Structural Comparison of Metallurgical Coke and Coke Used in Electric Furnaces for Alloy Production
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Structural Comparison of Metallurgical Coke and Coke Used in Electric Furnaces for Alloy Production G. A. Ulyeva* AO ArcelorMittal Temirtau, Temirtau, Kazakhstan *e-mail: [email protected] Received February 6, 2020; revised February 6, 2020; accepted February 21, 2020
Abstract—The microstructure of solid carbon-based reducing agents is assessed by electron microscopy. On the basis of the results, the mean size of pores, cracks, and pore walls in the reducing agents is determined. The structure formation of the special cokes is analyzed in relation to the raw materials and production technology employed. On that basis, their suitability for metal and alloy production in electric furnaces is assessed. Keywords: special coke, Recsil, Direcsil, blast-furnace coke, coke microstructure, pore size DOI: 10.3103/S1068364X20050075
We know that the ore and reducing agents used in metal production must meet high requirements, especially in terms of impurity content. The traditional reducing agents—such as charcoal, coal, coke, petroleum coke, peat briquets, peat coke, anthracite and semicoke—differ in properties and especially in structure. Special cokes also differ in structure and properties and in the method of controlling the process. We need a more systematic approach to the composition and properties of all such reducing agents [1]. We are particularly interested in the pore structure of the reducing agents, which ultimately determines their chemical activity and electrical resistivity. In fact, we need alternative reducing agents for use in the production of metals and alloys so as to minimize or end the consumption of coal for metal and alloy production in electric furnaces. In the present work, we compare the fracture microstructure of various traditional and nontraditional solid reducing agents (Figs. 1–22). The photographs of the microstructure are obtained by means of a JEOL JSM-5910 (Japan) scanning electron microscope at Karaganda State Industrial University. The mean pore size and the thickness of the pore walls are determined by a linear method. In Figs. 1 and 2, we present the fracture microstructure of blast-furnace coke produced from KZh (51%) and K (49%) coking coal in the blast-furnace shop at AO ArcelorMittal Temirtau. On heating in the absence of air, the coking coal is converted to a plastic liquid state. The plastic mass surrounds solid grains of noncoking coal. This is a cementation process. Accordingly, coke of sufficient strength may only be obtained from clinkering coal. On heating the coal
grains to 455°C, most of the plastic material decomposes. At lower temperatures, the plastic mass binds the individual grains into a monolithic mass. Above 450°C, the coal in the bound continuous mass begins to break down, with the formation of hydrocarbon compounds, ammonia, and other organic compounds. The gases formed distend the softened coal mass, forming numerous large pores [2]. Therefore, the microstructure of blast-furnace coke is characterized by very large pores, with thick fused walls. Foundry co
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