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...

Crude Steel

Crude Steel  Crude steel is the term used for the first solid steel product which is produced during the solidification of liquid steel in a steel melting shop. Crude steel is part of saleable steel when it is supplied to customers for its use or for further processing. Crude steel is normally processed into finished steel either by rolling or by forging processes. World steel association also includes liquid steel which goes into production of steel castings under crude steel for statistical purpose. Various common types of crude steel products (Fig 1) include (i) ingot, (ii) slab, (iii) bloom, (iv) billet, (v) round, and (vi) dog bone section. Crude steel products are also semi-finished products since they need further processing for the production of finished steel. Fig 1 Common types of crude steel products Ingot Ingot is the product obtained by pouring liquid steel into cast iron mould of a shape appropriate for the subsequent processing generally by hot rolling or forging into semi-finished or finished products. The shape generally resembles a truncated pyramid or truncated cone. The side surfaces can be corrugated and the corners are more or less rounded. Depending on its subsequent conversion requirements, ingot can be dressed and/or hot scarfed or cropped. The usual cross section of ingot is square, rectangular, round, oval, or polygon. Ingots with square cross section are used for rolling into billets, rails and other structural sections, whereas, ingots with rectangular cross section, are generally used for rolling into flat products. These ingots usually have a width which is two times or higher than the thickness. Round ingots are used for the production of seamless pipes. Polygonal ingots are used to produce tyres, and wheels etc. Low capacity steel melting shops with induction furnaces produce very...

Macro-Segregation in Steel Ingots...

Macro-Segregation in Steel Ingots With the large scale reduction of the crude steel production through the ingot casting route, there is now-a-days a tendency of producing extremely heavy weight steel ingots weighing over 600 t and continuous cast strands with thickness over 450 mm and rounds with diameter over 800 mm. These large size crude steel products are mainly applied for retaining components like reaction vessels for nuclear power plant and rotating components such as drive shafts of gas turbines and generator rotors. These high value products require high quality of the as-cast crude steel products, and hence, the production of the heavy crude steel products with adequate control of the quality is a big concern for steelmakers worldwide. The macro-scale segregation of alloying elements during the casting of steel ingots continues to afflict the manufacturers of steel ingots, despite many decades of research into its prediction and elimination. Defects such as A-segregates are still common, and components are regularly scrapped due to their presence, leading to increased economic and environmental costs. With the growth of the nuclear power industry, and the increased demands placed on new pressure vessels, it is now more important than ever that today’s steel ingots are as chemically homogeneous as feasible. During the solidification of alloys (liquid steel), solute is partitioned between the solid and liquid to either enrich or deplete the inter-dendritic regions. This obviously leads to variations in the composition on the scale of micro-metres (micro-segregation). Macro-segregation is a composition inhomogeneity in the scale from several millimeters to centimeters or even meters. The effects of macro-segregation are critically important in the present day applications of steel ingots and hence the ability to predict segregation severity and location is very important and highly sought after these days. Almost...

Steel ingots and their Casting during Steelmaking...

Steel ingots and their Casting during Steelmaking Ingot casting is a conventional casting process for liquid steel. Production of crude steel through the ingot casting route constitutes a very small percentage of global crude steel production. However, the method of casting of the liquid steel in ingot moulds is still fundamental for specific low-alloy steel grades and for special forging applications, where products of large dimension, high quality or small lot size are needed. Typical application for conventional ingot casting includes the power engineering industry (e.g. shafts for power generation plants, turbine blades), the oil and gas industry (conveying equipment, seamless tubes), the aerospace industry (shafts, turbines, engine parts), ship building (shafts for engines and drives), tool making and mechanical engineering (heavy forgings, cold, hot and high-speed steels, bearing, drive gears) as well as automotive engineering (shafts, axes). As the demand of heavy ingot increases nowadays, especially from the power engineering industry and ship industry, there is a tendency of producing extreme large ingots over 600 t and continuous cast strands with thickness over 450 mm and rounds with diameter up to 800 mm, which are mainly applied for pressure retaining components such as reaction vessels for nuclear power plant and rotating components like drive shafts of gas turbines and generator rotors. The moulds used for casting of ingots are made of cast iron. Cast iron is used for the production of the mould since the thermal coefficient of cast iron is lower than that of steel. Because of this property of cast iron, liquid steel on solidification contracts more than cast iron which makes detachment of ingot easier from the mould. Inner walls of the mould are coated by either tar or fine carbon. The coated material decomposes during solidification and this prevents sticking...

Ferro-Chrome

Ferro-Chrome Ferro-chrome (Fe-Cr) is an alloy comprised of iron (Fe) and chromium (Cr).  Besides Cr and Fe, it also contains varying amounts of carbon (C) and other elements such as silicon (Si), sulphur (S), and phosphorus (P). It is used primarily in the production of stainless steel. The ratio in which the two metals (Fe and Cr) are combined can vary, with the proportion of Cr ranging between 50 % and 70 %. Fe-Cr is frequently classified by the ratio of Cr to C it contains. The vast majority of Fe-Cr produced globally is the ‘charge chrome’. It has a lower Cr to C ratio and is most commonly produced for use in stainless steel production. The charge chrome grade was introduced to differentiate it from the conventional high carbon Fe-Cr (HC Fe-Cr). The second largest produced Fe-Cr ferro-alloy is the HC Fe-Cr which has a higher content of Cr than charge chrome and is being produced from higher grade of the chromite ore. Other grades of Fe-Cr are ‘medium carbon Fe-Cr’ (MC Fe-Cr) and ‘low carbon Fe-C’ (LC Fe-Cr). MC Fe-Cr is also known as intermediate carbon Fe-Cr and can contain upto 4 % of carbon. LC Fe-Cr typically has the Cr content of 60 % minimum with C content ranging from 0.03 % to 0.15 %.  However C content in LC Fe-Cr can be upto 1 %. In international trade, Fe-Cr is classified primarily according to its C content. The common categories of Fe-Cr used in international trade are as follows. Charge chrome with a base of 52 % Cr. HC Fe-Cr with C content ranging from 6 % to 8 %, base of 60 % Cr, and a maximum of 1.5 % Si. HC Fe-Cr with C content ranging from 6...

Ferro-Silicon

Ferro-Silicon Ferro-silicon (Fe-Si) is a metallic ferro-alloy having iron (Fe) and silicon (Si) as its main elements. In commercial terminology It is defined as a ferro-alloy containing 4 % or more of Fe, more than 8 % but not more than 96 % of Si, 3 % or less phosphorus (P), 30 % or less of manganese (Mn), less than 3 % of magnesium (Mg), and 10 % or less any other element. However, the regular grades of the ferro-alloy normally contain Si in the range of 15 % to 90 %. The usual Si contents in the Fe-Si available in the market are 15 %, 45 %, 65 %, 75 %, and 90 %. The remainder is Fe and minor elements. The minor elements, such as aluminum (Al), calcium (Ca), carbon (C), manganese (Mn), phosphorus (P), and sulphur (S) are present in small percentages in Fe-Si. Commercially, Fe-Si is differentiated by its grade and size. Fe-Si grades are defined by the percentages of Si and minor elements contained in the product. The principal characteristic is the percentage of Si contained in the ferro-alloy and the grades are referred to primarily by reference to that percentage. Hence 75 % Fe-Si contains around 75 % of Si in it. Fe-Si grades are further defined by the percentages of minor elements present in the product. ‘Regular grade 75 % Fe-Si’ denote that the product containing the indicated percentages of Si and recognized maximum percentages of minor elements. Other grades of Fe-Si differ from regular grades by having more restrictive limits on the content of elements such as Al, titanium (Ti), and/or Ca in the ferro-alloy. Fe-Si is also produced in a grade that contains controlled amounts of minor elements for the purpose of adding them to...