Alloy steel is
steel that is
alloy
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, ductilit ...
ed with a variety of
elements
Element or elements may refer to:
Science
* Chemical element, a pure substance of one type of atom
* Heating element, a device that generates heat by electrical resistance
* Orbital elements, parameters required to identify a specific orbit of ...
in total amounts between 1.0% and 50% by weight to improve its
mechanical properties. Alloy steels are broken down into two groups: low alloy steels and high alloy steels. The difference between the two is disputed. Smith and Hashemi define the difference at 4.0%, while Degarmo, ''et al.'', define it at 8.0%.
[Degarmo, p. 112.] Most commonly, the phrase "alloy steel" refers to low-alloy steels.
Strictly speaking, every steel is an alloy, but not all steels are called "alloy steels". The simplest steels are
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
(Fe) alloyed with
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...
(C) (about 0.1% to 1%, depending on type) and nothing else (excepting negligible traces via slight impurities); these are called
carbon steel
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:
* no minimum content is specified or required for chromium, coba ...
s. However, the term "alloy steel" is the standard term referring to steels with ''other'' alloying elements added deliberately ''in addition to'' the carbon. Common alloyants include
manganese
Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy u ...
(the most common one),
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...
,
chromium
Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.
Chromium metal is valued for its high corrosion resistance and h ...
,
molybdenum
Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with le ...
,
vanadium
Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an oxide layer ( pass ...
,
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...
, and
boron. Less common alloyants include
aluminium
Aluminium (aluminum in AmE, American and CanE, Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately o ...
,
cobalt
Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, ...
,
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish ...
,
cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 o ...
,
niobium
Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it ha ...
,
titanium
Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...
,
tungsten
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
,
tin,
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic t ...
,
lead
Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate ...
, and
zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...
.
The following is a range of improved properties in alloy steels (as compared to carbon steels):
strength,
hardness
In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion (mechanical), abrasion. In general, different materials differ in their hardn ...
,
toughness
In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.[wear resistance
Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology.
Wear in ...]
,
corrosion resistance
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
,
hardenability
The hardenability of a metal alloy is the depth to which a material is hardened after putting it through a heat treatment process. It should not be confused with hardness, which is a measure of a sample's resistance to indentation or scratching. I ...
, and
hot hardness
Hot or the acronym HOT may refer to:
Food and drink
*Pungency, in food, a spicy or hot quality
*Hot, a wine tasting descriptor
Places
* Hot district, a district of Chiang Mai province, Thailand
** Hot subdistrict, a sub-district of Hot Distri ...
. To achieve some of these improved properties the metal may require
heat treating
Heat treating (or heat treatment) is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are al ...
.
Although alloy steels have been made for centuries, their
metallurgy
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.
Metallurgy encompasses both the sci ...
was not well understood until
the advancing chemical science of the nineteenth century revealed their compositions. Alloy steels from earlier times were expensive luxuries made on the model of "secret recipes" and forged into such tools as knives and swords. Modern alloy steels of the
machine age were developed as improved
tool steel
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 h ...
s and as newly available
stainless steels. Today alloy steels find uses in a wide array of applications, from everyday hand tools and flatware to highly demanding applications such as in the turbine blades of jet engines and in nuclear reactors.
Because of the ferromagnetic properties of iron, some steel alloys find important applications where their responses to magnetism are very important, including in electric motors and in transformers.
Low-alloy steels
A few common low alloy steels are:
* D6AC
* 300M
* 256A
Material science
Alloying elements are added to achieve certain properties in the material. The alloying elements can change and personalize properties—their flexibility, strength, formability, and hardenability. As a guideline, alloying elements are added in lower percentages (less than 5%) to increase strength or hardenability, or in larger percentages (over 5%) to achieve special properties, such as corrosion resistance or extreme temperature stability.
Manganese, silicon, or aluminium are added during the
steelmaking
Steelmaking is the process of producing steel from iron ore and carbon/or scrap. In steelmaking, impurities such as nitrogen, silicon, phosphorus, sulfur and excess carbon (the most important impurity) are removed from the sourced iron, and allo ...
process to remove dissolved
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...
,
sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...
and
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...
from the
melt
Melt may refer to:
Science and technology
* Melting, in physics, the process of heating a solid substance to a liquid
* Melt (manufacturing), the semi-liquid material used in steelmaking and glassblowing
* Melt (geology), magma
** Melt inclusions, ...
. Manganese, silicon,
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...
, and copper are added to increase strength by forming solid solutions in ferrite. Chromium, vanadium, molybdenum, and tungsten increase strength by forming second-phase
carbide
In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece.
Interstitial / Metallic carbides
The carbides of th ...
s. Nickel and copper improve corrosion resistance in small quantities. Molybdenum helps to resist embrittlement. Zirconium, cerium, and calcium increase toughness by controlling the shape of inclusions. Sulfur (in the form of
manganese sulfide
Manganese(II) sulfide is a chemical compound of manganese and sulfur. It occurs in nature as the mineral alabandite (isometric), rambergite (hexagonal), and recently found browneite (isometric, with sphalerite-type structure, extremely rare, known ...
), lead, bismuth, selenium, and tellurium increase machinability. The alloying elements tend to form either solid solutions or compounds or carbides. Nickel is very soluble in ferrite; therefore, it forms compounds, usually Ni
3Al. Aluminium dissolves in the ferrite and forms the compounds Al
2O
3 and AlN. Silicon is also very soluble and usually forms the compound SiO
2•M
xO
y. Manganese mostly dissolves in ferrite forming the compounds MnS, MnO•SiO
2, but will also form carbides in the form of (Fe,Mn)
3C. Chromium forms partitions between the ferrite and carbide phases in steel, forming (Fe,Cr
3)C, Cr
7C
3, and Cr
23C
6. The type of carbide that chromium forms depends on the amount of carbon and other types of alloying elements present. Tungsten and molybdenum form carbides if there is enough carbon and an absence of stronger carbide forming elements (i.e.,
titanium
Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...
&
niobium
Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it ha ...
), they form the carbides W
2C and Mo
2C, respectively. Vanadium, titanium, and niobium are strong carbide forming elements, forming
vanadium carbide,
titanium carbide
Titanium carbide, Ti C, is an extremely hard ( Mohs 9–9.5) refractory ceramic material, similar to tungsten carbide. It has the appearance of black powder with the sodium chloride (face-centered cubic) crystal structure.
It occurs in nature ...
, and
niobium carbide
Niobium carbide ( Nb C and Nb2C) is an extremely hard refractory ceramic material, commercially used in tool bits for cutting tools. It is usually processed by sintering and is a frequent additive as grain growth inhibitor in cemented carbide ...
, respectively. Alloying elements also have an effect on the eutectoid temperature of the steel. Manganese and nickel lower the eutectoid temperature and are known as ''austenite stabilizing elements''. With enough of these elements the austenitic structure may be obtained at room temperature. Carbide-forming elements raise the eutectoid temperature; these elements are known as ''ferrite stabilizing elements''.
[Smith, pp. 395–396.]
See also
*
HSLA steel
*
Microalloyed steel
*
SAE steel grades
The SAE steel grades system is a standard alloy numbering system (SAE J1086 - Numbering Metals and Alloys) for steel grades maintained by SAE International.
In the 1930s and 1940s, the American Iron and Steel Institute (AISI) and SAE were both ...
*
Reynolds 531
References
Bibliography
*.
*Groover, M. P., 2007, p. 105-106, ''Fundamentals of Modern Manufacturing: Materials, Processes and Systems'', 3rd ed, John Wiley & Sons, Inc., Hoboken, NJ, .
*
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