Steel is an alloy produced from iron combined with a certain percentage of carbon to form a bcc crystalloid structure to ameliorate its structure and fracture resistance. Usage of steel in construction work had been started in the middle of the nineteenth century. Let’s discuss the reasons for the predominance of steel in construction work-
- Due to its high tensile strength, the construction of a steel skeleton is highly resistive to natural disasters like floods, earthquakes, etc.
- The density of bcc crystals is comparatively lower. Hence, steels are easier to transport.
- The world is heading towards sustainable development. So, the high recycling value of steel is attracting civil engineers.
There are four types of steel depending on the alloy material used at the time of production viz. Carbon steel, Alloy steel, Stainless steel, and Tool steel. They are made thus to serve the different purposes as elucidated following.
- Carbon Steel- Carbon steel is produced by adding carbon with iron ore. Carbon steel is categorized into 3 types following the amount of carbon present i.e. low, medium, and high carbon steel. The percentages of carbon range from 0.15-0.30%, 0.30-0.60%, and 0.60-1.5% respectively in the case of low, medium, and high carbon steel. The more carbon the less its ductility. The first one is utilized to make steel structures such as buildings, bridges, rivets, etc. Medium carbon steel is relatively strong and less ductile henceforth, it is convenient to make pressure vessels, forging shafts, boiler drums, hammers, etc. Due to good wear resistance and poor machinability, the latter one is used to produce tools like knives, springs, screwdrivers, and lathe tools.
- Alloy Steel-It is comprised of alloying elements like nickel, copper, chromium, and aluminum in a certain proportion with iron. The character of alloy steel varies depending on the element used, for example, the presence of silicon and nickel increases its magnetic properties. In general, it provides better ductility and toughness compared to carbon steel. Alloy steel is the obvious answer to the question of producing power generating equipment, structural components for automotive application, iron tubes, and ball bearings. The main drawbacks, in general, are its lower machinability and formability.
- Stainless steel-This type of steel is designed to prevent rusting. Iron, in the presence of humidity, is often oxidized and turned into a hydrated ferric oxide which is called rusting of iron. If 10-20% chromium is mixed with iron to make an alloy it can be prevented. Moreover, its heat resistance properties and high strength make it more convenient. As we observe in our daily life, household items are mainly made of stainless steel due to their corrosion resistivity. Medical equipment, food processing, and cutting tools are also made as this steel can be easily sterilized. High tensile strength allows us to make thinner containers out of stainless steel which, evidently so, reduces fuel and cleaning costs. Transportation of chemicals and liquids, as we see, is processed in a stainless steel container. Stainless steel is further grouped into four classes, martensitic, ferritic, austenitic, and duplex.
- Tool steel-This category is not unique but derived from the family of carbon steel and alloy steel to brush on its distinct properties such as hardness, wear resistance, toughness, and temperature durability. It is made of iron mixed with carbide-forming elements such as Vanadium, Molybdenum, and tungsten in different proportions. As the name suggests, tool steel is beneficial in manufacturing tools like drilling machines, cutting equipment, etc. which demand elevated heat resistance and softening temperature durability. It is graded by SAE and ASTM upon its purposes, e.g., air-hardening, water-hardening, shock-resisting, high-speed, hot-working, oil-hardening, etc.
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In layman’s language steel is primarily an alloy mixed with various elements designed to serve the sought target. In today’s world, the importance of steel in this era can never be blindfolded under any circumstances.