engleski

MICROSTRUCTURE TRANSFORMATIONS DURING AUSTEMPERING OF Ni; Mo; Cu-ALLOYED DUCTILE IRON

Studies have been conducted on ductile iron alloyed with 0.85% Ni, 0.51% Cu and 0.389% Mo and austempered at 380 °C using a range of austempering times from 15 to 360 minutes, The microstructural cunstituens developed during solidificationand throughout this range of time were identified. Microstructure examination was carried out by an optical and scanning electronic microscope. X-ray diffraction and C0Ka radiation was used to determine the kind of precipitated carbide and volume fraction of retained austenite. Volume fraction of the untransformed or parent austenite (UAV), nodule account and graphite amount were made by the LECO 2001 image analysis system. The mechanism and kinetics of austempering reactions as well as factors which influence the phase transformations were determined. Besides the microstructure inhomogenity, eutectic carbides and microviods the presence of Hagg's carbide, Fe2.5C, unordered Fe2C-L'32 and ordered Fe2C carbide in the initial stage of reaction were also confirmed.

microstructure transformations; austempered ductile iron

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