Mechanisms on Superfine Alumina Inclusions Formation by Al‐Deoxidation Reaction for liquid Iron

Abstract

In order to investigate the formation mechanism of alumina particles in early stages of Al-deoxidation reaction, the samples are prepared by Al-deoxidation for Fe-O (90 ppm) melt in confocal laser scanning microscope (CLSM). The shapes of alumina inclusions are irregular in various samples, and their equivalent radius is between 15 and 150 nm based on the observation of field emission scanning electron microscope (FESEM) with energy dispersive spectrometer (EDS). The size and number density of alumina inclusions increase with the increase of temperature of deoxidation while decrease with the increase of cooling rate. Based on the EDS results and Fe-Al phase diagram, it is found that the Al-deoxidation reaction zone is mainly composed of the FeAl, Fe 2 Al 5 , and FeAl 3 phase. The average size of alumina particles in the FeAl phase are larger than that of in the Fe 2 Al 5 phase. Alumina particle is not observed in the FeAl 3 phase by FESEM. The observation and estimation based on the growth mechanisms of inclusions indicate that the growth of nanoscale alumina with large size is controlled by the diffusion growth and Brownian collision in high temperature melt, while nanoscale alumina with small size are secondary precipitate phase in the process of solidification.

Thermodynamic Modelling on Nanoscale Growth of Magnesia Inclusion in Fe-O-Mg Melt

“…Firstly, the deoxidizers react with dissolved oxygen in molten steel to form various metastable structures, and then the metastable structures transform into stable crystal. This fact has been proved by several experiments [49,50]. Wasai et al [49] found a series of nanoscale alumina and silica in Al-deoxidation experiments by ultra-rapid cooling methods.…”

“…Wasai et al [49] found a series of nanoscale alumina and silica in Al-deoxidation experiments by ultra-rapid cooling methods. Zhao et al [50] found some nanoscale alumina in Al-deoxidation experiments by the same method. Therefore, the metastable magnesia forms at first in the process of Mg-deoxidation.…”

Thermodynamic insight into the growth of calcia inclusions at the nanoscale: the case of Fe–O–Ca melt

“…Wang et al 22,38,39 reported that the deoxidation thermodynamics in liquid iron have a close relationship with the structures and properties of deoxidaiton products, and suggested that the deoxidizers react with dissolved oxygen in molten steel to form various metastable intermediates at rst, and then the metastable intermediates transform into stable crystal inclusion. Wasai et al 40 and Zhao et al 41 found nanoscale inclusions in deoxidation experiments by ultra-rapid cooling process. Therefore, the metastable calcia form at rst in the process of Cadeoxidation as shown in As the Ca-deoxidation reaction proceeds, the thermodynamic driving force decreased gradually with the decreasing of the supersaturation ratio in Ca-deoxidation process.…”

Thermodynamic insight into the growth of nanoscale inclusion of Al-deoxidation in Fe–O–Al melt

“…In order to investigate the evolution process of alumina inclusion in liquid iron, several researchers 7 – 9 carried out their experiments of Al-deoxidation in iron melt by ultra-rapid cooling method. Zhao et al 7 carried out the Al-deoxidation experiments in Fe–O melt by ultra-rapid cooling methods and found the shapes of alumina inclusions are small and irregular in various experimental samples. They reported that the equivalent radius of alumina inclusions are between 15 and 150 nm 7 .…”

“…Zhao et al 7 carried out the Al-deoxidation experiments in Fe–O melt by ultra-rapid cooling methods and found the shapes of alumina inclusions are small and irregular in various experimental samples. They reported that the equivalent radius of alumina inclusions are between 15 and 150 nm 7 . Wasai et al 8 also found a series of small alumina from nanoscale to microscale in Al-deoxidation experiments by this methods.…”