This document discusses a seminar presentation on rare earth elements, their properties, and applications in steels. It begins with definitions of rare earth elements and provides information on their abundance in the Earth's crust. It then covers topics like electronic configuration, lanthanide contraction, industrial applications of rare earth elements in areas like electronics and renewable energy. The document focuses on the effects of rare earth elements in steels, including purification, modification of inclusions, microalloying, grain refinement, and their influence on steel microstructures. Diagrams and examples from industry are provided.

1. Malaviya National Institute of Technology Jaipur
Seminar on
Rare Earth Elements and their Properties and
their Applications in Steels
Presented by
Basitti Hitesh
M.Tech
12/11/2018 1

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Any of a group of chemically similar metallic elements comprising the lanthanide
series and (usually) scandium and yttrium. They are not especially rare, but they tend
to occur together in nature and are difficult to separate from one another. (Source:
Chemistry)
A rare-earth element (REE) or rare-earth metal (REM), as defined by IUPAC, is
one of a set of seventeen chemical elements in the periodic table, specifically the
fifteen lanthanides, as well as scandium and yttrium. (Source: Wikipedia)
Definition

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Lanthanides (lanthanoids), scandium, and yttrium are
presented in white font.
(Source: taken from 4 references (2007))
Abundance of Elements in the Earth’s Crust
Elements Crustal abundance (ppm)
Nickel (25Ni) 135
Zinc (30Zn) 76
Copper (29Cu) 86
Cerium (58Ce)a 66.5
Neodymium (60Nd) 41.5
Lanthanum (57La) 39
Yttrium (39Y) 33
Cobalt(27Co) 25
Scandium (21Sc) 22
Lead (82Pb) 12
Praseodymium (59Pr) 9.2
Thorium (90Th) 9
Samarium (62Sm) 7.05
Elements Crustal abundance (ppm)
Gadolinium (64Gd) 6.2
Dysprosium (66Dy) 5.2
Erbium (68Er) 3.5
Ytterbium (70Yb) 3.2
Tin (50Tn) 2.2
Europium (63Eu) 2
Holmium (67Ho) 1.3
Terbium(65Tb) 1.2
Lutetium (71Lu) 0.8
Silver (47Ag) 0.75
Thulium (69Tm) 0.52
Gold (79Au) 0.002
Promethium (61Pm) 10-15

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Electronic Configuration

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Lanthanide Contraction
The gradual decrease in a atomic and ionic size of lanthanides with increase in atomic number from
La to Lu because of imperfect shielding of 4f elctrons is called Lanthanide Contraction. The term
was coined by the Norwegian geochemist Victor Goldschmidt in his series "Geochemische
Verteilungsgesetze der Elemente".

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Cause of contraction
The cause of Lanthanide contraction is generally attributed to imperfect shielding of one
4f electron by another in the same shell. Thus as we move along the lanthanide series, the
nuclear charge and the number of 4f electron increase by one unit at each step. However
due to Imperfect shielding (because the shape of f orbitals is very much diffused) the
effective nuclear charge increases which cause contraction in the size of the Electron
charge cloud and thus each ion shrinks in comparison with its predecessor.
6s
5d
4f

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Sc Ti V Cr Mn
Y 159pm
Zr 91.22
79pm
Nb Mo Tc
La 156pm
Hf 178.4
78pm
Ta W Re
Ac Rf Db Sg Bh
3d
4d
5d
6d
Consequences
1. Size of Lanthanide ions
2. Density
3. Melting point and Boiling point
4. Electronegativity
5. Electrode potential
6. Resemblance of 2nd and 3rd transition series which makes difficult to separate the elements.
7. Basicity
8. Hydrolysis of ions
9. Thermal decomposition of oxysalts

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China control 97% of the world supply of REO

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World Rare Earth Mineral Resources
Rare earths are relatively abundant in the Earth's crust, but discovered minable
concentrations are less common than for most other ores. U.S. and world resources
are contained primarily in Bastnäsite and Monazite. Bastnäsite deposits in China
and the United States constitute the largest percentage of the world's rare-earth
economic resources, while monazite deposits in Australia, Brazil, China, India,
Malaysia, South Africa, Sri Lanka, Thailand, and the United States constitute the
second largest segment.
Apatite, cheralite, eudialyte, loparite, phosphorites, rare-earth-bearing (ion
adsorption) clays, secondary monazite, spent uranium solutions, and xenotime
make up most of the remaining resources. Undiscovered resources are thought
to be very large relative to expected demand.
“Quoted from the United States
Geological Survey's Mineral
Commodity Summary.”

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Mountain pass deposit, California, USA
Bayan Obo, Inner Mongolia, China
REM deposits
Ilímaussaq Alkaline Complex, South Greenland
Mount Weld, South-West Australia

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Monazite has a generalized chemical formula
CePO4. The name is derived from the Greek
monazeis, meaning “to be alone” because of the
isolated crystals of monazite, and the fact that it
was quite rare when first found.
Monazite
Fig. Monazite, Iveland Setesdal, Norway.
Bastnaesite was first described by the Swedish
chemist Wilhelm Hisinger as “basis-fluor-cerium”,
from the Bästnas mine near Riddarhyttan,
Västmanland, Sweden (Hisinger 1838). The general
formula of bastnaesite is Ce(CO3)F
Bastnaesite
Fig. Bastnaesite (yellowish material),
Mountain Pass California.

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Xenotime
Xenotime was first described by Berzelius in a
specimen from Hidra (Hitterø), Flekkefjord,
Vest-Agder, Norway (Berzelius 1824, 1825).
The name is derived from the Greek xenos—
“foreign” and time—“honor”. The
generalized chemical formula of xenotime is
YPO4.
Fig. Xenotime, Madagascar.

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Aeschynite
Aenigmatite
Allanite (Orthite)
Ancylite
Apatite
Brannerite
Britholite
Cerite
Cerianite
Cheralite
Churchite
Euxenite
Fergusonite
Florencite
Gadolinite
Huanghoite
Hydroxylbastnaesite
Kainosite
Loparite
Mosandrite
Parisite
Rinkite
Samarskite
Synchisite
Steenstrupine
Tengerite
Thalenite
Yttrotantalite
Zircon

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Applications

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Electronics:
Television screens, computers, cell phones, silicon chips, monitor displays, long life
rechargeable batteries, camera lenses, light emitting diodes (LEDs), compact
fluorescent lamps (CFLs), baggage scanners, marine propulsion systems.
Manufacturing:
High strength magnets, metal alloys, stress gauges, ceramic pigments, colorants in
glassware, chemical oxidizing agent, polishing powders, plastics creation, as additives for
strengthening other metals, automotive catalytic converters.
Medical Science:
Portable x-ray machines, x-ray tubes, magnetic resonance imagery (MRI) contrast agents,
nuclear medicine imaging, cancer treatment applications, and for genetic screening
tests, medical and dental lasers.
Applications

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Technology:
Lasers, optical glass, fiber optics, masers, radar detection devices, nuclear fuel rods,
mercury-vapor lamps, highly reflective glass, computer memory, nuclear batteries, high
temperature superconductors.
Renewable Energy:
Hybrid automobiles, wind turbines, next generation rechargeable batteries, biofuel
catalysts.
Other interesting facts about uses for rare earths:
The rare earth element europium is being used as a way to identify legitimate bills for the
Euro bill supply and to dissuade counterfeiting. An estimated 1 kg of rare earth
elements can be found inside a typical hybrid automobile. Holmium has the highest
magnetic strength of any element and is used to create extremely powerful magnets. This
application can reduce the weight of many motors.
Applications (cont.)

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Effect of Rare Earth Elements in steels

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Concept of Oxide Metallurgy
 Controlling the oxide distribution and properties in steel
(chemical content, melting point, size, and size distribution).
 Utilizing oxides as the core for heterogeneous nucleation to
refine grains and, at the same time, as the core for
heterogeneous nucleation of sulfides, nitrides, and carbides
to control the segregation distribution of sulfur, nitrogen,
and carbon, respectively.
 Suppressing grain growth by pinning the austenitic grain
boundary at high temperature with the help of oxides,
sulfides, nitrides, and carbide; utilizing the inclusions
dissolved in the austenite to affect the transformation from
austenite to ferrite and induce intra-grain ferrite; improving
the processing properties of steel by forming carbide in the
steel substrate.
Oxide

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JFE-EWEL (Excellent Quality in Large Heat Input Welded Joins), produced by JFE
Steel Corporation, Japan,
HTUFF (Super High HAZ Toughness Technology with Fine Microstructure Imparted
by Fine Particles) technique, developed by Nippon Steel,
Recently, a third-generation thermo-mechanical control process (TMCP) technique
(TMCP-Oxide metallurgy) was developed.
Industrial Applications
 On-line Accelerated Cooling Device: Super-OLAC
 Heat-Treatment On-Line Process: HOP
 Intensive Cooling Equipment Close to Mill: Super-CR

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Fig. Inclusion Precipitation Diagram
Based on thermodynamics
and phase equilibria
Considering a heat of steel in which the
Cerium and Sulphur contents are high but
the oxygen content is low.
Ce₂O₃→ Ce₂O₂S→ Ce₂S₃
The transformation of Ce₂O₃ to Ce₂O₂S
indicate that Ce₂O₃ will not be formed until
the ratio hs /ho ~ 4. 6.
Assuming a Sulphur content of 0.020%,
O.0040% oxygen may be required to
precipitate Ce₂O₃. Such concentrations
are possible in steelmaking and therefore
thermodynamic calculations may be used to
indicate the possible precipitation of Ce₂O₃

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Function of Cerium in Steel
 Cerium is widely applied in steel, in processes that can be classified into purification
modification of inclusions and micro-alloys.
 Cerium has the ability to improve the cleanliness of steel, as, for example, it can
deoxidize and desulfurize steel and prevent harm due to hydrogen, phosphor,
arsenic, stannum and lead.
 Cerium can not only purify liquid iron but also refine ingots and the
microstructures of continuous casted steel.
 The dissolving of cerium in the crystal lattice of iron results in lattice distortion that
improves the toughness of the resulting steel.
 Cerium can also segregate on the grain boundaries and thus overcome the weakness
due to the presence of other elements.

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Purification of Steel by Using Rare Earth Metals
The purification (deoxidization, desulfurization, and removal of elements with low
melting points) of steel by RE metals relies on their reactions with oxygen, sulfur, lead,
arsenic, tin, and antimony, which can easily form non-metallic compounds with high
melting temperatures. Purification is achieved when these non-metallic compounds
float to the upper slag and thus amount of impurities in the resulting steel can be
reduced. Based on the Gibbs free energy of RE compounds, when the oxygen content is
sufficiently low, RE elements combine with sulfur first and then remove it.

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Modification of Inclusions
The properties of steel are greatly improved when its grains are refined by RE elements,
and the products from deoxidization and desulfurization are modified by the addition
of RE elements to liquid steel. Products with high melting points easily cluster and
float, improving the inclusion distribution. Inclusions with high melting temperatures
are randomly distributed around the grain boundary when a small amount of RE
metal is added. Complete desulfurization can be achieved if the ratio of [RE] to [S] is
precisely controlled. Modification can be achieved when the [RE]/[S] ratio is >3.
Compounds of RE elements and sulfur can replace manganese sulfide (MnS), fully
eliminating elongated manganese sulfide inclusions. RE compounds, which look like
small spheres or spindles evenly distributed in steel, do not deform during casting.

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Micro-Alloying
In micro-alloying, the microstructure and texture are influenced by solid dissolution and
the reaction of the solid phase, and thus these can be manipulated to improve the
properties of steel. For RE metals, minute quantities dissolve in steel rather than form a
solid dissolution according to the Hume-Rothery principle. RE atoms form a
substitutional solid solution in the crystal by occupying the lattice section points using a
vacancy diffusion mechanism. The tested solubility of RE metals in steel is around
𝟏𝟎−𝟔~𝟏𝟎−𝟓 ppm magnitude based on the electrolysis of RE inclusions. Tiny amounts
of an RE metal dissolved in steel can distort the iron crystal lattice and enhance the
strength of the steel. RE metals tend to segregate at grain boundaries and eliminate the
local weaknesses due to sulfur and phosphor atoms in steel, improving the strength of
grain boundaries and shock resistance.

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Grain Refinement
Solid particles of RE compounds act as heterogeneous nucleation sites and can segregate
at the interface of crystalline structures, hindering cell growth; thermodynamic
conditions are thus needed to refine the steel grains with the addition of RE metals. The
effects of RE metals on the crystal structure of low-sulfur steel are reflected in the
thinning space of the dendrite arms. Research also shows that the heterogeneous
nucleation sites mainly composed of Ce2O3, which are formed after the addition of
RE metals in liquid steel due to their high melting point, can have the effects on grain size
of ultra-low carbon steel. The yield strength of the material was significantly improved
and the cast grain size was significantly reduced due to the increasing number of
nucleation sites of the solid and liquid phases.

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Influence of Rare Earth Metals and Cerium on the Microstructures
of Steel
In carbon RE steel, RE atoms exist in cementite as replacements of iron atoms rather than
as carbides. RE atoms tend to segregate at the interface of ferrite and cementite due to
their large radius and high aberration energy. RE atoms are thus mainly distributed at
the interface of cementite alloys and grain boundaries. The grain sizes of austenite
decrease significantly with the addition of a greater amount of RE metals. The austenite
grain size can be controlled to around 10μm when the amount of RE metals is more than
50 ppm. The segregation, diffusion, and precipitation of RE atoms at grain boundaries can
greatly affect steel properties. A limited amount of RE metals can improve the preservative
ability of steel, while an excess amount of RE metals can deteriorate this. It has been
reported that steel with 21 ppm of RE metals has the optimal properties of hardness and
inclusion modification.

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Fig. Cast microstructures of (a) CH13 (0.4C–5Cr–1.2Mo–1.0V) steel and (b) MCH13 steel.
High Carbon Martensite Low Carbon Martensite
Jie LAN et al. studied the Effect of Rare Earth Metals on the Microstructure and Impact
Toughness of a Cast 0.4C– 5Cr–1.2Mo–1.0V Steel

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Fig. Impact toughness of tempered CH13 and MCH 13 steels

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Fig. Optical microstructure of 316L TIG welded zone with 0.03% Ce. (a) Near fusion boundary
and (b) weld center (400×)
Samanta S et al. studied the Effects of Rare Earth Elements on Microstructures in TIG
Weldments of AISI 316L Stainless Steel

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Fig. SEM micrographs of weld metal zone with 0.03% Ce+0.8%Nb. (a) Near fusion boundary
and (b) weld center (400X)
Samanta S et al. studied the Effects of Rare Earth Elements on Microstructures in TIG
Weldments of AISI 316L Stainless Steel

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Fig. Oxidation behavior of weld zones under various conditions for base metal of 316L stainless
steel oxidized at 973 K in PO2 = 21.27 kPa for 240 h

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Acicular Ferrite
Di Zhang et al. studied the effects of rare earth element erbium and cerium on the
properties of welding surface.
With the addition of rare-earth element Er and Ce in the weld metal, the macro-hardness
increases to some extent and the wear resistance increases. The macro-hardness has
reached to be 39HRC which improved by 23.8%, and the relative wear resistance has
increased by 25.6%.
The rare-earth element can refine the weld microstructure, and can also increase the
ratio of acicular ferrite.
With the addition of rare-earth element, the distribution of carbide changes, formed
closed space truss structure, increased the wear resistance.

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M. Song et al. Studied the acicular ferrite formation in C–Mn steel after rare earth La
addition and the potency of different La-containing inclusions inducing the formation of acicular
ferrite have been investigated.
After adding about 0.020 mass% metal La into steel, there could be a large amount of acicular
ferrite formation in the 1100°C quenched microstructure. The size of effective inclusion for acicular
ferrite nucleation is mainly 1–4 μm.
Different types of rare earth containing non-metal inclusions have different abilities to induce
the nucleation of acicular ferrite. The best effective inclusion containing rare earth induce the
nucleation of acicular ferrite is La2O2S. When MnS attached to La2O2S forming complex inclusion,
the potency of La2O2S on nucleating acicular ferrite is enhanced significantly.
Fig. Microstructures of
tested steels quenched from
1100°C, (a) steel without
rare earth addition; (b) steel
with addition of 0.020
mass% La.

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Metal sheath
Powdered core
Kai Wang et al. investigated the effect of Rare-Earth Elements on the mechanical properties of Flux-Cored
Arc-Welded Metal with 10CrNi3MoV Steel
Chemical composition of REE-Si-Fe (wt. %).
Ce La Nd Pr Sm Ca Si Fe
12.56 4.43 1.41 0.55 4.53 3.1 40.9 Re
Chemical composition of 10CrNi3MoV steel (wt. %).
C Si Mn Ni Mo Cr V P S
0.11 0.31 0.39 2.72 0.23 1.05 0.08 0.010 0.005

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Fig.: Mechanical properties of FCAW-welded metals for different REE contents: (a) tensile properties; (b) low-
temperature impact toughness; and (c) microhardness.
Contd.

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Conclusions
 Rare earth elements are not really rare.
 Electronic configuration of lanthanides is the unique thing which separates lanthanides from other elements.
 Most of the REE (around 62%) are used as catalysts.
 Some lanthanides such as La, Ce, Er, Y increases the mechanical properties of steel welds upto a certain level
then decreases.
 RE metal elements have the ability to deoxidize and desulfurize steel more thoroughly than magnesium, which
can reduce the amounts of oxygen and sulfur to very low levels.
 It is indicated that steel modified by RE metals can have a number of better properties i.e., Impact toughness,
fatigue resistance, corrosion resistance and hot ductility, hardness, tensile properties and thus have a wider
range of applications.
 Rare earth elements addition in steel leads to the formation of acicular ferrite which increases the toughness
and also increases the crack growth resistance due the AF morphology.

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References

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Acknowledgement
I wish to express my deep sense of gratitude to my supervisor Prof. Upender Pandel,
Department of metallurgical and materials engineering, Malaviya National Institute of
Technology, Jaipur, who through his excellent guidance has enabled me to accomplish this
work. He has been great source of inspiration to me, all through. I am very grateful to him
for guiding me how to conduct research and how to clearly & effectively present the work
done.
I extend my sincere thanks to Prof. A. K. Bhargava, Head, Department of metallurgical
and materials engineering for providing the adequate means and support to pursue this
work.
I also thanks to Dr. R.K Duchaniya, D.P.G.C, Convener, Department of metallurgical and
materials engineering for providing the support to pursue this work.
Finally, I would like to add few heartfelt words for the people who were the part of the
project in various ways. Without their support, persistence and love I would not be where I
am today.

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Thank You