Steelmaking is the manufacturing of steel from iron ore or scrap. Pig iron is well known as the basic block of all ferrous metals, produced from refined iron ore in a blast furnace with the addition of charcoal, limestone, and air.
Steel is obtained from iron that loses some of its impurities like silica, phosphorus, and sulfur. These impurities are purposely removed because they cause serious weakness to the steel. The various methods of steelmaking are the open-hearth furnace process, the Bessemer process, and the basic oxygen process.
Steel can be obtained if pig iron is further refined and some amount of carbon is added. If this is done, the crystalline structure of the metal changes and steel is then obtained. This is the most common steelmaking process ever known. Well, in this reading, we’ll explore the various methods of steelmaking.
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What are the Methods of Steelmaking?
The various methods of steelmaking are divided into primary, secondary, and tertiary. however, the common methods of steelmaking are electric arc, hlsarna process, basic oxygen furnace, hydrogen induction method, open-hearth furnace process, and bessemer method.
Electric Arc
Electric arc furnace steelmaking involves melting iron from scrap or reduced iron using electric arcs. The furnace loads a batch of heat, sometimes with a “hot heel,” and gas burners are used to assist in melting. Fluxes are added to protect the vessel’s lining and improve impurity removal. This process uses furnaces with a capacity of around 100 tonnes, producing steel every 40-50 minutes.
Hlsarna Process
The HIsarna process, a type of blast furnace, directly processes iron ore into liquid iron or hot metal, making it more energy-efficient and carbon-neutral than traditional steelmaking methods. This process skips the manufacturing of pig iron pellets, resulting in a lower carbon footprint.
Basic Oxygen Furnace
A basic oxygen furnace is another process of steelmaking. Its manufacturing process is roughly 10 times faster than an open-heart furnace. This steelmaking process is achieved when high-purity oxygen blows through the molten pig iron, lowering carbon, silicon, manganese, and phosphorus levels. This sulfur and phosphorus level is reduced with the addition of a chemical cleaning agent called “fluxes.”
The addition of alloy to the steel help in creating different properties. For example, production of stainless steel, 10 to 30% of chromium will be added to the steel. It helps the steel to highly resist rust. And for the production of chrome-moly steel, chromium, and molybdenum will be added to the steel. It is known as very strong and light steel. Learn about the raw materials used in making iron and steel here!
Hydrogen Induction Method
In Sweden, a pilot plant tested the production of steel from direct-reduced iron, a renewable energy source. The process involves chemical reduction with hydrogen at 1,500°F (820°C), infused with carbon from coal in an electric arc furnace. The cost of this process is estimated to be 20-30% higher than conventional methods. However, a 2018 Science study predicts that prices will break even at €68 per tonne CO2, expected in the 2030s.
Open-hearth furnace process
In the process of steelmaking, iron ore, pig iron, and limestone are poured through the top of the open-hearth furnace which is then heated for about 1,600°f (871°c). After the heating process, the ore and limestone form slag that is lighter than iron so it floats on the top surface. Impurities like carbon oxidized float out of the iron into the slag. After all this, carbon steel is produced.
Bessemer process of Steelmaking
The second process on how steel is produced from pig iron is the Bessemer process. This steelmaking process also involves the oxidation of impurities in the pig iron which is achieved by blow air through the molten iron in a Bessemer converter, at this point, the heat of oxidation raises the temperature and keeps the iron molten.
Air plays an important role as it reacts with molten pig iron and makes the impurities from oxides, carbon monoxide burns off, and other impurities from slag.