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, Fe2Al5, and FeAl3 phase. The average size of alumina particles in the FeAl phase are larger than that of in the Fe2Al5 phase. Alumina particle is not observed in the FeAl3 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.