METALS Metals are found as compounds like oxides, carbonates, phosphates, and sulfides, etc. in nature. These compounds known as ores are treated to remove the impurities and to get the metal. All metals used in engineering are classified into two categories: 1- Ferrous Metals: In these metals, iron is the main constituent. Common ferrous metals in use are cast iron, wrought iron and different forms of carbon steel. 2- Non-Ferrous Metals: In these metals, iron is not the main constituent. Commonly used non-ferrous metals are aluminum, copper, zinc, silver, and tin, etc. OCCURRENCE OF IRON Iron is never available pure in nature. It has to be extracted in the form of pig iron from the various iron ores. Pig iron is the crudest and wrought iron is the purest form of iron. Different forms of iron and steel are obtained by purifying and suitably adjusting the composition of pig iron. The ores from which the pig iron is extracted are as follows: 1234- Magnetite (Fe3O4), it contains 70-75% iron. Hematite (Fe2O3), it contains 70% iron. Iron Pyrite (FeS2), contains 47% iron but is not preferred because of its higher Sulphur content which makes it brittle. Siderite (FeCO3), it contains about 40% iron. FERROUS METALS Pig Iron To remove impurities from the iron ore, carbon and flux are added while melting it. The refined product so obtained is the crudest form of iron, called pig iron. Pig iron is cast into rough bars called pigs. Uses: Cast iron, wrought, and mild steel are obtained by refining the pig iron. Cast Iron Pig iron is melted again with the limestone & coke and passed into molds of desired shapes and sizes to get a purer product known as cast iron. Molding the melted pig iron again reduces impurities and gives a more uniform product than could have not been obtained by directly molding the pig iron in its initial molten state. Carbon contents in cast iron vary between 2-4.5% Uses 1- It may be used for casting rainwater pipes, gratings, railings, manhole covers, etc. 2- Due to its high compressive strength, it may be used in making pure compression supports for heavy machinery, carriage wheels, and base plates, etc. 3- It is the basic material for the manufacturing of wrought iron and mild steel. Wrought Iron Nearly all carbon and other elements in pig iron are oxidized and may be left with 0.25% of carbon to obtain wrought iron. It is by far the purest form of iron in which the total impurities do not exceed 0.5%. Uses: It may be used for making roofing sheets, corrugated sheets, rods, pipes, gratings, plane and ornamental ironwork such as grills and gates. Carbon Steel The essential and major difference between carbon steel and cast iron is in their carbon contents. Steel goes on becoming harder and tougher with the increase in its carbon content. Up to a content of about 1.5%, all the carbon gets into a chemical combination with iron and none of it exists in the free state. If carbon contents increase beyond 1.5% then it does not combine with iron and remains present as free graphite. It is at this stage the metal falls in the category of cast iron. For a material to be classified as steel, there should be no free graphite in its composition. Types of Steel Dead mild steel Mild steel or Low carbon/soft steel Carbon Contents < 0.15% 0.15-0.30% Medium carbon steel 0.30-0.60% High carbon steel or hard steel 0.6-1.5% Properties of Mild Steel 1- Its structure is fibrous with dark bluish color. 2- It is ductile and malleable. 3- It is more tough and elastic than cast iron and wrought iron. 4- It is more prone to rusting than wrought iron. It corrodes easily. 5- It withstands shocks and impacts quite well. 6- It is not much affected by saline water. 7- It is equally strong in tension, compression and shear. Uses In construction works, it is used as reinforcement in RCC and rolled structural sections like Isection, T-section, channel section, angle section, plates, sheets, and bars, etc. Mild steel tubes are also used in the structures. Plane and corrugated sheets of mild steel are used as roof coverings. Mild steel is also extensively used in the manufacture of various machine parts, transmission towers, and industrial buildings. Mild Steel Bars • • • • Types: Plain bars, Deformed bars and Tor bars. Strengths: fy 40000 Psi, 60000 Psi, 80000 Psi, 100,000 Psi (Grade 40, 60, 80 and 100) Sizes: # 3 to # 11 (Dia 3/8” to 11/8”) Relevant Standards: ASTM A-615 and BS-4449 (for deformed bars) High-Tension Steel High-tension steel strikes a balance between strength and ductility by maintaining a carbon content between 0.25% and 0.60%. This makes it suitable for high-stress applications like prestressed concrete, bridges, and high-rise buildings. Rusting/ Corrosion and Preservation of Carbon Steel Rusting is a chemical process where iron reacts with oxygen to form iron oxides (rust). This reaction typically occurs at the surface of the metal. Rusting is accelerated in the presence of moisture and carbon dioxide, which dissolves in water to form carbonic acid, lowering the pH and promoting corrosion. Corrosion can be avoided by not letting moist air come in contact with the iron surface. The following methods may be adopted to minimize corrosion: 1. Tarring In this method, iron is dipped in hot bitumen so that a film is formed on the iron surface, which protects the iron from corrosion. Pipes or ends of poles to be embedded in the soil are usually given this treatment. 2. Painting Paints are applied on the surface of the metal to protect it. Exposed metal surfaces such as doors, windows, gates, railings, gratings, steel roof trusses, bridge structures, etc. are given this treatment, which has to be repeated after regular intervals. 3. Enameling Enamel provides better and long-lasting protection as compared to simple painting. This treatment is usually given to the same items as for painting. 4. Galvanizing Depositing a fine film of zinc on the steel surface is known as galvanizing. The surface to be galvanized is first cleared of all foreign materials by giving it an acid wash, followed by a wash with clean water. The surface is then dried and dipped in molten zinc. The fine film of zinc that gets deposited on metal protects its surface from contact with the atmosphere and consequent oxidation. Removal of the zinc film caused by wear or scratches exposes the surface to corrosion. 5. Tin Plating In this method, after cleaning the metal surface with acid wash followed by washing with clean water and then drying, it is dipped in a bath of molten tin. A protective covering of a tin layer is left on the surface, which is called tin plating. 6. Electroplating By the process of electrolysis, a thin film of nickel, chromium, cadmium, copper, etc. is deposited on the metal surface to be protected. The surface to be protected is made the cathode and the metal to be deposited is made the anode. COMMERCIAL FORMS OF CARBON STEEL Rolled Steel Sections Structural steel can be rolled into various shapes and sizes in rolling mills. Steel sections are usually designated by their cross-sectional shapes. The shapes of the rolled steel sections available today have been developed to meet structural needs. Cross-section and size are governed by several factors; the arrangement of material for optimum structural efficiency; functional requirements (surfaces that are easy to connect to, flat surfaces suitable for supporting other materials, etc.) dimensional and weight capacity, and material properties, etc. The various types of rolled structural steel sections are as follows: Structural steel – Hot Rolled Sections Round Bars These are available in circular cross-sections with diameters varying from 3/8” to 10/8”. They are widely used as reinforcement in concrete structures, construction of steel grillwork, etc. The commonly used cross-sections have diameters varying from 3/8” to 1”. Square Bars These are available in square cross-section with sides varying from 5 mm to 250 mm. They are widely used in the construction of steel grillwork, for windows, gates, etc. The commonly used cross-sections have sides varying from 5 mm to 25 mm. Flat Bars These are available in suitable widths varying from 10 mm to 400 mm with thickness varying from 3 mm to 40 mm. They are widely used in the construction of steel grillwork for windows and gates. Corrugated Sheets These are formed by passing steel sheets through grooves. These grooves bend and press steel sheets and corrugations are formed on the sheets. These corrugated sheets are usually galvanized, and they are referred to as the galvanized iron sheets or G.I. sheets. These sheets are widely used for roof covering. Corrugated sheets Expanded Metal This form of steel is available in different shapes and sizes. It is prepared from sheets of mild steel which are machine cut and drawn out or expanded. A diamond mesh appearance is thus formed throughout the whole area of the sheet. Expanded Metal The expanded metal is widely used for reinforcing concrete in foundations, roads, floors, bridges, etc. It is also used as lathing material and for partitions. Plates The plate sections of steel are available in different sizes with thicknesses varying from 5 mm to 50 mm. They are used mainly for the following purposes in the structural steelwork: (i) To connect steel beams for extension of the length; (ii) To serve as tension members of steel roof truss; and (iii) To form built-up sections of steel. Applications of Steel Plates Welded Wire Fabrics or Mesh Welded wire fabric is fabricated from a series of wires arranged at right angles to each other and electrically welded at all intersections. It is made from medium tensile steel drawn out from higher diameter mild steel bars. It is much stronger than mild steel and are available in different width rolls. It has various uses in reinforced concrete construction. It is mostly used for floor slabs on wellcompacted ground. Heavier fabric, supplied mainly in flat sheets, is often used in walls and for the primary reinforcement in structural floor slabs. It may also be used in road and runway pavements, box culverts and small canal linings. Application of Shotcrete on Welded Wire Mesh (Wikipedia) Cold Formed Steel Cold-formed steel refers to thin steel sheets that are shaped into structural components like beams, columns, and panels at room temperature through bending, pressing, or rolling processes. It is lightweight, strong, and corrosion-resistant, making it suitable for projects where reducing weight without sacrificing strength is essential. In civil engineering, cold formed steel is extensively used in constructing load-bearing and non-load-bearing walls, roof trusses, and floor systems in residential, commercial, and industrial buildings. Its adaptability makes it popular in prefabricated structures and lightweight steel framing systems, offering easy transportation and assembly. Additionally, cold formed steel is utilized in bridges, warehouses, and temporary structures due to its high strength-to-weight ratio and durability in diverse environments. Cold-Formed Steel Structure ALUMINIUM It is getting into wider usage in every field of Engineering. Modern and modified metallurgical processes have improved the strength and durability of aluminum to an extent that has made it versatile material for use by engineers. Properties 1. 2. 3. 4. 5. 6. It is highly ductile and malleable. It is very light in weight. It withstands corrosion very well. It is a very good conductor of electricity. It can be welded and riveted. It is very easy to work on. Uses It is used for making door and window frames, and corrugated sheets for roofing, solar panel frames, bridge decks, railings, posts, pillars, etc. in building construction. Aircraft and automobile parts are also made of aluminum. Its alloys with metals like copper, magnesium, manganese silicon, etc. have high tensile strength and hardness, still being lightweight and durable.
