The Relevance of Cast Iron - Report Example

Running head: CAST IRON – STILL RELEVANT TODAY? Cast Iron – Still Relevant Today? Course Tutor Date Introduction Cast iron has been featured prominently in the structural and mechanical work since the middle ages. Although this metal was a late entrant in the history of iron making, it found many uses that declared it as valuable. In the early ages of production, iron was extracted from its ore through a technique that has actually remained the same by virtue of applied fundamentals. Cast iron resulted from accidental overheating of wrought iron which compounded carbon impurities into it. Industrial revolution saw the emergence of different types of cast iron with a variation in physical, mechanical and chemical properties. The continued use of cast iron in the modern sphere is an amazing fact due to the developments that have taken place with some materials being dropped on the way as they have been considered obsolete by the prevailing structural standards. This essay seeks to discuss the factors behind the continued utilization of cast iron even as leaps have been made in the technological field of material science. Composition of Cast Iron In order to understand the reasons behind the relevance of cast iron in today’s world, it is important to understand the chemical composition. Cast iron is made up of iron, silicon, carbon and other impurities such as manganese, sulphur and phosphoric compounds. Cast iron is composed of up to 5% carbon and that lowers its melting point to make it possible for casting to be carried out at the foundries. The amount of carbon added to wrought iron determines the properties that final products of cast iron possess. Cast iron is non-malleable, hard and brittle metal with a crystalline structure that is found to be weak in terms of structural tension. The compression nature of cast iron is very good with a high ability to withstand distortion in its solid stage. All these are usually determined by the manufacturing techniques applied especially in coming up with the molten metal for casting (US General Services Administration, 2012). Figure 1: Iron carbon phase diagram for eutectoid and eutectic reactions (Yescas-Gonzalez & Bhadeshia, 2001). The carbon equivalence for cast iron is calculated by the formula in equation (i) below as the main determinant of the expected properties. Grey iron for example and white irons are differentiated by the presence of graphite and cementite respectively. Higher cooling rates in low carbon cast iron results into much anticipated grey cast iron that is most used and strongest cast material. Solidification process of cast iron is also important within this discussion as its relevance to the world today depends on how quickly it is produced for the market. In most cases when cast iron cools down, carbon usually precipitates to form cementite and graphite. Due to the nature of carbon compounds this depends on the prevailing factors during the cooling process. The austenite matrix phase leads to a final product that is composed of a maximum of 2% of the total weight. Cooling the austenite matrix mixture at an advanced stage of austenite phase leads to the formation of graphite precipitates for better machinability. The decomposition of austenite leads to pearlite due to eutectoid temperatures thereby resulting in grey cast irons. The conventional ferrite mixture that is obtained when excess carbon is deposited on existing graphite is highly regarded as brittle by material scientists (Yescas-Gonzalez & Bhadeshia, 2001). Grey cast iron consists of 3.2% carbon, 2.5% silicone and pure iron cooled past the eutectic phase resulting in a pearlite compound that contains a lot of graphite flakes. Due to the impure nature of iron ore, this mixture does not lack traces of eutectic phosphide which is also referred in other terms as an etchant. The alternating layers of cementite and pearlite found in this metal can be resolved by the lamellar structure that phosphides introduce into it. On comparison to spheroidal graphite containing cast iron is found to have a large amount of magnesium which introduces a higher percentage of magnesium. Generally, spheroidal cast iron consists of 3.2% carbon, 2.5% silicone, 0.05% magnesium and iron which results into a pearl matrix with graphite nodules in it. The composition of this metal result into a decarburised nodule deposit (Yescas-Gonzalez & Bhadeshia, 2001). Imposing heat treatment on spheroidal cast iron with the pearlite matrix through the annealing process lead to precipitation of carbon to form smaller graphite particles in what is referred as a ferrite matrix. This produces ductile properties in cast iron contrary to giving it desirable properties. Austempering the ductile cast iron further due to a chemical composition of 3.52% carbon, 2.51% silicone, 0.49% manganese, 0.15% molybdenum, 0.31% copper and iron gives the end product a 0% distortion property (Yescas-Gonzalez & Bhadeshia, 2001). Cast Iron is indispensable Despite the fact that cast iron resulted from a case of wrought iron extraction gone bad, the usability of this metal has proved indispensible to human life. According to Fearn (2001), continued use of cast iron in the modern world not only depends on the historical or traditional outlook of the products that still stand as monuments. The conversion of cast iron into useful items has advanced with technology despite its heavy dull nature. The earliest uses of cast iron were on cannons that were found to be reliable by the armies in terms of heat and wear resistance. Fireback were considered as the first modern items to be manufactured from cast iron starting from the 16th century. The effective maintenance of patterns impressed on this material found use in utensils such as cooking pots and bake plates, cauldrons, grinding mortars, bell metals among others (Fearn, 2001). Modern uses that have often been attached to cast iron include hardware, stair cases, columns, utensils, stoves, decorative and historic monuments, structural connectors, ordnance and car parts. The continued innovation on cast iron has introduced methods of dealing with the mechanical, physical and chemical setbacks. These problems which include rusting, failure of coatings and structural failures have been approached through chemical doping in order to tune the characteristics further. The corrosion problem for example has been eliminated by the introduction of chromium, copper, nickel and silicon. This method of metal doping is referred as alloying in a bid to prevent oxidation which is a major setback in cast iron material usage. The resulting alloys of cast iron are classified into three main groups namely; high chromium, high silicone and high nickel but in the case of silicone which occurs naturally in iron ores, it has to go beyond 3% in order to be regarded as an alloy. The maintenance of this metal is also at an advanced level that achieved rust prevention through design of compatible paints, welding and recreation techniques (U.S General Services Administration, 2012). Heat treatment of cast iron produces a bainitic microstructure with outstanding fatigue properties that ensure noise reduction on cast iron engines blocks. Other materials of the same stature such as aluminium have been rejected by manufacturers due to the space that such metals might occupy in order to achieve the same levels of strength. Austempering of ductile cast iron has proved to produce materials with more robust strengths and reliable when it comes to machining to the required final shape (Yescas-Gonzalez & Bhadeshia, 2001). Figure 2: A modern high performance TVR Tuscan built from ductile iron crank shaft with an ability to achieve up to speed 6 (Yescas-Gonzalez & Bhadeshia, 2001). According to O’Rourke (2003), regardless of the fact that cast iron is labelled as a dirt and cheaper metal that is characterised by brittle properties, its uses have continued to grow. The advantages that have been attributed to this abnormal growth include its light weigh in comparison to other materials of the same class, ability to achieve desired shape on machining, wear resistance and the damping capabilities. Cast iron is hailed due to its steel strength and ability to be machined quickly without considerable wear in tool. The damping properties that emerge from the presence of graphite are highly attributed by the engineering fraternity. Kenawy et al. (2001), points out that the improvements that have been engineered on the initial form of cast iron are due to better material science understanding. This has in turn advanced the production methods, curing and machining procedures. Cast iron has now been found to compete effectively with other low cost steel materials such as steel due to achievable machining speed of up to 400m2 through application of the normal carbide tools. Longer lasting parts have been machined through the continuous process of casting which has considerably reduced costs of maintenance. The ability to mould this metal into complex shapes through the continuous casting process has also advanced the competitive edge of grey cast iron prod8cts due to the properties that arise from the homogenized microstructure. Today cast iron is traded in homogenized bars that are then extruded into shapes that are required to various shapes required by various clientele bases. This proves that usage of cast iron shall be continued even as critic speculate on its distinction at one point (Kenawy, Abdel-Fattah, Okasha, & EL-Gazery, 2001). Conclusion The fact that iron is referred as any ancient metal has not stopped it from competing effectively with other materials of the same standard. The relevance of its innovations still remains due to continued support from the material scientists who are always on a lookout of how to better this important engineering material. Alloying has been carried out with metals such as chromium, copper, nickel and silicon in a bid to remove some of the undesired traits in order to make iron more relevant and wanted. One of the significant modern uses that is worth noting is its usage on mechanical engine parts such as the crank shaft. References Fearn, J. (2001). Cast Iron. Oxford: Osprey Publishing. Kenawy, M. A., Abdel-Fattah, A. M., Okasha, N., & EL-Gazery, M. (2001). Mechanical and Structural Properties of Ductile Cast Iron. Egypt. J. Sol., Vol. (24), No. (2), Pp 151-159. O’Rourke, B. (2003, March 15). A look at Today's Cast Iron. Retrieved September 5, 2013, from http://www.productionmachining.com/articles/a-look-at-today39s-cast-iron U.S General Services Administration. (2012, February 24). Cast Iron: Characteristics, Uses and Problems. Retrieved September 3, 2013, from http://www.gsa.gov/portal/content/111738 Yescas-Gonzalez, A. M., & Bhadeshia, H. K. (2001). Cast Irons . Retrieved September 3, 2013, from http://www.msm.cam.ac.uk/phase-trans/2001/adi/cast.iron.html Read More