Maraging steel is used in aircraft, with applications including landing gear, helicopter undercarriages, slat tracks and rocket motor cases – applications which require high strength-to-weight material. Maraging steel offers an unusual combination of high tensile strength and high fracture toughness. Most high-strength steels have low toughness, and the higher their strength the lower their toughness. The rare combination of high strength and toughness found with maraging steel makes it well suited for safety-critical aircraft structures that require high strength and damage tolerance.

1. Maraging Steels
Mr. MANICKAVASAHAM G, B.E., M.E., (Ph.D.)
Assistant Professor,
Department of Mechanical Engineering,
Mookambigai College of Engineering,
Pudukkottai-622502, Tamil Nadu, India.
Email:mv8128351@gmail.com
Dr. R.Narayanasamy, B.E., M.Tech., M.Engg., Ph.D., (D.Sc.)
Retired Professor (HAG),
Department of Production Engineering,
National Institute of Technology,
Tiruchirappalli-620015, Tamil Nadu, India.
Email: narayan19355@gmail.com
1

2. Maraging steel is used in aircraft, with applications including landing gear, helicopter undercarriages,
slat tracks and rocket motor cases – applications which require high strength-to-weight material.
Maraging steel offers an unusual combination of high tensile strength and high fracture toughness.
Most high-strength steels have low toughness, and the higher their strength the lower their
toughness.
The rare combination of high strength and toughness found with maraging steel makes it well suited
for safety-critical aircraft structures that require high strength and damage tolerance.
Introduction
2

3. 3
Cont.
Maraging steel is strong, tough, low-carbon martensitic steel which contains hard precipitate
particles formed by thermal ageing.
The term ‘maraging’ is derived from the combination of the words martensite and age-hardening.
Maraging steel contains an extremely low amount of carbon (0.03% maximum) and a large
amount of nickel (17–19%) together with lesser amounts of cobalt (8–12%), molybdenum (3–5%),
titanium (0.2–1.8%) and aluminium (0.1–0.15%).
Maraging steel is essentially free of carbon, which distinguishes it from other types of steel.
The carbon content is kept very low to avoid the formation of titanium carbide (TiC) precipitates,
which severely reduce the impact strength, ductility and toughness when present in high
concentration.
Because of the high alloy content, especially the cobalt addition, maraging steel is expensive.

4. 4
Cont.
Maraging steel is produced by heating the steel in the austenite phase region (at about 850 °C),
called austenitising, followed by slow cooling in air to form a martensitic microstructure.
The slow cooling of hypoeutectic steel from the austenite phase usually results in the formation of
ferrite and pearlite; rapid cooling by quenching in water or oil is often necessary to form martensite.
 However, martensite forms in maraging steel upon slow cooling owing to the high nickel content
which suppresses the formation of ferrite and pearlite.
The martensitic microstructure in as-cooled maraging steel is soft compared with the martensite
formed in plain carbon steels by quenching.
However, this softness is an advantage because it results in high ductility and toughness without
the need for tempering.
The softness also allows maraging steel to be machined into structural components, unlike
hard martensitic steels that must be tempered before machining to avoid cracking.

5. 5
Cont.
After quenching, maraging steel undergoes a final stage of strengthening involving thermal
ageing before being used in aircraft components.
Maraging steel is heat-treated at 480–500 °C for several hours to form a fine dispersion of hard
precipitates within the soft martensite matrix.
The main types of precipitates are Ni3Mo, Ni3Ti, Ni3Al and Fe2Mo, which occur in a high volume
fraction because of the high alloy content.
Carbide precipitation is practically eliminated owing to the low carbon composition.
Cobalt is an important alloying element in maraging steel and serves several functions.
Cobalt is used to reduce the solubility limit of molybdenum and thereby increase the volume
fraction of Mo-rich precipitates (e.g. Ni3Mo, Fe2Mo).
Cobalt also assists in the uniform dispersion of precipitates through the martensite matrix.
Cobalt accelerates the precipitation process and thereby shortens the ageing time to reach
maximum hardness.
Newer grades of maraging steel contain complex Ni50(X,Y,Z)50 precipitates, where X, Y and Z are
solute elements such as Mo, Ti and Al.

6. 6 The precipitates in maraging steel are effective at restricting the movement of dislocations, and
thereby promote strengthening by the precipitation hardening process.
Figure 1 shows the effect of ageing temperature on the tensile strength and ductility of maraging
steel.
As with other age-hardening aerospace alloys such as the 2XXX Al, 7XXX Al, β-Ti and α/β-Ti alloys,
there is an optimum temperature and heating time to achieve maximum strength in maraging steel.
 When age-hardened in the optimum temperature range of 480–500 °C for several hours it is
possible to achieve a yield strength of around 2000 MPa while retaining good ductility and toughness.
 Over-ageing causes a loss in strength owing to precipitate coarsening and decomposition of the
martensite with a reversion back to austenite.
The strength of maraging steels is much greater than that found with most other aerospace structural
materials, which combined with ductility and toughness, makes them the material of choice for heavily
loaded structures that require high levels of damage tolerance and which must occupy a small space
on aircraft.
Cont.

7. 7
Cont.
Figure 1. Effect of ageing temperature on the strength and ductility
(percentage elongation to failure) of a maraging steel.

8. 8
Metallurgy and Properties
Maraging steels are low-carbon martensitic steels which employ substitutional alloying
elements to achieve precipitation strengthening (age-hardening).
A variety of steels have been developed which utilize this approach to achieve high strength at
low carbon levels; for example, the martensitic precipitation-hardened stainless steels could be
considered maraging steels.
However, as Beiber’s original development of maraging compositions focused on steels
containing high levels of nickel (20–25 wt%) with additions of, aluminum, titanium and niobium to
impart precipitation hardening, it is customary to regard maraging steels as low-carbon
precipitation-strengthened non-stainless martensitic steels (Beiber, 1960; Decker and Floreen,
1988).

9. 9
The discovery by Decker et al. (1962) of the effectiveness of combined additions of cobalt and
molybdenum in producing precipitation strengthening in Fe–Ni martensites led to the introduction in
the early 1960s of what might be regarded as the standard grades of maraging steels, designated
18NiCo(200), 18NiCo(250) and 18NiCo(300) in Table 1 (Decker and Floreen, 1988; Magnee et al.,
1974), where the 200, 250, and 300 refer to the nominal yield strengths in kips per square inch
(ksi).
There are higher-strength versions of the cobalt-containing maraging steels and some of these
compositions are also given in Table 1. Representative mechanical properties of the conventional
cobalt-containing maraging steels are given in Table 2 (Magnee et al., 1974).
Cont.

10. 10
Alloy C Ni Co Mo Ti Al Mn Si
18NiCo(200) 0.03 18 8.5 3.3 0.2 0.10 0.10 0.10
18NiCo(250) 0.03 18 8 4.8 0.4 0.10 0.10 0.10
18NiCo(300) 0.03 18.5 9.0 4.8 0.7 0.10 0.10 0.10
18NiCo(350) 0.03 18 12 4.2 1.5 0.10 0.10 0.10
13NiCo(400) 0.03 13 15 10 0.2 – 0.10 0.10
18NiCo(500) 0.03 8 18 14 0.2 – 0.10 0.10
Table 1. Nominal compositions of Fe–Ni–Co maraging steels (wt%)
Cont.

11. 11
Cont.
Alloy
Aging
temperature
(°C)
Yield strength
(MPa)
Ultimate tensile
strength (MPa)
Fracture
toughness
(MPa m1/2)
Charpy
(J)
18NiCo(200) 480 1316 1380 140 60
18NiCo(250) 480 1635 1690 100 35
18NiCo(300) 480 1835 1910 70 25
18NiCo(350) 480 2427 2468 40 16
13NiCo(400) 525 2530 2569 55 –
Table 2. Properties of conventional Fe–Ni–Co maraging steels

12. 12
Cracking Resistance in Smooth Materials
Maraging steel in the strength range 1240–1720 MPa tested as U-bends in seawater displayed
good resistance, as it did not fracture in periods of up to 2–3 years although there was considerable
general corrosion and fouling.
However, microcracks were observed after 6 months.
Similar behavior 24,27 of U-bend and bent beam specimens can be expected in industrial or marine
atmospheres, although general corrosion is less severe.
By comparison, AISI 4340 at strength levels of 1660 MPa failed in about 1 week in both seawater
and atmospheric tests.
Maraging steel of yield strength at or above 2060 MPa was not resistant and failed rapidly.

13. 13
Cont.
Welds in maraging steel are somewhat less resistant than base plate.
U-bend exposure of 1240 MPa strength welds survived for up to 2 years in seawater, while at
1380 MPa, failures occurred in 2–18 months.29

14. 14
It is possible to provide cathodic protection to materials of up to 1720 MPa yield strength, by coupling
to mild steel or possibly to zinc.24,27
However, zinc and metals more active than zinc tend to induce hydrogen embrittlement.
Welds up to 1380 MPa may be cathodically protected by zinc, but at impressed potentials of −1.25 V
(vs. the standard calomel electrode), both 1240 and 1380 MPa welds fail rapidly due to hydrogen
embrittlement.29
Hence, although tests on smooth specimens indicate that cathodic protection of maraging steel is
possible, tests on specimens with preexisting cracks indicate a greater sensitivity to hydrogen
embrittlement during cathodic polarization.29
Cont.

15. 15
Cont.
The use of cathodic protection on actual structures must therefore be applied with caution, and the
application of less negative potentials than are indicated to be feasible in smooth specimen tests is to
be recommended if it is assumed that structures contain crack-like defects.
Further evidence of the relative resistance of maraging steel is reproduced in Figure 2.
Also shown is the beneficial effect in smooth surface tests of cold rolling; shot peening has a similar
beneficial effect.29

16. 16
Cont.
Figure 2. Bent-beam test results in aerated distilled water. These specimens were exposed to the
environment at a stress of 70% of yield.
Reproduced from Setterlund, R.B., 1965. Materials Protection 4 (12), 27.

17. 17
Morphologies of reverted austenite in maraging steels: (a) matrix austenite (Schnitzer et al., 2010b); (b) lath-like austenite (A =
austenite, M = martensite) (Schnitzer et al., 2010b); (c) recrystallised austenite (Viswanathan et al., 2005) (d) Widmanstätten
austenite (Kim and Wayman, 1990).
(reprinted from Materials Science and Engineering: A, 398, U.K. Viswanathan, G.K. Dey, V. Sethumadhavan, Effects of austenite
reversion during overageing on the mechanical properties of 18 Ni (350) maraging steel, 367–372, 2005, with permission from
Elsevier); (reprinted from Materials Science and Engineering: A, 128, Sung-Joon Kim, C. Marvin Wayman, Precipitation behavior and
microstructural changes in maraging Fe-Ni-Mn-Ti alloys, 217–230, 1990, with permission from Elsevier)

18. 18
Microstructure of 18Ni (250) Maraging steel, a) lath martensite after forging-light
microscopy, b) lath martensite-SEM, c) lath martensite-TEM, d) Ti(N,C) at austenite
grain boundary-TEM

19. 19
Cont.
Overview of high strength steel concepts (Scripta Materialia 60 (2009) 1141)

20. 20
Applications of Maraging Steel
Production tools Aerospace and aircraft parts
Aluminium and zinc dies
Casting and forging dies
Carbide die holders
Extrusion press rams, dies, and containers
Gears for machine tools
Index plates
Pistons
Springs
Stub shafts
Cold reducing mandrels
Anchor rails
Arresting hooks
Gimbal ring pivots
Rocket motor cases
Load cells
Shock absorbers for lunar rover
Universal flexures
Military Others
Cannon recoil springs
Lightweight portable military bridges
Rocket motor cases
Auto-racing car parts (rods, shafts, gears)
Uranium enrichment plants parts (rotors, shafts)
Cable sockets
Hydraulic hoses
Pump impellers and casings
Tensile test equipment
Rotors for ultracentrifuges
Different application areas of maraging steels.

21. 21
Cont.

22. 22 Maraging steels are low-carbon martensitic steels which employ substitutional alloying elements
to achieve precipitation strengthening (age-hardening).
From: Reference Module in Materials Science and Materials Engineering, 2018
References:
Warren M. Garrison, Malay K. Banerjee,
Martensitic Non-Stainless Steels: High Strength and High Alloy☆,
Reference Module in Materials Science and Materials Engineering,
Elsevier,
2018,
Thank You
Authors of Technical articles and Scopus Journals are
Acknowledged.