Study of the scull composition in the blast furnace hearth of Kosaya Gora steel-works, producing ferromanganese with application of schungite (report 1)

Processes of lining erosion and scull formation effect considerably the blast furnace (BF) campaign duration. Among factors, influencing the processes, impacts are distinguished, stipulated by the kind of smelted product as well as materials used for scull formation. In the BF No. 2 of Kosaya Gora steel-works within the campaign from October 1999 until November 2015, 930,000 t of high-carbon ferromanganese (mainly ФМн78 grade) and 110,000 t of foundry iron were produced. After it stoppage for overhaul, samples of the scull were picked out and studied. It was revealed, that the scull of walls of BF hearth has a laminated structure and consists of crystallization products of metal and slag melts, namely: graphite, iron carbides, manganese carbides, iron, ferromanganese, slag components. At the macro level the scull has a lamellar structure. Since during the last campaign the blast furnace apart from ferromanganese was smelting foundry iron rather long time, in the samples, picked out at the level of iron notch at some distance from the cooler, the scull metallic phase mainly consisted of iron and iron carbide. In the sample picked out at a big distance from the cooler, in the scull metallic phase the following phases were discovered by X-ray structural and Moessbauer methods: ferromanganese; complicated manganese and iron carbides, as well as α-iron. Quantity of slag components in the scull decreases in direction from iron notch level to the hearth that speaks about splitting (still in the BF hearth) slag and metallic components of the heat products. In the scull content different slag components present: silicate (38.3–47.2% SiO2) with high content of К2О + Na2O (до 32.2%), MnO (up to 7.5%) and FeO (up to 33.2%). During the quick cooling of the components on the hearth cooler, different compositions are formed: X-ray amorphous “glassy phase”, olivine composition slags of Ca(Mn,Fe,Mg)SiO4 type, wollastonite, melilite with high amount of iron and manganese. Fine inclusions of titanium nitride are presented in the scull in a small amount, as well as manganese and silicon nitrides and carbonitrides, perofskite CaTiO, the role of which is insignificant in the scull forming.