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Steel is the Silver Lining of Modern Civilizations
The era when the silver lining of civilization started evolving on the heart of our planet, since then early blacksmiths discovered that iron became harder and stronger when left in charcoal furnaces. This is the way how invention of iron-Steel and charcoal come together in 13th century BC. As the earth revolves, years have passed and humans have witnessed the moments of ‘Industrial Revolution’, invention of ‘Bessemer Process’ through to the various High-Tech processed applications of the present day Steel Making. Steel is the world's most popular material in terms of construction because of its unique combination of durability, workability, and cost. In the year 2020, the global demand for steel is estimated to be around 2 billion metric tons. To meet, such a gigantic demand of steel various industries such ArcelorMittal, Hebei Steel Group, Baosteel, POSCO, Tata Steel and Nippon Steel are constantly developing the most efficient way of development of steel with less time consumption.
Brief about steel and its grades
Steel is an alloy of primarily iron and carbon. It also contains various alloying elements such as Manganese, Molybdenum, Titanium, and Vanadium. Addition of carbon reduces the melting temperature and increases the hardness of steel. There are more than 1000 types of steel available and the density of steel varies depending upon the alloying constituents but usually ranges between 7,750 and 8,050 kg/m3or 7.75 and 8.05 g/cm3. There are different grades of steel. Carbon Steels includes low carbon steels, medium carbon steels and high carbon steels. Alloy Steels includes common alloy metals as manganese, silicon, nickel, and chromium. Stainless Steels contain about 10 percent chromium and are classified as austenitic, ferritic, and martensitic steel. Tool Steels are steels that are alloyed with high temperature and hard metals, such as molybdenum and tungsten.
Material Properties of Steel Required for Design
Steel used for different application purposes require certain material properties to be fulfilled. They can be classified as:
Strength:
Yield strength is the most important property that a designer needs as it is the basis used for most of the rules given in design codes. The product standards also specify the permitted range of numerical values for the ultimate tensile strength (UTS).
Toughness:
It is in the nature of all materials to have some imperfections. In steel these imperfections takes place in the form of very small cracks. If the steel is insufficiently tough, the 'crack' can propagate rapidly, without plastic deformation and results in ‘brittle fracture'. The risk of brittle fracture increases with thickness, tensile stress, and stress raises and at colder temperatures.
Ductility:
It is a measure of the degree to which a material can strain or elongate between the onset of yield and eventual fracture under tensile loading as demonstrated in the figure below. The designer relies on ductility for a number of aspects of design, including redistribution of stress at the ultimate limit state, bolt group design, reduced risk of fatigue crack propagation and in the fabrication processes of welding, bending and straightening.
Weldability:
All structural steels are essentially weldable. Welding involves locally melting the steel, which subsequently cools. The cooling can be quite fast because the surrounding material, e.g. the beam, offers a large 'heat sink' and the weld (and the heat introduced) is usually relatively small. This can lead to hardening of the 'heat affected zone' (HAZ) and to reduced toughness. The greater the thickness of material, the greater the reduction of toughness.
Durability:
One of the most important properties is the corrosion prevention. Although special corrosion resistant steels are available these are not normally used in building construction. The exception to this is weathering steel . The most common ways of providing corrosion protection to construction steel is organic coating or galvanizing.
The Modern Steel Manufacturing Process
Methods for steel manufacturing have risen significantly since industrial production began in the late 19th century. Modern methods, however, are still based the same methods as the original Bessemer process, which uses oxygen to lower the carbon content in iron. Modern steel making can be divided into six steps:
Iron Making:
Ore of Iron are mined, which contains a combination of iron with oxygen and various other unwanted substances, generally known as "gangue". The first metallurgical step is to reduce iron ore to metallic iron, a process which is mostly carried out in a blast furnace, using coke as both a fuel and reducing agent. The metallic iron manufactured by such a furnace contains a relatively high proportion of carbon (4%) and is passed to the steelmaking process as a liquid at approximately 1450 degree Celsius, called "hot metal".
Primary Steel Making:
There are two primary methods and those are mainly BOS (Basic Oxygen Furnace) and EAF (Electric Arc Furnace) methods.
BOS add recycled scrap steel to the molten iron in a converter. At very high temperatures, oxygen is blown through the metal, which reduces the carbon content to between 0-1.5 percent.
EAF, however feed recycled steel scrap through use high power electric arcs (temperatures up to 1650 °C) to melt the metal and convert it to high-quality steel.
Secondary Steel Making:
It involves treating the molten steel produced from both BOS and EAF routes to adjust the steel composition. This is done by adding or removing certain elements and/or manipulating the temperature and production environment. Depending on the types of steel required, the following secondary steelmaking processes can be used and they are mainly stirring, ladle furnace, ladle injection and degassing.
Continuous Casting:
Continuous casting, also called strand casting, is the process whereby molten metal is solidified into a "semi finished" billet, bloom, or slab for subsequent rolling in the finishing mills.
Shaping and forming:
The steel that is cast is then formed into various shapes, often by hot rolling; a process that eliminates cast defects and achieves the required shape and surface quality. The modern rolling mill is a huge installation, incorporating highly complex electronic control systems. The amount of work to which the steel is subjected, and the schedule on which this work is carried out, have significant effects on its physical characteristics – it dictates whether the steel can be subsequently bent, machined, cut, or subjected to any other heavy engineering operation, or formed into tubes, pipes or wire.
Final Manufacturing, fabrication and finishing:
This is the secondary forming techniques which give the steel its final shape and properties. This includes cold rolling operations, drilling, joining, coating, heat treatment, and surface treatment.
Applications of Steel
Steel is used in a wide number of applications in modern construction, including the building of railways, roads, buildings, appliances and other infrastructures. In fact, most modern structures, such as skyscrapers, stadiums, airports and bridges, are created with a durable steel skeleton. Steel applications can be mostly divided into 5 sectors:
Construction:
Sustainable steel structures can be built quickly at a low price. Steel, in its various forms and alloys, can be designed to meet the requirements of unique projects, which allow it to be incorporated into infrastructure in all environments. Steel can be found in low and high-rise buildings, hospital, colleges, stadiums, stations, reinforced concrete, bridge deck plates, pier and suspension cables, harbors, offices and so on.
Transport:
Engineering steels are wrought steels that are designed to have certain specific levels of elasticity, strength, ductility, and corrosion resistance. Different types of steel are used in various car body parts, doors, engines, gear box, steering, suspension, wheel axles and interior. Steel is found in various transport material such as trucks, trains, rails, ships, jet engines, aircraft carriages and so on.
Energy Sectors:
All segments of the energy sector, including nuclear, wind power, electric and natural gas, demand steel for infrastructure. Steel is also used for resource extraction, such as in offshore platforms, quarrying equipment, cranes, and forklifts. Many of the energy projects depends on the steel and they are mainly oil and gas wells, pipelines, electricity power turbines, electricity pylons, wind turbines, electromagnetic shields.
Packaging Industry:
Steel packaging protects goods from water, air, and light exposure, and is fully recyclable. This method of storage has been around for over 200 years. The steel is tin plated to prevent corrosion and then coated with a polymer, lacquered, and printed. The majority of steel packaging goes towards food and beverage container, followed by a general line, aerosols, and closures (e.g., bottle caps).
Appliances:
About 70 percent of the weight of typical household appliances is made from steel. Steel is found in appliances like fridges, washing machines, ovens, microwaves, sinks, cutlery and so on.
