The Comparative Study of the Microstructure and Phase Composition of Nanoausferritic Ductile Iron Alloy Using SEM, TEM, Magnetometer, and X-Ray Diffraction Methods

In this paper the microstructure and phase composition of ausferritic ductile iron alloy were investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction methods. In order to obtain the nanoausferritic microstructure in the alloy, the austempering heat treatment was performed at relatively low temperature. As a result, a specific kind of microstructure, containing nanocrystalline ausferrite and retained austenite blocks, was obtained in each heat-treated sample. The volume fractions of phases were determined using different methods: MicroMeter software for scanning electron micrographs, stereological analysis for transmission electron micrographs, quantitative analysis of the X-ray diffraction spectra and magnetometer measurements. All methods revealed a high amount of retained austenite which varied as a function of the austempering treatment parameters. It was shown that the quantitative phase composition measured by X-ray diffraction and magnetometer, in all samples investigated, differs significantly from the stereological measurements and image analysis performed through the MicroMeter software. The possible reasons of the observed differences were discussed.