portmanteau
In linguistics, a blend—also known as a blend word, lexical blend, or portmanteau—is a word formed by combining the meanings, and parts of the sounds, of two or more words together.
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 ...
s that possess superior strength and toughness without losing
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 ...
. ''Aging'' refers to the extended heat-treatment process. These steels are a special class of very-low-
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 ...
ultra-high-strength steels that derive their strength from
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
of intermetallic compounds rather than from carbon. The principal alloying metal is 15 to 25 wt%nickel. Secondary alloying metals, which include
cobalt
Cobalt is a chemical element; it has Symbol (chemistry), 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. ...
,
molybdenum
Molybdenum is a chemical element; it has Symbol (chemistry), symbol Mo (from Neo-Latin ''molybdaenum'') and atomic number 42. The name derived from Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals hav ...
and titanium, are added to produce intermetallic precipitates.
The first maraging steel was developed by Clarence Gieger Bieber at Inco in the late 1950s. It produced 20 and 25 wt% Ni steels with small additions of
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 ...
, titanium, and
niobium
Niobium is a chemical element; it has chemical symbol, symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and Ductility, ductile transition metal. Pure niobium has a Mohs scale of mineral hardness, Mohs h ...
. The intent was to induce age-hardening with the aforementioned intermetallics in an iron-nickel martensitic matrix, and it was discovered that Co and Mo complement each other very well. Commercial production started in December 1960. A rise in the price of Co in the late 1970s led to cobalt-free maraging steels.
The common, non-stainless grades contain 17–19 wt% Ni, 8–12 wt% Co, 3–5 wt% Mo and 0.2–1.6 wt% Ti. Addition of chromium produces corrosion-resistant stainless grades. This also indirectly increases hardenability as they require less Ni; high-Cr, high-Ni steels are generally austenitic and unable to become
martensite
Martensite is a very hard form of steel crystalline structure. It is named after German metallurgist Adolf Martens. By analogy the term can also refer to any crystal structure that is formed by diffusionless transformation.
Properties
Mar ...
when heat treated, while lower-Ni steels can.
Alternative variants of Ni-reduced maraging steels are based on alloys of Fe and Mn plus minor additions of Al, Ni and Ti with compositions between Fe-9wt% Mn to Fe-15wt% Mn qualify used.. The manganese has an effect similar to nickel, i.e. it stabilizes the austenite phase. Hence, depending on their manganese content, Fe-Mn maraging steels can be fully martensitic after quenching them from the high temperature austenite phase or they can contain retained austenite. The latter effect enables the design of maraging-transformation-induced-plasticity (TRIP) steels.
Properties
Due to the low carbon content (less than 0.03%) maraging steels have good machinability. Prior to aging, they may also be cold rolled to as much as 90% without cracking. Maraging steels offer good weldability, but must be aged afterward to restore the original properties to the heat affected zone.
When heat-treated the alloy has very little dimensional change, so it is often machined to its final dimensions. Due to the high alloy content maraging steels have a high hardenability. Since ductile Fe-Ni martensites are formed upon cooling, cracks are non-existent or negligible. The steels can be nitrided to increase case hardness and polished to a fine surface finish.
Non-stainless varieties of maraging steel are moderately
corrosion
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 engine ...
Maraging steels are usually described by a number (e.g., SAE steel grades 200, 250, 300 or 350), which indicates the approximate nominal tensile strength in thousands of pounds per square inch (ksi). The compositions and required properties were defined in US military standard MIL-S-46850D.Military Specification 46850D: STEEL : BAR, PLATE, SHEET, STRIP, FORGINGS, AND EXTRUSIONS, 18 PERCENT NICKEL ALLOY, MARAGING, 200 KSI, 250 KSI, 300 KSI, AND 350 KSI, HIGH QUALITY, available from http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-S/MIL-S-46850D_19899/ The higher grades have more cobalt and titanium in the alloy; the compositions below are taken from table 1 of MIL-S-46850D. As of July 1, 2024, that standard was cancelled by the U.S. Military and replaced with a number of SAE AMS specifications, which now govern each grade in a separate specification, as enumerated below. MIL-S-46850D, Notice 3 is a notice of cancellation issued 1 July 2024, and specifies the replacement specifications listed. U.S. users can obtain the original MIL standard as well as the associated notices from the search tool at https://quicksearch.dla.mil/qsSearch.aspx
This family is known as the 18Ni maraging steels, from its nickel percentage. There is also a family of cobalt-free maraging steels which are cheaper but not quite as strong; one example is Fe-18.9Ni-4.1Mo-1.9Ti. There has been Russian and Japanese research in Fe-Ni-Mn maraging alloys.
Heat treatment cycle
The steel is first annealed at approximately for 15–30 minutes for thin sections and for 1 hour per thickness for heavy sections, to ensure formation of a fully austenitized structure. This is followed by air cooling or quenching to room temperature to form a soft, heavily dislocated iron-nickel lath (untwinned) martensite. Subsequent aging ( precipitation hardening) of the more common alloys for approximately 3 hours at a temperature of produces a fine dispersion of Ni3(X,Y) intermetallic phases along dislocations left by martensitic transformation, where X and Y are solute elements added for such precipitation. Overaging leads to a reduction in stability of the primary, metastable, coherent precipitates, leading to their dissolution and replacement with semi-coherent Laves phases such as Fe2Ni/Fe2Mo. Further excessive heat-treatment brings about the decomposition of the martensite and reversion to austenite.
Newer compositions of maraging steels have revealed other intermetallic stoichiometries and crystallographic relationships with the parent martensite, including rhombohedral and massive complex Ni50(X,Y,Z)50 (Ni50M50 in simplified notation).
Processing of maraging steel
The maraging steels are a popular class of structural materials because of their superior mechanical properties among different categories of steel. Their mechanical properties can be tailored for different applications using various processing techniques. Some of the most widely used processing techniques for manufacturing and tuning of mechanical behavior of maraging steels are listed as follows:
* Solution treatment: As described in the section of Heat treatment cycle, the maraging steel is heated to a specific temperature range, after which it is quenched rapidly. In this step the alloying elements are dissolved, and a homogeneous microstructure is achieved. Homogeneous microstructure thus achieved improves the overall mechanical behavior of maraging steels such as fracture toughness and fatigue resistance.
* Aging of maraging steels: It is an important processing step as this step leads to precipitation of intermetallic compounds such Ni3Al, Ni3Mo, Ni3Ti, etc. The semicoherent precipitates obtained during normal aging and incoherent precipitates obtained after overaging contribute to improvement of mechanical behavior by activating various strengthening mechanisms related to hindering of dislocation motion by precipitates. Strengthening mechanisms such as precipitate hardening where precipitates hinder dislocation motion via Orowan mechanism or dislocation bowing lead to increase in the ultimate tensile strength of maraging steels. Aging is also beneficial for reducing the microstructural heterogeneities which may occur due to non-uniform thermal distribution along the building direction in arc additive manufactured samples.
* Laser Powder Bed Fusion (LPBF): Laser Powder Bed Fusion is an additive manufacturing technique used to create components of intricate geometries using a powder metal which is fused together layer by layer using localized high power-density heat source such as a
laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...
. The materials can be tailored to have specific mechanical properties by optimizing the process parameters associated with LPBF. It has been observed that processing parameters such as laser scanning speed, power and the scanning space can have significant effects on the mechanical properties of 300 maraging steel such as
tensile strength
Ultimate tensile strength (also called UTS, tensile strength, TS, ultimate strength or F_\text in notation) is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials, the ultimate ...
toughness
In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.austenite reversion and disappearance of cellular microstructure. On the other hand, aging treatment after solution treatment increases the microhardness and tensile strength of steel which is attributed to formation of precipitates such as Ni3Mo, Ni3Ti, Fe2Mo. The impact toughness increases after solution treatment but decreases after aging treatment, which can be attributed to the underlying microstructure consisting of tiny precipitates acting as regions of stress concentrators for crack formation. Formation of nanoscale precipitates of intermetallic compounds after aging process lead to marked increase in yield and ultimate tensile strength but substantial reduction in ductility of the material. This change in macroscopic behavior of the material can be linked to the evolution of microstructure from dimple to quasi-cleavage fracture morphology. Aging followed by solution treatment of selective laser melted steels also reduces the amount of retained austenite in the martensitic matrix and lead to change in the grain orientation. Aging can reduce the plastic anisotropy to some extent, but directionality of properties is largely influenced by its fabrication history.
* Severe plastic deformation: It leads to increase in dislocation density in the materials which in turn assists in the ease of formation of intermetallic precipitates due to availability of faster diffusion pathways through the dislocation cores. It has been observed that plastic deformation before aging leads to reduced peak aging time and increase in peak hardness. Precipitate morphology in severely plastically deformed steel changes and becomes plate-like when overaged which is attributed to higher dislocation density. This in turn leads to significant reduction in ductility and increase in strength of the material. Along with morphology, the orientation of precipitates also play an important role in micromechanism of deformation as they induce anisotropy to the mechanical properties.
Uses
Maraging steel's strength and malleability in the pre-aged stage allows it to be formed into thinner rocket and missile skins than other steels, reducing weight for a given strength. Maraging steels have very stable properties and, even after overaging due to excessive temperature, only soften slightly. These alloys retain their properties at mildly elevated
operating temperature
An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
s and have maximum service temperatures of over . They are suitable for engine components, such as crankshafts and gears, and the firing pins of automatic weapons that cycle from hot to cool repeatedly while under substantial load. Their uniform expansion and easy machinability before aging make maraging steel useful in high-wear components of
assembly line
An assembly line, often called ''progressive assembly'', is a manufacturing process where the unfinished product moves in a direct line from workstation to workstation, with parts added in sequence until the final product is completed. By mechan ...
s and dies. Other ultra-high-strength steels, such as AerMet alloys, are not as machinable because of their carbide content.
In the sport of
fencing
Fencing is a combat sport that features sword fighting. It consists of three primary disciplines: Foil (fencing), foil, épée, and Sabre (fencing), sabre (also spelled ''saber''), each with its own blade and set of rules. Most competitive fe ...
, blades used in competitions run under the auspices of the
Fédération Internationale d'Escrime
The International Fencing Federation (''Fédération Internationale d'Escrime'') commonly known by the acronym FIE, is the international Sport governing body, governing body of Olympic Games, Olympic fencing. Today, its head office is at th ...
are usually made with maraging steel. Maraging blades are superior for
foil
Foil may refer to:
Materials
* Foil (metal), a quite thin sheet of metal, usually manufactured with a rolling mill machine
* Metal leaf, a very thin sheet of decorative metal
* Aluminium foil, a type of wrapping for food
* Tin foil, metal foil ma ...
and
épée
The (, ; ), also rendered as epee in English, is the largest and heaviest of the three weapons used in the sport of fencing. The modern derives from the 19th-century , a weapon which itself derives from the French small sword. This contains a ...
because crack propagation in maraging steel is 10 times slower than in carbon steel, resulting in less frequent breaking of the blade and fewer injuries. Stainless maraging steel is used in
bicycle
A bicycle, also called a pedal cycle, bike, push-bike or cycle, is a human-powered transport, human-powered or motorized bicycle, motor-assisted, bicycle pedal, pedal-driven, single-track vehicle, with two bicycle wheel, wheels attached to a ...
frames (e.g. Reynolds 953 introduced in 2013) and
golf
Golf is a club-and-ball sport in which players use various Golf club, clubs to hit a Golf ball, ball into a series of holes on a golf course, course in as few strokes as possible.
Golf, unlike most ball games, cannot and does not use a standa ...
club heads. It is also used in surgical components and hypodermic syringes, but is not suitable for scalpel blades because the lack of carbon prevents it from holding a good cutting edge.
Maraging steel is used in oil and gas sector as downhole tools and components due to its high mechanical strength. The steel's resistance to hydrogen embrittlement is critical in downhole environments where exposure to hydrogen sulfide (H₂S) can lead to material degradation and failure.
American musical instrument string producer Ernie Ball has made a specialist type of
electric guitar
An electric guitar is a guitar that requires external electric Guitar amplifier, sound amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar. It uses one or more pickup (music technology), pickups ...
string out of maraging steel, claiming that this alloy provides more output and enhanced tonal response.
The production, import, and export of maraging steels by certain entities, such as the United States, is closely monitored by international authorities because it is particularly suited for use in gas centrifuges for uranium enrichment; lack of maraging steel significantly hampers the uranium-enrichment process. Older centrifuges used aluminum tubes, while modern ones use carbon fiber composite.
Physical properties
*
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 ...
: 8.1 g/cm3 (0.29 lb/in3)
* Specific heat, mean for 0–100 °C (32–212 °F): 452 J/kg·K (0.108 Btu/lb·°F)
*
Melting point
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...
:
*
Thermal conductivity
The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1.
Heat transfer occurs at a lower rate in materials of low ...
tensile strength
Ultimate tensile strength (also called UTS, tensile strength, TS, ultimate strength or F_\text in notation) is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials, the ultimate ...
: typically . Grades exist up to
* Elongation at break: up to 15%
* KIC fracture toughness: up to 175 MPa·m
*
Young's modulus
Young's modulus (or the Young modulus) is a mechanical property of solid materials that measures the tensile or compressive stiffness when the force is applied lengthwise. It is the modulus of elasticity for tension or axial compression. Youn ...
Hardness
In materials science, hardness (antonym: softness) is a measure of the resistance to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by Pressing (metalworking), pressing or abrasion ...