Abstract Studies have been conducted on the effect of overstressing in rotary bending fatigue on the fatigue properties of an annealed and austempered ductile iron containing 1.5 Ni–0.3 Mo. For various R ratios S–N curves were determined and the fatigue limit estimated. It was found that the fatigue limit was a function of the level of overstressing and cycle ratio. In the case of austempered samples a beneficial effect of overstressing was observed at a certain level of overstressing. This was related to the work hardening behaviour of the austenite phase. In annealed samples, a reduction in the fatigue limit was observed at all levels of overstressing. Copyright © 1995, Wiley Blackwell. All rights reserved
(EFFECT OF OVERSTRESSING ON FATIGUE BEHAVIOUR OF AUSTEMPERED DUCTILE IRON) Prasad Rao, P.; Padmaprabha
1995
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.
1994
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.
(Inst of Engineers (India), Low stress dry sand abrasive wear behaviour of austempered ductile iron) Prasad Rao, P.
1995
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.
(Minerals, Metals and Materials Society, Dependence of Fracture Toughness of Austempered Ductile Iron on Austempering Temperature) Prasad Rao, P.; Putatunda, S.K.
1998

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