STEEL According to the World Steel Association, there are over 3,500 different - PowerPoint Presentation

1.    STEELAccording to the World Steel Association, there are over 3,500 different grades of steel, encompassing unique physical, chemical and environmental properties.In essence, steel is composed of iron and carbon, although it is the amount of carbon, as well as the level of impurities and additional alloying elements that determines the properties of each steel The carbon content in steel can range from 0.1-1.5%, but the most widely used grades of Steel contain only 0.1-0. 25% carbon. Elements such as manganese, phosphorus and sulphur are found in all grades of steel, whereas manganese provides beneficial  effects, Phosphorus and Sulphur are deleterious to Steel’s Strength and DurabilityDifferent types of steel are produced according to the properties required for their application, and various grading systems are used to distinguish steels based on these properties. According to the American Iron and Steel Institute (AISI), steels can be broadly categorized into four groups based on their chemical Compositions: Carbon Steels Alloy Steels Stainless SteelsTool Steels   1

2. Carbon Steels:Carbon steels contain trace amounts of alloying elements and account for 90% of total steel production. Carbon steels can be further categorized into three groups depending on their carbon content:Low Carbon Steels/Mild Steels contain up to 0.3% carbonMedium Carbon Steels contain 0.3 – 0.6% carbonHigh Carbon Steels contain more than 0.6% carbon Alloy Steels:Alloy steels contain alloying elements like: Manganese, Silicon, Nickel, Titanium, Copper, Chromium And Aluminumin varying proportions in order to manipulate the steel's properties, such as:: Hardenability, Corrosion Resistance, Strength, Formability, Weldability Or Ductility. 2

3. Applications for alloys steel include: Pipelines, Auto Parts, Transformers, Power generators and Electric motors.Stainless Steels:Stainless steels generally contain between 10-20% chromium as the main alloying element and are valued for high corrosion resistance. With over 11% chromium, steel is about 200 times more resistant to corrosion than mild steel. These steels can be divided into three groups based on their crystalline structure:Austenitic: Austenitic steels are non-magnetic and non heat-treatable, and generally contain: 18% chromium8% nickel and less than 0.8% carbonAustenitic steels form the largest portion of the global stainless steel market and are often used in:Food Processing Equipment, Kitchen Utensils and Piping.3

4. Ferritic: Ferritic steels contains: Trace amounts of Nickel, 12-17% Chromium, less than 0.1% Carbon, along with other alloying elements:, such as Molybdenum, Aluminum or Titanium. These magnetic steels cannot be hardened with heat treatment, but can be strengthened by cold working.Martensitic: Martensitic steels contain : 11-17% chromiumless than 0.4% nickel and up to 1.2% carbon. These magnetic and heat-treatable steels are used in knives, cutting tools, as well as dental and surgical equipment. Tool Steels: Tool steels contain: Tungsten Molybdenum Cobalt and Vanadium in varying quantities to increase heat resistance and durability, making them ideal for cutting and drilling equipment.4

5. The art and technology needed for the production of iron was well developed in ancient India. The Asoka pillars, such as the one situated in the Qutub Minar complex is an example of high skills of its makers. The quality of iron used is so good that after more than hundred years it is still rust free. However iron was not used in buildings and bridges during the ancient and medieval period because of the following reasons :For Buildings and Bridges, superior quality alternative materials like very strong bricks, stones, strong and durable timber and high strength mortars were available.Fairly complicated forms of construction like the variable thickness barrel roofs, circular and elliptical arches, spherical and elliptical domes and other types of structures were used.A barrel shell roof made from bricks and mortar only at Bara Immambara, Lucknow is known to be the largest shell roof of its kind in the world.5

6. Types of Structures :- From structural point of view Shell StructuresFramed StructuresShell Structures :- These are mostly made up of plates and sheets. In such structures loads are mostly taken up by plates which serves as covering material also. Tanks, airplanes and shell roof coverings are some of the examples of shell structures. The main advantage is the saving in the cost of the construction material.Framed Structures:- Framed structures consist of elongated members assembled together, such as roof truss, beams, etc. In framed structures the load is mostly transmitted by the frames and the later do not act as a covering material.However, framed structures are more commonly used, as shell structures pose some difficulties. The knowledge of shell structures is not widely spread and such structures are not economical for certain layouts and spans.6

7. Field of ApplicationShell Systems  Gas holders and tanks for the storage and distribution of gases.Tanks and reservoirs for the storage of liquids.Bin and bunkers for the storage of loose materials like cement, grains etc. Ship hulls, airplane fuselage, etc. Framed Structures Railway, highway and other large span bridges.Very tall multistory buildings, exhibition pavilions, etc.Hangers, shipyards, railway platforms, etc. Transmission towers, television masts, cranes, etc.7

8. Advantages and Disadvantages of Steel StructuresAdvantagesThe ability to resist high load with a comparatively small size and light-weight of members.Due to high density, steel is completely non porous.The possibility of industrializing the construction work by the use of prefabricated and mechanized erection at the construction site.A very long service life, provided care is taken.The possibility of disassembling or replacing some steel members of a structure for strengthening purpose.Disadvantages The main drawback of steel members is their susceptibility to corrosion. Second drawback is its low fire resistance. At high temperatures steel loses most of its strength, leading to excessive deformation or failure.8

9. Magnetite (Fe2O4) Contains 70 % – 75 % ironHematite ( Fe2O3 ) Contains about 70 % ironIron Pyrites ( FeS2 )Contains about 47 % ironSederite (FeCO3 ) Contains about 40 % ironComposition and Properties of Structural SteelIron is not available in pure form in nature. It has to be extracted from various iron ores in the form of Pig Iron. Some of the iron ores from which the iron is extracted are: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 and is called Pig Iron.Cast Iron :- The Pig Iron is re melted with lime stone and coke and poured into moulds of desired shapes and sizes to get cast iron. Carbon varies from 2 % - 4.5 %9

10. Steel The essential difference between cast iron and steel is their amount of carbon content. Steel goes on becoming harder with the increase in its carbon content. Up to a content of 1.5% all the carbon gets into chemical combination with iron and none of it exists in free state.If carbon content increases beyond 1.5% then it does not combine with iron and is present as free graphite. It is at this stage that the metal falls in the category of cast iron and the carbon content may be increased up to 4.5 %. Therefore for a material to be classified as steel there should be no free graphite.Depending upon the carbon content, the steel is characterized as follows Mild Steel ( IS 226 – 1962 ) designated as St 42 – S  High Tensile Structural Steel ( IS – 961-1962 ) designated as St 58 – HT St 55 – HTW High Yield strength Deformed Bars (HYSD)[IS 1786 – 1985] designated as Fe 415, Fe 500, Fe 55010

11. Constituents in PercentagesDesignationCarbonSulphurPhosphorusSiliconSulphur & PhosphorusMild steel St 42 – S 0.250.060.06--High tensile SteelSt 58 – HTSt 55 – HTW0.300.220.060.060.060.06-0.0.1-Table 1 Chemical Composition11

12. PHYSICAL PROPERTIES [ BIS 1786 – 1985 ]Proof Stress/Yield Stress; percentage elongation and tensile strength for all sizes of deformed bars/wires determined in accordance with IS 1608 – 1972 and read in conjunction with IS 226 – 1975 shall be as given in table 2S. NoPropertyGradeFe 415Fe 500 Fe 55010.2 percent proof/Yield Stress, Min, N/mm24155005502Elongation, Percent, Min14.51283Tensile Strength, Min.10 percent more than the actual Yield stress but not less than 485N/mm28 percent more than the actual Yield stress but not less than 545N/mm26 percent more than the actual Yield stress but not less than 585N/mm2Table 2 Mechanical Properties of High Strength Deformed Bars and Wires12

13. Type of SteelClass of SteelNominal Size or Thickness (mm)Guaranteed Min. Yield Stress (N/mm2)Tensile Strength, Min. N/mm2Percentage elongation min. %IS 226 – 1962(St 42 – S)Plate Sections and Flats6 to 2021 to 40over 40260240230420420420232323Bars (round, square, hexagonal)10 to 20over 202602404204202323IS 961 – 1962 (St – 58 HT GradePlates, Section, Flats and bars6 to 2829 to 4545 to 63over 6336035033030058058058055020202020IS 961 – 1962 (St – 55 HTW GradePlates, Section, Flats and bars6 to 1617 to 3233 to 63over 6336035034029055055052050020202020Table 3 Mechanical (Tensile) Properties of Structural Steels13