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

Abstract

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.

Microstructural Characteristics, Mechanical and Wear Behaviour of Aluminium-Alloyed Ductile Irons Subjected to Two Austempering Processes

“…This is because the finer grains of ausferrite are obtained by nucleation and growth. In the present case, the large super-cooling at a lower temperature (260°C) facilitates more nuclei formation and/or partial transformation, after which the austempering at a higher temperature (400°C), ensures the growth and completion of the transformation [32]. Thus, boundary strengthening and phase hardening (ausferrite) are the operational micro-mechanisms that are responsible for the improved hardness.…”

“…The inhomogeneity that characterized the ausferrite morphology may be due to the micro-segregation effect in the ferrite and retained austenite comprising the ausferrite. It could also be due to an incomplete reaction in the entire austenite which remains untransformed in the microstructure [31][32][33]. For most of the compositions, the results of the image analysis used to estimate the volume fractions of the phases revealed that the single step austempering process yielded slightly higher ausferrite content compared with the two step austempering process.…”

Archives of Foundry Engineering

“…It has also been found that the new material based on bentonite-modified polyethylene wax reduces casting shrinkage and slightly increases viscosity, which is therefore excellent for lost-wax casting. After the casting process, quality control is essential, especially when new casting methods [18][19][20][21] or new materials are introduced, such as in the case of casting patterns made of composites based on polyethylene-ceramic waxes. Destructive and non-destructive research techniques are used to analyse the surface quality of castings, internal defects, shape or continuity of the structure.…”