The Process of Steal-Making - Essay Example

Steal Making Abstract Metallurgy, engineering and steel processing make steel more useful for industrial and domestic use. Steel fabrication increases its usability through human and machine processing. Stronger and better steel structures and equipment can be manufactured through fabrication procedures such as rolling, shearing, blanking and welding. The strength and mechanical properties of steel are, however, determined by additives such as carbon, manganese and sulfur, which increase the toughness, tensile strength, ductility and the ability of steel to resist corrosion. This paper explores steel making, fabrication techniques, material science and properties that make steel one of the most useful components in engineering and construction. Introduction Steel is the most important metallic material used in engineering and construction. In 2013 alone, the net global steel production was 1,607.2 million metric tons. China, the largest producer, contributed almost 49% of the total global output, the European Union’s total output of 779.0 million metric tons. Overall, the world’s steel production has increased steadily, signaling the rising importance of steel (Yap 20). Steel has been previously used for the production of tools and other implements in many parts of the world before it became the most common material in modern times. Steel making has continually evolved from the ancient production in bloomery furnaces to the current efficient mass production (Murr 42). Steel is itself not a singular material, but rather a combination primarily composed of iron and carbon which form an alloy. Other components of steel include manganese, phosphorous, silicon, oxygen and sulfur. Mass production of steel became more efficient starting in the 17th Century with the development of blister and crucible steel (Murr 50). In 1856, the Englishman Henry Bessemer invented a steel smelting technique called the Bessemer process. The entry of the Bessemer process in the 19th Century was perhaps the defining point for mass steel production. Other production techniques such as the Siemens-Martins process and the Gilchrist-Thomas process followed, but they served to refine the steel production process further. Steel is, therefore, popular for construction and many other uses since unlike other forms of iron such as wrought iron; it is harder and possesses tensile strength. The report shall describe the various processes undertaken in the formation of steel (Huaixiang, Zhang and Xingqi n.p). Material Properties of Steel that determine its Suitability The efficacy of steel, its properties and suitability for a particular application are determined by among other things, the method of manufacture and chemical composition. Heat treatment is among the determinants of the strength and properties of steel. However, the constituent elements of steel such as carbon, sulfur, manganese, niobium and vanadium play a more significant role in dictating the physical qualities of steel. They affect the hardness, ductility (ability to be molded or shaped) and ease of welding (Cansizonglu 114). Smelting of iron has to take place in low oxygen conditions after which carbon can be allowed to dissolve in the iron. The mixture is still not called steel as the excess carbon has to be removed. Thereafter, 11% chromium is added to form a hard corrosion-resistant oxide that is commonly called stainless steel. The ratio of elements in the alloy dictates the density of steel, but on average the density of steel ranges from 7,750 to 8,050 kg/m3 (Murr 46). Adding nickel in the alloy increases the toughness of steel. Similarly, maintaining low levels of sulfur enhances its ductility. At the same time, heating and cooling at different levels of production radically influences the specific components of steel and ultimately alters its mechanical performance (e.g. fracture toughness, see Figure 1). Therefore, material combination, heat application as well as mechanical treatment of steel during production will determine the strength and performance of steel (Huaixiang, Zhang and Xingqi n.p). Plane Stress Behavior Plane Strain Behavior Thickness B Figure 1: Kc (Fracture toughness) decreases with increasing sample material thickness (B) (Calister, 194). When steel is rolled or formed, mechanical working takes place. It means that, the more steel is subjected to rolling, the stronger it becomes. The thickness of steel can then be reduced while maintaining strength. Heat treatment is the process of rolling steel. It results in its cooling. Rolling steel ends at a temperature of about 7500C. When this steel is left to cool, it is referred to as ‘As-rolled steel’. The heating of ‘As-rolled’ steel up to 9000C results in a more refined grain size and toughness. This kind of steel is called ‘Normalized steel.’ However, steel can still be heated up to 9000C and then rolled. The process also increases the toughness and refines the grain size of steel just like the normalization process, but eliminates the need for reheating the steel. This procedure produces what is referred to as ‘Normalized-rolled steel’ (Senthilkumar and Ajiboye 144). Mechanical Properties of Steel Steel is usually produced for different purposes and possesses variations in mechanical properties. Therefore, the diverse types of steel come with different strength levels and toughness depending on the alloys produced and heat treatment applied. It is, thus, important to test the type of steel and determine its suitability for particular applications. For instance, steel can be tested for ductility, impact strength, and resistance to penetration or tensile strength or the ability to support weight (Senthilkumar and Ajiboye 144). Tensile strength can be calculated through establishing a relationship between stress and strain. For example, stress can be calculated by dividing the total of the force applied by the cross-sectional area of the provided steel sample. Strain can be measured by dividing the increase in length (in mm) by the original length in mm (Huaixiang, Zhang and Xingqi n.p). Stress and strain are related through the elasticity of the steel. Elasticity of steel is analyzed based on the stretch it achieves upon application of the load and its ability to re-coil once the load has been removed. On the contrary, the material might be unable to revert to its original length and get deformed permanently. It is called plasticity and implies the steel has exceeded its elastic limit. Seel with more carbon is prone to stress. Other types of steel become very brittle under cold temperatures which are usually below 300C. Fabrication of Steel Steel fabrication refers to the process of preparing steel, and its metal components ready for use industrially or in construction. Fabrication might involve procedures such as bending, cutting, and assembly. It might also involve shearing, chiseling or sawing. Human labor and automated machine processes play an important role in the fabrication process. Fabrication of steel occurs on two levels: in the steel production process and the metal machining process for construction or machinery (Senthilkumar and Ajiboye 147). i. Fabrication in the steel production process: Fabrication of steel is a complex procedure that takes two approaches: first, the raw material or integral fabrication and secondly, the electric arc fabrication. a. Raw Material or Integral Fabrication: Most of the steel produced, about 60%, is fabricated using this method. The process involves heating up of materials needed in making steel, melting down the materials and mixing it into steel (Cansizonglu 120). b. The Electric Arc Fabrication: The electric arc fabrication process is faster and easier to implement than the raw material/integral fabrication. The method makes use of recycled steel as the raw materials that is then introduced to the furnace and melted down. It is usually a procedure involving heat, and once the materials have been properly mixed, steel becomes the end product. The EAF process is responsible for the production of approximately 30% of all steel produced worldwide (Huaixiang, Zhang and Xingqi n.p). ii. Metal Machining or Construction Fabrication: This process is aimed at the production of customized items such as building parts or industrial steel products. Steel fabricators combine bending, rolling and drilling techniques that subject the steel through temperature variations. Metal fabricators can transform engineering drawings and plans into structures such as bridges, cars and ships. In many cases, fabricators combine forces with welders to cut, bend and assemble steel parts into functional structural projects (Senthilkumar and Ajiboye 150). Fabrication Methods and Techniques Designing and Drawing Before the fabrication of steel for the manufacture of engineering and structures, a design must be in place. Figure II shows a chart of the design process. The drawings set the framework for measuring material dynamics of steel as well as its ability to tolerate stress, tension and structural design dynamics (Rakhit 20). Figure 2: Sample steel fabrication procedure (Calister 184). Custom Bending Custom bending is one of the most common steel fabrication techniques involving heavy machinery. V-shaped bends and creases in steel sheet metal processing uses custom bending technique. A steel fabricator uses machines such as the press brake or machine press together with a punch and die. The main hindrance in this process is the tendency of steel sheet metal to increase in length when bent. To counter this increase, steel fabricators factor in the anticipated increase in length in their bent material (Senthilkumar and Ajiboye 151). Carbon levels not exceeding 2% enable the steel to acquire bending properties and elasticity which exceeds those possessed by iron. For instance, the elastic modulus across different types of steel is 190-210 (GPa). At the same time, various types of steel will bear different levels of tensile strength and elongation. Stainless steels can elongate by 12%-40% and have a tensile strength of 515-827 (MPa). On the other hand, tool steels are tougher with elongation of 5%-25% while its tensile strength stands at 640-2000 MPa. It allows tool steels to suit the tool-making properties attributed to it. Nickel is responsible for the increased strength and toughness of steel. Levels of sulfur in steel also have to be reduced to make it harder (Cansizonglu 116). Steel Metal Rolling Rolling is a technique used to reduce the thickness of steel while increasing the length. The tensile and ductility properties of steel make this process possible. Rolling, however, requires the application of force in metal rollers that lengthen and compress the steel as figure III depicts. Rollers are placed above and below the steel. The machines also have to ensure that the strength and composition of the steel are retained (Senthilkumar and Ajiboye 149). Rolling is mostly done in the presence of heat with temperatures of 2200oF. Billet Equiaxed Grains Grains return to equiaxed form Because of the heat Figure 3: Hot Rolling Process of Steel Processing (Rakhit 127). Furthermore, the rolling machines have to be hard enough to roll and stretch the steel according to specifications. For instance, most forms of carbon steel possess an elastic modulus (GPa) of 190-210. The rolling machines require surfaces hard enough to achieve the required effect in the steel being processed. Many household appliances, vehicular body parts such as airplanes are processed through steel metal rolling techniques (Cansizonglu 118). Steel Cutting Virtually, no steel fabrication process can take place without the appropriate material sizes in place. Thus, cutting is a core technique of the steel fabrication process. Raw steel materials to be worked on have to be broken down to the right sizes before fabrication commences. Starting with the largest pieces, a cutting technique called ‘shearing’ transforms rough sheets of steel into smaller manageable sizes. Fabricators can then use smaller machines to make precise and more complex cuts. Steel possesses different levels of hardness depending on the alloys and the carbon content. For example, carbon steels present hardness levels of between 86-388, which is measured in Brinell per 3000 kg. Tool steels used for cutting materials possess a hardness of 210-620 which makes it hard enough to cut through other forms of steel with less hardness (Cansizonglu 120). Steel Blanking, Piercing and Punching Most of the procedures involved in these processes are similar to the shearing technique. Punches and dies, which are mechanical equipment used in the process are, need to be strong and rigid enough to handle the force applied. Figure IV shows a schematic of a die punch setup (Quazi, Razak and Amol 45). Blanking Force Punch Holding force Holding Force Sheet Metal Die Blank Cushion Ejector Clearance Figure 4: The Die Punch Setup (Quazi et al. 47). Die function in the blanking process has to be configured in such a way that about 5% of the metal thickness on either side is evaluated for gauge thickness. Carbon properties in the steel allow for an elastic modulus of 190-210 (GPa). Hole sizes for the piercing and punching should not be less than 1.5 times the thickness of the steel sheets. It will prevent distortion while the process is being carried out. Also, the spacing between the holes should not be under half the diameter of the hole (Murr 50). Conclusion The applicability of steel in engineering and construction continues to increase and improve. For instance, newer technologies such as layered fabricated technologies utilize the electron beam melting technologies. Structural optimization and direct metal fabrication technologies, however, continue to be the most common approaches. Other improvements include the fabrication of alloy and metal components using additive technologies. These technologies also form examples of three-dimensional materials science. Engineering and construction works continue to feature steel use in bridges, building superstructures, vehicles and household goods. Steel continues to evolve in technology and production processes of the modern era. References [1] Calister, William. Material Science and Engineering: An Introduction, 3rd Edition, John Wiley & Sons, Inc. New York, (1994): 193-195. Print. [2] Cansizonglu, Omer et.al. "Applications of Structural Optimization in Direct Metal Fabrication." Rapid Prototyping Journal, 14(2) (2008): 114-122. Print. [3] Huaixiang, Cao, Hao Zhang and Qiu Xingqi. Effects of Stress on Pitting Corrosion Behavior of Low-Carbon Steel. Conference. New York: American Society of Mechanical Engineers, 2013. Print. [4] Murr, L.E et.al. "Fabrication of Metal and Alloy Components by Additive Manufacturing: Example of 3D Materials Science." Journal of Materials Research and Technology, 1(1) (2012): 42-54. Print. [5] Quazi, Taib, et al. "Blanking Process Optimization Using Taguchi Method." 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