'''Maraging steels''' (a [[portmanteau]] of "[[martensitic]]" and "aging") are [[steel]]s ([[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 [[Mass fraction (chemistry)#Mass concentration|wt.%]] [[nickel]].<ref name=degarmo>{{citation|last=Degarmo|first=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[[aluminium]], Tititanium, and Nb[[niobium]] 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>
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 [[austenite|austenitic]] and unable to transform to [[martensite]] when heat treated, while lower-nickel steels can transform to martensite. Alternative variants of Ninickel-reduced maraging steels are based on alloys of Feiron and Mnmanganese plus minor additions of Alaluminium, Ninickel and Tititanium where compositions between Fe-9wt.% Mn to Fe-15wt.% Mn have been used.<ref name=maraging2>{{citation|last= Raabe|first=D.|last2= Sandlöbes|first2 =S.|last3= Millan|first3=J. J.|last4=Ponge|first4=D.|last5=Assadi|first5=H.|last6=Herbig|first6=M.|last7=Choi|first7=P.P.| title= Segregation engineering enables nanoscale martensite to austenite phase transformation at grain boundaries: A pathway to ductile martensite
|publisher= Acta Materialia|pages=6132–6152|year=2013|volume=61 |issue=16}}.</ref> The Mnmanganese has a similar effect as Ninickel, i.e. it stabilizes the austenite phase. Hence, depending on their Mnmanganese content, Fe-Mn maraging steels can be fully martensitic after quenching them from the high temperature austenite phase or they can contain retained austenite.<ref name=tripmar2>{{citation|last= Dmitrieva|first=O.|last2=Ponge|first2 =D.|last3= Inden|first3=G. |last4= Millan|first4=J.|last5= Choi|first5=P. |last6= Sietsma|first6=J. |last7= Raabe|first7=D.|title= Chemical gradients across phase boundaries between martensite and austenite in steel studied by atom probe tomography and simulation|publisher= Acta Materialia|page=364|year=2011|volume=59|doi= 10.1016/j.actamat.2010.09.042|ISSN=1359-6454|arxiv=1402.0232}}</ref> The latter effect enables the design of maraging-TRIP steels where TRIP stands for Transformation-Induced-Plasticity.<ref name=tripmar>{{citation|last= Raabe|first=D.|last2=Ponge|first2 =D.|last3= Dmitrieva|first3=O. |last4= Sander|first4=B.|title= Nano-precipitate hardened 1.5 GPa steels with unexpected high ductility|journal= Scripta Materialia|page=1141|year=2009|volume=60|doi=10.1016/j.scriptamat.2009.02.062 }}</ref>
