Btec Level 3 Mechanical Engineering

Topics: Oxygen, Steel, Welding Pages: 7 (2032 words) Published: May 16, 2013
Assessment 2 – 40580/02


Plain carbon steel is essentially an alloy of iron and carbon which also contains manganese and a variety of residual elements. These residual elements were either present within the raw materials used in the production process e.g. iron ore and scrap steel additions, or they were added in the production process for a specific purpose, e.g. deoxidization by means of silicon or aluminium. Hence they are called residual elements to distinguish them from alloying elements that are deliberately added according to specified minimum amounts. The term “cleanliness” refers to the amounts of various phases such as oxides, sulphides and silicates that can be present in steel. The smaller the amount of these phases, the cleaner the steel. For many years steels have been produced by casting the molten steel into moulds and allowing it to solidify into ingots which were then processed by rolling etc. steel produced by ingots is subdivided into four categories according to the deoxidization process used. These categories are rimmed, capped, semi-killed and killed steel. When un-deoxidized steel is cast into an ingot, carbon monoxide is evolved during solidification because the solubility of oxygen decreases as the temperature decreases.


Steels that contain specified amounts of alloying elements, other than carbon and the commonly accepted amounts of manganese, copper, silicon, sulphur and phosphorus are known as alloy steels. Alloying elements are added to change mechanical or physical properties. Alloy steels are melted together in an electric furnace. This step usually involves 8 to 12 hours of intense heat. Next, the mixture is cast into one of several shapes including blooms, billets and slabs. After various forming steps, the steel is heat treated and then cleaned and polished to give it the desired finish. The semi-finished steel goes through forming operations, beginning with hot rolling, in which the steel is heated and passed through huge rolls. After the steel is formed, most types must go through an annealing step. Annealing is a heat treatment in which the steel is heated and cooled under controlled conditions to relieve internal stresses and soften the metal. Some steels are heat treated for higher strength. However, heat treatment requires careful control, for even small changes from the recommended temperature, time, or cooling rate can seriously affect the properties.


Plain carbon steel is used in many industries such as in the construction of roads, railways, infrastructures, appliances, and buildings. Carbon steel is used to erect a strong and lasting frame to most modern buildings, steel beams (girders), joists and studs are engineered to create the skeleton of a building. Steel is also used in a variety of construction materials, such as pipes, tubing, plates, bolts, nails, screws and equipment like tools, bulldozers, cranes etc.


In the construction industry, gears, pipes, beams, w shape beams , boilers, pressure valves and other things are fabricated from alloy steels. By coupling additional elements to the carbon and iron based building metal you can strengthen it to withstand quite a bit more. Alloy steels can be non-magnetic, high-quality, and corrosion-proof. Furthermore they can be used in highly demanding applications such as commercial steel buildings, turbine blades in jet engines, spacecrafts and nuclear reactors. Stainless steel is the most widely known alloy steel. What distinguishes stainless steel from carbon steels is that it contains a minimum of 10% chromium. As a consequence, stainless steel building metal is resistant to staining, and is rust proof, which makes it perfect for cooking utensils, cutlery, jewelry as well as aircraft parts, architectural components, and surgical implements.


In the production of aluminium, first the ore is mixed with a hot concentrated solution of sodium hydroxide. The NaOH...
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