κ-Carbides are a special class of

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 ...

structures. They are most known for appearing in steels containing

manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...

and

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

where they have the

molecular formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as paren ...

Properties

Structure

κ-Carbides crystallise in the

perovskite Perovskite (pronunciation: ) is a calcium titanium oxide mineral composed of calcium titanate (chemical formula ). Its name is also applied to the class of compounds which have the same type of crystal structure as , known as the perovskite (stru ...

structure type with the

space group In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...

''Pm3m'' (Nr. 221). This structure was, inter alia, elucidated with XRD-measurements on

steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

alloys containing κ-carbide precipitates but also on single crystals of

-κ-carbides with a molecular formula of Mn_3.1Al_0.9C and a

lattice parameter A lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal. A simple cubic crystal has ...

of ''a=3.87Å''. In

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

s where diverse arrangements of the atoms are possible, a considerable effect of the short range ordering, e.g. of

iron Iron is a chemical element; it has symbol Fe () 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, forming much of Earth's o ...

and

on the microscopic properties of the

, has been observed. This is especially important for the role as

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

-traps in

Composition

A first glance at the composition of a steel alloy is achieved by analysing its surface with

EDX edX is an American For-profit higher education in the United States, for-profit massive open online course provider. It was founded by MIT and Harvard. It is a subsidiary of 2U (company), 2U. History edX was founded in May 2012 by the admi ...

-technique. Depending on the content of the alloying

element 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 o ...

s of the

, different types of κ-carbides can form. They occur in both

ferritic A ferrite is one of a family of iron oxide-containing magnetic ceramic materials. They are ferrimagnetic, meaning they are attracted by magnetic fields and can be magnetized to become permanent magnets. Unlike many ferromagnetic materials, mos ...

(α-Fe) and

austenitic 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 ...

(γ-Fe) steels. Typical alloying

s are

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

, and

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

Magnetism

SQUID A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...

measurements on

polycrystalline A crystallite is a small or even microscopic crystal which forms, for example, during the cooling of many materials. Crystallites are also referred to as grains. Bacillite is a type of crystallite. It is rodlike with parallel longulites. S ...

Mn_3.1Al_0.9C revealed a soft

ferromagnet Ferromagnetism is a property of certain materials (such as iron) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromag ...

ic behaviour of this κ-carbide with a

Curie temperature In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Curie ...

of 295±13 K, a

remanent Remanence or remanent magnetization or residual magnetism is the magnetization left behind in a ferromagnetic material (such as iron) after an external magnetic field is removed. Colloquially, when a magnet is "magnetized", it has remanence. The ...

magnetic moment In electromagnetism, the magnetic moment or magnetic dipole moment is the combination of strength and orientation of a magnet or other object or system that exerts a magnetic field. The magnetic dipole moment of an object determines the magnitude ...

of 3.22 ''μ_B'' and a

coercive field Coercivity, also called the magnetic coercivity, coercive field or coercive force, is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized. Coercivity is usually measured in ...

of 1.9 mT.

DFT The Department for Transport (DfT) is a ministerial department of the Government of the United Kingdom. It is responsible for the English transport network and a limited number of transport matters in Scotland, Wales, and Northern Ireland t ...

-simulations confirmed these findings and indicated that other κ-carbides behave similarly.

Occurrence

κ-carbides are typically found as

precipitate In an aqueous solution, precipitation is the "sedimentation of a solid material (a precipitate) from a liquid solution". The solid formed is called the precipitate. In case of an inorganic chemical reaction leading to precipitation, the chemic ...

s in high-performance steels. A common example is the TRIPLEX

with the generic composition Fe_xMn_yAl_zC containing 18-28 %

, 9-12 %

and 0.7-1.2 %

(in mass %). It is a high-strength, low-

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

consisting of

γ–

solid solution A solid solution, a term popularly used for metals, is a homogeneous mixture of two compounds in solid state and having a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word "solutio ...

, nano size κ-carbides and α– ferrite. Other similar

s are known for their high

ductility Ductility refers to the ability of a material to sustain significant plastic Deformation (engineering), deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic def ...

. κ-carbides are usually formed from areas enriched in carbon through

spinodal In thermodynamics, the limit of local stability against phase separation with respect to small fluctuations is clearly defined by the condition that the second derivative of Gibbs free energy is zero. : 0 The locus of these points (the inflecti ...

decomposition and are key determinants of the properties of these steels. The low

is e.g. obtained after a

hot rolling In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to impart a desired mechanical property. The concept is simi ...

post-process. Upon cooling, different domains of

austenite 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 ...

and ferrite are formed and κ-carbides form at the boundaries of these domains. Continuing the cooling process leads to a phase transition of

to ferrite and the κ-carbides are released as a result of an

eutectoid A eutectic system or eutectic mixture ( ) is a type of a homogeneous mixture that has a melting point lower than those of the constituents. The lowest possible melting point over all of the mixing ratios of the constituents is called the ''eutec ...

transformation in form of a

. The κ-carbides can have an additional strengthening effect on

steels Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high elastic modulus, yield strength, fracture strength and low raw material cost, steel is one of the m ...

because they can function as a

trap to counteract

hydrogen embrittlement Hydrogen embrittlement (HE), also known as hydrogen-assisted cracking or hydrogen-induced cracking (HIC), is a reduction in the ductility of a metal due to absorbed hydrogen. Hydrogen atoms are small and can Permeation, permeate solid metals. O ...

Ab-initio ( ) is a Latin term meaning "from the beginning" and is derived from the Latin ("from") + , ablative singular of ("beginning"). Etymology , from Latin, literally "from the beginning", from ablative case of "entrance", "beginning", related to ...

-simulations have shown that

can occupy the same site as

in the κ-carbide precipitates or an initially empty

interstitial {{Short pages monitor