Steel is a versatile building material valued for its strength, durability, and ease of recycling. Raw materials for steel include iron, carbon, and various metals, with limestone and silicon added to remove impurities and make the steel more workable. A blast furnace is used to prepare pure metal from the ore, with oxygen injected to separate impurities and create pure metal. Steel can be recycled easily, with higher percentages of recycled steel requiring an electric arc furnace.
Steel has been an important part of construction since the 1800s, due to its versatility as a building material. Its popularity is largely due to its strength and ease of manufacture. Raw materials for steel vary because different steels can be made to suit their end uses, from softer steel for machining to very hard steel for security devices or safes. All steel products are valued for their strength, durability and ease of recycling when no longer needed.
The key ingredient for steel is iron found in the ground in the form of oxide, a chemical mixture of iron and oxygen mixed with rock. Oxidized iron is common in steel products as they age, because the same molecule is known as rust, which occurs when iron and oxygen recombine over time. A high-temperature vessel called a blast furnace is used to prepare pure metal from the ore. Before the iron can be put into the kiln, it typically goes through several processing steps to remove the waste rock and concentrate the iron percentage in the ore.
In a blast furnace, iron ore and other raw materials for steel are added and heated to very high temperatures. When the mixture is melted, oxygen is injected using a hollow tube called a lance, which causes the mixture to become even hotter. At very high temperatures, the oxygen is separated from the iron oxide, resulting in pure metal. Impurities called slag rise to the top of the furnace and are removed, resulting in a molten mixture of iron and other additives.
There are hundreds of different steel compositions or alloys, but there are a few common raw materials for steel. Carbon is a key ingredient in all steels, but is present in low concentrations. The oxygen in the ore reacts with the carbon added to the kiln, stripping it from the iron oxide molecule. A pure form of carbon called coke is required in a blast furnace and is prepared by heating the coal to high temperatures to remove any organic compounds.
Iron with carbon percentages above two percent is referred to as cast iron, which is hard but more brittle. Other raw materials for steel include various metals, silicon and limestone. Limestone, which is calcium carbonate, is called flux and is added at regular intervals to the kiln to form slag and remove impurities. The silicon removes the oxygen in the kiln and makes the steel more workable or easier to bend or work with.
A blast furnace may use some recycled steel, but is typically limited to about 30% by weight. Steel is easily recycled, but for higher percentages of recycled steel, a different furnace called an electric arc furnace is used. An electric arc furnace uses two electrodes suspended within the furnace, between which a high electric current is passed creating high temperatures. The raw materials for the steel are already contained in the recycled material and only small amounts of additives may be needed to create the desired steel composition.
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