OPTIMIZATION OF ISOTHERMAL TRANSFORMATION PERIOD FOR AUSTEMPERED DUCTILE IRON
DOI:
https://doi.org/10.7494/mafe.2017.43.4.313Keywords:
ADI, stabilized austenite, process window, EBSD, austemperingAbstract
The present paper examines and compares the influence of austempering parameters such as temperature and time on the isothermal transformation and microstructural changes of ductile iron. To identify the compositional and structural changes during an isothermal transformation, a very wide austempering period is chosen at a transformation temperature for the precise determination of the process window. XRD, optical, and scanning electron microscopic techniques are exploited to identify and analyze the changes in the austempered structure, at austempering temperatures of 250°C and 400°C. The various structural parameters like austenite volume fraction (Vg, its carbon content (Cg), lattice parameter, and the average cell size of the ferrite are ascertained. Electron backscattered diffraction (EBSD) analysis is used to identify the carbide precipitation obtained due to the austempering Stage-II reaction. It is noticed that, at the end of the austempering Stage-II reaction, there is a significant reduction in the volume fraction of stabilized austenite and it’s carbon content, as the microstructure at this stage not only contains ausferrite but also additional precipitated iron carbides. With an increase in austempering time, the austenite and ferrite volume fraction increase until the austenite becomes stabilized with sufficient carbon. The increase in the lattice parameter of the austenite during austempering corresponds to the rise in carbon content within the austenite. A rise in the austempering temperature leads to a reduction in the volume fraction of the ferrite and an increase in the stabilized austenite volume fraction. The optimum isothermal transformation period for austempered ductile iron is established, based on the period during which the maximum content of the austenite volume fraction, its carbon, the lattice parameter, and the average cell size of the ferrite are maintained.
Downloads
References
Ductile Iron Data for Designing Engineer. Rio Tinto Iron & Titanium Inc., Montreal 1990
Metzioff K.E., Fang L.Y., Loper C.R.: AFS Transactions, 47 (1995), 103–112
Voigt R.C., Loper C.R.: Austempered ductile iron – process control and quality assurance. Proceedings of the 1st International Conference on Austempered Ductile Iron, ASM, (1984), 83–90
Janowak J.F., Gundlach R.B.: Development of a ductile iron for commercial austempering. Transactions AFS, 86 (1983), 377–386
Vĕchet S., Kohout J., Bokůvka O.: Fatigue properties of nodular cast iron. Únavové vlastnosti tvárné litany, Zilinska univerzita, Zilina 2002
Rouns T.N., Rundman K.B.: Constitution of austempered ductile iron and the kinetics of austempering. AFS Transactions, 95 (1987), 851–874
Tanaka Y., Kage H.: J. Development and Application of Austempered Spheroidal Graphite Cast Iron. Materials Transactions, 33, 6 (1992), 543–557
Parhad P., Likhite A., Bhatt J., Peshwe D.: The Effect of Cutting Speed and Depth of Cut on Surface Roughness During Machining of Austempered Ductile Iron. Transactions of the Indian Institute of Metals, 68, 1 (2015), 99–108
Senczyk D.: Laboratorium z rentgenografii structuralnej. Politechnika Poznańska, Poznań 1974
Aranzabal J., Gutierrez I., Rodriguez-Ibabe J.M., Urcola J.J.: Influence of the Amount and Morphology of Retained Austenite on the Mechanical Properties of an Austempered Ductile Iron. Metallurgical and Materials Transactions A, (1997), 1143–1156
Cullity B.D.: Elements of X-Ray Diffraction. Addison–Wesley Publishing Company, Reading, MA, USA 1956.
Keough J.R.: An ADI Market Primer. Foundry Management and Technology, 123, 11 (1995), 28–31
Seshan S.: ADI – the under-exploited wonder cast iron. Transaction of Indian Foundryman, National
Seminar, SG-50. Golden Jubilee Celebration, 84–92 (1998)
Fuller A.G.: Effects of Graphite Form on Fatigue Properties of Pearlitic Ductile Irons. AFS Transactions, 77–102A (1997), 527–538
Navara E., Zimba J.: Ausferritic Ferrous Alloys – a Challenge to Industry and Research. Acta Metallurgica Slovaca, 10, 1 (2004), 244–252
Christian J.W.: The Theory of Transformations in Metals and Alloys. Pergamon Press, Oxford – New York 1965, 778–786
Bhadeshia H.K.D.H.: Bainite in steels: transformations, microstructure and properties. Institute of Materials, London 1992
Takahashi M., Bhadeshia H.K.D.H.: A Model for the Microstructure of Some Advanced Bainitic Steels. Materials Transaction of the Japan Institute of Metals, 32 (1991), 689–696
Thomson R.C., James J.S., Putman D.C.: Modelling microstructural evolution and mechanical properties of austempered ductile iron. Materials Science and Technology, 16, 11–12 (2000), 1412–1419
Ductile Iron Society: Ductile Iron Data for Design Engineers. http://www.ductile.org/didata/pdf/didata2.pdf, 9
Durhamfoundary, austempered ductile iron castings. http://www.durhamfoundry.com/austempered_ductile_iron.htm
Polishetty A.: Machinability and microstructural studies on phase transformations in Austempered Ductile Iron. A thesis submitted to Auckland University of Technology, Aucland 2011
