”, Surface and Coatings Technology, Volume 202, Issue 16, 15 May 2008, Pages 4036–4040.

[34] Uma Batra , Nimish Batra, J. D. Sharma,” Wear Performance of Cu-Alloyed Austempered Ductile Iron”, Journal of Materials Engineering and Performance, April 2013, Volume 22, Issue 4, pp 1136-1142.

[35] Susil K. Putatunda,”Development of austempered ductile cast iron (ADI) with simultaneous high yield strength and fracture toughness by a novel two-step austempering process”, Materials Science and Engineering: A, Volume 315, Issues 1–2, 30 September 2001, Pages 70–80.

[36] Susil K. Putatunda,”Influence of austempering temperature on microstructure and fracture toughness of a high-carbon, high-silicon and high-manganese cast steel”, Materials & Design, Volume 24, Issue 6, September 2003, Pages 435–443.

[37] Ayman H. Elsayeda, M.M. Megahedc, A.A. Sadekd, K.M. Abouelelae,” Fracture toughness characterization of austempered ductile iron produced using both conventional and two-step austempering processes”, Materials & Design, Volume 30, Issue 6, June 2009, Pages 1866–1877.

[38] Olivera Erića, Milan Jovanovića, Leposava Šid¯ aninb, Dragan Rajnovićb, Slavica Zeca,” The austempering study of alloyed ductile iron”, Materials & Design, Volume 27, Issue 7, 2006, Pages 617–622.

[39] Baydogan Murat , Seckin Izzet Akray,” Successive Boronizing and Austempering for GGG-40 Grade Ductile Iron”, Journal of Iron and Steel Research, International, Volume 16, Issue 2, March 2009, Pages 50–54.

[40] MH Shaeri , H Saghafian, SG Shabestari,” Effects of Austempering and Martempering Processes on Amount of Retained Austenite in Cr-Mo Steels (FMU-226) Used in Mill Liner”, Journal of Iron and Steel Research, International, Volume 17, Issue 2, February 2010, Pages 53–58.

[41] Gazda,” Determination of thermal effects accompanying the austempering of copper–nickel ductile iron”, Thermochimica Acta, Volume 499, Issues 1–2, 20 February 2010, Pages 144–148.

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[42] Khalil-Allafi Jafara, Amin-Ahmadi Behnamb,” Influence of Mold Preheating and Silicon Content on Microstructure and Casting Properties of Ductile Iron in Permanent Mold”, Journal of Iron and Steel Research, International, Volume 18, Issue 3, March 2011, Pages 34–39.

[43] Marina Dojcinovica, Olivera Ericb, Dragan Rajnovicc, Leposava Sidjaninc, Sebastian Balosc,” Effect of austempering temperature on cavitation behaviour of unalloyed ADI material”, Materials Characterization, Volume 82, August 2013, Pages 66–72.

[44] Marcin Górny , Edward Tyrała, Hugo Lopez,” Effect of Copper and Nickel on the Transformation Kinetics of Austempered Ductile Iron”, Journal of Materials Engineering and Performance, October 2014, Volume 23, Issue 10, pp 3505-3510.

[45] Saranya Panneerselvama, Codrick J. Martisa, Susil K. Putatundaa, , , James M. Boileaub,” An investigation on the stability of austenite in Austempered Ductile Cast Iron (ADI),” Materials Science and Engineering, Volume 626, 25 February 2015, Pages 237–246.

[46] Paolo C. Priarone, Matteo Robiglio, Luca Settineri ,” Milling of Austempered Ductile Iron (ADI) with recycled carbide tools”, Milling of Austempered Ductile Iron (ADI) with recycled carbide tools, pp 17.

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