1. Journal Articles
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Item Low stress dry sand abrasive wear behaviour of austempered ductile iron(1995) Prasad, Rao, P.Austempered ductile iron containing 0.9 Ni and 0.3 Mo and subject to low stress dry sand abrasive testing shows that wear behaviour is very sensitive to heat treatment conditions. It is concluded that large retained austenite content promotes wear resistance.Item Investigations on the fracture toughness of austempered ductile iron alloyed with chromium(2003) Prasad, Rao, P.; Putatunda, S.K.An investigation was carried out to examine the influence of chromium content on the plane strain fracture toughness of austempered ductile iron (ADI). ADIs containing 0, 0.3 and 0.5 wt.% chromium were austempered over a range of temperatures to produce different microstructures. The microstructures were characterized by optical microscopy and X-ray diffraction. Plane strain fracture toughness of all these materials was determined and correlated with microstructure and chromium content. The chromium content was found to influence the fracture toughness through its influence on the processing window. Since the chromium addition shifts the processing window to shorter durations, the higher chromium alloys at higher austempering temperatures tend to fall outside of the processing window, resulting in less than optimum microstructure and inferior fracture toughness. A small chromium addition of 0.3 wt.% was found to be beneficial for the fracture toughness of ADI. 2002 Elsevier Science B.V. All rights reserved.Item Influence of austenitising temperature on the formation of strain induced martensite in austempered ductile iron(2008) Daber, S.; Ravishankar, K.S.; Prasad, Rao, 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 Hardening mechanism in spinodal CuNiCr alloys(1987) Prasad, Rao, P.; Agrawal, B.K.; Rao, A.M.Spinodal decomposition in two CuNiCr alloys has been investigated. The variations in strain amplitude, wavelength of composition modulation and yield stress increment were studied with aging time. It was found that the variation in yield stress increment with aging time followed monotonically the variations in strain amplitude and wavelength of composition modulation. It was concluded that theories which relate amplitude to yeild stress best explain the strengthening mechanism. Experimental values were found to correlate well with the theory of Kato, Mori and Schwartz. 1987.Item Formation of strain-induced martensite in austempered ductile iron(2008) Daber, S.; Prasad, Rao, P.The present work has been taken up to study the influence of microstructure on the formation of martensite in austempered ductile iron. Ductile iron containing 1.5 wt.% nickel and 0.3 wt.% molybdenum was subjected to two types of austempering treatments. In the first, called as conventional austempering, the samples were austempered for 2 h at 300, 350 or 400 C. In the second treatment, called as stepped austempering, the samples were initially austempered at 300 C for 10, 20, 30, 45 or 60 min. These were subsequently austempered for 2 h at 400 C. Tensile tests revealed considerable variation in the strain-hardening behaviour of the samples with different heat treatments. In the case of samples subjected to conventional austempering, it was found that strain-hardening exponent increased with increasing austempering temperature. In the case of samples subjected to stepped austempering, increased strain hardening was observed in samples subjected to short periods of first step austempering. Study of the microstructures revealed that increased strain hardening was associated with the formation of strain-induced martensite. There was a greater propensity for the formation of strain-induced martensite in the samples containing more of blocky austenite. Retained austenite in the form of fine films between sheaths of ferrite was relatively more stable. Studies revealed that the morphology, size and carbon content of the retained austenite were important parameters controlling their tendency to transform to martensite. 2007 Springer Science+Business Media, LLC.Item Flow stress - grain size relationship in aluminum(1975) Shiroor, V.S.; Kulkarni, A.G.; Prasad, Rao, P.; Parameswaran, V.R.[No abstract available]Item Effect of thermomechanical treatment on the phase transformation in Cu-44Ni-5Cr alloy(1994) Raghavendra, Bhat, R.; Prasad, Rao, P.Cu-44Ni-5Cr alloy has been subjected to thermomechanical treatment which consisted of plastic deformation of as-quenched material by 50, 65 and 80% reduction in thickness followed by ageing in the interval of 500 to 650 C for various durations of time. Progress in age-hardening was studied by means of hardness measurement and X-ray diffraction studies. The wavelength of composition modulation and strain amplitude were measured. It was found that age-hardening was a result of interaction between spinodal decomposition and recovery processes. Prior deformation was found to enhance the kinetics of both spinodal decomposition and coarsening. It was concluded that this resulted from increased vacancy concentration and increased coherency strain in the cold-worked material. 1994 Chapman & Hall.Item Effect of temperature and strain rate on tensile behaviour of M250 maraging steel(1996) Venkatanarayana, G.; Arumugham, S.; Lakshmanan, T.S.; Prasad, Rao, P.The effect of temperature and strain rate on the 0-2% yield strength, ultimate tensile strength, and percentage elongation of M250 maraging steel was investigated under uniaxial tensile conditions in the temperature range from 25 (room temperature) to 550 C and strain rate range 10-4-10-1 s-1. Up to 400 C the steel shows essentially strain rate insensitive behaviour with a gradual decrease in the 0-2% yield strength and ultimate tensile strength. The elongation remains constant at all strain rates up to 300 C. Fractographic analysis indicates that the increasing strain rate induces strain constraint resulting in an increased dimple size. An elongated structure was observed at temperatures above 400 C. X-ray diffraction reveals the presence of reverted austenite in the specimens tested at 550 C. 1996 The Institute of Materials.Item Dependence of Fracture Toughness of Austempered Ductile Iron on Austempering Temperature(1998) Prasad, Rao, P.; Putatunda, S.K.Ductile cast iron samples were austenitized at 927 C and subsequently austempered for 30 minutes, 1 hour, and 2 hours at 260 C, 288 C, 316 C, 343 C, 371 C, and 399 C. These were subjected to a plane strain fracture toughness test. Fracture toughness was found to initially increase with austempering temperature, reach a maximum, and then decrease with further rise in temperature. The results of the fracture toughness study and fractographic examination were correlated with microstructural features such as bainite morphology, the volume fraction of retained austenite, and its carbon content. It was found that fracture toughness was maximized when the microstructure consisted of lower bainite with about 30 vol pet retained austenite containing more than 1.8 wt pet carbon. A theoretical model was developed, which could explain the observed variation in fracture toughness with austempering temperature in terms of microstructural features such as the width of the ferrite blades and retained austenite content. A plot of KIC2 against ?? (X?C?)1/2 resulted in a straight line, as predicted by the model.Item Effect of microstructure on the fatigue strength of an austempered ductile iron(1994) Shanmugam, P.; Prasad, Rao, P.; Rajendra, Udupa, K.; Venkataraman, N.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.