Industrially Significant Elements and Compounds of Steel - Term Paper Example

?Steel Introduction Steel is an alloy of iron and carbon. Steel cannot be mined directly from the earth’s surface. Iron is the main source of steel. Iron is found in different concentrations at\round the world. It constitutes about 5 percent of the earths crust. However, iron alone is not useful; it is not hard enough to be molded into shapes. In addition, iron is too weak to carry weights. To ensure its usage in the manufacture of goods, iron must be alloyed with other minerals. Carbon is the best and readily avail able element that is alloyed with iron. Carbon is found in large quantities from wood and coal (Hall, 1997). According to Hall (1997), Iron is mixed with carbon to form either steel or cast iron. Iron ore, immediately extracted from the ground is rich in iron content or is concentrated. The concentration is then reduced in a blast furnace by the use of coke and limestone flux. The resulting product from the furnace is called pig iron. Pig iron is strong enough to be molded into various c shapes. Cast iron and its different types are produced at the foundry industries. The different types of cast iron produced at foundry industries include ductile iron, gray iron, and malleable iron. However, a larger percentage of cast iron is further refined to produce steel. Generally, steel can be said to be an alloy whereby iron predominates and carbon is used. Carbon is normally below 2 percent in content in the alloy. Good qualities of steel ere ensured by modifying the concentration of carbon in the alloy. Further, other elements such as silicon, manganese, and phosphorous are used to ensure that the steel produced is of high quality. Steel is the major metal consumed in large quantities around the world. Industrially Significant Elements and Compounds Steel is classified into three categories known as carbon steel, stainless steel and alloy steel. However, all steels are seen as being alloys. Steels are categorized as alloys because they contain other metals apart from manganese, silicon and phosphorous. These compounds are introduced as deliberate additions to the iron and carbon mixture (Hall, 1997). According to Hall (1997), Carbon steel varies on the ability of strength, how easily they can be welded and how easily they can be formed as well as their ability to be used in the formation of machines. Carbon steels are produced according to the range of quality. This is due to the level of certain element concentration. However, all carbon steel can rust if exposed to air, salts and acids. Further, when carbon steel is bound to be exposed to some corrosive materials, they can be coated with paint or epoxy. Other metals can also be used to coat carbon to prevent any effects caused by corrosive materials. Currently, the readily available metal coatings of steal include zinc and other compound of zinc or aluminum. These steel metal coatings are used in food and beverage industries for safety measures. Another important element of steel to be considered is the stainless steel. Stainless steels are produced with the main aim of preventing rust or corrosion. Apart from coating the surface of carbon steel, this only ensures that there is no corrosion while the coating is intact. Steel industries also use another element known as Chromium. Chromium can be used solely or with other alloying metals. Stainless steels normally contain about 50 percent iron and 9.5 percent chromium. Chromium oxide film of the surface of steel ensures that it is well protected from corrosive materials. The unique property of chromium oxide that makes it suitable for use on steel surfaces is that it is inert. When the stainless steel is cut, or is chipped, its protective cover is able to reform due to its exposure to oxygen (Hall, 1997). Several type of stainless steel can be produce. The commonest type of stainless steel is called Austenitic or type 300 series. This type of steel is composed of a considerable amount of expensive nickel which prevents any corrosion from salts and acids. Stainless steel is often used in food processing industries to ensure the good safety of the food products. On the contrary, alloy steel are those that are not carbon or stainless. In the United States, about 10 percent of steel production is reported to be alloy steel. Alloy steels include large tones of high strength and low-alloy carbon steels. Around the world, close to 5 percent of steel production has got alloying metals different from manganese, silicon and phosphorous. In most cases, a single alloy element may be added, however, it is recommended to use several alloy metals for a beneficial combination of effects. One quality of alloy steels is that they are produced in bar or plate form but not in flat rolled sheet or coil. However, Stainless steel or carbon cannot be produced in bar or plate form (Hall, 1997). Alloy steels can be used to make products such as shafts, machine parts, pumps, tools, gears and other critical components. Several ranges of alloy steels exist. Low alloy steels, for instance, contain less than 5 percent of all alloying elements such as silicon, carbon, and manganese. High alloy steels contain more than 5 percent of all alloying elements. One important category of steel includes tool steels. Tool steels normally contain vanadium which is used in the production of applications ranging from dies for the extrusion or forging of metals to shear blades and hand held tools. .bin addition, high speed steels are alloy steels composed of molybdenum, tungsten, vanadium and in rare cases, cobalt. Cobalt is used to make metal cutting drills, taps, and reamers in machine tools. Stainless steel, high alloy and certain kinds of carbon steels are commonly referred to as specialty steels (Hall, 1997). Reaction Conditions and Processes The production of the major steel classes such as carbon, alloy and stainless steel follow similar processes. However, the production techniques may differ according to the source of the metallic iron used in the process of production. The first step in the steel production is to get the iron. Steel is manufacture from iron; it is therefore a product of iron. In most cases, iron ore is reduced to pig iron in a blast furnace in an integrated steel mill. In the United States, integrated mill and its three separate parts operate together to produce iron for the steel making process. The steel making process includes the sinter plant, the coke ovens, and the blast furnace process (Segui, 2012). In the first process, known as sinter plant, iron ore is blended with coke powder together with limestone flux. This mixture is subsequently heated to a high temperature. The temperature should be at that point where the mixture turns into a porous cake known as sinter. The heating process requires a temperature of up to 1000o C, after which it is cooled with water. The next step involves the crushing of the sinter and the coke. They are then fed into the top of the blast furnace. The process continues progressively, where the heat generated from the combustion process of coke causes oxygen from the iron oxide ore to mix up with the carbon from the coke. This combination of oxygen with carbon leaves the iron in liquid form. Further, the iron ore mixes with the flux and the residual coke as to produce slag. The slag as well as the liquid iron arte normally collected at the bottom of the furnace. Other elements such as the new sinter, coke and flux are added at the top (Hall, 1997). After the metallic iron has been produced, whether as pig iron or in any other form, it is directed into a Basic Oxygen Furnace (BOF). A BOF is a vessel capable of holding up to 300 tones of liquid metal. Oxygen is blown over the BOF at a high pressure. Oxygen, once blown over the BOF at high pressure, reacts with the carbon in the iron charge. The products of this reaction include heat, carbon monoxide as well as carbon dioxide. To trap impurities in the furnace, elements such as fluorspar and magnesite are used (Segui, 2012). In other furnaces such as the Electric arc furnaces (EFs), lime is added as a slag forming agent. Further, electrodes are introduced into the furnace to just above the scrap charge. According to Hall (1997), powerful current is then directed through the shredded iron and the steel scrap. The high temperature heat generated by the electrodes ensures that the metal is able to melt. In the same way as the BOF, oxygen in this case is used to refine the molten metal to steel by removing extra carbon as a gas and other impurities in a slag. The molten steel in the furnace goes through several processes before it is cast into a solid shape. There are two processes involved after the production of the molten steel. These processes occur in the ladle. The ladle is the vessel that caries the liquid steel from the blast furnace. The ladle is used to lower or increase the temperature of steel. It can also be used to operate the alloying, stirring, and mixing operations to improve the chemistry of the steel. This process is known as metallurgy (Hall, 1997). Vacuum degassing is a process under metallurgy. During this process, the ladle is put in a vacuum compartment and the steel is stirred. The stirring ensures that gases including nitrogen, hydrogen and oxygen dissolved in the steel are removed. In the production of stainless steel, argon-oxy gen decarburization (AOD) process is normally used. In this process, a mixture or argon and oxygen is put into the metal at the bottom of the AOD vessel. The main purpose of the oxygen gas is to oxidize excess carbon while argon gas ensures that c chromium is not lost in the slag (Hall, 1997). According to Segui (2012), the final stage of steel production involves casting of the steel into various shapes. This is normally done by pouring the liquid steel into moulds. In traditional molding processes, the liquid steel was cast into ingots also known as solid blocks. They would then be transported to a rolling mill for reheating and rolling into a finished shape. However, ingot casting has since been replaced by continuous casting. Liquid steel is normally poured into a tundish. Tundish is a funnel like vessel big enough to hold temporarily the volume of steel being poured from the ladle; from the tundish, the steel flows slowly down a mould with the cross sectional shape in which the steel is required. Since the steel cools and solidifies as it goes down, it must be removed out through the curved mould at a steady speed to leave space for additional steel entering at the top. Finally, the solidified steel is cut into different shapes and lengths suitable for the rolling mill. Design and Operation of Industrial Equipment After the complex processes that lead to the casting of the steel have been exercised, the product is still a semi finished steel. This product is known as a slab, a bloom or a billet, depending on its size and cross section. In the steel design, ingots must be reheated and rolled into one of these same shapes. It is important to note that slabs used to roll plates and coils of flat rolled steel, are of rectangular cross section. They are expected to be at least twice as wide as thick. Slab sizes normally range from 34 to 100 inches in width and from 4 to 10 inches in length. On the contrary, blooms are used to make heavy, long steel products such as rails and beams. Beams and rails are usually square or rectangular in shape. If they are in rectangular shape, then the width must be less than twice the thickness, if this is not the case, then the product will have to be classed as a slab. Further, Billets are a smaller version of blooms. They are semi finished shapes of steel with sides of less than 6 inches, or 150 millimeters. Blooms and billets can be cast with a round cross-section which is then used in the production of seamless tubing (Segui, 2012). Currently, the most effective casters are called thin slab casters. Thin slab casters are used to make slabs less than 2 inches thick by the new flat rolled steel mini mills. For long products, near net shape casters produce a shape whose cross section in some instances is described as a dog bone. Dog bone shape is a shape that roughly looks like a finished steel beam. Shapes that have not been fully finished are often sold to other steel companies. However, the unfinished shapes can also be sold to other customers like manufacturers or steel fabricators. To turn the unfinished products into finished products, the unfinished products must be heated again and molded into a shape known as a steel mill product. Most steel mill products are made on hot rolling mills to the finished shape that is suitable for customers in the market (Hall, 1997). Conclusion Steel is a very important metal in the world. Without steel, Industrialization in the world would not have taken place. Steel ensures that there is steady production of goods that can meet consumer demands. The unique property of steel is that its is cost effective to produce and to build, strong and design flexible, durable and safe, environmentally friendly as well, as being resistant to fire. Another important quality of steel include is ability to be used in the steel frame production and construction. References Hall, C (1997). Steel Phoenix: the Fall and Rise of the U.S. Steel Industry. New York, Palgrave Macmillan. Segui, W (2012). Steel Design. New York, Cengage Learning. Read More