Cast iron
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.
Cast iron was used in ancient China to mass-produce weaponry for warfare, as well as agriculture and architecture.
[2] During the 15th century AD, cast iron became utilized for cannons and shot in Burgundy, France, and in England during the Reformation.
A high percentage of silicon forces carbon out of solution, forming graphite and producing grey cast iron.
Other alloying agents, manganese, chromium, molybdenum, titanium, and vanadium counteract silicon, and promote the retention of carbon and the formation of those carbides.
Carbon as graphite produces a softer iron, reduces shrinkage, lowers strength, and decreases density.
Sulfur, largely a contaminant when present, forms iron sulfide, which prevents the formation of graphite and increases hardness.
[6] 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.
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.
These mechanical properties are controlled by the size and shape of the graphite flakes present in the microstructure and can be characterised according to the guidelines given by the ASTM.
As the iron carbide precipitates out, it withdraws carbon from the original melt, moving the mixture toward one that is closer to eutectic, and the remaining phase is the lower iron-carbon austenite (which on cooling might transform to martensite).
Since carbide makes up a large fraction of the material, white cast iron could reasonably be classified as a cermet.
White iron is too brittle for use in many structural components, but with good hardness and abrasion resistance and relatively low cost, it finds use in such applications as the wear surfaces (impeller and volute) of slurry pumps, shell liners and lifter bars in ball mills and autogenous grinding mills, balls and rings in coal pulverisers.
The slow process allows the surface tension to form the graphite into spheroidal particles rather than flakes.
They also have blunt boundaries, as opposed to flakes, which alleviates the stress concentration problems found in grey cast iron.
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.
Along with careful control of other elements and timing, this allows the carbon to separate as spheroidal particles as the material solidifies.
[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.
[2] Because cast iron is comparatively brittle, it is not suitable for purposes where a sharp edge or flexibility is required.
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.
[13]: 43 Deep within the Congo region of the Central African forest, blacksmiths invented sophisticated furnaces capable of high temperatures over 1000 years ago.
Numerous testimonies were made by early European missionaries of the Luba people pouring cast iron into molds to make hoes.
[15] Al-Qazvini in the 13th century and other travellers subsequently noted an iron industry in the Alburz Mountains to the south of the Caspian Sea.
The bridge had been badly designed, being trussed with wrought iron straps, which were wrongly thought to reinforce the structure.
The centres of the beams were put into bending, with the lower edge in tension, where cast iron, like masonry, is very weak.
Crucial lugs for holding tie bars and struts in the Tay Bridge had been cast integral with the columns, and they failed in the early stages of the accident.
Cast iron was also used sometimes for decorative facades, especially in the United States, and the Soho district of New York has numerous examples.
[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.
