Production and Types of Cast Iron
– Cast iron is made from pig iron, which is the product of melting iron ore in a blast furnace.
– It can be made directly from molten pig iron or by re-melting pig iron along with other elements.
– Carbon and silicon content are adjusted to desired levels, typically 2-3.5% and 1-3% respectively.
– Cast iron can be melted in a cupola, electric induction furnaces, or electric arc furnaces.
– After melting, the molten cast iron is poured into a holding furnace or ladle.
– Cast iron properties are changed by adding alloying elements such as carbon, silicon, manganese, chromium, molybdenum, titanium, vanadium, nickel, copper, sulfur, and tin.
– Silicon forces carbon out of solution, forming graphite and producing grey cast iron.
– Manganese neutralizes sulfur and forms manganese sulfide, preventing the formation of graphite.
– Nickel refines the pearlite and graphite structure, improves toughness, and evens out hardness.
– Chromium reduces free graphite, produces chill, and stabilizes carbides.
– Copper decreases chill, refines graphite, and increases fluidity.
– Carbon and silicon are the main alloying elements in cast iron.
– Manganese, chromium, molybdenum, titanium, and vanadium counteract silicon and promote carbon retention.
– Nickel and copper increase strength and machinability.
– Sulfur forms iron sulfide, which prevents graphite formation and increases hardness.
– Tin can be added as a substitute for chromium.
– Grey cast iron is the most commonly used and widely used cast material.
– Grey cast iron has a graphitic microstructure, giving it a grey appearance.
– White cast iron displays white fractured surfaces due to the presence of iron carbide called cementite.
– Eutectic carbides in white cast iron increase bulk hardness due to their high hardness and volume fraction.
– The remaining phase in white cast iron is lower iron-carbon austenite.
Properties and Applications
– Grey cast iron has lower tensile strength and shock resistance compared to steel, but comparable compressive strength to low- and medium-carbon steel.
– Mechanical properties of grey cast iron are controlled by the size and shape of graphite flakes.
– White cast iron offers high hardness and abrasion resistance, making it suitable for wear surfaces of slurry pumps, ball mills, coal pulverisers, and backhoe digging buckets.
– White cast iron is brittle and not suitable for structural components.
– Malleable cast iron is heat-treated to transform carbon into graphite and ferrite, resulting in spheroidal particles and alleviating stress concentration problems.
– Malleable cast iron has properties similar to mild steel.
– Ductile cast iron has graphite in the form of tiny nodules with concentric layers, providing spongy steel-like properties without stress concentration effects.
– Ductile cast iron can be cast in larger sections.
– Grey cast iron is used in engine cylinder blocks, flywheels, gearbox cases, and machine-tool bases.
– White cast iron is used for bearing surfaces.
– Malleable iron is used in axle bearings, track wheels, and automotive crankshafts.
– Ductile or nodular iron is used for gears, camshafts, and crankshafts.
– Ni-hard type 2 cast iron is suitable for high strength applications.
– Cast iron is used in various applications such as engine blocks, pipes and fittings, cookware, manhole covers, and agricultural machinery.
Historical Significance
– Earliest cast iron artifacts date back to the 5th century BC in China.
– Cast iron was cheaper than steel and commonly used for implements in ancient China.
– Chinese developed a method of annealing cast iron to reduce brittleness.
– Blacksmiths in the Congo region invented sophisticated furnaces for casting iron over 1000 years ago.
– Cast iron technology was transferred from China to the West, with England becoming a major producer.
– Cast iron was first used for structural purposes in the late 1770s with the construction of the Iron Bridge by Abraham Darby III.
– Thomas Telford also adopted cast iron for bridge construction during the Industrial Revolution.
– Cast-iron bridges were commonly used during the Industrial Revolution.
– Cast iron columns revolutionized building construction, allowing for multi-storey buildings without thick walls.
– Cast iron was extensively used in textile mills to replace flammable wood structures.
Advantages of Cast Iron
– Cast iron is an affordable material.
– It has a high strength-to-weight ratio.
– Cast iron has excellent machinability.
– It offers good corrosion resistance.
– Cast iron has a long lifespan.
Disadvantages of Cast Iron
– Cast iron is brittle in nature and susceptible to cracking.
– It is heavy in weight.
– Cast iron has limited design flexibility.
– It is difficult to weld. Source: https://en.wikipedia.org/wiki/Cast_iron
Cast iron is a class of iron–carbon alloys with a carbon content more than 2% and silicon content around 1-3%. Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its carbon appears: white cast iron has its carbon combined into an iron carbide named cementite, which is very hard, but brittle, as it allows cracks to pass straight through; grey cast iron has graphite flakes which deflect a passing crack and initiate countless new cracks as the material breaks, and ductile cast iron has spherical graphite "nodules" which stop the crack from further progressing.
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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 brittle, except for malleable cast irons. With its relatively low melting point, good fluidity, castability, excellent machinability, resistance to deformation and wear resistance, cast irons have become an engineering material with a wide range of applications and are used in pipes, machines and automotive industry parts, such as cylinder heads, cylinder blocks and gearbox cases. It is resistant to damage by oxidation but is notoriously difficult to weld.
The earliest cast-iron artefacts date to the 5th century BC, and were discovered by archaeologists in what is now Jiangsu, China. Cast iron was used in ancient China for warfare, agriculture, and architecture. During the 15th century AD, cast iron became utilized for cannon in Burgundy, France, and in England during the Reformation. The amounts of cast iron used for cannons required large-scale production. The first cast-iron bridge was built during the 1770s by Abraham Darby III, and is known as the Iron Bridge in Shropshire, England. Cast iron was also used in the construction of buildings.
