A brief introduction to what maraging steels are and their applications.

1. UNIVERSITY OF LAGOS, AKOKA, YABA
DEPARTMENT OF METALLURGICAL AND MATERIALS
ENGINEERING
TERM PAPER
ON
METALLURGY OF MARAGING STEEL
SUBMITTED BY
GROUP 2 MEMBERS OF PHYSICAL METALLURGY (MME 405)
ADESINA JOSHUA OLUWATIMILEHIN 140406038
ODUNOSHO MICHAEL ADEDAMOLA 140406034
AJUKWU EMEKA PATRICK
OKEKARU CHARLES
OLAYINKA TEMITOPE DANIEL
ANAH SUNDAY
THOMAS ABEL OPEYEMI 140406030
OLUMU AYOMIDE
ODINA KINGSLEY
JOHNSON JIMI
TUESDAY, MARCH 13, 2018

2. METALLURGY OF MARAGING STEEL
Introduction:
Maraging steels are carbonfree iron-nickel alloys with additions of cobalt,
molybdenum, titanium and aluminium. Maraging steels are characterized with
superior strength combined with excellent toughness properties and weldability.
The term ‘maraging’ refers to the strengthening mechanisms and was coined from
a combination of martensite and age-hardening; ‘mar’ refers to martensite and
‘aging’ refers to the age hardening heat treatment.
Maraging steel is forged by a martensitic transformation followed by subsequent
age-hardening. 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. Theprincipal alloying element is 15 to 25 wt.% nickel
(Ni). Secondary alloying elements, which include cobalt (Co), molybdenum (Mo),
aluminium (Al), and titanium (Ti), are added to produceintermetallic precipitates.
The initial development of these steel carried out by C. G. Bieber of The
International Nickel Company (Inco) in the late 1950s was on 20 and 25 wt. % Ni
steels to which small additions of aluminium (Al), titanium (Ti), and niobium (Nb)
were made.
The density of maraging steel is equivalent to 8 g/cm3 and the melting point is
1413oC. Maraging steels are considered as the best tooling materials. It possess
excellent mechanical properties like higher yield strength and UTS. Besides, it has
higher impact strength, fatigue strength, compressive strength, toughness, ductility,
hardness, and wear resistance. It has excellent machinability characteristics and
readily cold and hot formed. Maraging steels are highly resistant to crack
propagation and possess good wettability and polishability. For heat treating,

3. maraging steels require lower furnace temperature. Uniform and predictable
shrinkage occurs during heat treatment. Minimal distortion occurs during thorough
hardening and free from the formation of carburized or decarburized layers on its
surface. Maraging steels have the unique combination of ultra-high yield and
tensile strength, ductility, and fracture toughness of any ferrous materials. It can
retain its strength up to 350oC. Having a very low carbonmartensite, the structure
is soft and readily machinable. It can be surface hardened by nitriding.
Maraging Steel is two times harder than stainless steel and 85% harder than pure
titanium. Maraging steel alloys are twice as hard as stainless steel and 35%
stronger than the hardest titanium alloy. On the Rockwell Scale of Hardness,
stainless steel is 23-26, titanium alloys 28-41 and Maraging Steel 52-55.
GRADES OF MARAGING STEEL
Maraging steel comes in different grades (200, 250, 300, 350 grades). This grade
number refers to the maximum achievable yield strength in thousands of pounds
per square inch (in ksi), and this is often dependent on the initial composition,
alloy content, and the thermo-processes. The commonality (for the most part) of
these different grades is that all maraging steels typically contain 18% Nickel. The
other alloying elements (such as cobalt or titanium) are variable. The higher grades
have more cobalt and titanium in the alloy; the table below shows the composition
of different grades of maraging steel
Maraging steel compositions
Element Grade 200 Grade 250 Grade 300 Grade 350
Iron Balance Balance Balance Balance
Nickel 17.0 – 19.0 17.0 – 19.0 18.0 – 19.0 18.0 – 19.0
Cobalt 8.0 – 9.0 7.0 – 8.5 8.5 – 9.5 11.5 – 12.5

4. Molybdenum 3.0 – 3.5 4.6 – 5.2 4.6 – 5.2 4.6 – 5.2
Titanium 0.15 – 0.25 0.3 – 0.5 0.5 – 0.8 1.3 – 1.6
Aluminium 0.05 – 0.15 0.05 – 0.15 0.05 – 0.15 0.05 – 0.15
Table 2: Composition and required properties as defined in MIL-S-46850D
Source: http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-S/MIL-S-
46850D_19899/
Maraging steel250 is an 18 percent nickel steel that has been strengthened with
cobalt. Maraging 250, like all maraging steels, goes through an aging process that
forces the metal to coolfrom its molten state to its solid state over an artificially
long time. This process results in tempered steel that has both high levels of
strength and hardness. It will also resist certain stresses and maintain its structure
in environments that would cause irreparable changes to many other steels. The
properties that make Maraging 250 particularly appealing to many industries is its
workability. This allows Maraging 250 to be more versatile than many other alloys
in its class. However, it is still the alloy’s strength and resistance to extreme
temperatures that make it a truly effective material in a wide range of atmospheres.
After Maraging 250 has undergone heat treatment, it demonstrates excellent
mechanical properties. It will reach a yield strength of 240 ksi and a fracture
toughness of 75 k1c. These properties have made Maraging 250 effective in the
construction of missile and rocket motor cases, landing and takeoff gear, and high
performance shafting.
Maraging steel300 is an iron-nickel steel alloy that, as with all maraging steels,
exhibits high levels of strength and hardness. However, Maraging 300 also
possesses an extreme resistance to crack propagation, even in the most extreme
environments. Maraging 300 is often used in applications where high fracture
toughness is required or where dimensional changes have to remain at a minimal

5. level. The unique properties of Maraging 300 have made it an integral part of the
aircraft and aerospaceindustries. It is often used in rocket motor casings and the
landing gear for certain planes. Maraging 300 is also effective in the design of
power shafts and low-temperature cooling systems.
Maraging steel350 refers to crystalline tempered steel. Martensite, which is
created through an aging process.When aging is used, steel is forced to coolfrom
its molten state to its solid state over a prolonged period of time. The result is a
metal that is harder and stronger than it would be had the steel been allowed to
coolat a natural rate. Maraging 350 is an alloy that has become an integral material
in the airplane and aerospaceindustries. Due to its strength and its ability to
withstand extreme conditions including frequent and sudden changes in speed and
temperature, Maraging 350 is used in the production of rocket motor cases, takeoff
and landing gear, and certain munitions created by defense companies. Maraging
350 also has uses in less drastic applications such as die casting and high
performance shafting.
HEAT TREATMENTOF MARAGING STEEL
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-

6. 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).
Figure 1: Schematic diagram of a typical heat treatment cycle for a 18% Ni
maraging steel.
PHYSICAL METALLURGY OF MARAGING STEEL
The effects of the alloying elements in maraging steel are discussed below:
a. Nickel (Ni); is an austenitic stabilizing element. It increases hardenability
and resistance to fatigue and corrosion

7. b. Cobalt (Co) and Molybdenum (Mo); it helps retain hardness at high
temperature and gives good wear resistance.
c. Titanium (Ti); it stabilizes the ferrite, refine grain structure and raises the
creep strength.
d. Aluminium (Al); it also stabilizes the ferrite, form nitride and refine grain
size.
Figure 2: Figure showing the microstructure of maraging steel.
MARAGING STEELAPPLICATIONS
One of the many advantages that maraging steel have is their malleability.
Maraging steels are highly sought in applications that require precise and specific
geometries and demand operation at high loads. Examples of suchapplications are:
1. Rocket motor casings. These casings need to be comprised of material that
can be molded according to specified design, and demand the ability to
contain the highly pressurized inner contents.
2. Takeoff and landing gear in aircraft. These components are often susceptible
to high stresses and malleability is important here.

8. 3. Fencing blades. Fracture resistance makes maraging steel an attractive
choice in the sportof fencing. This reduces the risk of fencing related
injuries.
4. Vasco Max alloys are maraging steels containing 18% Ni. These alloys are
produced by vacuum melting and it can be converted into the mill product
forms such as like billets, bars, rods, coils, and wires. It is most suitable for
die castings. It has superior ductility, toughness, low coefficient of thermal
expansion and elasticity, excellent tempering resistance, good corrosion
resistance and thermal conductivity. The benefits of maraging steels are its
excellent resistance to heat checking and small stresses in thermal cycling,
less softening in use, less erosion and oxidation.
5. Maraging steels are typically applied to producemissile and rocket motor
cases, wind tunnel models, recoil springs, flexures, AC Motors, high
performance shafting gears and fasteners, extrusion tools, casting dies, and
core pins. Engine components such as crankshafts and gears that work at
warm temperatures and the firing pins of automatic weapons that cycle from
hot to coolrepeatedly while under substantial loads and impacts are made
from maraging steels. Their uniform expansion and ease machinability
characteristics makes it useful in high wear portions of assembly lines and as
well as in die manufacturing.

9. REFERENCES
1. https://en.wikipedia.org/wiki/Maraging_steel
2. http://www.imoa.info/molybdenum-uses/molybdenum-grade-alloy-steels-
irons/maraging-steels.php
3. http://www.france-metallurgie.com/introduction-to-metallurgy-of-maraging-
steels-us/#
4. Decker, R. F., Eash, J. T., and Goldman, A. J., “Eighteen Percent Nickel
Maragin Steel,” Trans. ASM, 55,58-76 (1962).
5. Decker, R. F., Novak, C. J., and Landig, T. W., “Developments and
Projected Trends in Maraging Steels,” Jnl. Metals, 19 (11), 60-66 (1967).
6. Sadowski, E. P., “12% Ni Maraging Steel,” Metals Eng. Quart, 5,56-
64(1965)
7. Novak, C. J. and Diran, L. M., “Effects of Residual Elements in Maraging
Steels,” Jnl. Metals, 15, 200-204 (1963)
8. Hall, A. M., and C. J Slunder. “The metallurgy, behaviour and applications
of 18 Ni maraging steel.” NASA, SP-5051 (1968).