Maraging steel: Difference between revisions

'''Maraging steels''' (a [[portmanteau]] of "[[martensitic]]" and "aging") are [[steel]]s ([[iron]] [[alloys]]) that are known for possessing superior strength and toughness without losing [[malleabilityductility]], although they cannot hold a good cutting edge. ''Aging'' refers to the extended heat-treatment process. These steels are a special class of very-low-[[carbon]] ultra-high-strength steels that derive their strength not from carbon, but from [[precipitation hardening|precipitation]] of [[intermetallic]] compounds. The principal alloying element is 15 to 25 [[Mass fraction (chemistry)#Mass concentrationpercentage|wt.%]] [[nickel]].<ref name=degarmo>{{citation|lastlast1=Degarmo|firstfirst1=E. Paul|last2=Black|first2 =J. T.|last3=Kohser|first3=Ronald A.|title=Materials and Processes in Manufacturing|publisher=Wiley|page=119|year=2003|edition=9th|isbn=0-471-65653-4}}</ref> Secondary alloying elements, which include [[cobalt]], [[molybdenum]], and [[titanium]], are added to produce [[intermetallic]] [[precipitates]],.<ref name=degarmo/> 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 Al, Ti, and Nb were made; a rise in the price of cobalt in the late 1970s led to the development of cobalt-free maraging steels <ref name=sha-guo>{{cite book | title=Maraging Steels: Modelling of Microstructure, Properties and Applications | first1=W | first2=Z | last1=Sha | last2=Guo | publisher=Elsevier | date=2009-10-26}}.</ref>

Due to the low carbon content (less than 0.03%)<ref>Adrian P Mouritz, [https://www.sciencedirect.com/topics/materials-science/maraging-steel ''Introduction to Aerospace Materials''], p. 244, Elsevier, 2012 {{ISBN|0857095153}}.</ref> 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]].<ref name=degarmo/>

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 [[nitridization|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]].

! scope="col" | ElementGrade 250

! scope="col" | Grade 200300

! scope="col" | Grade 250350

||Iron||balance||balance||balance||balance||

||Nickel||17.0-190–19.0||17.0-190–19.0||18.0-190–19.0||18.0-190–19.0||

||Cobalt||8.0-90–9.0||7.0-80–8.5||8.5-95–9.5||11.5-125–12.5||

||Titanium||0.15-015–0.25||0.3-03–0.5||0.5-05–0.8||1.3-13–1.6||

||Aluminium||0.05-005–0.15||0.05-005–0.15||0.05-005–0.15||0.05-005–0.15||

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 exemplarexample is Fe-18.9Ni-4.1Mo-1.9Ti. There has been Russian and Japanese research in Fe-Ni-Mn maraging alloys.<ref name=sha-guo/>

The steel is first [[annealing (metallurgy)|annealed]] at approximately {{convert|820|C|F}} for 15–30 minutes for thin sections and for 1 hour per {{cvt|25&nbsp;|mm|in|sigfig=1}} thickness for heavy sections, to ensure formation of a fully [[austenitization|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 {{cvt|480 |to |500&nbsp;°|C|F|sigfig=2}} produces a fine [[dispersion (chemistry)|dispersion]] of Ni₃(X,Y) intermetallic phases along dislocations left by martensitic transformation, where X and Y are [[solution|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 phase]]s such as Fe₂Ni/Fe₂Mo. Further excessive heat-treatment brings about the decomposition of the martensite and reversion to austenite.

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.<ref>{{cite news|author=Joby Warrick |url=httphttps://www.washingtonpost.com/world/national-security/nuclear-ruse-posing-as-toymaker-chinese-merchant-allegedly-sought-us-technology-for-iran/2012/08/11/f1c66d9a-e265-11e1-ae7f-d2a13e249eb2_story.html?wpisrc=nl_headlines |title=Nuclear ruse: Posing as toymaker, Chinese merchant allegedly sought U.S. technology for Iran |publishernewspaper=The Washington Post |date=2012-08-11 |accessdate=2014-02-21}}</ref> 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]]s and have maximum service temperatures of over {{convert|400|°C|F|sigfig=2}}.{{Citation needed|date=August 2008}} 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]]s and [[die (manufacturing)|dies]]. Other ultra-high-strength steels, such as [[Aermet|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 (sword)|foil]] and [[épée]] because crack propagation in maraging steel is 10 times slower than in carbon steel, resulting in less bladefrequent breakagebreaking of the blade and fewer injuries.<ref>{{efn-lr|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 (material)|fatigue]] is a plastic phenomenon rather than microstructural.</ref>}}<ref name="Juvinall">{{cite book|title = Fundamentals of Machine Component Design |edition = Fourth |last1 = Juvinall |first1 = Robert C. |last2= Marshek |first2= Kurt M. |year = 2006 |publisher = John Wiley & Sons, Inc. |isbn = 978-0-471-66177-1 |page = 69}}</ref> Stainless maraging steel is used in [[bicycle]] frames (e.g. Reynolds 953 introduced in 2013)<ref>{{Cite web|title=Reynolds turns 120: The history of Reynolds Technology|url=https://www.reynoldstechnology.biz/the-history-of-reynolds-technology/|access-date=2022-12-29|website=www.reynoldstechnology.biz|date=20 December 2018 |language=en}}</ref> and [[golf]] club heads.<ref>{{Cite web|title=Maraging Steel in Golf Clubs|url=https://www.golfcompendium.com/2021/01/maraging-steel-golf-clubs.html|access-date=2022-12-29|website=Golf Compendium|language=en}}</ref> 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.

* [[Density]]: 8.1 &nbsp;g/cm³³ (0.29&nbsp;lb/in³³)

* [[Specific heat]], mean for 0–100&nbsp;°C (32–212&nbsp;°F): 813 452&nbsp;J/kg·K (0.108 &nbsp;Btu/lb·°F)

* [[Melting point]]: 2,575&nbsp;°F, 1,413&nbsp;°{{cvt|1413|C|F}}

* [[Thermal conductivity]]: 25.5 &nbsp;W/m·K

* Mean [[coefficient of thermal expansion]]: 11.3×10⁻⁶&nbsp;K⁻¹ (20.3×10⁻⁶&nbsp;°F⁻¹)

* [[yield strength|Yield tensile strength]]: typically {{convert|1400|–|2400|MPa|psiksi|abbr=on}}<ref>http{{cite web |url=https://www.imoa.info/molybdenum-uses/molybdenum-grade-alloy-steels-irons/maraging-steels.php |title=Maraging Steels |website=imoa.info|publisher=International Molybdenum Association|access-date=8 April 2015}}</ref>

* Ultimate [[tensile strength]]: typically {{convert|1.6|–|2.5|GPa|psiksi|abbr=on}}. Grades exist up to {{convert|3.5|GPa|psiksi|abbr=on}}

* K_IC fracture toughness: up to 175 &nbsp;MPa·m^{{frac|1|2}}

* [[Young's modulus]]: {{convert|210|GPa|psie6psi|abbr=on}}<ref>{{Cite journal

| issue = 1-61–6

* [[Shear modulus]]: {{convert|77|GPa|psie6psi|abbr=on}}

* [[Bulk modulus]]: {{convert|140|GPa|psie6psi|abbr=on}}

*[http://www.matthey.ch/en/alloys/maraging-steels-durnico-durimphy-ultrafort-durinox-phynox Maraging Steelsteel data sheets] {{Webarchive|url=https://web.archive.org/web/20160815131638/http://www.matthey.ch/en/alloys/maraging-steels-durnico-durimphy-ultrafort-durinox-phynox |date=2016-08-15 }}