Cast iron

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A small cast iron pan.jpg
Examples of cast iron

Cast iron is a class of ironcarbon alloys with a carbon content of more than 2% and silicon content around 1–3%. [1] 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.


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. [2] 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. [3] 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.


Cast iron is made from pig iron, which is the product of melting iron ore in a blast furnace. Cast iron can be made directly from the molten pig iron or by re-melting pig iron, [4] often along with substantial quantities of iron, steel, limestone, carbon (coke) and taking various steps to remove undesirable contaminants. Phosphorus and sulfur may be burnt out of the molten iron, but this also burns out the carbon, which must be replaced. Depending on the application, carbon and silicon content are adjusted to the desired levels, which may be anywhere from 2–3.5% and 1–3%, respectively. If desired, other elements are then added to the melt before the final form is produced by casting.[ citation needed ]

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 ]


Alloying elements

Iron-cementite meta-stable diagram Iron carbon phase diagram.svg
Iron-cementite meta-stable diagram

Cast iron's properties are changed by adding various alloying elements, or alloyants. Next to carbon, silicon is the most important alloyant because it forces carbon out of solution. A low percentage of silicon allows carbon to remain in solution forming iron carbide and the production of white cast iron. A high percentage of silicon forces carbon out of solution forming graphite and the production of grey cast iron. Other alloying agents, manganese, chromium, molybdenum, titanium and vanadium counteracts silicon, promotes the retention of carbon, and the formation of those carbides. Nickel and copper increase strength, and machinability, but do not change the amount of graphite formed. The carbon in the form of graphite results in 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. The problem with sulfur is that it makes molten cast iron viscous, which causes defects. To counter the effects of sulfur, manganese is added because the two form into manganese sulfide instead of iron sulfide. The manganese sulfide is lighter than the melt, so it tends to float out of the melt and into the slag. The amount of manganese required to neutralize sulfur is 1.7 × sulfur content + 0.3%. If more than this amount of manganese is added, then manganese carbide forms, which increases hardness and chilling, except in grey iron, where up to 1% of manganese increases strength and density. [6]

Nickel is one of the most common alloying elements because it refines the pearlite and graphite structure, 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. 0.15–0.5% vanadium is added to cast iron to stabilize cementite, increase hardness, and increase resistance to wear and heat. 0.1–0.3% zirconium helps to form graphite, deoxidize, and increase fluidity. [6]

In malleable iron melts, bismuth is added, on the scale of 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

Pair of English firedogs, 1576. These, with firebacks, were common early uses of cast iron, as little strength in the metal was needed. BLW Pair of firedogs.jpg
Pair of English firedogs, 1576. These, with firebacks, were common early uses of cast iron, as little strength in the metal was needed.

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 tensile strength and shock resistance than steel, but its compressive strength is comparable to low- and medium-carbon steel. 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. [7]

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 metastable phase cementite, Fe3C, rather than graphite. The cementite which precipitates from the melt forms as relatively large particles. 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). These eutectic carbides are much too large to provide the benefit of what is called precipitation hardening (as in some steels, where much smaller cementite precipitates might inhibit [plastic deformation] by impeding the movement of dislocations through the pure iron ferrite matrix). Rather, they increase the bulk hardness of the cast iron simply by virtue of their own very high hardness and their substantial volume fraction, such that the bulk hardness can be approximated by a rule of mixtures. In any case, they offer hardness at the expense of toughness. 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, and the teeth of a backhoe's digging bucket (although cast medium-carbon martensitic steel is more common for this application).[ citation needed ]

Cross section of chilled cast-iron roll Querschnitt Schalenhartguss.jpg
Cross section of chilled cast-iron roll

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 heat treated for a day or two at about 950 °C (1,740 °F) and then cooled over a day or two. As a result, the carbon in iron carbide transforms into graphite and ferrite plus carbon. The slow process allows the surface tension to form the graphite into spheroidal particles rather than flakes. Due to their lower aspect ratio, the spheroids are relatively short and far from one another, and have a lower cross section vis-a-vis a propagating crack or phonon. They also have blunt boundaries, as opposed to flakes, which alleviates the stress concentration problems found in grey cast iron. In general, the properties of malleable cast iron are more like those of mild steel. There is a limit to how large a part can be cast in malleable iron, as it is made from white cast iron.[ citation needed ]

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

Comparative qualities of cast irons [10]
NameNominal composition [% by weight]Form and conditionYield strength [ ksi (0.2% offset)]Tensile strength [ksi]Elongation [%]Hardness [ Brinell scale ]Uses
Grey cast iron (ASTM A48)C 3.4, Si 1.8, Mn  0.5Cast500.5260 Engine cylinder blocks, flywheels, gearbox cases, machine-tool bases
White cast ironC 3.4, Si 0.7, Mn 0.6Cast (as cast)250450 Bearing surfaces
Malleable iron (ASTM A47)C 2.5, Si 1.0, Mn 0.55Cast (annealed)335212130 Axle bearings, track wheels, automotive crankshafts
Ductile or nodular ironC 3.4, P 0.1, Mn 0.4, Ni  1.0, Mg 0.06Cast537018170Gears, camshafts, crankshafts
Ductile or nodular iron (ASTM A339)Cast (quench tempered)1081355310
Ni-hard type 2C 2.7, Si 0.6, Mn 0.5, Ni 4.5, Cr 2.0Sand-cast55550High strength applications
Ni-resist type 2C 3.0, Si 2.0, Mn 1.0, Ni 20.0, Cr 2.5Cast272140Resistance to heat and corrosion


Cast-iron artifact dated from 5th century BC found in Jiangsu, China Chengqiao artifact no. 35 cast iron.png
Cast-iron artifact dated from 5th century BC found in Jiangsu, China
Diorama model of a Han dynasty blast furnace blower Eastern Han Blast Furnace Blower Model (10340434095).jpg
Diorama model of a Han dynasty blast furnace blower
The Iron Lion of Cangzhou, the largest surviving cast-iron artwork from China, 953 AD, Later Zhou period Iron Lion of Cangzhou 2007.jpg
The Iron Lion of Cangzhou, the largest surviving cast-iron artwork from China, 953 AD, Later Zhou period
Cast-iron drain, waste and vent piping Cast fe and cu dwv piping.jpg
Cast-iron drain, waste and vent piping
Cast-iron plate on grand piano Steinway Grand Piano Iron Plates and Strings.jpg
Cast-iron plate on grand piano

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. [12] Although steel was more desirable, cast iron was cheaper and thus was more commonly used for implements in ancient China, while wrought iron or steel was used for weapons. [2] The Chinese developed a method of annealing cast iron by keeping hot castings in an oxidizing atmosphere for a week or longer in order to burn off some carbon near the surface in order to keep the surface layer from being too brittle. [13] :43

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. Henry VIII initiated the casting of cannon in England. Soon, English iron workers using blast furnaces developed the technique of producing cast-iron cannons, which, while heavier than the prevailing bronze cannons, were much cheaper and enabled England to arm her navy better. The technology of cast iron was transferred from China. [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. This is close to the silk route, so that the use of technology derived from China is conceivable. [15] The ironmasters of the Weald continued producing cast irons until the 1760s, and armament was one of the main uses of irons after the Restoration.

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 Manchester terminus of the Liverpool and Manchester Railway, but problems with its use became all too apparent when a new bridge carrying the Chester and Holyhead Railway across the River Dee in Chester collapsed killing five people in May 1847, less than a year after it was opened. The Dee bridge disaster was caused by excessive loading at the centre of the beam by a passing train, and many similar bridges had to be demolished and rebuilt, often in wrought iron. 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.

Nevertheless, cast iron continued to be used in inappropriate structural ways, until the Tay Rail Bridge disaster of 1879 cast serious doubt on the use of the material. 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. In addition, the bolt holes were also cast and not drilled. Thus, because of casting's draft angle, the tension from the tie bars was placed on the hole's edge rather than being spread over the length of the hole. The replacement bridge was built in wrought iron and steel.

Further bridge collapses occurred, however, culminating in the Norwood Junction rail accident of 1891. Thousands of cast-iron rail underbridges were eventually replaced by steel equivalents by 1900 owing to the widespread concern about cast iron under bridges on the rail network in Britain.


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

Cast-iron waffle iron, an example of cast-iron cookware Belgian waffles cooked in a Krampouz cast-iron waffle iron.JPG
Cast-iron waffle iron, an example of cast-iron cookware

Related Research Articles

<span class="mw-page-title-main">Alloy</span> Mixture or metallic solid solution composed of two or more elements

An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, opacity, and luster, but may have properties that differ from those of the pure metals, such as increased strength or hardness. In some cases, an alloy may reduce the overall cost of the material while preserving important properties. In other cases, the mixture imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength.

<span class="mw-page-title-main">Metallurgy</span> Field of science that studies the physical and chemical behavior of metals

Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys.

<span class="mw-page-title-main">Steel</span> Metal alloy of iron with other elements

Steel is an alloy of iron and carbon with improved strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels, which are resistant to corrosion and oxidation, typically need an additional 11% chromium. Because of its high tensile strength and low cost, steel is used in buildings, infrastructure, tools, ships, trains, cars, bicycles, machines, electrical appliances, furniture, and weapons.

<span class="mw-page-title-main">Pig iron</span> Iron alloy

Pig iron, also known as crude iron, is an intermediate good used by the iron industry in the production of steel. It is developed by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with silica and other constituents of dross, which makes it brittle and not useful directly as a material except for limited applications.

<span class="mw-page-title-main">Wrought iron</span> Iron alloy with a very low carbon content

Wrought iron is an iron alloy with a very low carbon content in contrast to that of cast iron. It is a semi-fused mass of iron with fibrous slag inclusions, which give it a wood-like "grain" that is visible when it is etched, rusted, or bent to failure. Wrought iron is tough, malleable, ductile, corrosion resistant, and easily forge welded, but is more difficult to weld electrically.

<span class="mw-page-title-main">Cementite</span> Compound of iron and carbon

Cementite (or iron carbide) is a compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe3C. By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure. It is a hard, brittle material, normally classified as a ceramic in its pure form, and is a frequently found and important constituent in ferrous metallurgy. While cementite is present in most steels and cast irons, it is produced as a raw material in the iron carbide process, which belongs to the family of alternative ironmaking technologies. The name cementite originated from the theory of Floris Osmond and J. Werth, in which the structure of solidified steel consists of a kind of cellular tissue, with ferrite as the nucleus and Fe3C the envelope of the cells. The carbide therefore cemented the iron.

<span class="mw-page-title-main">Austenite</span> Metallic, non-magnetic allotrope of iron or a solid solution of iron, with an alloying element

Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K (727 °C); other alloys of steel have different eutectoid temperatures. The austenite allotrope is named after Sir William Chandler Roberts-Austen (1843–1902). It exists at room temperature in some stainless steels due to the presence of nickel stabilizing the austenite at lower temperatures.

<span class="mw-page-title-main">Pearlite</span> Lamellar structure of ferrite and cementite

Pearlite is a two-phased, lamellar structure composed of alternating layers of ferrite and cementite that occurs in some steels and cast irons. During slow cooling of an iron-carbon alloy, pearlite forms by a eutectoid reaction as austenite cools below 723 °C (1,333 °F). Pearlite is a microstructure occurring in many common grades of steels.

<span class="mw-page-title-main">Carbon steel</span> Steel in which the main interstitial alloying constituent is carbon

Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:

<span class="mw-page-title-main">Tool steel</span> Any of various steels that are particularly well-suited to be made into tools and tooling

Tool steel is any of various carbon steels and alloy steels that are particularly well-suited to be made into tools and tooling, including cutting tools, dies, hand tools, knives, and others. Their suitability comes from their distinctive hardness, resistance to abrasion and deformation, and their ability to hold a cutting edge at elevated temperatures. As a result, tool steels are suited for use in the shaping of other materials, as for example in cutting, machining, stamping, or forging.

<span class="mw-page-title-main">Refractory</span> Materials resistant to decomposition under high temperatures

In materials science, a refractory is a material that is resistant to decomposition by heat or chemical attack that retains its strength and rigidity at high temperatures. They are inorganic, non-metallic compounds that may be porous or non-porous, and their crystallinity varies widely: they may be crystalline, polycrystalline, amorphous, or composite. They are typically composed of oxides, carbides or nitrides of the following elements: silicon, aluminium, magnesium, calcium, boron, chromium and zirconium. Many refractories are ceramics, but some such as graphite are not, and some ceramics such as clay pottery are not considered refractory. Refractories are distinguished from the refractory metals, which are elemental metals and their alloys that have high melting temperatures.

<span class="mw-page-title-main">Ductile iron</span> Type of cast iron

Ductile iron, also known as ductile cast iron, nodular cast iron, spheroidal graphite iron, spheroidal graphite cast iron and SG iron, is a type of graphite-rich cast iron discovered in 1943 by Keith Millis. While most varieties of cast iron are weak in tension and brittle, ductile iron has much more impact and fatigue resistance, due to its nodular graphite inclusions.

<span class="mw-page-title-main">Case-hardening</span> Process of hardening the surface of a metal object

Case-hardening or Carburization is the process of introducing carbon to the surface of a low carbon iron or much more commonly low carbon steel object in order to enable the surface to be hardened.

<span class="mw-page-title-main">Tempering (metallurgy)</span> Process of heat treating used to increase the toughness of iron-based alloys

Tempering is a process of heat treating, which is used to increase the toughness of iron-based alloys. Tempering is usually performed after hardening, to reduce some of the excess hardness, and is done by heating the metal to some temperature below the critical point for a certain period of time, then allowing it to cool in still air. The exact temperature determines the amount of hardness removed, and depends on both the specific composition of the alloy and on the desired properties in the finished product. For instance, very hard tools are often tempered at low temperatures, while springs are tempered at much higher temperatures.

The equivalent carbon content concept is used on ferrous materials, typically steel and cast iron, to determine various properties of the alloy when more than just carbon is used as an alloyant, which is typical. The idea is to convert the percentage of alloying elements other than carbon to the equivalent carbon percentage, because the iron-carbon phases are better understood than other iron-alloy phases. Most commonly this concept is used in welding, but it is also used when heat treating and casting cast iron.

<span class="mw-page-title-main">Gray iron</span> Alloy of iron and carbon

Gray iron, or grey cast iron, is a type of cast iron that has a graphitic microstructure. It is named after the gray color of the fracture it forms, which is due to the presence of graphite. It is the most common cast iron and the most widely used cast material based on weight.

<span class="mw-page-title-main">Malleable iron</span>

Malleable iron is cast as white iron, the structure being a metastable carbide in a pearlitic matrix. Through an annealing heat treatment, the brittle structure as first cast is transformed into the malleable form. Carbon agglomerates into small roughly spherical aggregates of graphite, leaving a matrix of ferrite or pearlite according to the exact heat treatment used.

Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties.

<span class="mw-page-title-main">Mangalloy</span> Alloy steel containing around 13% manganese

Mangalloy, also called manganese steel or Hadfield steel, is an alloy steel containing an average of around 13% manganese. Mangalloy is known for its high impact strength and resistance to abrasion once in its work-hardened state.


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Further reading