Optimum percentage of burnt lime and mill scale in the slag for modification of pig iron
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Optimum Percentage of Burnt Lime and Mill Scale in the Slag for Modification of Pig Iron M.A. SHAKER The pig iron production at The Egyptian Iron and Steel Co. (E1-Tabbin, Helwan, Cairo, Egypt) is characterized by its relatively high S, Mn, and P contents. This fact reflects its influence on the suitability of locally produced pig iron for iron foundries and in the workability of steel ingots that are produced from this grade of pig iron in the steel converters. Therefore, the main objective of the present work is to study the modification of Egyptian pig iron composition and the effect of burnt lime and mill scale ratio in the multicomponent mixture of slag on a simultaneous removal of sulfur, phosphorus, silicon, and manganese from Egyptian pig iron. The chemical analysis of the pig iron after treatment indicates a significant reduction of these elements. Electron microscopy and X-ray microanalysis techniques have also been used to identify the burnt lime and mill scale ratio in the slag on modification of pig iron. As a result of this investigation, an optimum percentage of burnt lime and mill scale in the slag for this multicomponent mixture of slag is found to be [3 pct CaF2 + 37 pct Na2Co3 + 60 pct (40 pct CaO + 60 pct Fe203)] at low temperature (1250 ~ The desulfurization technique of hot metal has made remarkable progress during the last few years. Extra low sulfur commercial irons which contain sulfur less than 0.01 pct can easily be obtained. The desulfurization, dephosphorization, and manganese removal technique of hot metal cannot be easily made. One of the most important tasks in iron- and steelmaking is the elimination of phosphorus in liquid iron. Phosphorus as Fe3P forms a ternary eutectic with y-iron and Fe3C known as steadite, which is one of the last melts to solidify at 950 ~ on the grain boundaries. Steadite is a hard and brittle constituent which reduces M.A. SHAKER, Associate Professor, is with the Faculty of Engineering and Technology, Suez Canal University, Port Said, Egypt. Manuscript submitted June 1, 1990. 96--VOLUME 23B, FEBRUARY 1992
toughness and ductility and cannot be eliminated by heat treatment. In the literature, E~,2,31 it is recommended that phosphorus content be below 0.05 pct to avoid embrittlement. It has been reported t41 that the type of fracture during the transition temperature in impact test depends, to some extent, on the amount of S, P, and Mn segregation on the grain boundaries. The considerable gains in ductility and toughness can be realized when the sulfur level is minimized.[5,6] Manganese additions have also been observed to enhance brittle intergranular fracture, t7'81 The precise causes of this enhancement are still unknown. Also, it has been suggested that manganese might cause an increase of phosphorus segregation on the grain boundariesJ 9] This segregation would, in turn, weaken the boundaries and cause fracture to proceed along them. t~~ Various investigations fl:-~61 have used NazCO3 to achieve simultaneous desulfurization and dephosphorization of iron
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