Steel is a popularly used alloy consisting mainly of iron and some carbon content (between 0.2% – 2.1% by weight) depending on its grade. Using carbon is the most cost effective way to alloy materials for iron, but other metals like manganese, tungsten etc. are also routinely used. Carbon and other elements act as hardening agents and prevent dislocation in the iron atom from sliding past one another. Varying amounts of alloying metals are used to control the qualities of hardness, ductility, and tensile strength of the resulting steel. Increased carbon content can make steel stronger than iron but this will also make it less ductile. While steel is not something that you can just get the ingredients for and cook up in your garage or backyard, it can be useful for different projects to know how steel is made. This way you will be better informed about what kind of steel you will need.
Here are the steps involved in steel making:
- Iron ore is dumped into a blast furnace along with coke (a pure carbon derived from coal) and limestone (for removing impurities).
- At the end the iron emerges from the blast furnace. This iron is free from most chemical impurities and contains a small percentage amount of carbon. Generally about 1% of carbon is observed in this mixture, but will vary depending on what kind of steel is to be made.
- Now this iron is transferred to a basic oxygen furnace (BOF) and is combined with various quantities of scrap steel. This amount is always less than about 30% of the finished steel.
- Once all the materials are in place inside the furnace a jet of pure oxygen is sprayed on them. This oxygen combines with the carbon in the steel to form carbon dioxide and carbon monoxide.
- These fumes are separated and the purified molten iron or carbon steel as it is now called, is left behind. This whole procedure of converting the iron into carbon steel take less than about an hour in a basic oxygen furnace (BOF). Once this reaction is complete the hot carbon steel is transferred to a giant ladle
- Now other metals, for example nickel, chromium, manganese etc are added to the carbon steel to create different steel alloys as per requirement. Most steel alloys go through a degassing process, which removes any gases that could have dissolved in the molten steel by exposure to inert gases in the atmosphere.
- when the required properties of steel are achieved the molten steel alloy is ready to be cast. To cast, this molten steel is now poured into a mold of desired shape and size and allowed to cool over time.
Steel has had a very long and diverse history and can be separated from wrought iron or cast iron only by including different amounts of carbon into the smelting process. Steel is an amazingly useful metal as it is not only strong but also flexible. It is used in construction of high rise buildings and long bridges. In fact steel is so popular that you can find it almost anywhere, including house hold appliances to rail roads and cars. The modern world as we know it, can be said to be build out of steel.
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