TOPIC 3 : STEEL WORK

3.1 Steel Iron a. Pig Iron b. Cast Iron c. Wrought Iron d. Mild Steel

FERROUS METAL o Iron o Steel o Stainless steel

What is iron??? Pure iron is a metal but is rarely found in this form on the surface of the earth because it oxidizes readily in the presence of oxygen and moisture.

IRON One of the most abundant metallic material in the earth’s crust (about 4-5%) Found in the form of ores as oxides, carbonates, silicates, and sulfides The most important iron-bearing minerals or iron ores are hematite and magnetite

IRON (cont.) The most commonly used ore is Hematite (Fe2O3) Contains about 70% of pure iron Specific gravity in the range of 4.5 to 5.3

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Steel & Iron Production

Broken into two categories: Primary and Secondary steelmaking. Primary steelmaking uses mostly new iron as the feedstock, usually from a blast furnace. Secondary steelmaking uses scrap steel as the primary raw material.

Primary steelmaking method of primary steelmaking in which carbon-rich molten pig iron is made into steel. To the process segment!!!!

Process Molten iron from a blast furnace is poured into a large refractory- lined container called a ladle; The metal in the ladle is sent directly for basic oxygen steelmaking or to a pretreatment stage. Pretreatment of the blast furnace metal is used to reduce the refining load of sulfur, silicon, and phosphorus. In desulfurising pre treatment, a lance is lowered into the molten iron in the ladle and several hundred kilograms of powdered magnesium are added. Sulfur impurities are reduced to magnesium sulfide in a violent exothermic reaction. The sulfide is then raked off. Similar pretreatment is possible for desiliconisation and dephosphorisation using mill scale (iron oxide) and lime as reagents. The decision to pretreat depends on the quality of the blast furnace metal and the required final quality of the BOS steel.

3. Charging process!! Filling the furnace with the ingredients. The BOS process is autogenous: the required thermal energy is produced during the process. Maintaining the proper charge balance, the ratio of hotmetal to scrap, is therefore very important. The BOS vessel is one-fifth filled with steel scrap. Molten iron from the ladle is added as required by the charge balance. A typical chemistry of hotmetal charged into the BOS vessel is: 4% C, % Si, 0.08%-0.18% P, and % S.

The vessel is then set upright and a water-cooled lance is lowered down into it. The lance blows 99% pure oxygen onto the steel and iron, igniting the carbon dissolved in the steel and burning it to form carbon monoxide and carbon dioxide, causing the temperature to rise to about 1700°C. This melts the scrap, lowers the carbon content of the molten iron and helps remove unwanted chemical elements. It is this use of oxygen instead of air that improves upon the Bessemer process, for the nitrogen (and other gases) in air do not react with the charge as oxygen does. High purity oxygen is blown into the furnace or BOS vessel through a vertically oriented water-cooled lance with velocities faster than Mach 1.

Fluxes (burnt lime or dolomite) are fed into the vessel to form slag which absorbs impurities of the steelmaking process. During blowing the metal in the vessel forms an emulsion with the slag, facilitating the refining process. Near the end of the blowing cycle, which takes about 20 minutes, the temperature is measured and samples are taken. The samples are tested and a computer analysis of the steel given within six minutes. A typical chemistry of the blown metal is % C, % Mn, % Si, % S and P.

Tapping process The BOS vessel is tilted again and the steel is poured into a giant ladle. This process is called tapping the steel. The steel is further refined in the ladle furnace, by adding alloying materials to give the steel special properties required by the customer. Sometimes argon or nitrogen gas is bubbled into the ladle to make sure the alloys mix correctly. The steel now contains 0.1-1% carbon. The more carbon in the steel, the harder it is, but it is also more brittle and less flexible. After the steel is removed from the BOS vessel, the slag, filled with impurities, is poured off and cooled.

PRODUCTION OF IRON Iron is produced in a blast furnace The main function of the blast furnace is to reduce the ore to metal, followed by separation of the metal from the impurities The iron ore in the form of pellets is charged into the furnace with coke and limestone

BLAST FURNACE

HISTORY!!! OKAY.. SANGAT MEMBOSANKAN.. TP KENA TAHU…JUGAK!

WHAT IS BLAST FURNACE??? A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron.

fuel and ore are continuously supplied through the top of the furnace, while air (sometimes with oxygen enrichment) is blown into the bottom of the chamber, so that the chemical reactions take place throughout the furnace as the material moves downward. The end products are usually molten metal and slag phases tapped from the bottom, and flue gases exiting from the top of the furnace.

History An illustration of furnace bellows operated by waterwheels, from the Nong Shu, by Wang Zhen, 1313 AD, during the Yuan Dynasty of China. The left picture illustrates the fining process to make wrought iron from pig iron, with the right illustration displaying men working a blast furnace, of smelting iron ore producing pig iron, from the Tiangong Kaiwu encyclopedia, 1637.

The first blast furnace in Russia opened in 1637 near Tula and was called the Gorodishche Works. The blast furnace spread from here to the central Russia and then finally to the Urals Representation of blast furnaces and other iron making processes from the 19th century

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Modern furnaces The blast furnace remains an important part of modern iron production. Modern furnaces are highly efficient, including Cowper stoves to pre- heat the blast air and employ recovery systems to extract the heat from the hot gases exiting the furnace. Competition in industry drives higher production rates. The largest blast furnaces have a volume around 5580 m3 (190,000 cu ft) and can produce around 80,000 tonnes (88,000 short tons) of iron per week.

Blast furnace diagram 1.Hot blast from Cowper stoves 2.Melting zone (bosh) 3.Reduction zone of ferrous oxide (barrel) 4.Reduction zone of ferric oxide (stack) 5.Pre-heating zone (throat) 6.Feed of ore, limestone, and coke 7.Exhaust gases 8.Column of ore, coke and limestone 9.Removal of slag 10.Tapping of molten pig iron 11.Collection of waste gases

Secondary steelmaking An electric arc furnace (EAF) is a furnace that heats charged material by means of an electric arc.

The furnace is primarily split into three sections.. To be continued…

Sambung semula…

The furnace is primarily split into three sections.. To be continued…

the shell, which consists of the sidewalls and lower steel 'bowl'; the hearth, which consists of the refractory that lines the lower bowl; the roof, which may be refractory-lined or water- cooled, and can be shaped as a section of a sphere, or as a frustum (conical section). The roof also supports the refractory delta in its centre, through which one or more graphite electrodes enter.