You may have seen steel all around you – buildings, tools, machines, cars, trains, watches, cutlery items, railway tracks etc. It is commonly used as building material. It is not a pure metal but an alloy of iron. Steel is world’s most recycled material with a recycling rate of over 60% globally.
Steel is iron mixed with varying amounts of carbon (0.1% to 1.5%). Iron is a metal while carbon is a non-metal. There are around 3500 different grades of steel depending on the carbon content. The properties of each steel grade depend on both its chemical composition and its method of manufacture. Most widely used grades of steel contain 0.1-0.25% carbon. Based on its application, the different grades of steel are produced. Steels are broadly categorized into 4 groups depending on their chemical composition – carbon steel, alloy steel, tool steel and stainless steel.
Carbon steel is the one in which carbon content ranges from 0.12-2.0%. It is quite hard but less malleable. Low carbon stels containing up to 0.3% carbon or the lowest amount of carbon is called wrought iron and used for fencing, chain links and railings. Medium type (0.3 – 0.6% carbon) is type used widely in construction of buildings, bridges, components of automobile, refrigerators, washing machines etc. High carbon steels with more than 0.6% carbon is used in making wires and cutting tools. Carbon stel with ultrahigh carbon content is referred to as cast iron. It is extremely strong but highly susceptible to corrosion. It is widely used in a variety of structural and decorative applications.
Alloy steels is an alloy of iron with varying proportion of elements like manganese, silicon, nickel, titanium, copper, chromium and aluminium. Its uses include pipelines, auto parts, electric motors, generators and transformers.
Stainless steel contains 10-20% chromium. Addition of chromium makes it highly corrosion resistance as against carbon stel and also brings luster to the product made out of it. It is widely used in making kitchen utensils, food processing equipments, piping, cutting tools, dental and surgical equipments.
Tool steels are alloy of iron and varying quantities of tungsten, molybdenum, cobalt and vanadium. The addition of these impurities makes it more heat resistant and durable. It is used for making cutting and drilling equipments.