By | June 21, 2016

Steel is one of the essential metals (alloys) playing an important role for the growth and development of modern technological society. It has various uses in our day to day life. Therefore, we are to produce it in various industrials processes that can produce a huge amount to meet the increasing of it.here we will discuss steel making process.

                           Fig 1. steel making process

What Is Steel making process?

Steel making is the method of processing and producing steel from iron ore and scrap. It focuses on removing the slugs and other unwanted materials like phosphorus, sulphur, silicon, nitrogen, and excess carbon from the raw iron. The next step targets on alloying it by adding various elements like manganese, chromium, nickel, and vanadium. Needless to say,   different grades of steel metals can be produced by mixing these in different proportion. The qualities of the steels can be controlled by decreasing or increasing dissolved gasses like oxygen and nitrogen.

Steel making Processes

Although men started producing steel since very earlier days, the commercialization was not started until it became 19th century. Before 19th, the crucible process was the only way of producing steel. After that the Bessemer process and Siemens-Martin process became popular in the 1850s and 1860s respectively. These methods become popular for steel making into a heavy industry.

In the present day, we have two popular methods used for making steel in commercial processes. These are basic oxygen steel making and electric arc furnace (EAF) steel making. With basic oxygen steel making process liquid pig-iron and scrap steel are collected.

History of Steel making

If we hark to the human history, we will find that almost all civilizations made steel in small quantities. Since the introduction of the Bessemer process in the 19th century, it has become highly popular and people adapted it for the mass production of steel.

Modern Processes of Steel making

Modern steel making process uses a blast furnace for manufacturing steel. It can be divided into two categories: primary and secondary. Primary steel making includes “converting liquid iron from a blast furnace and steel scrap into steel via basic oxygen steel making or melting scrap steel and/or direct reduced iron (DRI) in an electric arc furnace”.

The secondary process involves alloying. Here alloying agents are like manganese, chromium, nickel, and vanadium are added and dissolved gasses are sent through the lower portion. Dissolved gasses play an important role in controlling the quality of the steel.

Given below are these two important parts in detail

Primary Steel making Process

It is the process of making steel from carbon-rich molten pig iron. The process was introduced and developed in 1948 by Robert Durrer. However, VOEST and OAMG commercialized this method in 1952–53. The name LD converter came after the name of the two Austrian towns Linz and Donawitz.

As oxygen is passed through the molten pig iron to lower the carbon content of the alloy, the process is also called basic oxygen steelmaking. The word basic is added with it for the chemical nature of the refractories- magnesium oxide and calcium oxide. The basic principal of it is to lower carbon content in pig iron in order to make pure steel from it.

In this method, iron ore is mixed with coke and heated highly in order to form an iron-rich clinker called ‘sinter’. Sintering is an important part of the overall process. It plays a significant role in reducing waste and provides an efficient raw material for iron making. The process emphasizes on continuous casting. Exothermic heat is created with the continuous oxidation reactions at the time of blowing.

The step by step processes are as follows:

Molten pig iron is poured from a blast furnace into a large refractory-lined container called a ladle.

In the next step, the metal in the container is sent directly for applying basic oxygen steelmaking process. After that high purity oxygen at a pressure of 100-150 psi (pounds per square inch) is sent into the vessel at the supersonic speed that directly hits the surface of the iron bath through a water-cooled lance kept at few feet above the bath. The purpose of doing this is to reduce phosphorus, sulphur and silicon phosphorus before charging the hot metal into the converter. In the case of external desulphurising pretreatment, a lance is lowered into the molten iron in the ladle and quite a few hundred kilograms of powdered magnesium are added. Consequently, the sulphur impurities get reduced and become magnesium sulphide in a violent exothermic reaction.

After that the sulfide is raked off. The decision to pretreat depends on the quality steel needed. The BOS process is autogenous. It means the thermal energy required for this process is produced during the time of oxidation process. Therefore, maintaining the right charge balance is highly necessary.  It fully controls the hot metal, melt, cold scrap, etc. The BOS vessel can be tilted up to 360° and it can be inclined towards the deslagging side for charging scrap for giving the hot metal required the charge. For charging the BOS vessel iron scrap (25%-30%) or steel is used.

Now this is the next step to set vessel upright and cooling it with cold water. After that a copper tipped lance with 3-7 nozzles is gradually lowered down into it and pure oxygen is passed through it at supersonic speed. It oxygen must be 99% pure. When it will be passed over the hot metal, the carbon within it will be dissolved to produce steel. At first, the carbon will form monoxide and then carbon dioxide. This carbon dioxide increases the temperature and raises the temperature up to 1700 °C.

It melts the scrap, reduces the carbon contents (present in molten iron) and removes unnecessary chemical elements. Needless to say, using oxygen instead of air definitely improves the Bessemer process. This happens due to the presence of nitrogen in the air. Besides, other gasses in the air give a bit adverse result.

Burnt lime or dolomite is fed well into the vessel to form slag. It absorbs impurities at the time of making steel.

The BOF vessel is tilted towards the slagging side. After that, the steel is poured through a tap hole into a steel ladle with basic refractory lining. This method is called tapping the steel. Now the steel is refined in the ladle furnace mixing various alloy materials, depending on the properties required.  There are some special cases where either nitrogen or argon is bubbled into the ladle for mixing the alloy perfectly.

Secondary steel making

Apart from primary steelmaking process, there is secondary steelmaking process commonly performed in ladles. This is this method is often called as ladle (metallurgy). There are a few operations conducted in ladles include de-oxidation (or “killing”). There are alloy addition, inclusion chemistry modification, inclusion removal, homogenisation, vacuum degassing, and de-sulphurisation.

HIsarna steel making

Apart from Secondary steelmaking process, there is HIsarna steelmaking process which goes under primary steelmaking. In this method, steel is produced directly from iron ore. The process is on a Cyclone Converter Furnace – a new type of blast furnace. HIsarna process is more effective and energy-efficient. It has a lower carbon footprint than traditional steelmaking processes.

Steel Making Process Video

This video shows the complete process of making steel. Move pointer over each element on the image to reveal its name. Click on plants for details of their manufacturing process.

Steel Making Process

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