FIELD OF THE INVENTION:
The present invention relates to a rail steel and ,in particular, vanadium micro-alloying
high strength rail with improved yield ratio (YS/UTS). More particularly, the invention is
directed to a vanadium micro alloyed rail steel including finer pearlitic microstructure and
smaller inter lamellar spacing thereby achieving desired improved properties. A preferred
chemistry is selectively used for the rail steel of the invention to achieve desired high
strength, moderately high toughness and fairly high wear resistance. The selective addition
of vanadium is directed to promote fine grain size, increased hardenability and improve
wear resistance through the precipitation of its carbides and nitrides. 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. The rail steel developed according to the present invention by
selective microalloying of vanadium is found to have about 40% higher wear resistance, an
improved yield ratio of over 0.58(YS/UTS=560/960> 0.58) and even smaller inter-lamellar
spacing of 0.18nm, as against yield ratio of 0.52(YS/UTS=465/880>0.52) and inter lamellar
spacing of 0.34nm as for the conventional grade rails. Thus the present grade of rail steel
(V-rail) provides superior strength and more advantageously, moderate toughness and fairly
high wear resistance achieved through micro-alloying of Vanadium generally less than 0.15
wt % in C-Mn steel. The process further helps achieving fully fine pearlitic microstructure
wherein interlamellar spacing is still smaller facilitating achieving the above said desired
properties in the rail steel. Such rails obtained by following the process of the invention is
suitable for advantageous use in situations like narrow curves, tracks on mountain region,
heavy haul for ore and coal transportation and having enhanced service life under stated
extreme operating conditions and thus having wide application in railway transportation.
BACKGROUND ART:
To cater the growing need of railroad traffic, in terms of speed, load and track curvatures or
switches/crossings and geographical location including high altitude rail transport, various
rail sections have been developed to carry/haul passenger coaches or goods carriage for
industrial needs. The chemistry of rail steel is influenced depending on its application and
service conditions. Conventionally, the Flat Bottom Grade 700 rail steel has a ferritic-
pearlitic microstructure, whereas the high strength rail steels belonging to Grade 900 and
above, comprising completely pearlitic microstructure. It is well known to persons
associated in the art of rail steel manufacturing and processing that factors like pearlitic
2

interlamellar spacing, prior austenitic grain size and pearlitic colony size largely influence
tensile strength and yield strength of fully pearlitic steel. More importantly, the strength of
pearlitic rail steel is controlled by factors like thickness of the cementite lamellae, spacing
between the lamellae, grain size and strengthening of the matrix by solid solution hardening
are the principal determinants.
Persons skilled in the art and involved in research in the related field, have already been
able to establish quantitative relationship between the interlamellar spacing and 0.2%-proof
stress for fully pearlitic rail steel. It is observed and concluded with certainty that the yield
point(YS) and ultimate tensile strength(UTS) increases as the interlamellar spacing
decreases in an uniform matrix of fine pearlite. Further it has been observed that the
interlamellar spacing is controlled by processing the steel with different cooling rates and
resultantly by controlling the carbon diffusion rate at the pearlite growth front or by
controlling the diffusion rate by adding other elements. More particularly, the important
desired property of the rail steel being wear resistance that increases with increase in
tensile properties. The strength of rail steel and consequently the wear resistance also
increase with basic microstructural constituents of steel like pearlite, bainite etc.
Advantageously, the pearlitic structure improves wear resistance without seriously affecting
the toughness. However, a fine pearlitic structure with smaller interlamellar spacing is
preferred widely as desired microstructure for rail steel. Further, the toughness of fully
pearlitic steel is predominantly controlled by thickness of cementite lamellae and size of
prior austenite grain size and it is observed that as thickness of lamellae decreases,
toughness improves. The thinner cementite lamellae can withstand more deformation than
thicker ones without fracture. In this respect, the 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 further tend to reduce the cementite
lamellae thickness thereby improve the ductility and toughness of high strength rails.
It has also been seen in prior knowledge that there exist a clear relationship between
wear resistance and tensile strength. Therefore, the different rail steel grades are classified
according to their tensile strength. As pearlite is an important feature of the microstructure
contributing to good wear resistance, carbon is considered as an essential alloying element
in rail steels. However, it is not only the amount of pearlite that is important but also its
morphology defining the shape and spacing between the cementite lamellae. The finer the
3

structure of pearlite, the higher is its strength whilst still retaining reasonable toughness.
The wear resistant rails of Grade 900 have a coarse pearlitic microstructure with sufficient
ductility and toughness for general applications. In some places like narrow curves and
mountain regions, and mainly for heavy haul ore and coal transportation, strength greater
than that exhibited by Grade 900 rails are needed.
There has been thus a continuing need for developing a steel grade for the rail steel which
would on one hand provide the required higher strength and wear resistance for high load
/speed haulage of passenger and goods traffic on railway track, including on curved or slope
track subjected to higher magnitude of wear, with moderately high toughness and longer
service life. The desired properties of higher Yield ratio (YS/UTS) and wear resistance
coupled with moderately higher toughness is obtained by preferred processing of said rail
steel obtained through selective addition of Vanadium in C-Mn steel, advantageously
providing fine pearlitic microstructure and reduced interlamellae spacing , following selective
process steps ensuring the desired end properties in rail steel overcoming the limitations of
the existing rail steel having coarse pearlitic microstructure.
OBJECTS OF THE INVENTION:
It is thus the basic object of the present invention to a grade of steel with high strength and
wear resistance with moderately high toughness for successful performance especially for
application in rail tracks involving severe operating conditions.
A further object of the present invention is directed to said rail steel having higher strength
and wear resistance properties achieved without adversely affecting the toughness, by
advantageous micro alloying to favor fine pearlitic microstructure and preferred smaller
interlamellar spacing favoring higher yield ratio (YS/UTS) and commensurate wear
resistance with moderately high toughness properties, superior to the existing grades in the
same category.
A still further object of the present invention, directed to a Vanadium micro-alloyed high
strength rail with moderately high value of toughness adapted to be applied for rail traffic in
adverse conditions like altitudes/slopes, narrow curves and on high axle load and speed with
superior performance and longer service life.
4

A still further object of the present invention, directed to a Vanadium micro-alloyed high
strength rail with moderately high value of toughness, said improvement in properties is
achieved by selective Vanadium addition in steel enabling to retard grain growth/grain
refinement at elevated temperatures and its favored affinity for carbon and nitrogen.
A still further object of the present invention, directed to a Vanadium micro-alloyed high
strength rail steel with moderately high value of toughness, wherein Vanadium promotes
fine grain size, increases hardenability and improves wear resistance through the
precipitation of its carbides and nitrides or carbonitride particles.
A still further object of the present invention, directed to a Vanadium micro-alloyed high
strength rail steel with moderately high value of toughness, wherein the strengthening
effect of Vanadium is advantageously pronounced in low carbon steels.
A still further object of the present invention, directed to a Vanadium micro-alloyed high
strength rail steel with moderately high value of toughness, wherein the development of
pearlitic steel is directed to refinement of pearlite, the microstructure of said steel product
involving selective steel composition, deformation and heat treatment.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to a vanadium micro-alloyed high
strength rail with improved yield ratio comprising:
a chemical composition of :
Carbon : 0.60-0.80 wt%;
Silicon :0.10-0.60 wt%;
Sulphur : upto 0.025 wt %;
Phosphorous : upto 0.025 wt %;
5

Manganese : 0.70-1.40 wt%; and
Vanadium : 0.03-0.20 wt%.; and
having a pearlitic microstructure with fine inter lamellar spacing.
A further aspect of the present invention is directed to a vanadium micro-alloyed high
strength rail having mechanical properties comprising:
YS (MPa): > 560;
UTS (MPa): >960;
YS/UTS : > 0.58;
Elongation (%): > 11;
Hardness (BHN): > 270.
According to a still further aspect of the present invention directed to a vanadium micro-
alloyed high strength rail having impact and fracture toughness comprising:
Impact Charpy (Joule) > 8 RT; and
Fracture Toughness (MPaVm): >42 RT.
A still further aspect of the present invention directed to a vanadium micro-alloyed high
strength rail having metallurgical properties comprising:
Interlamellar Spacing, µm : <0.18 ; and
Microstructure : Fully fine pearlitic.
6

Another important aspect of the present invention directed to a process for the manufacture
of vanadium micro-alloyed high strength rail with improved yield ratio comprising steel
making in BOF, ladle furnace treatment, RH degasser ,Continuous casting in blooms ,Hot
rolling; and cooling wherein blooms were cast maintaining a super heat of 20 to 30°C;
Casting speed of .0.45 to 0.85 meters/minute; Soaking at 1270 to 1280°C; and Hot rolled
maintaining a finishing temperature of 870+/- 15°C and finally air cooled.
A still further aspect of the present invention directed to a process for the manufacture of
vanadium micro-alloyed high strength rail wherein the blooms are cast maintaining the
superheat of 30°C and with the casting speed of 0.45 to 0.85 meters/minute, blooms are
soaked at 1270°C to 1280°C and hot rolled in selective rail profile maintaining said finishing
temperature.
A still further aspect of the present invention directed to a process for the manufacture of
vanadium micro-alloyed high strength rail wherein the hot rails are cut mostly in 13 meters
and 26 meters length and normal air cooled.
According to yet another aspect of the present invention directed to said process for the
manufacture of vanadium micro-alloyed high strength rail wherein after cooling at room
temperature the rails are straightened in horizontal and vertical straightening machine.
The present invention and its objects and advantages are described in greater details with
reference to the accompanying non limiting illustrative figures and example.
7

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure l(a): is the illustration of optical microphotograph of microstructure of as-rolled
Grade 880 Rail;
Figure 1(b): is the illustration of the optical microphotograph of microstructure of as-rolled
Vanadium micro alloyed Rail steel of the present invention.
Figure 2(a): is the illustration of SEM microphotograph of microstructure of as rolled and
heat treated, Grade 880 Rail;
Figure 2(b): is the illustration of the optical microphotograph of microstructure of as rolled
and heat treated Vanadium micro alloyed Rail steel of the present invention, showing the
favored formation of fine pearlite and smaller interlamellar spacing;
Figure 3: is the illustration of the comparative wear characteristics of vanadium micro
alloyed rail steel of the present invention against the existing 880 Grade steel.
Figure 4: is the illustration of the flow chart for the process of producing the vanadium
micro alloyed high strength rail steel with improved Yield Ratio according to the invention.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
The present invention is directed to developing a vanadium micro alloyed rail steel with
superior strength and wear resistance and moderate toughness by addition of selective
weight percent of Vanadium in micro amount generally below 0.20 wt%. It is already
described that with the ever increasing adverse service condition and wheel/ axle load for
freight transport and requirement of high speed rail traffic negotiating on narrow curved
track, there had been an increasing demand of rail steel properties in terms of higher
strength, wear resistance and toughness. It has been determined through research and
experiments, that there exist well established quantitative relationship between the
interlamellar spacing and 0.2%-proof stress for fully pearlitic rail steel. The strength and
8

wear resistance further controlled by the factors like pearlitic interlamellar spacing, prior
austenitic grain size and pearlitic colony size largely influence tensile strength and yield
strength of fully pearlitic steel. More importantly, the strength of pearlitic rail steel is
controlled by factors like thickness of the cementite lamellae, spacing between the lamellae,
grain size and strengthening of the matrix by solid solution hardening.
It is thus the basic intent of the present invention to achieve the desired strength, wear
resistance and toughness properties by modifying the microstructure and morphology of
processed steel by selective vanadium micro alloying of C-Mn steel, favoring refinement of
pearlites in the steel matrix to thinner thicknesses and reducing the inter lamellar spacing,
through a combined approach of selective composition, deformation/rolling and heat
treatment.
Besides the pearlite-refining elements such as Cr and Mn in conventional practice, small
additions of micro alloying element such as vanadium and niobium is 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 and heat treatment or both.
As already described, Vanadium is well known in the art of steel making, for its ability to
retard grain growth at elevated temperatures and for its beneficial affinity for carbon and
nitrogen. Selective Vanadium alloying in steel promotes fine grain size, increases
hardenability and improves wear resistance through the precipitation of its carbides and
nitrides. These effects of vanadium is applied gainfully in the present invention in producing
rail steels of desired higher Yield ratio and fine pearlitic structure with smaller interlamellar
spacing. 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, in the range of 0.03 to 0.20 wt % and generally less than 0.15 wt%.
Micro alloying in said quantity, 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. Vanadium as
alloying element also retards the recovery and recrystallization of austenite by forming very
9

fine precipitates during hot rolling. Also the effect of vanadium on transformation
temperature is seen on the microstructure generally with regard to pearlite content and
bainite morphology, dislocation density and grain size, also to some extent. 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. The strengthening effectsof vanadium become more
pronounced toward the end of and after hot rolling at temperatures approaching 700°C,
when precipitation of vanadium carbonitride begins and continue well into the ferrite region
for low carbon steels.
The development of fully fine pearlitic rail steels is thus directed to the refinement of
pearlite, desired formation of the microstructure of a steel product being basically the result
of steel composition, deformation and heat treatment. The resulting vanadium micro alloyed
and selectively processed steel of the present invention is thus adapted to ensure steel
properties ensuring an increase in tensile strength of over 960MPa and a Yield
Ratio(YS/UTS) of 0.58, coupled with commensurate wear resistance of the rails and
consequently longer service life even under severe operating conditions. The method for
achieving a rail steel having above said properties is described with reference to an
embodiment of the present invention as illustrated in the following example:
EXAMPLE
The vanadium micro alloyed rail steel developed to provide the desired strength and wear
resistant properties along with moderately high toughness, are produced in laboratory scale
proceeding through the following experimental steps:
Experiments are carried out through a number of Laboratory heats , made to study the
influence of C, Mn, Si, and V on the strength of the rail steel. From the experiments
different microstructures having different inter lamellar spacing were developed and
observed. Finally, the pearlitic microstructures with fine inter lamellar spacing resulted in
rail steel of desired high strength and Yield ratio superior to the existing grades. Such
pearlitic microstructures with fine inter lamellar spacing then scaled up and adapted to the
industrial production in plant.
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1. Experimental Laboratory scale process steps:
a. heats were made in 100 Kg capacity medium frequency air induction furnaces with
frequency 3000 cycles; Power rating of the furnace was 225 KVA.
b. Low carbon steel scrap was used as charge material.
c. A synthetic slag with composition 60% lime, 25% Al shots and 15% CaF2 was used.
d. Ingots were cast into 25 Kg mould and cooled into the mould itself for 24 hrs.
e. Hot rolling of ingot was carried out in experimental rolling mill. The details of the
rolling parameters followed are given below:
i) Drafting schedule : Total passes used - 7.
ii) Soakaing temperature : 1250°C, Soaking time : 2.5 hrs
iii) Finishing temperature : 930°C
iv) Initial size of ingot : 100x100mm
v) Final size of plate : 25mm thick
vi) Cooling instruction : Air cooling of plates
Final size of the plate obtained after rolling was 25mm thick.
The chemistry of the final product so obtained, is as follows:
Chemical composition (wt %)

2. The in plant production of the vanadium micro alloyed rail steel of the invention
involved:
i) 110-tone heat produced through BOF-LF-RH-CC route,
ii) Blooms were cast maintaining the super heat of 30°C and with the casting speed
of about 0.85metre/minute.
iii) The cast blooms were soaked at 1280°C for 1-2 Hrs.
iv) The blooms were hot rolled in R-60 rail profile maintaining a finishing
temperature 870±15°C.
v) Hot rails were cut in 13 and 26metere lengths using hot saw.
vi) Hot saw cut rails cooled by normal air-cooling.
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Vii) After cooling at room temperature rails were straightened in horizontal and
vertical straightening machine.
After straightening rails according to the invention , they were passed through eddy current
and ultrasonic testing machines. Before dispatching rails were inspected for any defects,
dimension and straightness.
The accompanying Figure 4 shows the flow chart of the process, which has resulted in
producing rails with desired high strength, improved wear resistance, and associated
favored mechanical properties.
Wear resistance test of this product was done by pin on disc method on Budenberg make
(England) wear testing machine. Tests were carried out with different loads for comparative
Wear characterization of the invented product against existing normal 880 grade rails. It is
evident from the accompanying Figure 3, that wear resistance of Vanadium micro-alloyed
rail is about 40% higher than that of normal C-Mn 880 grade rail.
Reference is now invited to the accompanying Figure 1(a) and 1(b) wherein the optical
microphotographs of micro structures of the as rolled rail steel of conventional 880 grade
and the vanadium micro alloyed steel of the present invention has been illustrated.
Reference is next invited to the accompanying Figure 2(a) and 2(b) wherein SEM
microphotographs of micro structures of the as rolled and heat treated rail steel of
conventional 880 Grade and the vanadium micro alloyed steel of the present invention has
been illustrated. The figures clearly shows the formation of thin and fine pearlitic lamellar
structure and the favored reduced inter lamellar spacing directed to provide desired superior
tensile strength, Yield Ratio and wear resistance with moderately high toughness, meeting
the severe application requirements of rail traffic ensuring longer life.
The properties obtained are given in the following Table 1 and Table 2(conforming to IRS-
T-12-96). Also the accompanying Table 3 provide comparative data on the metallurgical
parameters derived from the micrographic analysis of the new grade of rail steel over the
conventional 880 grade.
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Table 1: Mechanical Properties

It is thus possible by way of this invention to produce a grade of vanadium micro alloyed rail
steel adapted to meet the requirement of more adverse service condition such as narrow
curve, high altitude/slope, high axle/wheel load and speed etc by ensuring higher strength,
higher Yield Ratio, improved wear resistance and moderately high toughness and ductility,
achieved through refinement of resulting homogenous fully fine pearlitic lamellar
microstructure of said vanadium microalloyed steel, obtained through the combined effect of
the composition, deformation by way of hot rolling and selective heat treatment based on
the composition and desired microstructure. The rail steel of the present invention is thus
superior in terms of strength, Yield Ratio (YS/UTS), wear resistance, hardenability and
toughness far superior over the existing grades and ensuring longer service life compared to
the existing Grades of highest performance e.g grade 900 or equivalent, and thus having
wide application tracks and accessories in the rail transportation.
13

WE CLAIM:
1. A vanadium micro-alloyed high strength rail with improved yield ratio comprising:
a chemical composition of:
Carbon : 0.60-0.80 wt%;
Silicon :0.10-0.60 wt%;
Sulphur : upto 0.025 wt %;
Phosphorous : upto 0.025 wt %;
Manganese : 0.70-1.40 wt%; and
Vanadium : 0.03-0.20 wt%.; and
having a pearlitic microstructure with fine interlamellar spacing.
2. A vanadium micro-alloyed high strength rail as claimed in claim 1 having mechanical
properties comprising:
YS (MPa): > 560;
UTS (MPa): >960;
YS/UTS : > 0.58;
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Elongation (%): > 11;
Hardness (BHN): > 270.
3. A vanadium micro-alloyed high strength rail as claimed in anyone of claims 1 or 2
having impact and fracture toughness comprising:
Impact Charpy (Joule) > 8 RT; and
Fracture Toughness (MPa√): >42 RT.
4. A vanadium micro-alloyed high strength rail as claimed in anyone of claims 1 to 3 having
metallurgical properties comprising:
Interlamellar Spacing, µm : <0.18 ; and
Microstructure : Fully fine pearlitic.
5. A process for the manufacture of vanadium micro-alloyed high strength rail with
improved yield ratio as claimed in anyone of claims 1 to 4 comprising steel making in
BOF, ladle furnace treatment, RH degasser, Continuous casting in blooms ,Hot rolling;
and cooling wherein blooms were cast maintaining a super heat of 20°C to 30°C ;Casting
speed of 0.80 to 0.85 meters/minute, preferably 0.85 meters/minute; Soaking at
1270°C to 1280°C; and Hot rolled maintaining a finishing temperature of 870+/- 15°C
and finally air cooled.
15

16
6. A process for the manufacture of vanadium micro-alloyed high strength rail as claimed
in claim 5 wherein the ingots are cast maintaining the superheat of 30°C and with the
casting sped of about 0.85 meters/minute, ingots are soaked at 1280°C and hot rolled in
selective rail profile maintaining said finishing temperature.
7. A process for the manufacture of vanadium micro-alloyed high strength rail as claimed
in anyone of claims 5 or 6 wherein the hot rails are cut in 13 and 26 meters length and
normal air cooled.
8. A process for the manufacture of vanadium micro-alloyed high strength rail as claimed
in claim 7 wherein after cooling at room temperature the rails are straightened in
horizontal and vertical straightening machine.
9. A vanadium micro-alloyed high strength rail with improved yield ratio and its process of
manufacture substantially as hereindescribed and illustrated with reference to the
accompanying examples and figures.

A rail steel composition having Vanadium Micro-alloying directed to achieving high
strength(UTS 960MPa) and improved yield ratio (YS/UTS) of over 0.52 coupled with high
wear resistance and moderate toughness. More particularly, the invention relates to a
vanadium micro alloyed rail steel directed to achieve even fully fine pearlitic microstructure
and smaller interlamellar spacing less than 0.18µm and thereby achieving desired improved
properties. A preferred chemistry is selectively used for the rail steel of the invention to
achieve desired high strength, moderately high toughness and fairly high wear strength are
achieved. The selective addition of Vanadium in the range of 0.03 to 0.20 wt% and
generally less than 0.15 wt % in C-Mn steel is able 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.