Civil Engineering Materials: Chapter 10 - Steel PDF

Civil Engineering Materials Sivakugan/Gnanendran/Tuladhar/Kannan Chapter 10...

Civil Engineering Materials Sivakugan/Gnanendran/Tuladhar/Kannan Chapter 10 Steel © 2018 Cengage Learning®. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 1 Civil Engineering Materials Sivakugan/Gnanendran/Tuladhar/Kannan Introduction Steel forms a critical component of construction, machinery, and manufacturing industries. Structural steel is produced from iron ore, and contains 0.2 – 1.5 wt% carbon, as well as other elements. Modern steel manufacturing processes like basic oxygen steelmaking and the electric arc furnace have made steel one of the most efficient and versatile construction materials. © 2018 Cengage Learning®. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 2 Civil Engineering Materials Sivakugan/Gnanendran/Tuladhar/Kannan Advantages of Steel High strength-to-weight ratio reduces dead load (self-weight) of structures. High stiffness and ductility. Termite- and rot-proof. Homogeneous material with uniform and predictable properties. Similar tension and compression properties. Steel sections can be fabricated at a factory (excellent quality control). Does not require expensive formworks for construction. 100% recyclable and has high scrap value. Easy to repair. Steel structures can be dismantled and reassembled. © 2018 Cengage Learning®. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 3 Civil Engineering Materials Sivakugan/Gnanendran/Tuladhar/Kannan Limitations of Steel Properties can degrade at high temperatures or during a fire. Concrete encasing can protect steel from fire damage. Susceptible to corrosion, leading to loss of strength. Protective coatings are paints are used to prevent corrosion. Brittle failure can occur at low temperatures. Buckling failure can occur in slender steel members. © 2018 Cengage Learning®. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 4 Civil Engineering Materials Sivakugan/Gnanendran/Tuladhar/Kannan Iron- and Steel-Making Early iron was wrought– impurities were removed by heavy hammering. Blast furnaces enabled smelting– the process of melting a metal out of its ore. Molten iron is directly poured into molds to produce cast iron. An intermediate product called pig iron could also be produced. In 1856, the Bessemer process was invented. Hot air is blown through molten pig iron and limestone, reducing carbon and other impurities and producing steel. By the late 19th century, the open-hearth process was used. Pig iron and scrap metal are melted with limestone in an open-hearth furnace. Modern steelmaking uses main the basic oxygen steelmaking (BOS) and electric arc furnace (EAF) methods. © 2018 Cengage Learning®. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 5 Civil Engineering Materials Sivakugan/Gnanendran/Tuladhar/Kannan Basic Oxygen Steelmaking (BOS) An adaptation of the Bessemer process where pure oxygen is used instead of air. BOS is the main bulk production process used around the world. Uses 25 – 35% steel scrap to make new steel. Molten pig iron and scrap steel are fed into a BOS vessel. High-pressure oxygen is blown on the molten metal to remove impurities, producing slag. Exothermic oxidation reactions increase the temperature of the furnace. © 2018 Cengage Learning®. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 6 Civil Engineering Materials Sivakugan/Gnanendran/Tuladhar/Kannan Electric Arc Furnace Uses scrap steel to produce new steel. Scrap steel and limes are heated using an electric arc, causing them to melt. Oxygen is blown into the furnace to remove impurities, producing slag. Slag is removed, and then molten steel can be removed. © 2018 Cengage Learning®. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 7 Civil Engineering Materials Sivakugan/Gnanendran/Tuladhar/Kannan Wrought Iron A relatively pure iron alloy with very low carbon content (0.02 – 0.08%). Iron ore is heated with charcoal or coal, and released oxygen combines with carbon. A spongy mass of bloom is produced that contains traces of charcoal and slag. Impurities and slag are driven off by hammering the hot bloom. Produced since the Iron Age and used in construction in the 19th century (ex: Eiffel Tower). Currently limited to decorative purposes due to steel production. © 2018 Cengage Learning®. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 8 Civil Engineering Materials Sivakugan/Gnanendran/Tuladhar/Kannan Cast Iron Has relatively high carbon content (2 – 4%). Iron heated at high temperatures absorbs carbon, resulting in molten iron. Flux (ex: limestone) is used to remove impurities. Molten iron is cast into desired shapes. Grey cast iron contains carbon flakes. It is easy to cast but cannot be worked. White cast iron contains carbides of iron. It has better tensile strength and malleability. Cast iron is hard, brittle and not malleable. © 2018 Cengage Learning®. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 9 Civil Engineering Materials Sivakugan/Gnanendran/Tuladhar/Kannan Cast Iron (cont.) It is strong in compression but weak in tension. Cast iron was used in compressive structures such as arches and columns. It was replaced by steel for construction at the end of the 19th century, but is still used in cookware, piping, and engine blocks. © 2018 Cengage Learning®. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 10 Civil Engineering Materials Sivakugan/Gnanendran/Tuladhar/Kannan Carbon Steel Contains carbon in the range of 0.12 – 2%, manganese up to 1.65%, and silicon up to 0.6%. Can be classified based on carbon content. Low-carbon steel: