Refractories in steel making


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Refractories in steel making

  1. 1. Subject : Refractories in Metallurgy (MY-204) submitted to SIR RIZWAN Group members:  Shahrukh Ahmed (MY-058)  M.Bilal Ayub (MY-018)  Waqas Ahmed (MY-071)  Ammar Ahmed (MY-068)  Shahzeb Jawed (MY-062) Refractories in Steel making
  2. 2. Refractories in steel making Steel: Steel is an alloy of iron, with carbon being the primary alloying element. The carbon content of steel is between 0.002% and 2.1% by weight. Too little carbon content leaves (pure) iron quite soft, ductile, and weak. Carbon contents higher than those of steel make an alloy commonly called pig iron that is brittle and not malleable. Steel making proceess: steelmaking is the process for producing steel from iron and ferrous scrap. In steelmaking, impurities such as nitrogen, silicon,phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce different grades of steel. Limiting dissolved gases such as nitrogen and oxygen, and entrained impurities (termed "inclusions") in the steel is also important to ensure the quality of the products cast from the liquid steel. There are two major furnaces used for steel making: Furnaces:  Basic oxygen furnace  Electric arc furnace In furnace refractories plays a vital role. Refractory materials are used in linings for furnaces, kilns, incinerators and reactors. They are also used to make crucibles. Refractory: Refractory materials must be chemically and physically stable at high temperatures. Depending on the operating environment, they need to be resistant to thermal shock, be chemically inert, and/or have specific ranges of thermal conductivity and of the coefficient of thermal expansion. Refractory used in Basic oxygen furnace: The Basic Oxygen Furnace (BOF), is a tiltable vessel lined with refractories such as magnesia carbon brick. The main function of the BOF is to decarburise the hot metal using pure oxygen gas. BASIC MAGNESITE BRICK: Basic Magnesite Brick is a high performance refractory based on specially selected high purity seawater magnesite with additional carbon content to improve slag resistance. This quality is specifically designed for use in basic oxygen furnaces and other arduous operating environments in the steelmaking industry.
  3. 3. Refractories used in electric arc furnace: Electric furnaces are classified as arc furnaces or induction furnaces, according to the heating method. The arc furnace is used far more extensively for steelmaking because its capacity is large and production efficiency is high.
  4. 4. Magnesia Carbon Bricks: Our magnesia carbon bricks are catering to the requirements of diverse industrial sectors. Carbon brick is made in pressure from dead burned magnesia (or fused magnesia) and carbon material ( full crystal graphite) with binder of pitch and resin. It is unburned brick, magnesia- carbon brick at high temperature forms combination of carbon frame. Magnesia carbon brick is widely applicable in steel electric arc, combined blowing converter, ladle, torpedo, refined ladle etc.
  5. 5. Ramming mass: Ramming Mass is basically burnt magnesite. Some chemicals are mixed with dead magnesite to form ramming mass. Before it is packed, the ramming mass we manufacture is tested thoroughly. This ramming mass and silica ramming mass are supplied in their purest form by us. LADLE REFRACTORIES: At the continuous caster, the ladle and tundish are lined with a powdery monolithic refractory material which is applied by stamping or gunning. Magnesia Alumina Carbon Brick: Alumina Magnesia Carbon Bricks are used in Ladle Sidewall and Bottom impact areas. It is formulated with very high purity Alumina and Magnesia. Magnesia Carbon Brick: Magnesia Carbon Brick is resin-bonded and made with a high proportion of fused grain magnesite for very high erosion and slag resistance. It offers good oxidation resistance due to use of high purity flake graphite. Uses include Electric Arc Furnace sidewalls, hotspots and coldspots, and ladle furnace slag lines.Magnesia Carbon Brick is formulated for high wear areas in the electric arc furnaces and ladle slaglines. It is manufactured with very high purity, large crystal size and 100% (96 Grade) electro fused Magnesia, high purity Graphite and Antioxidants. High Alumina Brick: High Alumina refractories are made from high quality bauxite and corundum with very low impurity content. They offer great strength at high temperatures and excellent
  6. 6. resistance to abrasion, mechanical wear, slag corrosion, metal penetration and attacks of various fluxes. Continuous casting: Continuous Casting is the process whereby molten steel is solidified into a "semifinished" billet, bloom, or slab for subsequent rolling in the finishing mills. Prior to the introduction of Continuous Casting in the 1950s, steel was poured into stationary molds to form "ingots". Since then, "continuous casting" has evolved to achieve improved yield, quality, productivity and cost efficiency. Figure 1 shows some examples of continuous caster configurations. Steel from the electric or basic oxygen furnace is tapped into a ladle and taken to the continuous casting machine. The ladle is raised onto a turret that rotates the ladle into the casting position above the tundish. Referring to Figure 2, liquid steel flows out of the ladle (1) into the tundish (2), and then into a water-cooled copper mold (3). Solidification begins in the mold, and continues through the First Zone (4) and Strand Guide (5). In this configuration, the strand is straightened (6), torch-cut (8), then discharged (12) for intermediate storage or hot charged for finished rolling. Some other refractories used in steel plant: Magnesia or Magnesia–Lime Group: This group includes all refractories made from synthetic magnesites and dolomite. These consti- tute the most important group of refractories for the basic steelmaking processes. All these mate-rials are used primarily as a source of magnesia (MgO).
  7. 7. Magnesia: Modern high-purity magnesias are produced in well controlled processes. The principal sources of magnesias are brines (often deep well type) and seawater. . Magnesium hydroxide, Mg(OH)2, is pre-cipitated from these sources by reaction with calcined dolomite or limestone; one source uses a novel reactor process. The resultant magnesium hydroxide slurry is filtered to increase its solids content. The filter cake can then be fed directly to a rotary kiln to produce refractory grade magnesia, but more commonly now the filter cake is calcined at about 900–1000°C (1650 –1830°F), usually in mul-tiple-hearth furnaces, to convert the magnesium hydroxide to active magnesia. This calcined magne-sia is then briquetted or pelletized for firing into dense refractory-grade magnesia, usually in shaft kilns which reach temperatures around 2000°C (3630°F). The end product is sintered magnesia. Fused magnesia is produced by melting a refractory grade magnesia or other magnesia precursor in an electric arc furnace. The molten mass is then removed from the furnace, cooled, and broken up to begin its path for use in refractories. The impurities in magnesia are controlled by the composition of the original source of the magne-sia (brine or seawater), the composition of the calcined dolomite or limestone, and the processing techniques. In particular the amounts and ratio of CaO and SiO2 are rigorously controlled, and the B2O3 is held to very low levels. The end results are high-grade refractory magnesias which are ready for processing into refractory products Dolomite: Dolomite has excellent refractoriness and is thermodynamically very stable in contact with steel or steelmaking slags. CaO is the most stable of the common refractory oxides at steelmaking temperatures. Siliecious Group: Fused Silica:Fused silica is produced by actual fusion of specially selected, very high grade silica sands in elec-tric arc, electrical resistance, or other furnace procedures. Crystalline raw material is converted into an amorphous glass, or fused silica. Properties of this fused raw material vary considerably from those of the original quartz sand, in particular fused silica has very low thermal expansion. Fused sil-ica products exhibit low thermal conductivity, high purity and excellent resistance to thermal shock. Silicon Carbide: Commercial silicon carbide (SiC) used as a refractory raw material is manufactured by abrasive grain producers in electric furnaces from a mixture of coke and silica sand. The finished material is extremely hard (9.1 MOH’s scale) with high thermal conductivity and good strength at elevated temperatures, as well as very good resistance to thermal shock. Silicon carbide dissociates at 2185°C (3965°F) and oxidizes slowly in air, but is relatively stable under reducing conditions. The material is serviceable at 1535–1650°C (2800–3000°F) for many applications.
  8. 8. High Alumina Group: Sillimanite: Andalusite, sillimanite and kyanite comprise the water-free, natural aluminum silicate varieties of minerals known as the sillimanite group. Andalusite and kyanite are the more common commercial materials. These minerals are normally about 60% alumina, with the balance composed primarily of silica with minor iron and titania impurities, Table 3.15. Andalusite and sillimanite have several important characteristics; when heated at high temperatures, the refractory mineral mullite (3AL2O3•2SiO2) is formed. Complete mullite occurs at 1300–1400°C (2372–2552°F). This mineral is a key component of many high-alumina materials. Bauxite: Bauxite in the crude state is a naturally occurring group of minerals composed primarily of either gibbsite (Al2O3•3H2O), diaspore, or boehmite [AlO(OH)], and various types of accessory clays. Refractory grade calcined bauxites are a specific form as found in Table 3.16. These are produced from low iron, low silica materials in rotary kiln calcining operations or down-draft kilns. Calcin-ing temperatures are in the 1400–1800°C (2550–3275°F) range. Crude bauxite is converted to the minerals corundum (Al2O3) and mullite (3Al2O3•2SiO2) — both very refractory components. Important features of bauxites are maximum alumina values (85% or more desired), maximum bulk specific gravity, and minimum impurities Processed Alumina Group: Several types of chemically and thermally processed aluminas are used in refractories. These include calcined, tabular, and fused alumina. In general, calcined aluminas are used to promote refractory binding during manufacture or use whereas tabular or fused products form very stable aggregates. Tabular alumina is formed by cal-cination at 1925°C (3500°F), whereas fused alumina is more dense after total melting and rapid solidification. Carbon group: Various carbon forms are used to an ever increasing extent in refractories. For example, modern refractories use various graphite forms in combination with oxides to impart special properties. The graphite may be synthetic in nature as produced by heating calcined petroleum coke to 3000°C (5400°F) or may be natural graphite(s) from China, Mexico, Canada etc. Some all-carbon or all-graphite refractories may be produced for applications in highly reducing atmospheres. Generally, graphites are used in refractories in order to reduce the wetting characteristics of the refractory material with respect to slag corrosion and to increase the thermal conductivity which will result in better thermal shock resistance. In oxide-carbon refractories, the carbon content may range anywhere from as low as 4–5% up to as high as 30–35%. Note that as the graphitic content increases, the thermal conductivity of the refractory increases, but the density of the refractory decreases. This result is primarily due to the fact that the density of graphite is much less than the density of the other refractory materials being used. There are other contrasting differences in the morphology of the graphite as compared to the other refractory materials. The graphite materials, which are used in refractories, are commonly of a flaky structure; therefore, these flakes do not lend themselves to the same particle packing phenomena as do granular particles.
  9. 9. References:  Chp no 3, steel making refractories, D.H hubble, chief refractory engg. U.S steel corp. ( 0.pdf)  
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