Faculty Publications
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Item Effect of Austempering Heat Treatment Parameters on the Microstructure and Dry Sliding Wear Behaviour of AISI 9255 High Silicon Steel(Elsevier Ltd, 2017) Acharya, P.A.; Syamkrishna, P.; Ravishankar, K.S.The present investigation is focused to evaluate the dry sliding wear behavior of AISI 9255 high silicon steel austempered at different temperatures and durations. Here three batches of cylindrical test specimens were prepared from as-received high silicon steel and were austenitized at 900 °C for 30 minutes, followed by austempering heat treatment in a salt bath maintained at temperatures 300, 350 and 400 oC for durations between 1 to 4 hours. The samples after austempering were cooled to room temperature in open air. The microstructural analysis was done by using optical microscopy, scanning electron microscopy and x-ray diffraction (XRD) and also hardness test was done using micro vickers hardness tester and correlated to the specific wear rate of the austempered steel. Results indicate that specific wear rate decreases with increase in austempering time and increases with increasing temperature. Specific wear rate was found to be lowest at austempering temperature of 300 °C, which exhibits lower ausferritic structure having high hardness. At higher austempering temperature 400 °C, specific wear rate was observed to be high because of upper ausferritic microstructure having lower hardness. Results reveal that the material with high hardness shows high wear resistance i.e., the one austempered at 300 °C showed superior sliding wear resistance than the rest. © 2017 Elsevier Ltd.Item Workability Study on Austempered AISI 1018(Institute of Physics Publishing helen.craven@iop.org, 2018) Nagendhra, S.; Rami Reddy, A.S.; Preetham Kumar, G.V.Workability of a material is a complex technological concept that is related to both material and process characteristics. Austempering is a heat treatment process that is applied to ferrous metals, mostly steel and ductile iron. The present work was carried out to study the workability and the properties of AISI 1018 steel in austempering and annealing condition and then comparing with each other. Workability testing was carried out using collar type specimen by compressing it till the crack. Workability diagrams have been plotted as a function of axial and hoop strains at failure. The result shows that, the austempering process increases the tensile strength and hardness as well as the workability. Thus the austempering process has an effect on strength and hardness. © Published under licence by IOP Publishing Ltd.Item Rotating bending fatigue tests were carried out on austempered ductile iron containing 1.5 wt% nickel and 0.3 wt% molybdenum. The ductile iron was austenitized at 900 or 1050 °C and then austempered at 280 or 400 °C for different lengths of time to obtain different microstructures. The fatigue strength was correlated with the amount of retained austenite and its carbon content, which were both determined by X-ray diffraction technique. While the tensile strength decreased with increasing retained austenite content, the fatigue strength was found to increase. Carbide precipitation was found to be detrimental to fatigue strength. Lower austenitizing temperature resulted in better fatigue strength. © 1994 Chapman & Hall.(Kluwer Academic Publishers, Effect of microstructure on the fatigue strength of an austempered ductile iron) Shanmugam, P.; Prasad Rao, P.; Rajendra Udupa, K.; Venkataraman, N.1994Item Ductile cast iron was austenitized at four different temperatures and subsequently austempered at six different temperatures. Plane strain fracture toughness was evaluated under all the heat treatment conditions and correlated with the microstructural features such as the austenite content and the carbon content of the austenite. Fracture mechanism was studied by scanning electron microscopy. It was found that the optimum austempering temperature for maximum fracture toughness decreased with increasing austenitizing temperature. This could be interpreted in terms of the microstructural features. A study of the fracture mechanism revealed that good fracture toughness is unlikely to be obtained when austempering temperature is less than half of the austenitizing temperature on the absolute scale. © 2002 Elsevier Science B.V. All rights reserved.(Elsevier BV, Investigations on the fracture toughness of austempered ductile irons austenitized at different temperatures) Prasad Rao, R.; Putatunda, S.K.2003Item Influence of austenitising temperature on the formation of strain induced martensite in austempered ductile iron(2008) Daber, S.; Ravishankar, K.S.; Prasad Rao, P.P.The present work was taken up to study the influence of austenitising temperature on the formation of strain-induced martensite in austempered ductile iron. Ductile iron containing 1.5 wt.% nickel, 0.3 wt.% molybdenum and 0.5 wt.% copper was subjected to austempering treatments which consisted of three austenitising temperatures, namely 850, 900 and 950 °C, and three austempering temperatures, namely 300, 350 and 400 °C. Tensile tests were carried out under all the heat-treatment conditions and strain-hardening behaviour was studied by applying Hollomon equation. Microstructures were studied by optical microscopy and X-ray diffraction. It was found that increasing austenitising temperature increased the tendency for the formation of strain-induced martensite at all the austempering temperatures. © 2008 Springer Science+Business Media, LLC.Item Study of wear behaviour of ductile iron subjected to two step austempering(2010) Kumari, R.; Prasad Rao, P.P.An investigation was carried out to examine the influence of two step austempering on microstructural parameters and the wear behaviour of austempered ductile iron. Ductile iron was austenitised at 900 °C for 30 min, and then austempered successively at two different temperatures. It was first austempered at 300 °C for different durations from 2 min to 30 min and subsequently austempered at 400°C for 2 h, after which it was quenched to room temperature. Resulting microstructures were characterised through optical microscopy and X-ray diffraction. Mechanical properties were studied through hardness measurement and tensile testing. Wear studies were carried out using a pin-on-disc machine. Wear rate was found to decrease with increasing time at the first step temperature of 300 °C. At short austempering times at 300 °C, the amount of austenite was instrumental in improving the wear resistance through formation of deformation induced martensite. Wear rate was found to depend on yield strength, austenite content and its carbon content. © Carl Hanser Verlag GmbH & Co. KG.Item Improvement in fracture toughness of austempered ductile iron by two-step austempering process(2010) Ravishankar, K.S.; Prasad Rao, P.P.; Udupa, K.R.Ductile cast iron samples were austenitised at 900°C and subjected to two types of austempering called as conventional austempering and two-step austempering. Five different temperatures, 280, 300, 320, 350, 380 and 400°C, with an austempering time of 2 h, were chosen for conventional austempering. For two-step austempering process, the first step temperatures were 280, 300 and 320°C. The samples were austempered at each of these temperatures for different times, i.e. 10, 20, 30, 45 and 60 min, and then upquenched to higher temperature of 400°C for 2 h. Fracture toughness and tensile studies were carried out under all these austempering conditions. During conventional austempering, the fracture toughness initially increased with increasing austempering temperature, reached a peak value of 63 MPa m 1/2 and dropped with further increase in temperature. During the two-step austempering, fracture toughness was found to increase with increasing first step time. The curve shifted to higher values of fracture toughness as the first step temperature was decreased and the maximum value of 78 MPa m 1/2 was obtained. The results of the fracture toughness study and the fractographic examination were correlated with microstructural features such as bainitic morphology, the volume fraction of retained austenite, and its carbon content. Ferrite lath size and stability of the retained austenite were found to influence the fracture toughness. © 2010 W. S. Maney & Son Ltd.Item Effect of heat treatment on properties of sinter forged Fe-Cu-C-Cr steel(Zibeline International Publishing Sdn. Bhd., 2019) Kulkarni, V.R.; Nayak, J.; Dabhade, V.V.Powder metallurgy is industrially well appreciated manufacturing technique. Many components are now manufactured by powder metallurgical route than conventional manufacturing techniques. It is customary for wrought steels to compare the properties of alloy in austempered condition with that in hardened and tempered condition. However limited data is available for austempered powder metallurgical components. In this work sinter forging technique is used to prepare samples from metal powders and subjected to austempering as well as conventional hardening and tempering heat treatments. Effect of these heat treatments on the microstructure, hardness and wear properties of Fe-2Cu-0.7C-2Cr sinter forged alloy are studied. From the results it is concluded that though hardness in hardened and tempered condition is lower (26 HRc) than that of austempered condition (39 HRc) its wear performance is better. © 2019 Rockefeller University Press. All rights reserved.