Reagents for Desulphurization of Hot Metal...

Reagents for Desulphurization of Hot Metal Sulphur (S), present in solid steel as iron sulphide (FeS) inclusions, has several detrimental effects on steel processing and on steel’s physical properties. During deformation, the iron sulphide inclusions act as crack initiation sites and zones of weakness. Such inclusions from sulphur adversely affect steel’s toughness, ductility, formability, weldability, and corrosion resistance. An increase in manganese (Mn) however, helps prevent formation of iron sulphide, which is highly detrimental to steel’s hot workability and also leads to severe cracking. Sulphur is such an undesirable element in steel that its removal is desired. The ever increasing requirements to steel properties and the growing demand for steel qualities and quantities with lowest sulphur contents of down to 0.001 %, has made it necessary for the steel makers to carry out the desulphurization of hot metal. Presently hot metal is regularly being desulphurized to below 100 ppm, and in some steel plants, to 10 ppm. Besides the increased requirements of steel quality, other reasons which necessitate desulphurization of hot metal are reduced scrap quality and increasing cost of high quality iron ores. In the desulphurization process, powdered desulphurization reagents are injected into the hot metal through an immersed lance using an inert carrier gas such as argon or nitrogen, as shown in Fig 1. Since desulphurization is a diffusion-controlled reaction, and related to the reactive surface area available for reaction, the desulphurization reagents are to be as fine grained as possible. However, flowability is reduced with very fine grains and hence it is necessary to find an optimum between efficiency and conveying ability. In order to obtain good flow characteristics, normally a fluxing agent is added during the grinding operation, so that pneumatic transport during injection does not pose any problems. Fig...

Synthetic Slag for Secondary Steelmaking...

Synthetic Slag for Secondary Steelmaking Synthetic slag consists of prepared mixture of several individual oxides which is used during secondary steelmaking to assist the steel treatment in the ladle from the viewpoint of effective refinement. Synthetic slag practice is normally used to obtain clean steels and also for the desulphurization of the liquid steel. Secondary steelmaking is a critical quality control step between the primary steelmaking and the continuous casting of the liquid steel. A key feature for success with the secondary steelmaking processes is the slag control. Use of synthetic slag which is specifically designed to have the required chemical composition and physical properties helps in the slag control. The  desirable properties of the synthetic slag include (i) slag is to have high sulphide capacity, (ii) it is to be basic in nature, (iii) it is to be fluid to obtain faster reaction rates, and (iv) it is not to cause excessive refractory wear. The secondary steelmaking slag is in liquid form in the ladle and floats on the surface of liquid steel which is usually at temperature of 1,600 deg or higher. It acts like a sponge to absorb the impurities consisting mainly of sulphur and non-metallic inclusions. The design of the slag is a critical step impacting the efficiency of the steel refining processes during the secondary steelmaking. Slag regime in secondary steelmaking significantly influences the final quality of the produced steel, particularly with respect to the achieved desulphurization of steel. One of the possibilities for influencing the slag regime is the application of synthetic slags to the ladle slag, formed from slag-making additions during the liquid steel tapping. Synthetic slag practice during secondary steelmaking maximizes the efficiency of the steel refining process by (i) improving steel quality, (ii) improving productivity,...

Desulphurization of Hot Metal Oct16

Desulphurization of Hot Metal...

Desulphurization of Hot Metal Removal of sulphur from hot metal is called desulphurization of hot metal. Sulphur is a desirable element in steel when good machinability is required from the steel product. However it is an unwanted element in most of the applications of steel due to the following reasons. Sulphur affects both internal and surface quality of steel Sulphur contributes to the steel brittleness and when it exists in sulphide phase it acts as a stress raiser in steel products. It forms undesirable sulphides which promotes granular weakness and cracks in steel during solidification. It has adverse effect on the mechanical properties. It lowers the melting point and intergranular strength and cohesion of steel. Unlike other impurities which are removed from the hot metal by oxidation in the oxygen converter, the most economic method of removing sulphur from the hot metal is by reduction either in the transfer ladle or in the charging ladle, before it is charged in the converter. A number of technologies have been developed for the external desulphurization of hot metal but all of them have the basic requirement of a reagent and a method of mixing. The difference between the technologies used is the properties of the reagents, the effectiveness of the reagent to remove sulphur and the effectiveness of the mixing method to get the reagent into solution. . Also the effectiveness of hot metal desulphurization is inversely proportional to the desulphurization reagent injection rate. The most popular desulphurizing process today is deep injection of desulphurizing agent in the hot metal. Desulphurization process Dip lance process is the most economical, effective and reliable method of desulphurization hot metal. It consists of pneumatic injection of fine grained desulphurization reagent into the hot metal with high dosing precision via...