Dissolution of FeNb in liquid steel

Niobium is a well-established microalloying element for the production of High-Strength LowAlloy (HSLA) steels and it is usually added in amounts smaller than 0.10% in the form of standard ferroniobium (FeNb).[1]. The operational practice at the melt shop, as well as controlled dissolution trials in the laboratory and on an industrial scale, have shown that standard FeNb dissolves very rapidly and with high recovery yields. It was verified that the addition of FeNb requires good control of some parameters, such as deoxidation temperature, stirring time and particle size. For each application, CBMM produces lumpy material in a wide range of size distributions. Taking advantage of using very fine particles, recently CBMM has developed a new briquetting process in order to agglomerate FeNb fines smaller than 2 mm to make them robust enough for easy handling during their addition to the molten steel. This paper aims at presenting a review of the FeNb characterization, the dissolution rate of lumpy and briquetted fines, as well as showing the mechanism of dissolution at the FeNb/steel interface. In the laboratory trials it was observed that briquetted FeNb fines dissolve faster than the lumpy material at temperatures of 1560°C, 1600°C and 1640°C. It was verified that the difference between the dissolution rate of FeNb briquettes and lumpy material is less significant for higher temperatures (1640°C). The industrial trials showed that the complete dissolution of briquettes and lumpy material occurred in less than 10 minutes at 1570°C and that the yield of the niobium addition was higher than 98% for both materials. (AU) © 2015 Companhia Brasileira de Metalurgia e Mineração (CBMM)