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INDUSTRIAL CHEMISTRY IRON & STEEL INDUSTRY Dr. G. SANGAMI & Dr. V. BALAKUMAR Assistant Professor Department of Chemistry Sri Ramakrishna College of Arts & Science January 2023
INTRODUCTION • It is a basic industry and forms the backbone of industrial development in any country. • It provides raw material for making • Industrial machinery • Electrical machinery • Defence equipment • Railway tracks • Dams • Houses and • host of other industrial and consumer goods.
Steel is the most widely used engineering material. •Steels are alloys of iron and carbon in which carbon varies in between 0.008 to 2%. •Steels are most important to the society because of their wide range of properties and versatile applications. •Steels containing only carbon as the alloying element are referred to as plain carbon steel. •The properties of steels depend upon the percentage of carbon and the amount of these phases.
Pure Iron, Allotropy •Pure Iron is also referred to as Ingot Iron or Pig Iron. •It is obtained from the blast furnace by reduction of iron ore. •Pure Iron also contains small traces of Mn, P, S and Si. •It is an Allotropic metal. (It is defined as the ability of a single substance to exist in more than one physical form). •Allotropy is the existence of metal in more than one type of lattice structure (e.g. B.C.C / F.C.C.)at various levels of temperature. •At room temperature, iron is B.C.C. in lattice structure, whereas on heating at 910°C it changes to F.C.C. •Allotropy of Iron is also termed as Polymorphism of Iron
FUNCTION OF CARBON IN STEEL AND ITS CLASSIFICATION • Carbon steel is an iron-carbon alloy, which contains up to 2.1 wt.% carbon. • For carbon steels, there is no minimum specified content of other alloying elements, however, they often contain manganese. • The maximum manganese, silicon and copper content should be less than 1.65 wt.%, 0.6 wt.% and 0.6 wt.%, respectively. • Carbon steel or plain-carbon steel is a metal alloy. It is a combination of two elements iron and carbon. • It is separated into three main subcategories - high carbon steel, medium carbon steel, and low carbon steel.
Types of carbon steel and their properties • Carbon steel can be classified into three categories according to its carbon content: • Low-carbon steel (or mild-carbon steel), • Medium-carbon steel and • High-carbon steel . Low-carbon steel Low-carbon steel is the most widely used form of carbon steel. These steels usually have a carbon content of less than 0.25 wt.%. They cannot be hardened by heat treatment (to form martensite) so this is usually achieved by cold work. Carbon steels are usually relatively soft and have low strength. They do, however, have high ductility, making them excellent for machining, welding and low cost.
High-strength, low-alloy steels (HSLA) are also often classified as low-carbon steels, however also contain other elements such ascopper, nickel, vanadium and molybdenum. High-strength, low-alloy steels, as the name suggests, have higher strengths, which is achieved by heat treatment. They also retain ductility, making them easily formable and machinable.
High-carbon steel High-carbon steel has a carbon content of 0.60– 1.25 wt.% and a manganese content of 0.30 – 0.90 wt.%. It has the highest hardness and toughness of the carbon steels and the lowest ductility. High-carbon steels are very wear-resistant as a result of the fact that they are almost always hardened and tempered. Tool steels and die steels are types of high-carbon steels, which contain additional alloying elements including chromium, vanadium, molybdenum and tungsten. The addition of these elements results in the very hard wear-resistant steel, which is a result of the formation of carbide compounds such as tungsten carbide (WC).
Medium-carbon steel Medium-carbon steel has a carbon content of 0.25 – 0.60 wt.% and a manganese content of 0.60 – 1.65 wt.%. The mechanical properties of this steel are improved via heat treatment involving autenitising followed by quenching and tempering, giving them a martensitic microstructure. Heat treatment can only be performed on very thin sections, however, additional alloying elements such as chromium, molybdenum and nickel can be added to improve the steels ability to be heat treated and thus hardened. Hardened medium-carbon steels have greater strength than low-carbon steels, however this comes at the expense of ductility and toughness.
Examples & Applications Low-carbon steel Low carbon steels are often used in automobile body components, structural shapes (I-beams, channel and angle iron), pipes, construction and bridge components, and food cans. Medium-carbon steel As a result of their high strength, resistance to wear and toughness, medium-carbon steels are often used for railway tracks, train wheels, crankshafts, and gears and machinery parts requiring this combination of properties. High-carbon steel Due to their high wear-resistance and hardness, high-carbon steels are used in cutting tools, springs high strength wire and dies.
Production and processing • Carbon steel can be produced from recycled steel, virgin steel or a combination of both. Virgin steel is made by combining iron ore, coke (produced by heating coal in the absence of air) and lime in a blast furnace at around 1650 °C. • The molten iron extracted from the iron ore is enriched with carbon from the burning coke. • The remaining impurities combine with the lime to form slag, which floats on top of the molten metal where it can be extracted. • The resulting molten steel contains roughly 4 wt.% carbon. This carbon content is then reduced to the desired amount in a process called decarburisation. • This is achieved by passing oxygen through the melt, which oxidises the carbon in the steel, producing carbon monoxide and carbon dioxide.
Heat treatment is defined as an operation involving the heating and cooling of a metal or an alloy in the solid-state to obtain certain desirable properties without change composition. • The process of heat treatment is carried out to change the grain size, to modify the structure of the material and to relieve the stresses set up the material after hot or cold working. • The heat treatment is done to improve the machinability. • To improve magnetic andelectrical properties. • To increase resistance to wear, heat and corrosion and much more reason. • Heat treatment consists of heating the metal near or above its critical temperature, held for a particular time at that finally cooling the metal in some medium which may be air, water, brine or molten salts. • The heat treatment process includes annealing, case hardening, tempering, normalizing and quenching, etc.
Types of Heat Treatment Processes • Following are the different types of heat treatment processes: • Annealing • Tempering • Normalizing • Hardening
Annealing • Annealing is one of the most important processes of heat treatment. It is one of the most widely used operations in the heat treatment of iron and steel and is defined as the softening process. • Heating from 30 – 50°C above the upper critical temperature and cooling it at a very slow rate by seeking it the furnace. The main aim of annealing is to make steel more ductile and malleable and to remove internal stresses. This process makes the steel soft so that it can be easily machined. • Purpose of Annealing • It softens steel and to improve its machinability. • To refine grain size and remove gases. • It removes the internal stresses developed during the previous process. • To obtain desired ductility, malleability, and toughness. • It modifies the electrical and magnetic properties.
Procedure for Annealing • Depending on the carbon content, the steel is heated to a temperature of about 50° to 55°C above its critical temperature range. • It is held at this temperature for a definite period of time depending on the type of furnace and nature of work. • The steel is then allowed to cool inside the furnace constantly. • Application of annealing • It is applied to castings and forgings.
Tempering: • When the hardening process hardens a steel specimen, it becomes brittle and has high residual stress. • It is an operation used to modify the properties of steel hardened by quenching for the purpose of increasing its usefulness. • Tempering or draw results in a reduction of brittleness and removal of internal strains caused during hardening. • Steel must be tempered after the hardening process. • The tempering is divided into three categories according to the usefulness of steel required. • Low-temperature tempering. • Medium temperature tempering. • High-temperature tempering.
Purpose of Tempering • To relieve internally stressed caused by hardening. • To reduce brittleness. • Improve ductility, strength and toughness. • To increase wear resistance. • To obtain desired mechanical properties.
The steel after being quenched in the hardening process is reheated to a temperature slightly above the temperature range at which it is to be used, but below the lower critical temperature. • The temperature here varies from 100°C to 700°C. • The reheating is done in a bath of oil or molten lead or molten salt. • The specimen is held in the bath for a period of time till attains the temperature evenly, the time depends on the composition and desired quality of steel. • Now the specimen is removed from the bath and allow to cool slowly in still air. • Application of Tempering • It is applied to cutting tools, tools, and gears, which are hardened by the hardening process.
Normalizing: • The main aim of normalizing is toremove the internal stresses developed after the cold working process. • In this, steel is heated 30 – 50°C above its upper critical temperature and cooling it in the air. • It improves mechanical and electrical properties, machinability & tensile strength. • Normalizing is the process of heat treatment carried out to restore the structure of normal condition. • Procedure for Normalizing • The steel is heated to a temperature of about 40° to 50°C above its upper critical temperature. It is held at this temperature for a short duration. The steel is then allowed cool in still air at room temperature, which is known as air quenching.
Purpose of Normalizing • Promote uniformity of structure. • Application of Normalizing • It is applied castings and forgings to refine grain structure and to relieve stresses. • It is applied after cold working such as rolling,stamping and hammering. • To secure grain refinement. • To bring about desirable changes in the properties of steel.
Hardening: • The main aim of the hardening process is to makesteel hard tough. • In this process, steel is heated 30° – 40°C above the upper critical temperature and then followed by continues cooling to room temperature by quenching in water or oil. • It is the opposite process of annealing. • Purpose of Hardening • By hardening, it increases the hardness of steel. • To resist to wear • Allows the steel to cut other metals
Procedure for Hardening • The steel is heated above its critical temperature range. It is held at that temperature for a definite period of time. • The steel is then rapidly cooled in a medium of quenching. • The quenching medium is selected according to the degree of hardness desired. • The air, water, bring, oils and molten salts are used as quenching mediums. • A thin section such knife blades are cooled in air. Water is widely used medium but it results in the formation of bubbles on the surface of the metal.
Oil is used when there is a risk of distortion on cracks and is suitable for alloy steels. • The molten salts are used to cool thin section to obtain crack-free and impact-resistant products. • Application of Hardening • It is applied for • Chisels • sledgehammer • hand hammer • centre punches • Taps • Dies • Milling cutters • knife blades and gears
COLD ROLLING • In simple terms, cold rolling is the process of strengthening steel by changing its shape without using heat. • Cold rolling is a process by which metal is passed through rollers at temperatures below its recrystallization temperatures. • The metal is compressed and squeezed, increasing the yield strength and hardness of the metal. • Cold rolling of metal strip is a special segment within the metalworking industry. • The purpose of this process is to create thinner metal strips with a good dimensional accuracy and a dedicated surface quality for a variety of applications.
WORKING • Cold rolled steel usually has a fine surface finish, tight size tolerance, and excellent machinability. • Therefore, it is widely used in many applications, including manufacturing, construction, home appliances, automobiles, machinery, and so on. • Uses of cold rolled steel • Cold rolled steel usually has a fine surface finish, tight size tolerance, and excellent machinability. • Therefore, it is widely used in many applications, including manufacturing, construction, home appliances, automobiles, machinery, and so on.
Manufacturing Industry • Cold rolled steel is a widely used material in the manufacturing industry. The very common cold rolled products made by it include: • 1. Steel sheet — a thin, flat, and rectangular sheet of metal called cold rolled steel sheet. • 2. Steel coil — a finished, thin, and flat steel sheet or strip which has been wound or coiled after cold rolling, namely cold rolled steel coil. • 3. Tube — a steel piping with a hollow section and length that is much more than its diameter or circumference, known as cold rolled steel tube. • 4. Substrate of painted steel — CR steel has good formability and paintability, making it the base metal of many painted steel products like galvanized steel, galvalume steel, SuperDyma steel and PPGI steel. • In addition, other end products created by it include bars, strips, rods, and wires which are usually smaller than the same products available through hot rolling methods. • Cold Rolled Steel Sheet • CR Steel Coil • Cold Rolled Steel Tube
1. Construction • In the construction sector, cold rolled steel is commonly used for producing different steel structures such as columns, beams, joists, studs, floor decking, built-up sections and other components. • In addition, it has been used in many different construction projects like bridges, storage racks, grain bins, railways, transmission towers, drainage facilities, roofing & wall systems, sheds, buildings, garages, etc.
2. Machinery It’s proven that cold rolling can be potentially strengthened up to 20% compared to hot rolling. At the same time, this process offers cold rolled steel high stamping performance, no aging, good mechanical property, and low yield strength. Thus, it can be cut, bent, punched, drilled, and formed with excellent results. Therefore, more and more mechanical production factories will choose to use this material nowadays. 3. Home Appliances & Metal Furniture Due to cold-rolled work, this steel presents a glossy, smooth, and sturdy surface. Also, it has a tighter tolerance, meaning CRS can be rolled thinner by up to 50%. This makes it have a lot of uses in home appliances and metal furniture. For it not only guarantees a longer service life but also provides a more aesthetic and visually appealing surface. By far, the ordinary cold-rolled steel uses in this industry we can find include washing machines, dryers, office filing cabinets, school lockers, refrigerators, electric fans, microwave ovens, and so on.
4. Automotive Industry Steel is an intrinsic part of the automobile sector, in which cold rolled steel performs better than hot rolled steel. This is because cold rolled steel is relatively more finished wear-resistant, and shockproof. Therefore, in this industry, it is predominantly used to manufacture bodies and load-bearing elements of cars and vehicles. Also, it can be used to fabricate electric motors, automotive seat parts, pressings, fuel tanks, etc. 5. Other Uses The cold rolled steel uses are not limited to the above. It can also be applied in many other places. Here list some for your reference: – Lighting/plumbing fixtures, conveyor systems, aerospace parts, firearm parts, packing materials, hardware accessories. – Toolboxes, exhaust pipes, precision instruments, metal containers, lawnmowers, tables, chairs, water heaters, cans, etc.
Alloy steel has been alloyed with other elements, ranging from 1 to 50 weight percent, in addition to carbon, to improve the material's various qualities. • Various types of alloy steel are being produced today, such as high-strength low alloy (HSLA) steel, Stainless steel, microalloyed steel etc. • Several elements including molybdenum, manganese, nickel, chromium, vanadium, silicon and boron are alloyed with steel to create alloy steel. • Strength, hardness, wear resistance and toughness are improved by the use of these alloying components. • Amounts of alloying elements can range from 1 to 50%.
