Steel is one of the most widely used materials in the world. It is cheap, strong, versatile and recyclable. Developments within the steel production process have resulted in a reduction in CO2 emissions for the process.

Steel is used in applications such as railways, oil and gas, construction, knives and forks. Steel is an alloy of iron and carbon and can contain small quantities of silicon, phosphorus, sulfur and oxygen.

How Is Steel Made?

Initial Stage Of Making Steel

The opening process of making steel is to obtain it. Steel is extracted from iron ore, which is a natural material containing metallic iron found in the earth. This process is common with the other metals e.g copper and aluminium, however, they require a non-ferrous ore. Once the material is obtained, we must remove the ore, commonly by smelting, to leave the metal base behind. Smelting is a process of applying heat and a chemical reducing agent to remove the ore via decomposition, leaving the base metal. In our case of steel, this process releases oxygen as this makes up a large portion of iron ore. The product of this process is called pig iron, which has an extremely high carbon content, approximately 3.5 – 4.5%.

In industry, it is common to use a blast furnace for the mass production of steel. An alternative type of furnace used is an Electric Arc Furnace (EAF). The furnace is continually supplied with fuel (coke), ore and limestone via a conveyor belt. The purpose of limestone in this reaction is to act as a flux, which is crucial for removing the chemical impurities in the metal e.g. phosphorous. At the same time, a hot blast of air enters into the lower portion of the furnace. This allows the chemical reaction to occur throughout the furnace as the material makes its way down. The products of the process are generally molten metal and slag (a glass-like by-product), tapped at the base, along with the waste gases which use the top as an outlet. Steel is smelted via other processes but works to a similar principle as described above.

Second Stage

The molten steel is tapped from the base of the furnace into ladles. At this point manufacturers will add alloying elements while closely controlling the deoxidation, to give the steel the desired chemistry. For example, chromium, silicon and molybdenum will be added for stainless steel. From the ladles, the hot metal pours via a refractory shroud (pipe), to a tundish. A tundish is essential a holding bath that controls the flow rate of steel into open base copper moulds, while filtering out impurities. The moulds are water-cooled resulting in the molten steel contacting the mould to solidify. This is known as the primary cooling process. To prevent the metal sticking to the mould, the moulds are cooled in an oscillatory motion. Additionally, some form of lubrication helps prevent this. 

With only the outer layer of the metal solidified, now called a strand, is drawn out of the bottom of the mould through a curved arrangement of water-cooled support rolls. The rolls support the strand from the ferrostatic pressure, due to the large amounts of molten metal in the strand still solidifying. To aid the solidification rate, water is sprayed on the strands as it passes through the rollers. This process is known as the secondary cooling process.

Final Stage Of Making Steel

Following the secondary cooling process, the strand emerges horizontally, due to curved arrangement of the roller, in solid form. It is here when the strand is cut into predetermined lengths, commonly by gas torches. Determined by their shape and size, the solid comes out as billets (usually with an area of fewer than 230 cm²), blooms or slabs.

In many cases, these products need further rolling and processing which may flatten, roll or extrude them into their product to meet the customer requirements:

Semi-finished casting products	Final products
Billet	Bars
Blooms	Structural rods, rails and rods
Slabs	Sheet metal, plates, pipes and tubes

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