Modern steelmaking abhay deo 12met012 Metallurgy,giet Gunupur Content Introduction Types of steel Classification of carbon steel Process of steelmaking • • • • Basic oxygen furnace DRI based steel making Bessemer process Open hearth furnace production of steel Modern steelmaking process Introduction Steel is recyclable and hence is a “green material”. Steels are alloys of iron and other elements, primarily carbon, widely used in construction and other applications because of their hightensile strengths and low costs. Sir Henry Bessemer, (born Jan. 19, 1813, Charlton, Hertfordshire, Eng.—died March 15, 1898, London), inventor and engineer who developed the first process for manufacturing steel inexpensively (1856), leading to the development of the Bessemer converter. He was knighted in 1879. The above attributes make steel to be the most important engineering material. Around 2500 different grades are produced to cater the need of several industries ranging from structural to aero‐space. Types of Steel Low/mild Carbon steel 0.04-0.30%c Medium 0.3-0.60% Up to 2.11%c High 0.6-1.50% steel Nb, V, W, Cr, Ni etc Alloy steel Low alloy up to 5% Medium alloy up to 5-10% High alloy up to 10% Classification of carbon steel • Low. Often called mild steels, low-carbon steels have less than 0.30 percent carbon and are the most commonly used grades. They machine and weld nicely and are more ductile than higher-carbon steels. • Medium. Medium-carbon steels have from 0.30 to 0.45 percent carbon. Increased carbon means increased hardness and tensile strength, decreased ductility, and more difficult machining. • High. With 0.45 to 0.75 percent carbon, these steels can be challenging to weld. Preheating, postheating (to control cooling rate), and sometimes even heating during welding become necessary to produce acceptable welds and to control the mechanical properties of the steel after welding. Steelmaking process Basic oxygen steelmaking DRI based iron making • Electric Arc Furnace • Electric Induction furnace Bessemer process Open hearth process Basic oxygen steelmaking process • Basic oxygen steelmaking (BOS, BOP, BOF, and OSM), also known as LinzDonawitz-Verfahren steelmaking or the oxygen converter process is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. • Blowing oxygen through molten pig iron lowers the carbon content of the alloy and changes it into low-carbon steel. The process is known as basic because fluxes of burnt lime or dolomite, which are chemical bases, are added to promote the removal of impurities and protect the lining of the converter. • The process was developed in 1948 by Robert Durrer and commercialized in 1952–1953 by Austrian VOEST and ÖAMG. The LD converter, named after the Austrian towns Linz and Donawitz (a district of Leoben) is a refined version of the Bessemer converter where blowing of air is replaced with blowing oxygen Pig iron based/basic oxygen steelmaking Top-blown converter process Bottom blown converter (Q-BOP/OBM) Bath agitated process/KOMB Open hearth process • The open hearth process is a batch process and a batch is called a "heat". Heavy scrap, such as building, construction or steel milling scrap is added, together with pig iron from blast furnaces. • This process was known as the Siemens-Martin process, and the furnace as an "open-hearth" furnace Bessemer process • The Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron prior to the open hearth furnace. The key principle is removal of impurities from the iron by oxidation with air being blown through the molten iron. DRI based steelmaking • EAF and electric induction furnace are used. The first electric arc furnaces were developed by Paul Héroult, of France, with a commercial plant established in the United States in 1907 • An electric arc furnace (EAF) is a furnace that heats charged material by means of an electric arc. Arc furnaces differ from induction furnaces in that the charge material is directly exposed to an electric arc, and the current in the furnace terminals passes through the charged material. • An induction furnace is an electrical furnace in which the heat is applied by induction heating of metal. Induction furnace capacities range from less than one kilogram to one hundred tonnes capacity and are used to melt iron and steel, copper, aluminium and precious metals. • In EAF and Electric induction furnace sponge iron is used. Electric arc furnace Electric induction furnace Production of steel Modern steelmaking process Due to development of science and technology steelmaking process can also be updated, nowadays it can be carried out into three steps. It gives better steel properties and good quality. 1.primary steelmaking 2.secondary steelmaking /ladle metallurgy/post treatment of steel 3.casting process Primary steelmaking Primary steelmaking consists of refining of hot metal or scrap +hot metal to steel in a) BOF and b) Electric furnace. The objective is to refine hot metal to the nearly desired chemistry. Basic oxygen furnace steelmaking DRI based steelmaking Bessemer process Bessemer and OH process are Open hearth process outdated. Secondary steelmaking Stirring processes • Bottom injection • Lance injection Injection processes • Powder injection • Wire feeding Vacuum processes • Stream degassing • R-H degassing • D-H degassing Reheating processes • VOD process • VAD process • Ladle furnace Stirring processes • It is process of injection through the bottom of the ladle or by the means of a top lance. • Stirring consists of purging the liquid steel by inert gas generally argon or sometimes nitrogen. • The objective is all cases is to make sure that the steel is consistent in temperature and composition, and, if possible ,to remove impurities. Injection processes • It is possible to carry out deoxidation ,desulphurization and inclusion modification introducing suitable material in the form of powder or wire. • Material is blown into the molten steel in the ladle at a high pressure using submerged top lance with the help of a carrier gas. Vacuum processes • Vacuum is created about 0.5torr is induced to reduce the partial pressure of hydrogen ,nitrogen and carbon monoxide in the ambient atmosphere . • So, that degassing ,decarburization and deoxidation can be achieved. Reheating processes • Heat losses occur due to secondary steelmaking to atmosphere ,it is necessary to compensate the temperature by providing additional temperature. Casting processes • Continuous casting, also called strand casting, is the process whereby molten metal is solidified into a "semifinished" billet, bloom, or slab for subsequent rolling in the finishing mills. • Prior to the introduction of continuous casting in the 1950s, steel was poured into stationary molds to form ingots. Since then, "continuous casting" has evolved to achieve improved yield, quality, productivity and cost efficiency. • This process is used most frequently to cast steel (in terms of tonnage cast). Aluminium and copper are also continuously cast. • Sir Henry Bessemer, of Bessemer converter fame, received a patent in 1857 for casting metal between two contra-rotating rollers. The basic outline of this system has recently been implemented today in the casting of steel strip. Diagram of casting vertical, curved ,horizontal, strip casting Conclusion Steel can be re-used without effecting the environment Construction with Steel components is very fast compared to other materials Steel construction of buildings with steel components is resistant to termites and other destructive insects. Steel constructions are cheaper than any other construction methods. Steel construction is a fast method of construction. “Where there is metal, metallurgist should be there”
