FIELD OF THE INVENTION
The present invention relates to a pearlite steel composition with Ultimate Tensile
Strength (UTS). More particularly, the invention is concerned about a pearlite steel
composition with Ultimate Tensile Strength (UTS) having more than 1100 MPa or
110 kg/mm2 and a process for manufacturing the same. The composition as described
in the present embodiment is used in production of rail tracks.
BACKGROUND OF THE INVENTION
Modern railway systems are subject to intense use, with fast trains and large axle
loads. There are many criteria which determine the suitability of steel for rail track
applications. The primary requirement is structural integrity, which can be
compromised by a variety of fatigue mechanisms, by a lack of resistance to brittle
failure, by localised plasticity and by excessive wear. All of these depend on
interactions between engineering parameters, material properties and the environment.
The track material must obviously be capable of being manufactured into rails with a
high standard of straightness and also to avoid surface and internal defects which may
cause failure. Track installation requires that the steel should be weldable and that
procedures be developed to enable its maintenance and repair. Commercial success
depends also on material and life time costs.
Since the beginning of railroad traffic, various rail sections have been developed to
accommodate both commuter and industrial needs. The chemistry of rail steel
however, is different based on its use. The Flat Bottom Grade 700 rail steel also has a
ferritic-pearlitic microstructure, whereas the high strength rail steels grade 900 and
above, are completely pearlitic. It is well known that pearlitic interlamellar spacing;
prior austenitic grain size and pearlitic colony size influence tensile strength and yield
strength of fully pearlitic steel. For controlling the strength of pearlitic rail steel,
thickness of the cementite lamellae, spacing between the lamellae, grain size and
strengthening the matrix by solid solution hardening plays important role. Researchers
have determined the quantitative relationship between the interlamellar spacing and
0.2%-proof stress for fully pearlitic rail steel. The yield point and tensile strength
increases as interlamellar spacing decreases. Interlamellar spacing can be controlled

by processing the steel with different cooling rates (by controlling the carbon
diffusion rate at the pearlite growth front) or by controlling the diffusion rate by
adding other elements. The resistance to wear increases with increase in tensile
properties. Further it also varies with basic micro-structural constituents of steel like
pearlite, bainite etc. The pearlitic structure improves wear resistance without
seriously affecting the toughness. A fine pearlitic structure (with smaller interlamellar
spacing) is preferred widely as desired microstructure for rail steel.
Toughness of fully pearlitic steel is predominantly controlled by thickness of
cementite lamellae and size of prior austenite grain size; as thickness decreases
toughness improves. The thinner cementite lamellae can withstand more deformation
than thicker ones without fracture. Alloying elements such as chromium and
manganese play a major role in reducing the interlamellar spacing and thereby
improving the yield and tensile strength. These alloying elements reduce the
cementite lamellae thickness thereby improve the ductility and toughness of high
strength rails. Besides the pearlite-refming elements, small additions of micro alloying
element such as vanadium and niobium is also made to achieve still higher yield and
tensile strength. These micro alloying elements bring about the desired matrix
strengthening effect as a result of finely dispersed precipitates of their carbides and
carbonitrides in the steel matrix. Refinement of prior austenite grain structure is the
added advantage of micro-alloying additions. Strength and toughness of rail steels can
be obtained by means of alloying, heat treatment or both. Literature has shown the
addition of Cr, V, Nb, Mo and Cu depending on the specific requirements.
There is a clear relationship between wear resistance and tensile strength. Therefore,
rail steel grades are classified according to their tensile strength. Pearlite is an
important feature of the microstructure because it possesses good wear resistance,
hence, making carbon an essential alloying element in rail steels. However, it is not
only the amount of pearlite that is important but also its morphology, which means the
shape and the distance between the cementite lamellae. The finer the structure of
pearlite, the higher is its strength whilst still retaining reasonable toughness.
Therefore, and understandably, the development of pearlitic rail steels has been
focused on the refinement of pearlite. The formation of the microstructure of a steel
product is basically the result of steel composition, deformation and heat treatment.

The wear resistant rails of Grade 900 have a coarse pearlitic microstructure with
sufficient ductility and toughness for general applications. Tn some places like narrow
curves and mountainous regions, but mainly for heavy haul ore and coal
transportation, strengths greater than that exhibited by Grade 900 rails are needed; an
increase in tensile strength of about 200MPa doubles the wear resistance of the rails
and consequently their service life.
The further strengthening of pearlitic rails to 1100-1200MPa tensile strength is based
on increased pearlite refinement. The continuous cooling transformation (CCT)
diagram of Grade 900 steel reveals that the maximum strength of the pearlitic
microstructure is about 1200MPa and it shows two possibilities for achieving pearlite
refinement. Firstly, the field of austenite to pearlite transformation may be moved
through chromium additions, to the right where air-cooling of the railhead transforms
the austenite into fine pearlite with narrow interlamellar spacing. This type is the high
strength and highly wear resistant alloy Grade 1100, which cools in still air after
rolling. The second possibility is that the cooling rate of the rail head may be
accelerated to move the austenite to pearlite transformation of the Grade 900 steel to
the left in order to achieve a microstructure of fine pearlite; generating a 1100-
1200MPa tensile strength with the same steel composition.
Hyzak and Bernstein in a study of fully pearlitic microstructure in a steel containing
0.81wt% C has shown the dependence of hardness and yield strength on pearlite
spacing.
As Figure 1 schematically shows, the basic factors that define the microstructure of
pearlitic steel arc colony size (Dpc), lamellar spacing (λ), and volume fraction of
cementite (Vθ). To produce the heat-treated rail, the rail is subjected to slack
quenching from the austenite state (γ) at an appropriate cooling rate after completion
of hot rolling. During the cooling process, the lamellar spacing (λ) is refined, and the
hardness and wear resistance are improved. The lamellar spacing in the state-of-the-
art heat-treated rail is as fine as about 0.1 μm, which is nearly the limit that is
industrially achievable.
Volume Fraction of Cementite Vθ

When the carbon content in steel is raised, the volume fraction of cementite in pearlite
increases. The plastic deformation introduced in service by the rolling contact
between rail and wheel causes a drop in interlamellar spacing from the order of
micrometers to the order of nanometers, accompanied by a marked increase in rail
hardness. Hence, the surface hardness of the rail increases with the period of its usage,
enhancing the wear resistance of the rail.
Interlamellar Spacing λ
This value changes with the cooling rate used in the pearlite formation region and
increases with growing austenitizing temperature. Alloying elements, especially Mn,
Cr, Mo, V, Nb, significantly reduce the interlamellar spacing and the thickness of
cementite lamellae.
Impacts of interlamellar spacing on mechanical properties: •
• decrease in interlamellar spacing is accompanied by growth of ultimate tensile
strength and yield strength •
• weak effect upon elongation (especially with small prior austenite grain size) •
initiation of fatigue cracks depends solely on the interlamellar spacing, not on
the yield or ultimate tensile strength •
® with identical interlamellar spacing, niobium-alloyed steels exhibit higher
strength than those without Nb addition
Austenite Grain Size, d
In addition to cooling rate, nitride or carbonitride precipitates strongly promote grain
refinement. Austenite grain size in off-line processes depends largely on the
austenitizing temperature. The austenite grain size directly governs the pearlite grain
size existing upon transformation. Through this mechanism, it also affects, above all,
the plasticity properties: Results of an experiment conducted at Nippon Steel
Corporation have shown that achieving the minimum elongation (defined as 10% for
rails in North America used on high-load tracks), the austenite grain size should not
exceed 60 urn. Clayton et al suggested a relationship between yield strength and
microstructural parameters of rail steel.

Yield strength (MPa) = 2.18(1 -1/2) - 0.40(DPC -1/2) - 2.88(d -1/2) + 52.30 Where λ
= interlamellar spacing. DPC = pearlite colony size and d = austenite grain size.
Figure 2 illustrates the effects of microstructural control on the wear resistance. The
basic microstructure for evaluating the effect of microstructural control on wear
resistance is set to be the typical microstructure of ordinary rails, namely, Dpc
=150μm, A, =0.35um, and Vθ=41%. In this case, increasing the volume fraction of
cementite to 50% improves the wear resistance by 4.3%, whereas reducing the
lamellar spacing to 0.10μm improves the wear resistance by 30%. However, as
explained previously, the lamellar spacing of 0.10 μm obtainable by heat treating is
nearly the theoretical limit, and even finer spacing is difficult to obtain. Further, the
wear resistance is improved by 16% by refining the colony size down to 50μm.
Although the effect of refining the colony size has attracted little attention in the past,
it has become evident that such refinement effectively improves the wear resistance.
Above mentioned methods of microstructural control are applied to C-Mn pearlitic
rails.
Vanadium is known for its ability to retard grain growth at elevated temperatures and
for its beneficial affinity for carbon and nitrogen. Vanadium promotes fine grain size,
increases hardenability and improves wear resistance through the precipitation of its
carbides and nitrides. Thus, use is made of these effects in a large variety of steels
including rail steels. Vanadium is well-known micro alloying element, which is
chatacterised by its disproportionately strong effect on the structure and properties of
steel when present in minute quantities (generally less than 0.15%). It increases
strength and improves toughness, primarily through a combination of grain
refinement and precipitation strengthening both of which depends on the formation of
carbides and nitrides or carbonitride particles. By forming very fine precipitates
during hot rolling, the vanadium retards the recovery and recrystallization of
austenite. Effect of vanadium on transformation temperature are seen on the
microstructure (generally with regard to pearlite content and bainite morphology),
dislocation density and to some extent, grain size, as well. Vanadium as a carbide,
nitride or carbonitride former is the most soluble in austenite, therefore, its effects on
austenite recrystallization are weak at high and intermediate rolling temperatures,
where the carbonitrides revert to solid solution, but are more pronounced at lower

temperatures, where carbonitrides precipitate. Vanadium's strengthening effects
become more pronounced toward the end of and after hot rolling, at temperatures
approaching 700 C, when precipitation of vanadium carbonitride begins, continuing
well into the ferrite region in low carbon steels.
Schctky, 1e May and Dilewijns reported a medium carbon Cr-V-Ni-Cu rail
composition which combines the good performance of Cr-V rail steels with the
additional strengthening and corrosion resistance afforded by addition of copper. The
superior properties are related to a carbide precipitation hardening in a very fine
pearlitc matrix, which exhibits very little free ferrite. Chrome hardens the steel alloy
and gives greater wear and corrosion resistance. The vanadium also makes the alloy
harder and gives greater resistance to wear and impact. D V Chervyakov et al have
reported presence of vanadium up to 0.02-0.07wt% in rail steels which increases wear
resistance and reliability of railroads. American Vanadium company has reported the
relative wear of the vanadium steel rails is practically one half that of the carbon rails.
N A Fomin, A I Tkachenko, V A Palyanichka, M S Gordienko and N G Nikulin have
reported use of vanadium up to 0.03-0.06 in rail steels. It has been reported elsewhere
(Ferroalloys & Alloying Additives Handbook), that the wear resistance of rail steels is
improved considerably by the addition of 0.08-0.12 wt% vanadium. Wear resistant
rails of this type are used in curves, switches and other points to experience severe
service.
JP 2007051348 (A) entitled "Pearlite steel rail having excellent wear resistance and
fatigue damage resistance provides a pearlite steel rail having excellent wear
resistance and fatigue damage resistance has a composition comprising, by mass, C of
0.6 to 1.1%, Si of 0.1 to 1.2%, Mn of 0.4 to 1.5%, <=0.035% P, <=0.035% S and 0.01
to 1.0% W, further comprising, at need, one or two kinds selected from V of 0.001 to
0.50% and Nb of 0.001 to 0.05% and/or one or more selected from Cu of <=1.0%, Ni
of <=1.0%, Cr of <=1.5% and Mo of <=0.5%. In this document 'W was added as a
base element in their steel which demands enhanced input cost. It has also kept an
option of addition of adding one or two of V or Nb and one or two of Ni, Mo, Cr etc
in this prior art document.
EP 2006406 (A1) entitled "High-strength pearlite rail with excellent delayed-fracture
resistance" provides a high-strength pearlitic steel rail, which is inexpensive, and has

a tensile strength of 1200 MPa or more, and is excellent in delayed fracture properties.
Specifically, the rail contains, in mass percent, C of 0.6 to 1.0%, Si of 0.1 to 1.5%,
Mn of 0.4 to 2.0%, P of 0.035% or less, S of 0.0005 to 0.010%, and the remainder is
Fe and inevitable impurities, wherein tensile strength is 1200 MPa or more, and size
of a long side of an A type inclusion is 250 [mu]m or less in at least a cross-section in
a longitudinal direction of a rail head, and the number of A type inclusions, each
having a size of a long side of 1 [mu]m to 250 [mu]m, is less than 25 per observed
area of 1 mm 2 in the cross-section in the longitudinal direction of the rail head.
JP2000129397 (A) entitled "Pearlite type rail excellent in wear resistance and
ductility" provides a pearlite type rail preferably contg., by weight, 0.75 to 0.84% C,
0.10 to 1% Si, 0.40 to 2.5% Mn, <=0.035% P, <=0.035% S and 0.05 to 0.5% V is
prepd. In this way, a rail used in a severe environment such as a high axle load
railload heavy in railload weight and having many sharp curve parts is obtd.
Moreover, in the case one or >= two kinds of elements selected from 0.05 to 1.5% Cr,
0.1 to 1% Cu, 0.1 to 1% Ni and 0.1 to 2% Mo are incorporated in addition to the "
componential system, by solid solution strengthening, it can be hardened, and its wear
resistance can moreover be improved. Furthermore, in the case 0.0005 to 0.15% Nb is
incorporated, it is bonded with C in the steel after rolling to form fine carbides, so that
its wear resistance can moreover be improved.
The chemistry is designed to have a rail steel with the required properties with
minimum cost elevation by effective alloying addition of Chromium with Vanadium
thereby increases UTS value to more than 110 MPa and also Vanadium is added in
steel to embark precipitation strengthening which increases strength level as well as
retains ductility and enhances YS/UTS ratio. This base chemistry composition was
not known in the prior art.
Thus, there is a need to overcome the problems of the prior art. So, inventors have
developed 110 UTS steel composition which means a pearlitic steel with Ultimate
Tensile Strength (UTS) having more than 1100 MPa or 110 kg/mm2 and a process for
manufacturing the same.

OBJECTS OF THE INVENTION
An object of the present invention is to overcome the problems/disadvantages of the
prior art.
Another object of the present invention is to provide a pearlite steel composition with
Ultimate Tensile Strength (UTS) having more than 1100 MPa or 110 kg/mm2
Another object of the present invention is to provide a process for producing a pearlite
steel composition with Ultimate Tensile Strength (UTS) having more than 1100 MPa
or 110 kg/mm2
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a pearlite steel
composition (by weight %) of high strength 110 Ultimate Tensile Strength (UTS),
said steel composition comprising:
C: 0.60-0.80;
Si: 0.15-0.60;
S: 0.025 max;
P: 0.025 max;
Mn: 0.70-1.30;
Cr: 0.6-1.10; and
V: 0.03 - 0.20.
According to another aspect of the present invention there is provided a process for
manufacturing a pearlite steel composition (by weight %) of high strength 110
Ultimate Tensile Strength (UTS), said process steps comprising:
passing said steel in a known BOF (basic oxygen furnace) converter through a ladle
furnace (LF) and RH (Ruhrstahl Heraeus) adapted to remove gas inclusions;
degassing being adapted at RH for hydrogen removal;
maintaining vacuum for said degassing at around lowest possible level;
raising said degassing time being adapted for removal of hydrogen;
maintaining an appropriate temperature for said degassed steel;
exetensive sampling being followed by trimming addition;
casting said degassed steel into plural strand continuous bloom caster;
cutting said plural blooms based on profiles being rolled;

cooling said plural blooms to ambient temperature and charging in said furnace;
soaking said plural blooms for a predetermined period at a predetermined
temperature;
descaling said plural blooms and rolling said blooms through plurality of passes;
maintaining a predetermined finishing temperature;
anticambering of rails;
cooling of said rails;
straightening of said rails by means of a deflection triangle setting.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates schematic representation of pearlitic microstructure.
Figure 2 illustrates an improvement in wear resistance through microstructure control.
Figure 3 illustrates a schematic diagram of process steps of production of 110 UTS
rail.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
According to one aspect of the present invention there is provided a pearlite steel
composition with Ultimate Tensile Strength (UTS) having more than 1100 MPa or
110 kg/mm ' The chemical composition wt% of essential elements of steel is C of 0.60
- 0.80, Si of 0.15 - 0.60, S of 0.025 max, P of 0.025 max, Mn of 0.70 -1.30, Cr of 0.6-
1.10 and V of 0.03 - 0.20 and heats are made at BSP through BOF-LF-RH-CC route.
These heats are rolled at 910-950 °C. Properties of these heats show superior
mechanical properties in 110 UTS rail are Yield Strength (YS) MPa-700, Tensile
Strength (UTS) MPa-1100, Hardness BHN (320-360), Fracture Toughness (KIC),
MPa m (at -20 °C) is 24 (min. single value) and26 (min. mean value) respectively.
This steel is fully killed with Sillico- Manganese addition. Al is not used for killing
for the known reason of its chances of entrapping as inclusions causing problems
during casting and further deterioration of mechanical properties, if remained in steel.
Si-Mn is accepted in rail steel in amounts as mentioned under steel composition.
The following table shows the mechanical properties of the present invention vis-a-vis
Normal 90 UTS C-Mn rail:


According to another aspect of the present invention, there is provided process steps
for manufacturing pearlitic steel composition with Ultimate Tensile Strength (UTS)
having more than 1100 MPa or 110 kg/mm2. As shown in figure 3, the rail steel is
made in a BOF converter. Steel is passed through LF (Ladle furnace) & RH to remove
gas inclusions. Degassing time raised from 14-15 minutes to more than 17 minutes for
said steel for removal of hydrogen. The present invention adopted slow cooling
technique after bloom casting and adopted deep RH degassing to remove hydrogen to
achieve its minimum level in steel (<1.6ppm). Hydrogen being the most undesirable
gaseous element causes fracture if found beyond 2.5 ppm in the rail steel, thereby
removal of hydrogen was ensured. The vacuum level maintained at less than 1
milibar. Extensive sampling followed by trimming addition of alloying elements
done.
The degassed steel is continuously casted into a four or three strand continuous bloom
caster. The blooms are cut into a length of 5-5.8 m length depending upon the
different sections or profiles being rolled. The blooms are slowly cooled to ambient
temperature to check any micro-crack formation and charged into reheating furnace.

These blooms are soaked at 1200-1300 °C for 4-6 hours in a controlled heating
regime. Blooms are descaled just prior to rolling and rolled through 14 numbers of
different passes. Finishing temperature are maintained between 900-1000°C. Rails
after finishing transported to long rail finishing complex. Rails are pre-cambered in an
anti cambering device to combat excessive camber generation. After anti-cambering
the rails are cooled in forced air. Cooled rails are straightened in a straightening
machine with a predetermined deflection triangle setting of the rollers. The unique
steps in the present invention is maintaining C level below 0.75 to limit the hardness
increase to protect the service life of wheels and weld joints and also enhancing
YS/UTS ratio to more than 0.6 which normally hovers around 0.5. With the present
invention alloy YS/UTS ratio of more than 0.6 is achieved with excellent ductility and
the higher YS/UTS ratio rail is capable to withstand higher axle loads.
ADVANTAGES OF THE INVENTION
1. Minimum process cost and more economic.
2. Increased service life of wheels and weld joints.
3. Enhanced YS/UTS ratio.
4. Withstanding higher axle loads.
5. Excellent ductility
6. Excellent wear resistance.

WE CLAIM
1. A pearlite steel composition (by weight %) of high strength 110 Ultimate
Tensile Strength (UTS), said steel composition comprising:
C: 0.60 - 0.80;
Si:0.15-0.60;
S: 0.025 max;
P: 0.025 max;
Mn:0.70-1.30;
Cr: 0.6-1.10; and
V: 0.03 - 0.20.
2. A process for manufacturing a pearlite steel composition (by weight %) of
high strength 110 Ultimate Tensile Strength (UTS), said process steps
comprising:
passing said steel in a known BOF (basic oxygen furnance) converter through
a ladle furnace (LF) and RH (Ruhrstahl Heraeus) adapted to remove gas
inclusions;
degassing being adapted at RH for hydrogen removal;
maintaining vacuum for said degassing at lowest possible level;
raising said degassing time being adapted for removal of hydrogen;
maintaining an appropriate temperature for said degassed steel;
exetensive sampling being followed by trimming addition;
casting said degassed steel into plural strand continuous bloom caster;
cutting said plural blooms based on profiles being rolled;
cooling said plural blooms to ambient temperature and charging in said
furnace;
soaking said plural blooms for a predetermined period at a predetermined
temperature;
descaling said plural blooms and rolling said blooms through plurality of
passes;
maintaining a predetermined finishing temperature ;
anticambering of rails;
cooling of said rails;
straightening of said rails by means of a deflection triangle setting.

3. Process as claimed in claim 2, wherein said steel being passed through a
vacuum of about less than 1 milibar for hydrogen removal.
4. Process as claimed in claim 2, wherein said steel being passed through a
vacuum of about less than 1 milibar for more than 17 minutes for hydrogen
removal
5. Process as claimed in claim 2, wherein said blooms being soaked at about
1200-1300°C.
6. Process as claimed in claim 2, wherein said blooms being soaked for about 4-6
hours.
7. Process as claimed in claim 2, wherein said blooms being cut about 5-5.8 m
length.
8. Process as claimed in claim 2, wherein said blooms being rolled through
fourteen numbers of passes.
9. Process as claimed in claim 2 or 6, wherein said passes are different to each
other.
10. Process as claimed in claim 2, wherein said finishing temperatures being
maintained at about 900-1000 °C.
11. Process as claimed in claim 2, wherein said rails are anticambered in a
anticambering device.
12. Process as claimed in claim 2, wherein said steel being adapted to be cooled in
forced air.
13. Process as claimed in claim 2, wherein said rails being straightened in a
straightening machine with a new deflection triangle setting of rolls.

14. A pearlite steel composition (by weight %) of high strength 110 Ultimate
Tensile Strength (UTS) and a process for manufacturing the same as herein
substantially described and illustrated with the accompanying drawings.

The present invention relates to a pearlitie steel composition (by weight %) of high
strength 110 Ultimate Tensile Strength (UTS) and a process for manufacturing the
same. The chemical composition wt% of essential elements of steel is C of 0.60 -
0.80, Si of 0.15 - 0.60, S of 0.025 max, P of 0.025 max, Mn of 0.70 -1.30, Cr of 0.6-
1.10 and V of 0.03 - 0.20. The rail steel is made in a BOF converter. Steel is passed
through LF & RH to remove gas inclusions, adding different alloying elements and
maintaining suitable superheat. The degassed steel is continuously casted into a four
or three strand continuous bloom caster. The blooms are slowly cooled to ambient
temperature and charged into reheating furnace. These blooms are soaked at 1200-
1300 °C for 4-6 hours. Blooms are descaled just prior to rolling and rolled through 14
numbers of different passes. Finishing temperature are maintained between 900-
1000°C. After finishing the rails are cooled in air.