Cast iron
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Cast iron is a class of
Carbon (C), ranging from 1.8 to 4 wt%, and silicon (Si), 1–3 wt%, are the main alloying elements of cast iron. Iron alloys with lower carbon content are known as steel.
Cast iron tends to be
The earliest cast-iron artefacts date to the 5th century BC, and were discovered by
Production
Cast iron is made from
Cast iron is sometimes melted in a special type of blast furnace known as a cupola, but in modern applications, it is more often melted in electric induction furnaces or electric arc furnaces.[5] After melting is complete, the molten cast iron is poured into a holding furnace or ladle.[citation needed]
Types
Alloying elements
Cast iron's properties are changed by adding various alloying elements, or
Nickel is one of the most common alloying elements, because it refines the pearlite and graphite structures, improves toughness, and evens out hardness differences between section thicknesses. Chromium is added in small amounts to reduce free graphite, produce chill, and because it is a powerful carbide stabilizer; nickel is often added in conjunction. A small amount of tin can be added as a substitute for 0.5% chromium. Copper is added in the ladle or in the furnace, on the order of 0.5–2.5%, to decrease chill, refine graphite, and increase fluidity. Molybdenum is added on the order of 0.3–1% to increase chill and refine the graphite and pearlite structure; it is often added in conjunction with nickel, copper, and chromium to form high strength irons. Titanium is added as a degasser and deoxidizer, but it also increases fluidity. Vanadium at 0.15–0.5% is added to cast iron to stabilize cementite, increase hardness, and increase resistance to wear and heat. Zirconium at 0.1–0.3% helps to form graphite, deoxidize, and increase fluidity.[6]
In malleable iron melts, bismuth is added at 0.002–0.01% to increase how much silicon can be added. In white iron, boron is added to aid in the production of malleable iron; it also reduces the coarsening effect of bismuth.[6]
Grey cast iron
Grey cast iron is characterised by its graphitic microstructure, which causes fractures of the material to have a grey appearance. It is the most commonly used cast iron and the most widely used cast material based on weight. Most cast irons have a chemical composition of 2.5–4.0% carbon, 1–3% silicon, and the remainder iron. Grey cast iron has less
White cast iron
White cast iron displays white fractured surfaces due to the presence of an iron carbide precipitate called cementite. With a lower silicon content (graphitizing agent) and faster cooling rate, the carbon in white cast iron precipitates out of the melt as the
It is difficult to cool thick castings fast enough to solidify the melt as white cast iron all the way through. However, rapid cooling can be used to solidify a shell of white cast iron, after which the remainder cools more slowly to form a core of grey cast iron. The resulting casting, called a chilled casting, has the benefits of a hard surface with a somewhat tougher interior.[citation needed]
High-chromium white iron alloys allow massive castings (for example, a 10-tonne impeller) to be sand cast, as the chromium reduces cooling rate required to produce carbides through the greater thicknesses of material. Chromium also produces carbides with impressive abrasion resistance.[8] These high-chromium alloys attribute their superior hardness to the presence of chromium carbides. The main form of these carbides are the eutectic or primary M7C3 carbides, where "M" represents iron or chromium and can vary depending on the alloy's composition. The eutectic carbides form as bundles of hollow hexagonal rods and grow perpendicular to the hexagonal basal plane. The hardness of these carbides are within the range of 1500-1800HV.[9]
Malleable cast iron
Malleable iron starts as a white iron casting that is then
Ductile cast iron
Developed in 1948, nodular or ductile cast iron has its graphite in the form of very tiny nodules with the graphite in the form of concentric layers forming the nodules. As a result, the properties of ductile cast iron are that of a spongy steel without the stress concentration effects that flakes of graphite would produce. The carbon percentage present is 3-4% and percentage of silicon is 1.8-2.8%.Tiny amounts of 0.02 to 0.1% magnesium, and only 0.02 to 0.04% cerium added to these alloys slow the growth of graphite precipitates by bonding to the edges of the graphite planes. Along with careful control of other elements and timing, this allows the carbon to separate as spheroidal particles as the material solidifies. The properties are similar to malleable iron, but parts can be cast with larger sections.[citation needed]
Table of comparative qualities of cast irons
Name | Nominal composition [% by weight] | Form and condition | Yield strength [ ksi (0.2% offset)]
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Tensile strength [ksi] | Elongation [%] | Hardness [Brinell scale] | Uses |
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Grey cast iron (ASTM A48) | C 3.4, Si 1.8, Mn 0.5 | Cast | — | 50 | 0.5 | 260 | Engine cylinder blocks, flywheels, gearbox cases, machine-tool bases |
White cast iron | C 3.4, Si 0.7, Mn 0.6 | Cast (as cast) | — | 25 | 0 | 450 | Bearing surfaces |
Malleable iron (ASTM A47) | C 2.5, Si 1.0, Mn 0.55 | Cast (annealed) | 33 | 52 | 12 | 130 | Axle bearings, track wheels, automotive crankshafts |
Ductile or nodular iron | C 3.4, P 0.1, Mn 0.4, Ni 1.0, Mg 0.06 | Cast | 53 | 70 | 18 | 170 | Gears, camshafts, crankshafts |
Ductile or nodular iron (ASTM A339) | — | Cast (quench tempered) | 108 | 135 | 5 | 310 | — |
Ni-hard type 2 | C 2.7, Si 0.6, Mn 0.5, Ni 4.5, Cr 2.0 | Sand-cast | — | 55 | — | 550 | High strength applications |
Ni-resist type 2 | C 3.0, Si 2.0, Mn 1.0, Ni 20.0, Cr 2.5 | Cast | — | 27 | 2 | 140 | Resistance to heat and corrosion |
History
Cast iron and wrought iron can be produced unintentionally when smelting copper using iron ore as a flux.[11]: 47–48
The earliest cast-iron artifacts date to the 5th century BC, and were discovered by archaeologists in what is now modern Luhe County, Jiangsu in China during the Warring States period. This is based on an analysis of the artifact's microstructures.[2]
Because cast iron is comparatively brittle, it is not suitable for purposes where a sharp edge or flexibility is required. It is strong under compression, but not under tension. Cast iron was invented in China in the 5th century BC and poured into molds to make ploughshares and pots as well as weapons and pagodas.
Deep within the Congo region of the Central African forest, blacksmiths invented sophisticated furnaces capable of high temperatures over 1000 years ago. There are countless examples of welding, soldering, and cast iron created in crucibles and poured into molds. These techniques were employed for the use of composite tools and weapons with cast iron or steel blades and soft, flexible wrought iron interiors. Iron wire was also produced. Numerous testimonies were made by early European missionaries of the Luba people pouring cast iron into molds to make hoes. These technological innovations were accomplished without the invention of the blast furnace which was the prerequisite for the deployment of such innovations in Europe and Asia.[14]
In the west, where it did not become available until the 15th century, its earliest uses included cannon and shot.
Cast-iron pots were made at many English blast furnaces at the time. In 1707, Abraham Darby patented a new method of making pots (and kettles) thinner and hence cheaper than those made by traditional methods. This meant that his Coalbrookdale furnaces became dominant as suppliers of pots, an activity in which they were joined in the 1720s and 1730s by a small number of other coke-fired blast furnaces.
Application of the steam engine to power blast bellows (indirectly by pumping water to a waterwheel) in Britain, beginning in 1743 and increasing in the 1750s, was a key factor in increasing the production of cast iron, which surged in the following decades. In addition to overcoming the limitation on water power, the steam-pumped-water powered blast gave higher furnace temperatures which allowed the use of higher lime ratios, enabling the conversion from charcoal (supplies of wood for which were inadequate) to coke.[16]: 122
Cast-iron bridges
The use of cast iron for structural purposes began in the late 1770s, when Abraham Darby III built The Iron Bridge, although short beams had already been used, such as in the blast furnaces at Coalbrookdale. Other inventions followed, including one patented by Thomas Paine. Cast-iron bridges became commonplace as the Industrial Revolution gathered pace. Thomas Telford adopted the material for his bridge upstream at Buildwas, and then for Longdon-on-Tern Aqueduct, a canal trough aqueduct at Longdon-on-Tern on the Shrewsbury Canal. It was followed by the Chirk Aqueduct and the Pontcysyllte Aqueduct, both of which remain in use following the recent restorations.
The best way of using cast iron for bridge construction was by using arches, so that all the material is in compression. Cast iron, again like masonry, is very strong in compression. Wrought iron, like most other kinds of iron and indeed like most metals in general, is strong in tension, and also tough – resistant to fracturing. The relationship between wrought iron and cast iron, for structural purposes, may be thought of as analogous to the relationship between wood and stone.
Cast-iron beam bridges were used widely by the early railways, such as the Water Street Bridge in 1830 at the
Nevertheless, cast iron continued to be used in inappropriate structural ways, until the
Further bridge collapses occurred, however, culminating in the
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The Iron Bridge over the River Severn at Coalbrookdale, England (finished 1779)
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Original Tay Bridge from the north (finished 1878)
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Fallen Tay Bridge from the north
Buildings
Cast-iron columns, pioneered in mill buildings, enabled architects to build multi-storey buildings without the enormously thick walls required for masonry buildings of any height. They also opened up floor spaces in factories, and sight lines in churches and auditoriums. By the mid 19th century, cast iron columns were common in warehouse and industrial buildings, combined with wrought or cast iron beams, eventually leading to the development of steel-framed skyscrapers. Cast iron was also used sometimes for decorative facades, especially in the United States, and the Soho district of New York has numerous examples. It was also used occasionally for complete prefabricated buildings, such as the historic Iron Building in Watervliet, New York.[citation needed]
Textile mills
Another important use was in textile mills. The air in the mills contained flammable fibres from the cotton, hemp, or wool being spun. As a result, textile mills had an alarming propensity to burn down. The solution was to build them completely of non-combustible materials, and it was found convenient to provide the building with an iron frame, largely of cast iron, replacing flammable wood. The first such building was at Ditherington in Shrewsbury, Shropshire.[17] Many other warehouses were built using cast-iron columns and beams, although faulty designs, flawed beams or overloading sometimes caused building collapses and structural failures.[citation needed]
During the Industrial Revolution, cast iron was also widely used for frame and other fixed parts of machinery, including spinning and later weaving machines in textile mills. Cast iron became widely used, and many towns had foundries producing industrial and agricultural machinery.[18]
See also
- Ironwork – artisan metalwork (for architectural elements, garden features, and ornamental objects)
- Ironworks – a place where iron is worked (including historical sites)
- Meehanite
- Sand casting
- Cast-iron cookware
References
- ISBN 978-0-87170-867-0.
- ^ ISBN 978-90-04-09632-5.
- ISBN 978-0-521-55866-2.
- ^ Electrical Record and Buyer's Reference. Buyers' Reference Company. 1917.
- ^ ISBN 978-0-87263-326-1.
- doi:10.1520/a0247-10.)
{{cite web}}
: CS1 maint: numeric names: authors list (link - S2CID 234545510. Retrieved 29 September 2022.
- S2CID 137453839.
- ^ Lyons, William C. and Plisga, Gary J. (eds.) Standard Handbook of Petroleum & Natural Gas Engineering, Elsevier, 2006
- ISBN 978-0901462886.
- ISBN 978-0-521-87566-0.
- ^ Temple, Robert (1986). The Genius of China: 3000 years of science, discovery and invention. New York: Simon and Schuster. Based on the works of Joseph Needham>
- ISBN 92-3-103807-9
- ^ a b Wagner, Donald B. (2008). Science and Civilisation in China: 5. Chemistry and Chemical Technology: part 11 Ferrous Metallurgy. Cambridge University Press, pp. 349–51.
- ISBN 978-0901462886.
- ^ "Ditherington Flax Mill: Spinning Mill, Shrewsbury – 1270576". Historic England. Retrieved 29 June 2020.
- ^ [citation needed]
Further reading
- Harold T. Angus, Cast Iron: Physical and Engineering Properties, Butterworths, London (1976) ISBN 0408706880
- John Gloag and Derek Bridgwater, A History of Cast Iron in Architecture, Allen and Unwin, London (1948)
- Peter R Lewis, Beautiful Railway Bridge of the Silvery Tay: Reinvestigating the Tay Bridge Disaster of 1879, Tempus (2004) ISBN 0-7524-3160-9
- Peter R Lewis, Disaster on the Dee: Robert Stephenson's Nemesis of 1847, Tempus (2007) ISBN 978-0-7524-4266-2
- George Laird, Richard Gundlach and Klaus Röhrig, Abrasion-Resistant Cast Iron Handbook, ASM International (2000) ISBN 0-87433-224-9
External links
- Metallurgy of Cast Irons, Cambridge University
- Forensic engineering:the Tay Bridge disaster Archived 23 March 2023 at the Wayback Machine
- Spanish cast-iron bridges