Maraging steel

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Maraging steels (a portmanteau of "martensitic" and "aging") are steels (iron alloys) that are known for possessing superior strength and toughness without losing ductility. Aging refers to the extended heat-treatment process. These steels are a special class of low-carbon ultra-high-strength steels that derive their strength not from carbon, but from precipitation of intermetallic compounds. The principal alloying element is 15 to 25 wt% nickel. [1] Secondary alloying elements, which include cobalt, molybdenum and titanium, are added to produce intermetallic precipitates. [1] Original development (by Bieber of Inco in the late 1950s) was carried out on 20 and 25 wt% Ni steels to which small additions of aluminium, titanium, and niobium were made; a rise in the price of cobalt in the late 1970s led to the development of cobalt-free maraging steels. [2]

Contents

The common, non-stainless grades contain 17–19 wt% nickel, 8–12 wt% cobalt, 3–5 wt% molybdenum and 0.2–1.6 wt% titanium. Addition of chromium produces stainless grades resistant to corrosion. This also indirectly increases hardenability as they require less nickel; high-chromium, high-nickel steels are generally austenitic and unable to transform to martensite when heat treated, while lower-nickel steels can transform to martensite. Alternative variants of nickel-reduced maraging steels are based on alloys of iron and manganese plus minor additions of aluminium, nickel and titanium where compositions between Fe-9wt% Mn to Fe-15wt% Mn have been used. [3] The manganese has a similar effect as 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. [4] The latter effect enables the design of maraging-TRIP steels where TRIP stands for Transformation-Induced-Plasticity. [5]

Properties

Due to the low carbon content 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. [1]

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 FeNi 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-resistant and resist stress corrosion and hydrogen embrittlement. Corrosion-resistance can be increased by cadmium plating or phosphating.

Grades of maraging steel

Maraging steels are usually described by a number (200, 250, 300 or 350), which indicates the approximate nominal tensile strength in thousands of pounds per square inch; the compositions and required properties are defined in MIL-S-46850D. [6] The higher grades have more cobalt and titanium in the alloy; the compositions below are taken from table 1 of MIL-S-46850D:

Maraging steel compositions
ElementGrade 200Grade 250Grade 300Grade 350
Ironbalancebalancebalancebalance
Nickel17.0–19.017.0–19.018.0–19.018.0–19.0
Cobalt8.0–9.07.0–8.58.5–9.511.5–12.5
Molybdenum3.0–3.54.6–5.24.6–5.24.6–5.2
Titanium0.15–0.250.3–0.50.5–0.81.3–1.6
Aluminium0.05–0.150.05–0.150.05–0.150.05–0.15
Tensile Strength (MPa)1379172420682413

That 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 have been Russian and Japanese research in Fe-Ni-Mn maraging alloys. [2]

Heat treatment cycle

The steel is first annealed at approximately 820 °C (1,510 °F) for 15–30 minutes for thin sections and for 1 hour per 25 mm 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 480 to 500 °C 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).

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. [7] 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 temperatures and have maximum service temperatures of over 400 °C (752 °F).[ citation needed ] 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 lines 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, blades used in competitions run under the auspices of the Fédération Internationale d'Escrime are usually made with maraging steel. Maraging blades are superior for foil and épée because crack propagation in maraging steel is 10 times slower than in carbon steel, resulting in less blade breakage and fewer injuries. [lower-roman 1] [8] Stainless maraging steel is used in bicycle frames (e.g. Reynolds 953) and golf club heads. [9] [ citation needed ] 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.

American musical instrument string producer, Ernie Ball, has made a specialist type of electric guitar string out of Maraging steel, claiming that this alloy provides more output and enhanced tonal response. [10]

Maraging steel production, import and export by certain states, such as the United States, [11] is closely monitored by international authorities because it is particularly suited for use in gas centrifuges for uranium enrichment; [12] lack of maraging steel significantly hampers this process. Older centrifuges used aluminum tubes; modern ones, carbon fiber composite.[ citation needed ]

Physical properties

See also

Related Research Articles

Steel Metal alloy made by combining iron with other elements

Steel is an alloy of iron with typically a few percent of carbon to improve its strength and fracture resistance compared to iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant need typically an additional 11% chromium. Because of its high tensile strength and low cost, steel is used in buildings, infrastructure, tools, ships, trains, cars, machines, electrical appliances, and weapons. Iron is the base metal of steel. Depending on temperature, it can take two crystalline forms : body-centred cubic and face-centred cubic. It's the interaction of the allotropes of iron with the alloying elements, primarily carbon, that gives steel and cast iron their range of unique properties.

Heat treating Process of heating something to alter it

Heat treating 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 also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve the desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering, carburizing, normalizing and quenching. Although the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.

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.

Austenite 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.

High-strength low-alloy steel

High-strength low-alloy steel (HSLA) is a type of alloy steel that provides better mechanical properties or greater resistance to corrosion than carbon steel. HSLA steels vary from other steels in that they are not made to meet a specific chemical composition but rather specific mechanical properties. They have a carbon content between 0.05–0.25% to retain formability and weldability. Other alloying elements include up to 2.0% manganese and small quantities of copper, nickel, niobium, nitrogen, vanadium, chromium, molybdenum, titanium, calcium, rare earth elements, or zirconium. Copper, titanium, vanadium, and niobium are added for strengthening purposes. These elements are intended to alter the microstructure of carbon steels, which is usually a ferrite-pearlite aggregate, to produce a very fine dispersion of alloy carbides in an almost pure ferrite matrix. This eliminates the toughness-reducing effect of a pearlitic volume fraction yet maintains and increases the material's strength by refining the grain size, which in the case of ferrite increases yield strength by 50% for every halving of the mean grain diameter. Precipitation strengthening plays a minor role, too. Their yield strengths can be anywhere between 250–590 megapascals (36,000–86,000 psi). Because of their higher strength and toughness HSLA steels usually require 25 to 30% more power to form, as compared to carbon steels.

Martensitic stainless steel

Stainless steels may be classified by their crystalline structure into four main types: austenitic, ferritic, martensitic, and duplex.Martensitic stainless steel is a specific type of stainless steel alloy that can be hardened and tempered through multiple ways of aging/heat treatment.

Carbon steel 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% by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:

A shape-memory alloy is an alloy that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. It may also be called memory metal, memory alloy, smart metal, smart alloy, or muscle wire.

Tempering (metallurgy) Process of heat treating used to increase 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.

Titanium alloys are alloys that contain a mixture of titanium and other chemical elements. Such alloys have very high tensile strength and toughness. They are light in weight, have extraordinary corrosion resistance and the ability to withstand extreme temperatures. However, the high cost of both raw materials and processing limit their use to military applications, aircraft, spacecraft, bicycles, medical devices, jewelry, highly stressed components such as connecting rods on expensive sports cars and some premium sports equipment and consumer electronics.

Superalloy

A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, good surface stability, and resistance to corrosion or oxidation.

Orthodontic archwire

An archwire in orthodontics is a wire conforming to the alveolar or dental arch that can be used with dental braces as a source of force in correcting irregularities in the position of the teeth. An archwire can also be used to maintain existing dental positions; in this case it has a retentive purpose.

SAE steel grades

The SAE steel grades system is a standard alloy numbering system for steel grades maintained by SAE International.

Alloy steel

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. 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%. Most commonly, the phrase "alloy steel" refers to low-alloy steels.

Nickel titanium

Nickel titanium, also known as Nitinol, is a metal alloy of nickel and titanium, where the two elements are present in roughly equal atomic percentages. Different alloys are named according to the weight percentage of nickel, e.g. Nitinol 55 and Nitinol 60. It exhibits the shape memory effect and superelasticity at different temperatures.

AerMet alloy is an ultra-high strength type of martensitic alloy steel. The main alloying elements are cobalt and nickel, but chromium, molybdenum and carbon are also added. Its exceptional properties are hardness, tensile strength, fracture toughness and ductility. Aermet is weldable with no preheating needed. AerMet alloy is not corrosion resistant, so it must be sealed if used in a moist environment. AerMet is a registered trademark of Carpenter Technology Corporation.

TRIP steel are a class of high-strength steel alloys typically used in naval and marine applications and in the automotive industry. TRIP stands for "Transformation induced plasticity," which implies a phase transformation in the material, typically when a stress is applied. These alloys are known to possess an outstanding combination of strength and ductility.

HY-80

HY-80 is a high-tensile, high yield strength, low alloy steel. It was developed for use in naval applications, specifically the development of pressure hulls for the US nuclear submarine program and is still currently used in many naval applications. It is valued for its strength to weight ratio.

Ferritic stainless steel forms one of the four stainless steel families, the other three being austenitic, martensitic and duplex stainless steels

References

  1. However, the notion that maraging steel blades break flat is a fencing urban legend. Testing has shown that the blade-breakage patterns in carbon steel and maraging steel are identical due to the similarity in the loading mode during bending. Additionally, a crack is likely to start at the same point and propagate along the same path (although much more slowly), as crack propagation in fatigue is a plastic phenomenon rather than microstructural.


  1. 1 2 3 Degarmo, E. Paul; Black, J. T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, p. 119, ISBN   0-471-65653-4
  2. 1 2 Sha, W; Guo, Z (2009-10-26). Maraging Steels: Modelling of Microstructure, Properties and Applications. Elsevier.
  3. Raabe, D.; Sandlöbes, S.; Millan, J. J.; Ponge, D.; Assadi, H.; Herbig, M.; Choi, P.P. (2013), Segregation engineering enables nanoscale martensite to austenite phase transformation at grain boundaries: A pathway to ductile martensite, 61, Acta Materialia, pp. 6132–6152.
  4. Dmitrieva, O.; Ponge, D.; Inden, G.; Millan, J.; Choi, P.; Sietsma, J.; Raabe, D. (2011), "Chemical gradients across phase boundaries between martensite and austenite in steel studied by atom probe tomography and simulation", Acta Materialia, 59: 364–374, arXiv: 1402.0232 , doi:10.1016/j.actamat.2010.09.042, ISSN   1359-6454, S2CID   13781776
  5. Raabe, D.; Ponge, D.; Dmitrieva, O.; Sander, B. (2009), "Nano-precipitate hardened 1.5 GPa steels with unexpected high ductility", Scripta Materialia, 60 (12): 1141, doi:10.1016/j.scriptamat.2009.02.062
  6. 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/
  7. Joby Warrick (2012-08-11). "Nuclear ruse: Posing as toymaker, Chinese merchant allegedly sought U.S. technology for Iran". The Washington Post. Retrieved 2014-02-21.
  8. Juvinall, Robert C.; Marshek, Kurt M. (2006). Fundamentals of Machine Component Design (Fourth ed.). John Wiley & Sons, Inc. p. 69. ISBN   978-0-471-66177-1.
  9. "Reynolds Technology". www.reynoldstechnology.biz. Retrieved 2020-11-13.
  10. "Slinky M-Steel Electric Guitar Strings". Ernie Ball. Retrieved 2020-07-15. Ernie Ball M-Steel Electric Guitar Strings are made of a patented Super Cobalt alloy wrapped around a Maraging steel hex core wire, producing a richer and fuller tone with a powerful low-end response.
  11. Consolidated Federal Regulations part 110--export and import of nuclear equipment and material , retrieved 2009-11-11.
  12. Patrikarakos, David (November 2012). Nuclear Iran: The Birth of an Atomic State. I.B. Tauris. p. 168. ISBN   978-1-78076-125-1.
  13. http://www.imoa.info/
  14. Ohue, Yuji; Matsumoto, Koji (10 September 2007). "Sliding–rolling contact fatigue and wear of maraging steel roller with ion-nitriding and fine particle shot-peening". Wear. 263 (1–6): 782–789. doi:10.1016/j.wear.2007.01.055.