Steel is one of the most important metals in the world and is widely used in many industries. Steel manufacturing has been prevalent since the industrial revolution when steel started becoming a material in demand for making various types of machinery, weapons and construction. Steel in construction is the most important use of steel.
How is steel manufactured?
The common raw material for iron and steel industry is iron ore. The primary raw material used to manufacture steel is iron. All steel alloys are primarily iron and 0.002–2.1 % carbon by weight. Iron ore, coke and calcite (lime) are added to a blast furnace to produce molten iron. This iron is used as the raw material for steel manufacturing process.
As you all might already know the basic process followed for making steel is by mixing carbon and iron at very high temperatures, above 2600°F. This method is of two types:
I.Primary steel making
Primary steelmaking involves making steel from pig iron. Pig iron is smelted iron, from iron ore, which contains more carbon. This smelted iron undergoes the Basic Oxygen Steelmaking or BOS method or Electric Arc Furnace or EAF method.
- BOS method: Recycled scrap steel is added to the molten iron. Oxygen is blown into this mixture at a really high temperature, to reduce the overall carbon content and create equal oxidization throughout the molten metal.
- EAF method: Recycled steel scrap is put through high-power electric arcs with temperatures as high as 1650°C. The high-current electric arcs from electrodes melt large quantities of steel scraps into liquid. The furnace then blasts in oxygen, lime and fluorspar to purify the liquid and convert it to high quality steel.
II.Secondary steel making
Secondary steel making primarily involves refining the steel or adding various other elements to steel to make the steel feature rich. Elements are added at specific temperatures following different processes to create the desired composition. Processes like stirring, ladle-furnace, ladle injections, degassing, and CAS-OB (Composition Adjustment by Sealed Argon Bubbling with Oxygen Blowing) are used in secondary steel making.
Refining steel is done by injecting argon, nitrogen or oxygen through the base of the blast furnace.
The quantities of iron ore, lime and scrap steel that goes into steel making are precisely calculated to ensure correct temperatures are applied to the process of making steel from iron ore. This also ensures the perfect composition of the steel.
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Final step of steel production
The liquid steel from the furnace is then put into a mold to create solid steel. This could be steel billets, rods, bars, etc. Steel undergoes these processes to be shaped into its final form.
- Shaping – cold rolling/hot rolling methods
- Coating – galvanising with zinc, or cold coating and electro coating
- Heat treatment
- Surface treatment – to remove impurities
Steel is most widely used in the form of steel coil made from steel slabs. Steel coils are made by hot rolling, cold rolling, or by using the Electrolytic Tinplate (ETP) method.
Although all steel is made of iron and carbon, different types of steel contain different compositions of each element. Steel can include other elements like nickel, molybdenum, manganese, titanium, boron, cobalt, or vanadium.
Adding different elements during the secondary steel making process affects its material properties. The method of manufacture and treatment of the steel during this process further enhances those abilities. Nowadays, technology has helped develop computerised machines for steel making which can help adjust precise temperatures and treatments to obtain desired steel.
There are four main categories of steel used in various applications:
- Carbon steel – Made of iron and carbon, it is the most produced steel in the world. Carbon steel is classified into three subcategories – low carbon steel (0.03-0.15% carbon), medium carbon steel (0.25%-0.50% carbon), and high carbon steel (0.55%-1.10% carbon). The more the percentage of carbon, the harder it is to bend and weld.
- Tool steel – This steel features a mix of carbon, tungsten, chromium, vanadium, and molybdenum. Tool steel is known for its hardness and resistance to wear and tear making it perfectly suited for use in machining and tool making.
- Stainless steel – Stainless steel is an alloy of iron with chromium, nickel, and molybdenum. This is the most widely known steel alloy that is commonly used in food handling, food processing, medical instruments, hardware, and appliances as it has high corrosion resistance.
- Alloy steel – Alloy steel is produced by mixing metal and non-metal elements with carbon steel. These alloys highlight different environmental, chemical and physical properties according to the elements mixed to make the alloy.
A brief history of steel
During the industrial revolution in the early 19th century there was an increase in manufacturing and construction activities. This led to a sudden demand for large-scale production of steel especially in the transportation sector, particularly for developing the railway lines. However, steel production was inefficient because it took a lot of time to process iron into steel.
In the 1950s, Henry Bessemer, a British engineer discovered the process of mass-producing steel. Called as Bessemmer’s process, it was an important revolution in the world of steel which changed the face of steel manufacturing across the world.
Thanks to Bessemmer’s process, it was now possible to build large structures, bridges, railroads, etc. Soon there were famous steel bridges being built around the world, skyscrapers towering buildings in cities, laying of new railway tracks, etc., scaling up the manufacturing and construction industries.
In India, the production of iron and steel began in the 1800s under the reign of the East India Company after the industrial revolution. The Bengal Iron and Steel company was also a significant player in the steel industry at the time. The steel industry of India witnessed a spike when Jamshedji Nusserwanji Tata established Tata Steel, earlier named TISCO, in 1907.
Widespread steel manufacturing in India started in the early 1900s. It was used to lay railroads and in the construction industry for public buildings like railway stations and bridges.
India is one of the top steel producing nations of the world with an upward steel industry outlook for 2023 and beyond. There are many steel manufacturing companies in India manufacturing premium grade steel which are being exported to different parts of the world.
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