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.Sources: https://en.wikipedia.org/wiki/Cast_iron
