RESEARCH REVIEW PAPER

1. _____________________________________________________________________________
A Review on Casting and Characterisation of Multi-Component Low Density Steels
Sudhakar Geruganti,PHD(MATERIALSENGINEERING),
Schoolof Engineering Sciences and Technology,University of Hyderabad,Hyderabad,India
_____________________________________________________________________________
ARTICLE IN F O:
Keywords:
Automotive
Alloy Design
high-performance
composite technology
______________________________________________________________________________
ABSTRACT
Decreasing energyutilisationalong withenhancingsafetyrequirementsisaimportantgoal inmodern
AutomobileSector.Hence,we needtothe developinresearcha steel whichis tough,strongandaswell
as for automotive applications.NewerAlloydevelopmentiscore to the evolutionof mankind.
Comparativelyhigher(eithersingleorcombinationof) properties are alwayssoughtafter byengineers
as services industryis continuouslygetting verystringentandhighexpectations,enhancedlevelsof
reliabilityare mainly soughtbyendusers. Thisalwaysstretches the limitsof materialsprimarilythrough
differentalloydesignandenforcing composite technology. However,the numberof alloys newly
developedwasrestricteddue tothe inadequate scientificknowledgeandcharacterizationtechniques.
Most of the newermaterials(alloys)developed wasbytrial anderror. Significantprogressinscience
occurred from the 19th
centuryonward.This triggeredthe developmentof awide spectrumof alloys
whichwere primarlybasedonone principal alloyingelement.Duringthe latterpartof 20th
century,
advanced highstrength steels,nickel-based,aluminiumbased andtitanium-basedalloysmade inroads
intomultiple engineering fieldsandbiomedical applicationsaddingtothe convenienceandcomfortin
the life of humansandsimultaneouslystrengtheningthe defence forcesof the countries.
_________________________________________________________________________________

2. GRAPHICAL ABSTRACT:-

4. ABBREVATIONS:
AHSS: AdvancedHighStrengthSteel
P: Pearlite,Steel Phase.
M:Martensite,SteelPhase.
B:Bainite,SteelPhase.
VIM:VaccumInductionMelting,A furnace
heatingmaterial undervaccum.
VAR:VaccumArc Melting,Meltingof alloyusing
Electrode undervaccum.
FIG 1 &2 : SchematicDiagramof VARFurnace &
ARC Zone Details,anditsvariousparts.
FIG 3:Vaccum InductionMeltingFurnace
FIG 4:Casting andMeltingOperation
TABLE 1: low,Medium,HighEntropyAlloys
TABLE 2: Multi-ComponentAlloys withlow
densities
1. INTRODUCTION:
Multi-Component Low Density Steels:
Low Density is the main driving force for
developing Fe-C steels for automotive
applications. Alloying elements with a
lower density than Fe (7.8 g/cm3 ) are Al
(2.7 g/cm3 ), Si (2.3 g/cm3 ), Mn (7.21
g/cm3 ) and Cr (7.19 g/cm3 )[REF :8].They
are often added to Fe-C steels to reduce
the density as well as to control the phase
constitution. The lower density results from
the fact that these light elements change
the lattice parameter of steels and at the
same time reduce density by virtue of their
low atomic masses. For example, a 12%
aluminium addition will reduce the density
of iron by 17% of which lattice dilatation
contributes 10% and atomic mass reduction
contributes an additional 7%. Fig.
1a(graphical abstract) shows the effects of
alloying elements on density reduction in
ferritic steels up to a maximum of 16% alloy
content. The density of steel decreases
linearly with increasing addition of the
elements Al, C, Si and Mn. Considering its
strong effect on density reduction as well
the engineering aspects such as alloy
making and workability, Al has emerged as
the chief alloying element in low density
bulk steels. Sometimes, Si is added in
combination with Al. Austenitic steels have
a higher density (8.15 g/cm3 for c-Fe vs.
7.87 g/cm3 for a-Fe) and a lower elastic
modulus (195 GPa vs. 207 GPa) than ferritic
steels. The increase in the Al content and
the ferrite fraction will decrease the mass
density due to the smaller atomic weight of
Al compared to Fe as well as the difference
in atomic density between the austenite
(FCC) and ferrite (BCC) structures in steels .
The overall density reduction of the
coexisting austenitic and ferritic Fe(Mn, Al)
solid solutions was analysed, based upon
the combined effect of the lattice dilatation
and the average molar mass of the alloys.
The effectiveness of Al in density reduction
is almost the same in both the ferritic and
austenitic alloys, since the coefficients for
Al are nearly identical (0.098 vs 0.101). This
indicates a 1.3% reduction in density per
1% Al addition. The addition of C is very
effective in density reduction for austenitic
low density steels. The effectiveness of C is
about four times higher than than Al.An
increase in the Young’s modulus (E
modulus) improves the stiffness of
automotive parts and the body-in-white.
One of the critical disadvantages of low
density steels is that the addition of Al
decreases the Young’s modulus. The elastic
moduli of polycrystalline Fe-Al alloys in the
annealed state at room temperature are

5. shown in Fig. 1b (graphical abstract)as a
function of the Al content . The collected
data of the Young’s modulus were
measured with dynamic measurements
such as the resonance method or the
ultrasonic method, which are more precise
than those determined in quasi static
tensile test. Steel is the most important
building material for body construction in
the automotive industry due to its low
manufacturing cost, ability to be pressed
into complex shapes and weldability.
Nevertheless, the automotive industry is
continuously facing new challenges such as
regulatory demands for safer and more
fuel-efficient vehicles as well as demands
from the customers for improved
performance, comfort, and reliability. Thus,
the development of novel steels with
higher strength and improved
manufacturability became a priority for the
steel industry since the 1970’s when
regulations were implemented due to the
oil price crisis. This initiated the
development of new steel for, among
others, the automotive industry. Thus,
leading to significant mass reduction in
vehicles while increasing the safety of the
passengers by optimizing the properties of
the steel and its manufacturability. The
answer to this problem was the
development of advanced high strength
steels (AHSS), which combines properties of
those found in high strength steels such as
martensitic or bainitic with those of very
ductile steels,such as ferritic. AHSS are
steels with unique tailored properties made
possible due to the precise addition of
alloying elements and subsequent heat
treatment, which results in the formation
of multiple steel phases and a more
advanced structure. These steels evolved
from the high strength low alloy (HSLA)
steels in the late 1970’s. The 1st generation
of AHSS include Dual Phase, Complex Phase
(CP) and TRansformation Induced Plasticity
(TRIP) steels. These steels are characterized
by their enhanced elongation and strength
due to the combination of ferrite and
retained austenite achieved by subsequent
processing. These steels had a tensile
strength of approximately 300-700 MPa
and an elongation of 10-50%. The 2nd
generation AHSS developed from the desire
to improve mechanical properties of the 1st
generation by increasing the amount of
manganese which promotes austenite
formation. This resulted in steels with
enhanced mechanical properties by means
of subsequent hardening mechanisms,
strain-induced martensitic transformation
and mechanical twinning. Tensile stress and
elongation in these steels are in the range
of 900-1500 MPa and 40-60 %, respectively.
However, the 2nd generationAHSS were
limited to specific applications due to the
costly high manganese content (20-30%) as
well as problems related to processing.
The 3rd generation AHSS was developed
with the aim of combining the properties of
the 1st andthe 2nd generations, but at a
lower cost than that of the high manganese
2nd generation. The third generation AHSS-
steels have a broader range of tensile
strength and elongation properties, with
600-1200 MPa and 20-50 %,
respectively.Low density or Lightweight
materials have become increasingly critical
in thetransportation manufacturing
sectors,including aircraft, automobile,
heavy truck, rail, ship, and defense
manufacturing industries. Light metal and
alloys possess high strength-to-weight
ratios and low density, and are generally
defined bylow toxicity as opposed to heavy
metals.Light metals are often used for
materialsand operations where lightweight
andimproved performance properties
arerequired. Common applications

6. includechemical process, marine,
aerospace,and medical applications.Lighter
vehicles that are designed for consumers,
as well as the industry andmilitary sectors,
consume less fuel andprovide a better
performance. Inaddition to carrying larger
loads, lightervehicles can travel the same
distancesat reduced cost and release less
carbondioxide. In the present scenario,
Almost all the properties which a new
material requires can be obtained by
varying different alloy compositions. In
Iron-Carbide system, ferrite phase is soft
phase while Martensite phase is hard phase
,Cementite is very hard phase. Therefore
depending on the nature of properties
desired(whether soft or hard or very hard)
we can accordingly modify the phases to
get desiredproperties. If we require
moderate hardness, we can have 60%
ferrite and rest martensite. This can be
achieved by using ferritestabilisers
(Tungsten,chrominum,Vanadiumetc) while
Austenite Stabilisers Nickel ,Copper
,Aluminium etc on quenching (Austenite
yields) martensite. Only when very high
hardness is required we go for Cementite.
Similarly we have a range of alloying
elements suitable for various specific
properties and applications. Chrominum for
Corrosion and Oxidation .The lightweight of
automobile has become more and more
widely concerned with the needs of energy
conservation, environmental protection
and economy. The low density and high
strength steel of the Fe-Mn-Al-C system
combines the low density and excellent
mechanical properties, which complies with
this topic.The earliest information on low-
density steels dates back to 1933 which was
related to the first development of Fe-Mn-
Al-C system.Until 1958, the Fe-Mn-Al-C
system of low-density steel was developed
to replace the Fe-Cr-Ni system of stainless
steels (added too many expensive Ni and Cr
elements).At present, the Fe-Mn-Al-C
system low-density steel is a kind of steel
with high lightweight potential in the
automotive industry, in which the addition
of Al element leads to a decrease in density
and Young’s modulus. Adding 1wt% Al, the
steel density is reduced by 1.3%, and the
Young’s modulus is reduced by 2%.
Simultaneously,the addition of a large
amount of Al,Mn and C elements resulted
in the smelting, continuous casting,
formability, weldability, microstructure
evolution and deformation mechanism of
Fe-Mn-Al-C system steels, which are quite
different from those of traditional steels.
The lightweight Fe-Mn-Al-C systemsteel
can be classified into four categories: single
ferritic steels,ferrite based duplex steels,
austenite based duplex steels and
austenitic steels, according to the
composition of the alloy and the main
composition phase of room
temperature.The single ferritic steel has
similar tensile properties of 200—600 MPa
as the conventional high-strength low-alloy
steel (HSLA) and belongs to the first
generation of advanced high-strength steel
(1G-AHSS).Ferrite-based Fe-Mn-Al-C system
duplex steels are another promising
lightweighting scheme with a lower alloy
content that can be produced using ferrite
plastic deformation and retained austenite
TRIP and TWIP effect to increase steel
strength and plasticity.The ferrite based Fe-
Mn-Al-C double phase steel has superior
strength and ductility compared with the
first advanced high strength steel, and the
middle and upper level of their
performance belongs to the category of the
third generation advanced high-strength
steel (3G-AHSS).The austenitic-based
duplex steel is similar to ferritic-based
duplex steel, but it has higher alloy content
than ferritic-based dual-phase steel, and its
lower limit of performance belongs to the

7. 3G-AHSS category.The austenitic steels are
the most promising in terms of properties
and processing.The main constituent
phases of austenitic steel are austenite, a
small amount of ferrite and κ-carbide.The
mechanical properties of austenitic steels
are determined by the deformation of
austenite and the interaction of carbide-
austenite.The tensile properties of
austenitic light steel are similar to those of
high manganese TWIP steel, the strength of
600—1 500 MPa and the plasticity can
reach of 30%—80% (even up to ~100%), it
belongs to the category of the second
generation advanced high strength steel
(2G-AHSS). The stacking fault energy (SFE)
of Fe-Mn-Al-C system low-density high-
strength steel increases and short-range
ordered (SRO) phase and κ-type carbide are
precipitated with the addition of Al content
in steel.High-SFE low-density Fe-Mn-Al-C
system steel with various deformation
mechanisms such as novel microband
induced plasticity (MBIP), dynamic slip
band refinement (DSBR), shear band
induced plasticity (SIP) deformation
mechanism, transformation induced
plasticity (TRIP) and twinning induced
plasticity (TWIP) deformation
mechanisms.Thesedeformation
mechanisms are consistent with the B2 and
DO3 type of ordered phases, uniformly
arrange of the intragranular nano-sized κ-
carbides, dislocation slips, twins and phase
transitions.The precipitation of
intragranular κ-carbide is a unique
strengthening mechanism of austenitic Fe-
Mn-Al-C steel containing a large amount of
Al and C elements.
The applications of the Fe-Mn-Al-C system
steels in the automobiles are still not
prevalent due to the lack of knowledge
related to application properties so far.The
most important reason is that high Al
content leads to high Young’s modulus
reduction and high Mn content leads to
problems such as smelting, continuous
casting, and machining.The future
developments will therefore have to
concentrate on the alloying and processing
strategies and also on the methods to
increase the Young’s modulus. An improved
processing strategy and a high value for the
Young’s modulus will go a long way towards
upscaling these steels to real automotive
applications.
The fundamental research situation and
devoment of Fe-Mn-Al-C low-density high-
strength steel were summarized.The
composition design and the role of alloying
elementsof Fe-Mn-Al-C low-density high-
strength steel were introduced.The
microstructures of Fe-Mn-Al-C low density
high strength steel were analyzed.The
mechanism of formation of toughness and
toughness, stacking fault energy, physical
and mechanical properties of Fe-Mn-Al-C
series low density and high strength steels
were revealed, and the application
properties of Fe-Mn-Al-C alloys were
discussed.Finally, some future directions of
research on Fe-Mn-Al-C system low density
steels have been proposed.
II.Vacuum arc remelting (VAR)
VAR is a secondary melting process for
production of metal ingots with elevated
chemical and mechanical homogeneity for
highly demanding applications.The VAR
process has revolutionized the
specialty traditional metallurgical
techniques industry, and has made possible
incredibly controlled materials used in the
biomedical, aviation, and aerospace fields.
Overview
VAR is used most frequently in high value
applications. Essentially it is an additional
processing step to improve the quality of

8. metal. Because it is both time consuming
and expensive, a majority of
commercial alloys do not employ the
process. Nickel, titanium,[2] and
specialty steels are materials most often
processed with this method. The
conventional path for production of
titanium alloys includes single, double or
even triple VAR processing.Use of this
technique over traditional methods
presents several advantages:
 The solidification rate of molten
material can be tightly controlled. This
allows a high degree of control over
the microstructure as well as the ability
to minimize segregation
 The gases dissolved in liquid metal
during melting metals in open furnaces,
such
as nitrogen, oxygen and hydrogen are
considered to be detrimental to the
majority of steels and alloys. Under
vacuum conditions these gases escape
from liquid metal to the vacuum
chamber.
 Elements with high vapor pressure such
as carbon, sulfur,
and magnesium (frequently
contaminants) are lowered in
concentration.
 Centerline porosity and segregation are
eliminated.
 Certain metals and alloys, such as Ti,
cannot be melted in open air furnaces
Process description
The alloy to undergo VAR is formed into a
cylinder typically by vacuum induction
melting (VIM) or ladle refining (airmelt).
This cylinder, referred to as an electrode is
then put into a large cylindrical
enclosed crucible and brought to a
metallurgical vacuum (0.001–0.1 mmHg or
0.1–13.3 Pa). At the bottom of the crucible
is a small amount of the alloy to be
remelted, which the top electrode is
brought close to prior to starting the melt.
Several kiloamperes of DC current are used
to start an arc between the two pieces, and
from there, a continuous melt is derived.
The crucible (typically made of copper) is
surrounded by a water jacket used to cool
the melt and control the solidification rate.
To prevent arcing between the electrode
and the crucible side walls, the diameter of
the crucible is larger than that of the
electrode. As a result, the electrode must
be lowered as the melt consumes it.
Control of the current, cooling water, and
electrode gap is essential to effective
control of the process, and production of
defect free material.
Ideally, the melt rate stays constant
throughout the process cycle, but
monitoring and control of the vacuum arc
remelting process is not simple.[4] This is
because there is very complex heat transfer
going on involving conduction, radiation,
convection (within the liquid metal), and
advection (caused by the Lorentz Force).
Ensuring the consistency of the melt
process in terms of pool geometry, and
melt rate is pivotal in ensuring the best
possible properties from the alloy.
Materials and applications
The VAR process is used on many different
materials, however certain applications
almost always use a material that has been
VAR treated. A list of materials that may be
VAR treated include:
 Stainless Steel
o 15-5
o 13-8
o 17-4
o 304
o 316
 Alloy Steel
o 9310
o 4340 & 4330+V
o 300M
o AF1410
o Aermet 100
o M50
o BG42
o Nitralloy
o 16NCD13
o 35NCD16

9. o HY-100
o HY-180
o HY-TUF
o D6AC
o Maraging steels
o UT-18
o HP 9-4-30
 Titanium
o Ti-6Al-4V
o Ti-10V-2Al-3Fe
o Ti-5Al-5V-5Mo-3Cr
FIG 1: VACCUM ARC MELTING
 Nitinol
 Invar
 Nickel superalloys
o Inconel alloys
o Rene alloys
o RR1000
 Zirconium
 Niobium
 Platinum
 Tantalum
 Rhodium
Note that pure titanium and most titanium
alloys are double or triple VAR processed.
Nickel-based super alloys for aerospace
applications are usually VAR processed.
Zirconium and niobium alloys used in the
nuclear industry are routinely VAR
processed. Pure platinum, tantalum, and
rhodium may be VAR processed.
FIG 1 & 2 : SCHEMATIC DIAGRAM OF VAR
FURNACE AND ARC ZONE DETAIL
REFERENCE:11,12,13,14
III. Vacuum Induction Melting:-
Vacuum melting, casting and re-melting
equipment have been implemented in huge
numbers over the recent years mainly with
an intention to try and eradicate impurities
from the process wherever possible.
Vacuum induction melting (VIM) has some
specific advantages including, gas
elimination, chemical composition control,
process control and more. In recent years
the world of metallurgy has seen a massive
growth in installations of new melting, re-
melting and casting equipment under
vacuum. This development is driven by
various factors, but mainly by the
increasing demand from the aerospace and
power turbine industries, which pursue the
simple philosophy: “Impurities that are not
generated do not have to be removed.”
This means, especially for materials which
are used in rotating parts under high
thermal stress, that cleanliness is very
important and influences the lifetime of
such parts. For example, low cycle fatigue
(LCF) properties of turbine disks can be
directly related to both non-metallic
inclusion content and inclusion size of the
material. In aircraft and land based gas

10. turbines, most parts and components (eg,
turbine blades and vanes, turbine disks,
cases, shafts, bolts and combustors) that
undergo high thermal stress during
operation, are made of superalloys with
different amounts of alloying elements.
Most of these alloying elements have a high
affinity for oxygen, nitrogen and hydrogen,
therefore, during melting of such alloys
under air, formation of oxides and/or
nitrides will occur. These oxides have a
dramatic influence on mechanical
properties of the materials. To minimize or
avoid the formation of inclusions, it is
therefore necessary to protect the melt
from contact with air.
Vaccum Induction Melting (VIM) is the
melting of metals by induction done under
a vacuum. This process first became
important in the1950s; As a result of VIM,
the jet engine made the great advance in
performance and durability which has been
so important to both military and
commercial aviation.
The specific advantages of vacuum
induction melting include:
 Elimination of gases - under the very low
pressures obtained, .000001 atmosphere,
undesirable gases and potentially harmful
volatile elements are eliminated from the
charged raw materials as melting occurs
 Close control of chemical analysis -
exceptional and reproducible control of
reactive element containing compositions is
possible because of the lack of atmosphere
 Superior process control – independent
control of pressure, temperature and
inductive stirring provides an exceptional
opportunity for developing melt practices
specifically tailored to alloy composition
and desired properties
 Slag free melting - melting in a vacuum
eliminates the need for a protective slag
cover and decreases the potential of
accidental slag contamination or inclusions
in the ingot
 Melt protection - high vacuum prevents
deleterious contaminating reactions with
atmospheric gases
Some applications of vacuum
inductionmelting are:
 Refining of high purity metal and alloys
& Electrodes for remelting
& Master alloy stick Investment Casting
 Casting of aircraft engine components
 Vacuum induction melting is
indispensable in the manufacture of
superalloys. Compared to air-melting
processes such electric arc furnaces
(EAF) with argon oxygen
decarburization (AOD) converters, VIM
of superalloys provides a considerable
reduction in oxygen and nitrogen
contents. Accordingly, with fewer
oxides and nitrides formed, the
microcleanliness of vacuum- melted
superalloys is greatly improved
compared to air (EAF/AOD)-melted
superalloys.Additionally, high-vapor-
pressure elements (specifically lead and
bismuth) that may enter the scrap
circuit during the manufacture of
superalloy components are reduced
during the melting process. Accordingly,
the vacuummeltedsuperalloys
(compared to EAF/AODmelted alloys)
are improved in fatigue and stress-
rupture properties.
Control of alloying elements also may
be achieved to much tighter levels than
in EAF/AOD products. However,
problems can arise in the case of
alloying elements with high vapor
pressures, such as manganese. Vacuum
melting also is more costly than
EAF/AOD melting.The EAF/AOD process
allows compositional modification

11. (reduction of carbon, titanium,sulfur,
silicon, aluminum, etc.). In vacuum
melting, the charge remains very close
in composition to the nominal
chemistry of the initial charge made to
the vacuum furnace. Minor reductions
in carbon content may occur, and most
VIM operations now include a
deliberate desulfurization step.
However, the composition is
substantially fixed by choice of the
initial charge materials, and these
materials are inevitably higher-priced
than those that are used in arc-AOD.
REFERENCE:Vacuum Induction Melting Furnace
Design vacfurnace.com|300 ×23
FIGURES:VIM OPERATION,CROSS
SECTIONAL VIEWS & PARTS,FLOW-CHART.
Vacuum Induction Melting furnace (VIM) is
used in secondary refining or in metallurgy,

12. to refine alloys in a fluid state, by bringing
some change in temperature and their
chemical compositions. This in a way,
improves the quality of the raw materials
used in many complex alloys of the
complex devices of aerospace engineering.
Induction melting process involves inducing
swirly electrical currents in the metal, with
a source as the induction coil which carries
an alternating current. The swirly currents
melt the charge by heating it up.
The improvising of the materials eventually
makes them homogeneous and thereby
clean them by churning out all the
dissolved and bonded impurities. The
vacuum levels are set to be in the range of
10-1 to 10-4 mbar during this type of
refining phase and requires precise control
for melting.
Compared to other kinds, the melting
process is quite easier in VIM, attributing
the independent control of time, pressure,
temperature, and transport through melt
stirring. In the process of vacuum induction
melting, it is important to have flexibility in
controlling the alloy composition by
sampling and mixing up of the required
alloys.
Some important usage of vacuum induction
melting are:
# Refining of finest impurities from metals
and alloys
# Electrodes for remelting
# Investment casting
# Making casts of aircraft engine
components
REFERENCE: Therelek > Products > Vacuum Induction
Melting Furnace VIM
Features & Specifications
Title
Furnace Type Cold Wall (front loading,
Melt Zone Cylindrical
Temperature Range 800°C to 2200°C (furnace
Standard Applications Vacuum Induction Meltin
Vacuum 5 x 10-6 m.bar
Vacuum System
Rough Vacuum by Rotary
Molecular pump
Heating Elements Induction Coil
Instrumentation &
Automation Induction Coil Controller,
Applications:
 Used in aircraft engine components for
casting
 Used in making superalloys
 High purity metals and alloys are refined
 Re-melting of electrodes
 Investment casting
 Strip casting
Advantages:
 Small batch sizes
 A quick change in the program of steels
and alloys
 Easy operation
 Reduction in Oxidation losses
 Compositional tolerance achieved
 Precise Temperature control
 Low environmental pollution

13. 4. Processing of Lightweight Metals:
Lightweight metals are processed in a
variety of ways such as melt processing,
powder processing, thermo-mechanical
processing, forming, coatings, and joining
and assembly.
4.1 Melt Processing
Metal casting, which involves pouring
molten metal into a die or mold followed
by cooling it to solidify the component,
is an ancient process and even today
offers great potential to remove weight
off the metal structures. There are three
advanced melt processing techniques:
thin-wall casting, high-integrity casting,
and dissimilar-metal casting. Thin-wall
casting is a process where several types of
metals, such as aluminum and steel can be
cast.However, some complications occur
when working with molten metals; such
as maintaining proper flow and inhibiting
the metal from solidifying prior to filling
the mold. In high-integrity casting, certain
products should meet unique standards,
without microstructures and porosity
that are present throughout the cast
part. In dissimilar-metal casting, two or
more metals are used in a single casting
which provides considerable benefits.
Here, a product can be cast so that
parts of it are formed from one type of
metal and other parts are formed from a
different metal, employing the materials’
various properties where they are most
needed.
TABLE: 1
Properties realized by MCAS especially with
density values lower than 3g/cc targeted
for weight critical applications.The
development of lightweight MCAS was
triggered to stem global warming which is
deteriorating with every passing day due to
a significant expansion in automobile,
aerospace and maritime sectors.
TABLE: 2
Multi-Component Alloys with low
Densities.
Alloy System Density
Mg43(MnAlZnCu)57 2.51
Mg45.6(MnAlZnCu)54.4 2.30
Mg50(MnAlZnCu)50 2.20
AlLiMgZnSn 3.88
AlLi0.5MgZn0.5Sn0.2 2.98
it must be noted that in recent past
not many new alloys are introduced in
other metal systems particularly the one
exhibiting densities lower than
conventional aluminium alloys. To replace
aluminium alloys, magnesium technology is
rapidly emerging and do provide a viable
solution for weight reduction. However,
even in the case of magnesium alloys, the
number of commercial alloys are limited
and so is the spectrum of properties they
exhibit.2 In the context of classification of
alloys based on configurational entropy,

14. practically all conventional alloys come
under the category of low entropy alloys.
Over the past century, the properties of low
entropy or traditional alloys were tailored
primarily through controlled secondary
processing and/or heat treatment
processes. These methods of enhancing
and tailoring properties of traditional alloys
based on their end application are almost
saturated. To further note that the process
of heat treatment is an additional step for
microstructural engineering and adds to the
cost of the end material or finished
product. From the perspective of enhancing
properties, attention has to be placed on
compositional control and to develop multi-
component alloys where the secondary
phases are developed inherently during
processing step to exhibit a superior
combination of properties without the
need of heat treatment. The necessary
expectations from these multicomponent
alloys will be a superior combination of
properties when compared to conventional
alloys in any possible processed or heat-
treated state. This should lad to the
development of multiple component alloys
in both low and medium entropy
classifications besides MCAS. Judicious use
of alloying elements and a better
understanding of multi-component phase
diagram can enable the researchers to
move along this direction. While high-
density MCAS have their own niche
application areas, research in lightweight
multicomponent alloys in all the categories
(low, medium or high entropy) is the need
of the day for the better health of planet
earth and its inhabitants.
5. BULK COMBINATORIAL DESIGN OF
LOW-DENSITY AUSTENITIC STEELS
Here, we use a combinatorial
approach for rapid trend screening and
alloy maturation of metallurgically melted
and processed Fe-Mn-Al-C low-density
TWIP and j-carbide hardened steels. The
approach is referred to as rapid alloy
prototyping (RAP).49 We apply it here to
one group of Fe-30Mn1.2C-xAl (wt.%) TWIP
steels and to a second group of Fe-20Mn-
0.4C-xAl TWIP steels, both with varying Al
content (x) and different aging conditions.
In both cases, the samples were
synthesized by melting and casting in a
vacuum-induction melting (VIM) furnace
under 400 mbar Ar pressure. The system
was modified to enable synthesis of five
different alloys in one operation for each
alloy system. We used five Cu molds, which
could be moved stepwise inside the
furnace. They were successively filled with
melt from a 4-kg ingot. After each cast, the
remaining melt composition in the ingot
was adjusted by charging Al through an air
lock. After cooling and cutting, the 10 9 50
9 130-mm3 -sized blocks were hot rolled at
1100C into 2 ± 0.1-mm thick and 500-mm-
long sheets. These were reheated to 1100C,
water quenched, and cut perpendicular to
the rolling direction into sets of nine
segments with dimensions 2 9 60 9 55 mm3
for each alloy composition.
Homogenization was performed at 1100C
for 2 h under Ar, followed by water
quenching. Aging was conducted in air at
450C, 500C, 550C, and 600C for 0 h, 1 h,
and 24 h at each temperature, followed by
oil quenching. This results in a matrix of 45
different sample conditions. Scales were
removed from the surfaces by low-
pressure, fine-grit sandblasting after the
heat treatments. Samples for mechanical
testing and microstructure investigation
were prepared from the segments by
package spark erosion. Tensile testing was
conducted at room temperature with an

15. initial strain rate of 103 s1 . All values
plotted represent averages of three
Measurements for every material state.
Cross-sectional areas of selected samples
were prepared in the plane perpendicular
to the rolling direction by grinding and
polishing with standard metallographic
techniques. X-ray diffraction (XRD) analysis
was performed on the rolling plane of
samples ground to a thickness of 1 mm.
Further details of the method are explained
. The RAP method enabled us to screen two
different sets of five Fe-Mn-C-based
weight-reduced Al-containing compositions
each exposed to nine respective heat
treatments within 35 h. For each alloy base
set, synthesis, processing, mechanical
screening, and phase characterization are
included. The metallographic analysis
showed no cracks, pores, or
macrosegregations in the final materials.
The as-cast samples had a coarse dendritic
microstructure. Hot rolling and water
quenching resulted in a fully recrystallized
microstructure with a grain size of 20 lm
with some retained microsegregations of
Mn. Color-coding reflects individual aging
conditions. The data are reproduced from
an earlier publication.49 They show a clear
dependence of the mechanical behavior on
both composition and heat treatment. For
the reference material (no Al addition, i.e.,
ternary Fe-30Mn-1.2C alloy), the best
mechanical behavior is found for the as-
homogenized state, namely, 360 MPa YS,
high work hardening (830 MPa UTS), and
high ductility (77% TE). Aging of the Fe-
30Mn-1.2C alloy leaves the YS virtually
unchanged and increases the hardness.
6. Casting process:
I. The obtained columnar structure
corresponds to the high cooling rates
observed during continuous casting. The
columnar grains observed in all ingots
reveal a fast initial cooling provided by the
steel mould.II. The cooling rates during
casting of steel 2 and 3 were high enough
to promote formation of retained
austenite, bainite and martensite. The
cooling rate of steel 1; however, was slow
enough to obtain an almost complete
pearlite micro-structure.III. The initial
cooling rate MCASured is between 10-
20 ̊C/min, which is far from the primary
cooling values but as the time progressed,
the cooling rate approaches the low values
observed at the end of solidification of the
liquid core (1-2 ̊C/min). IV. Although the
measured cooling rates are not as high as
those in the mould, the micro-structures
observed reflect well the behavior in a
continuously cast product. Consequently,
the proposed ingot casting technique
seems promising to emulate the actual
casting process Micro-structure and
composition effects:V. Regarding the effect
of Mn on the phases developed, steels with
a higher content of Mn promoted austenite
stability at the expense of ferrite formation.
This in connection with a high heat transfer
rate enabled deformation of the austenite
structure to transform tomartensite. In
contrast, lower Mn-content resulted in a
higher fraction of ferrite. Steels with a
lower Mn content developed into pearlitic
structures formed due to slow cooling
rates. Finally, Ferrite was found more
commonly near the mould, whereas harder
phasesappeared more often in the
centre.VI. Regarding the effect of Mn on
the micro-structural features, similar
columnar structures with long and thick
columnar grains were obtained for
compositions higher than 2 %wt. Mn.
Moreover, such compositions resulted in
formation of dendritic structures compared
to Mn < 2 %wt. The overall grain size
seemed to decrease with the Mn content.

16. Modelling:
VII. Simulation results showed that
the upper half of the ingot solidified faster
than the lower half. This is contrary to
ingots produced industrially. The ingot
solidified faster from the top than from the
bottom as well as solidifying faster from the
long sides than the short sides. This is likely
due to the insulating effect of the sand
layer around the steel mould. which was
covering the ingot completely except the
top of the ingot, which was cooled by air
convection.VIII. The last solidified point
(liquid fraction) occurred in the bottom half
of the mould as also observed in the
analogous system with Bn-42Sn.IX. The
resistance at the metal/mould interface
was substantially lower than that of the
mould/sand interface and both seem to be
co-dependent.X. The model needs further
tuning to fit exactly the reference case, but
it provides a benchmark to test different
dimensions/thickness of the steel mould
and sand layer that could emulate cooling
rates during continuous casting.
FIG:4 CONTINUOUS CASTING
7. FUTURE WORK
The data obtained in this project is
not enough to draw complete conclusions
onhow the four main elements affect the
micro-structure. A few suggestions for
improved understanding of each steel are
asfollows:
I. A deeper analysis of the micro-structure
of steel 2 and 3, with focus onphase
analysis and application of different
etchants (e.g. “Le Pera”) that may
separateretained austenite from
martensite.
II. A full micro-structural analysis of steel 4
must be performed, from which more
conclusive relations may be drawn to its
measured cooling.
III. Further post-processing of
each steel followed by a
thorough micro-structural
analysis to improve the
understanding of what impact
these specific compositions have
on the steel
IV. A thorough analysis of the
defects observed in each steel.
V. Improvements on the heat
transfer model; results from the
ingotmodelling are the foundation
for future work on the factors
impacting heat transfer for a better
design of the casting experiments.
The steelsstudied in the final stage of the
project had both high strength and high
ductility. Further work is required to
investigate the forming of these steels.In
particular, focus should be on why these
steels,with precipitates <10nm exhibited
high ductility, while steels with a slightly
larger precipitate size (>10nm) had lower
ductility.
8. CONCLUSIONS

17. Development of new steel grades is a time-
consuming process which requires
understanding of the steel composition of
interest as well as knowledge of its
behaviour during casting, i.e., its
producibility. In order to achieve this
understanding, the present work was
focused on castingsteel ingots produced
through VIM-melting using an identical
methodology, followed by athorough
characterization involving phase
identification, columnar grain size
measurementsand hardness
measurements. In addition, one of the steel
castings was performed in combinationwith
temperature monitoring using
thermocouples attached through the mould
wall to obtainthe cooling rate. Finally,
numerical simulations were performed to
investigate the heat transferin an
analogous system (Bi-42Sn alloy), which
facilitate evaluation of the boundary
conditionsof the model for future
application to steel ingots. The following
conclusions can be drawn from the work:
9.CONCLUDING REMARKS
Development of traditional metallic alloys
using one or two principal alloying
elements has reached a saturation point.
Various secondary processing techniques
and simple to complex heat treatments
have been utilized to realize best properties
from these alloys over the last seven
decades. Multicomponent alloy design and
development is the way forward to realize
much superior combination properties. In
addition, such alloys have the potential to
eliminate the need for heat treatment to
further enhance the properties thus
reducing the cost of end material.
10. SUMMARY AND OUTLOOK
We presented an approach for the
metallurgical bulk-scale high-throughput
synthesis and processing of low-density
austenitic steels. As model sys tem, we
have chosen Fe-Mn-Al-C steels that exhibit
a wide spectrum of characteristics. To
reduce the density of such materials, the
focus was placed on the effect of variations
in the Al concentrations in the range
between 0 wt.% and 11 wt.%. For weight
measurements, some alloys with up to 13
wt.% Al were synthesized, revealing a
reduction in density by about 18%.
Additionally, two different Fe-Mn-C base
compositions were screened, namely one
with 20 wt.% Mn and 0.4 wt.% C and the
other one with 30 wt.% Mn and 1.2 wt.% C.
This relatively large set of material data
showed that increasing the Al content
promotes the formation of j-carbides and
ferrite. In case that a single-phase austenite
matrix is desired, the ferrite stabilizing
effect of Al must be compensated by an
increased Mn and C content. The latter
balance is also of very high relevance for
optimizing the stacking fault energy that
controls the TWIP effect. Two types of
austenitic Fe-Mn-Al-C steels were
addressed in more detail. The first one is a
type of low-The strain-hardening
characteristics of low-density austenitic
steels were discussed in terms of a
structure–property constitutive model. The
high strain-hardening capability of the low-
density TWIP steel results from the onset of
mechanical twinning at rather high stress
levels. Therefore, it is important in
corresponding alloy design strategies for
low-density TWIP steels to consider a
relatively high content in both Mn and C.
Otherwise, the stacking fault energy
becomes too high and twinning might
become ineffective or suppressed. The role
of j-carbides on the strain-hardening
behavior of the non-TWIP variants was
discussed in terms of Orowan bypassing of
elongated rods of such carbides. Further
strain-hardening effects associated with j-
carbides are still subject to further work
owing to our still limited knowledge about
the interaction of dislocations, twins, and j-

18. carbides. Likewise, the role and the alloying
limits of a further increased C content and
its effect on decoration, localization,
nonlinear effects, and cross slip of
dislocations is not yet clear and requires
further research.
11.RECENT DEVELOPMENTS
Recently, UCLA researchers developed a
new lightweight metal that contains
magnesium infused with thick silicon
carbide nanoparticles. The metal holds
potential for use in mobile electronics, cars,
airplanes, etc. They also developed a new,
scalable manufacturing technique that
could pave the way for super-strong yet
high-performance lightweight metals.
South Korean scientists have developed a
new class of steel alloy that is ultra-strong,
flexible, and low-cost. It has the same
strength-to-weight ratio as that of titanium.
In another study, researchers developed a
lightweight magnesium-matrix composite
that is light enough to float on water yet
strong as other composite materials used
today. It can tolerate temperatures over
400°C.
A study revealed that new lightweight
composite metal foams (CMFs) are more
effective at insulating against high heat
compared to traditional base metals and
alloys. This quality makes these CMFs a
potential candidate for use in space
exploration, storing and transporting
nuclear material, explosives, etc.
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Zhang, Yizhen Zhao, Sheng Huang, Shuo
Zhu, Fu Wang,* and Dichen Li
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