AU2021218136B2 - Pearlite steel rail with rail head hardened layer having uniform hardness gradient and preparation method thereof - Google Patents
Pearlite steel rail with rail head hardened layer having uniform hardness gradient and preparation method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/78—Combined heat-treatments not provided for above
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/04—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rails
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
-
- E—FIXED CONSTRUCTIONS
- E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
- E01B—PERMANENT WAY; PERMANENT-WAY TOOLS; MACHINES FOR MAKING RAILWAYS OF ALL KINDS
- E01B5/00—Rails; Guard rails; Distance-keeping means for them
- E01B5/02—Rails
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Architecture (AREA)
- Civil Engineering (AREA)
- Structural Engineering (AREA)
- Heat Treatment Of Articles (AREA)
Abstract
The present disclosure relates to the technical field of steel rail production,
and discloses a pearlite steel rail with a rail head hardened layer having an
uniform hardness gradient and a preparation method thereof. The method
comprises the successively performed steps of smelting with a revolving
furnace or an electric furnace, refining with a LF furnace, RH or VD
vacuum treatment, continuous casting to obtain steel billets, subjecting the
steel billets to rolling, heat treatment and processing the steel rail, wherein
the heat treatment is a multi-stage cooling process, and the chemical
components of the steel rail are controlled, the steel rail comprises: at least
one of 0.65-0.85% of C, 0.1-1% of Si, 0.1-1.5% of Mn, less than or equal
to 0.03% of P, less than or equal to 0.03% of S, 0.01-0.2% of Cr, 0.005
0.15% of Ni, 0.001-0.3% of Mo and 0.002-0.2% of V, and the balance of
Fe and inevitable impurities. The rail head part of the steel rail
manufactured with the method has a deep hardened layer with a depth more
than 25mm, and has an uniform hardness gradient.
To be published with FIG. 1.
1/1
Accompanying Drawings
FIG. 1
Description
1/1
Accompanying Drawings
FIG. 1
[0001] The present disclosure relates to the technical field of steel rail
production, in particular to a pearlite steel rail with a rail head hardened
layer having an uniform hardness gradient and a preparation method
thereof.
[0002] The railway industry of China is operating in a high-speed
development stage, the existing passenger-cargo mixed transportation lines
gradually reduce the operation of passenger trains along with an increase
of the dedicated passenger transport lines, its operation has transformed
into taking freight transportation as the dominant service, in the meanwhile,
the dedicated freight transportation lines have also developed towards the
trend of heavy load, the overall trend of the freight transportation lines is a
development towards the directions of high freight volume, heavy axle and
high traffic density. The trend has put higher requirements on the service
performance and service life of the steel rails on the line, the high efficiency
and safety of the railway freight transportation can be ensured only by improving the quality and performance of the steel rails.
[00031 At present, in order to improve the service performance and service
life of the steel rail, the main solution of the passenger-cargo mixed
transportation line and the dedicated freight transportation line is to adopt
a heat-treated pearlite steel rail with high performance, the higher wear
resistance and contact fatigue resistance is obtained by improving the
strength and hardness of the steel rail thereof, so as to reduce the abrasion
speed of the steel rail and the occurrence of damages such as surface cracks,
peeling and chipping.
[00041 In recent years, the means for enhancing hardness of the pearlite
steel rail by the steel rail manufactures at home and abroad mainly
comprises the steps of carrying out an accelerated cooling on a rail head of
the steel rail by an off-line or on-line heat treatment mode, so as to refine
the pearlite structure of a part of the rail head of the steel rail and obtain
higher strength and hardness by means of refining the crystal grains, the
related patent technologies are specified as follows:
[00051CN10468632 has a tile of invention "Rail for straight-curve
transition section and a production method of rail", it discloses that the rail
is provided with three hardness zones from a rail head to a rail head comer
area, wherein the three hardness zones have different hardness, the first
hardness zone has a lowest hardness, the second hardness zone has high
hardness, andthe third hardness zone has the highest hardness, the steel rail having different hardness in each area is obtained by using different accelerated cooling strengths during the on-line heat treatment, so as to improve the service life and safety factor of the steel rail in the straight curve transition section. However, the characteristic of different hardness in each area of the rail head in the steel rail obtained in the patent is only distributed from the surface to a shallow hardened layer, and the abrasion condition of the steel rail after a long-term use is still not optimistic.
[00061 CN104060075 has a title of invention "Heat treatment method for
improving depth of hardened layer of steel rail", it discloses a steel rail heat
treatment method for increasing depth of hardened layer of steel rail by
using rolling waste heat in an online heat treatment mode to perform
multistage accelerated cooling on the steel rail, the heat treatment method
comprises the steps of naturally cooling the steel rail after finish rolling
until the center temperature of a rail head tread is 660-730°C, then carrying
out two accelerated cooling stages with different cooling speeds, subjecting
the steel rail to an air cooling to room temperature, such that the rail head
part can obtain a deep hardened layer with a thickness exceeding 25mm,
the position which is 25mm below the surface layer of a rail head has the
hardness value equal to that of the surface layer of the rail head, a wear test
is performed to prove that the wear resistance of the steel rail in a
continuous wear process under long-term service can be improved.
However, the patent does not consider that there is a large hardness difference between the high hardness area and the unhardened area during the actual service period of the steel rail, the rail part with a large hardness difference is prone to generate defects such as cracks under the impact of train wheels during its service life in the line, the defects will impose an adverse influence on the safe service of the steel rail.
[0007] CN102220545 has a title of invention "High-carbon and high
strength heat treated steel rail with high wear resistance and plasticity and
manufacturing method thereof', it discloses a high-carbon and high
strength heat treated steel rail meeting the use requirements of heavy load
railways, the steel rail comprises the following chemical components in
percentage by weight: C: 0.80%~-1.20%, Si: 0.20%~-1.20%, Mn:
0.20 %~-1.60 %, Cr: 0.15 %~-1.20 %, V: 0.01%~0.20 %, Ti: 0.002 %~
0.050%, P0.030%, SO0.030%, AlO0.010%, NGO0.0100%andthe
balance of iron and inevitable impurities; carrying out online heat treatment
after rolling, carrying out an accelerated cooling on the rail head and the
rail bottom to 400-500°C, and then carrying out air cooling to room
temperature. The tensile strength of the rail head of the steel rail produced
by the patent is more than 1,330MPa, the hardness of the rail head is more
than 380HB, and the depth of a hardened layer is more than 25 mm.
However, the steel rail produced by the patent has high content of alloy
elements such as Cr and Ti, high production cost and poor welding
performance of the steel rail, the accelerated cooling process and equipment used herein are complex, thus it is difficult to promote the process.
[0008] In the relevant patents for improving hardness of the pearlite steel
rail at present, a part of patents can improve the hardness of a surface layer
or an internal hardened layer of the steel rail, but there is a certain gap
between the obtained steel and the actual application requirement of the
rail line; although some of the steel rails disclosed in some patents have a
deep hardened layer in the rail head, both the chemical components and the
production process of the steel rails are complex, which is not conducive
to popularization and application of said patents.
[0009] The present disclosure aims to solve the problems in the prior art
concerning a large hardness difference between the high hardness area and
the unhardened area during the actual service period of the steel rail, the
rail part with a large hardness difference is prone to generate cracks under
the impact of train wheels during its service life in the line, high production
cost, the complex production process of the steel rails, and poor welding
performance of the steel rail, and provides a pearlite steel rail with a rail
head hardened layer having an uniform hardness gradient and a preparation
method thereof.
[0010] In order to achieve the above objects, a first aspect of the present disclosure provides method for preparing a pearlite steel rail with a rail head hardened layer having an uniform hardness gradient, the method comprises the successively performed steps of smelting with a revolving furnace or an electric furnace, refining with a LF furnace, RH or VD vacuum treatment, continuous casting to obtain steel billets, subjecting the steel billets to rolling, heat treatment and machining the steel rail;
[0011] wherein the heat treatment is a multi-stage cooling process, and
specifically comprises the following steps:
[0012] (1) first stage cooling: when the temperature of the running surface
of the steel rail after the finish final rolling is within a range of 760-900°C,
subjecting the running surface of the steel rail, gauge corner and field
corner of the rail head, gauge face and field face of the rail head and two
rail head comers of the rail head to an accelerated cooling treatment for 50
150 seconds at a cooling rate of 2-6°C/s;
[0013] (2) second stage cooling: subjecting the running surface of the steel
rail, gauge corner and field corner of the rail head, gauge face and field
face of the rail head and two rail head comers of the rail head of the cooled
steel rail obtained after step (1) to an accelerated cooling treatment for 20
seconds at a cooling rate of 1-5°C/s;
[0014] (3) third stage cooling: subjecting the cooled steel rail obtained
after step (2) to an air cooling to room temperature;
[0015] controlling the chemical components of the steel rail, the steel rail comprises the following chemical components in percentage by weight: at least one of 0.65-0.85% of C, 0.1-1% of Si, 0.1-1.5% of Mn, less than or equal to 0.03% of P, less than or equal to 0.03% of S, 0.01-0.2% of Cr,
0.005-0.15% of Ni, 0.001-0.3% of Mo and 0.002-0.2% of V, and the
balance of Fe and inevitable impurities.
[0016] Preferably, the steel rail comprises the following chemical
components in percentage by weight: at least one of 0.68-0.82% of C, 0.2
0.7% of Si, 0.6-1.2% of Mn, less than or equal to 0.025% of P, less than or
equal to 0.02% of S, 0.05-0.15% of Cr, 0.005-0.1% of Ni, 0.001-0.2% of
Mo and 0.02-0.1% of V, and the balance of Fe and inevitable impurities.
[0017] Preferably, a cooling medium used in the heat treatment is water
mist and/or compressed air.
[0018] Preferably, the continuous casting is a bloom billet protection
continuous casting.
[0019] Preferably, the steel billet is descaled by using high pressure water
before subjecting the steel billet to rolling.
[0020] Preferably, the rolling is carried out in an universal rolling mill.
[0021] Preferably, the air cooling is performed on a walking beam cooling
bed.
[0022] Preferably, the processing course comprises: straightening the steel
rails by using a horizontal and vertical composite straightening machine.
[0023] A second aspect of the present disclosure provides a pearlite steel rail with a rail head hardened layer having an uniform hardness gradient prepared with the aforementioned method, wherein the running surface of the steel rail has a Brinell hardness within a range of 360-400 HB; the rail head part of the steel rail has a hardened layer with a depth more than mm, and when an inner depth of the rail head increases for every 5mm, the Brinell hardness of the hardened layer decreases by 3 ~ 6 HB.
[0024] Preferably, the steel rail has a tensile strength larger than 1,200MPa
and an elongation rate greater than or equal to 10%.
[0025] The present disclosure adopts the methods of controlling the
chemical components of the steel rail and the heat treatment process, the
manufactured and produced pearlite steel rail has an uniform hardness
gradient without the need of adding a plurality of micro-alloy elements, the
running surface of the steel rail has a Brinell hardness within a range of
360-400 HB; the rail head part of the steel rail has a deep hardened layer
with a depth more than 25mm, and deep hardened layer has an uniform
hardness gradient, when an inner depth of the rail head increases for every
mm, the Brinell hardness of the hardened layer decreases by 3-6 HB on
average, the deep hardened layer can be matched with the abrasion process
and the work hardening of the steel rail during the long-term service,
thereby reduce the abrasion speed of the steel rail and the occurrence of
surface defects such as cracks, peeling and chipping of the steel rail,
improve the service performance and the service life of the steel rail, enhance the safety of train operation, and the preparation method is simple and easy to operate.
[0026] FIG. 1 is a schematic diagram of the section hardness measurement
position of the rail head in the test example.
[0027] The following content describes in detail the specific embodiments
of the present disclosure with reference to the drawing. It should be
understood that the specific embodiments detailed herein only serve to
explain and illustrate the present disclosure, instead of imposing a
limitation thereto.
[0028] The terminals and any value of the ranges disclosed herein are not
limited to the precise ranges or values, such ranges or values shall be
comprehended as comprising the values adjacent to the ranges or values.
As for numerical ranges, the endpoint values of the various ranges, the
endpoint values and the individual point values of the various ranges, and
the individual point values may be combined with one another to produce
one or more new numerical ranges, which should be deemed have been
specifically disclosed herein.
[0029] A first aspect of the present disclosure provides a method for preparing a pearlite steel rail with a rail head hardened layer having an uniform hardness gradient, the method comprises the successively performed steps of smelting with a revolving furnace or an electric furnace, refining with a LF furnace, RH or VD vacuum treatment, continuous casting to obtain steel billets, subjecting the steel billets to rolling, heat treatment and processing;
[0030] wherein the heat treatment is a multi-stage cooling process, and
specifically comprises the following steps:
[0031] (1) first stage cooling: when the temperature of the running surface
of the steel rail after the finish final rolling is within a range of 760-900°C,
subjecting the running surface of the steel rail, gauge corner and field
corner of the rail head, gauge face and field corner of the rail head and two
rail head comers of the rail head to an accelerated cooling treatment for 50
150 seconds at a cooling rate of 2-6°C/s;
[0032] (2) second stage cooling: subjecting the running surface of the steel
rail, gauge corner and field corner of the rail head, gauge face and field
face of the rail head and two rail head comers of the rail head of the cooled
steel rail obtained after step (1) to an accelerated cooling treatment for 20
seconds at a cooling rate of 1-5°C/s;
[0033] (3) third stage cooling: subjecting the cooled steel rail obtained
after step (2) to an air cooling to room temperature;
[0034] controlling the chemical components of the steel rail, the steel rail comprises the following chemical components in percentage by weight: at least one of 0.65-0.85% of C, 0.1-1% of Si, 0.1-1.5% of Mn, less than or equal to 0.03% of P, less than or equal to 0.03% of S, 0.01-0.2% of Cr,
0.005-0.15% of Ni, 0.001-0.3% of Mo and 0.002-0.2% of V, and the
balance of Fe and inevitable impurities.
[0035] The reasons for limiting the content of the main chemical elements
of the steel rail according to the present disclosure are described in detail
below:
[0036] Carbon (C) is the most important and cheapest element for
obtaining desirable comprehensive mechanical property of the pearlite
steel rail and promoting pearlite transformation of the steel rail. When the
content of C is less than 0.65%, the proper strength, hardness and the wear
resistance of the steel rail cannot be ensured under the production process
disclosed by the present disclosure; when the content of C is more than
0.85%, the steel rail has excessive strength parameter, too low toughness
and plasticity and excessively high proportion of carbide under the
production process of the present application, thereby affecting the fatigue
performance of the steel rail and having an adverse effect on the safe use
of the steel rail; thus the carbon content in the present disclosure is limited
within a range of 0.65-0.85%.
[0037] The main functions of Silicon (Si) in steel reside in suppressing the
formation of cementite and being used as a solid solution strengthening element, increasing hardness of the ferrite matrix, and improving the strength and hardness of steel. When the content of Si is less than 0.10%, the solid solution amount is low, so that the strengthening effect is not obvious; when the Si content is more than 1.00%, the steel is prone to generate a local segregation, the toughness and plasticity of steel will be reduced, the safe use of the steel rail is adversely affected. Therefore, the
Si content in the present disclosure is defined within a range of 0 .10-1.00%.
[0038] Manganese (Mn) is indispensable for improving the strength of
ferrite and austenite in steel. When the Mn content is less than 0.10%, it
can hardly achieve the effect of increasing the hardness of carbide thereby
increasing the strength and hardness of steel; when the content of Mn is
more than 1.50%, it will coarsen the crystal grain size, and obviously lower
the toughness and plasticity of steel; in addition, Mn has a significant
influence on the diffusion of C in steel, an abnormal structure such as
bainite or martensite may be generated in the Mn segregation region, and
the welding performance of the steel rail is affected. Therefore, the Mn
content in the present disclosure is defined within a range of 0.10-1.50%.
[0039] Chromium (Cr) is used as a carbide forming element, can form
various carbides with carbon in steel; moreover, Cr can be used for
uniformly distributing carbide in steel, reducing the size of carbide and
improving the wear resistance of the steel rail. When the Cr content is less
than 0.01%, the hardness and the proportion of the formed carbide are lower; when the Cr content is more than 0.20%, the hardenability of the steel rail is too high, the steel rail is prone to generate harmful bainite and martensite structures, the steel rail cannot be ensured to be a pearlite structure, and the safe use of the steel rail is adversely affected. Therefore, the Cr content in the present disclosure is limited to a range of 0.01- 0 .2 0 %.
[0040] Phosphorus (P) and sulfur (S) are impurity elements which cannot
be completely removed from the steel rail. P will perform segregation at
the grain boundary of the steel rail structure, so that the toughness of the
steel rail is seriously reduced; S is easy to form MnS inclusions in steel,
which is harmful to the wear resistance and contact fatigue resistance of
the steel rail. Therefore, the content of P in the present disclosure shall be
controlled below 0.030%; the content of S shall be controlled below
0.030%.
[0041] The main role of Nickel (Ni) in steel is a solid solution
strengthening element, increasing the ferrite matrix hardness to improve
the strength and hardness of pearlite steel rails. When the Ni content is less
than 0.005%, its effect is small, and cannot produce the solid solution
strengthening effect; when the Ni content is more than 0.15%, the
toughness of the ferrite phase in the steel will be decreased, resulting in a
reduction in the fatigue resistance of the steel rail. Therefore, the N content
in the present disclosure is limited to a range of 0 .0 0 5 -0 . 15 %.
[0042] The primary functions of Molybdenum (Mo) in steel reside in improving the equilibrium transformation temperature of pearlite steel, increasing the supercooling degree and enhancing the effect of refining the pearlite lamella subjected to an accelerated cooling, so as to improve hardness of the steel rail. When the Mo content is less than 0.001%, the effect of improving the supercooling degree is small, it cannot make contribution to improving hardness of the steel rail; when the Mo content is more than 0.30%, it results in a decrease in the phase transition rate of the pearlite structure, and it is prone to produce a martensite structure which adversely affects the toughness and plasticity of the steel rail. As a result, the Mo content in the present disclosure is defined within a range of
0.001-0.30%.
[0043] Vanadium (V) is a precipitation strengthening element in pearlite
steel, forms carbonitride in the cooling process of the steel rail, and
improves the strength and hardness of the steel rail, thereby enhancing
wear resistance of the steel rail. When the content of V is less than 0.002%,
the precipitation strengthening degree is too small to play a desired role;
when the content of V is more than 0.20%, its capability of improving the
strength and the hardness of the steel rail is reduced, and excessive
precipitation strengthening effect may cause excessive precipitated phases
in steel and have negative effect on the toughness of the steel rail. Therefore,
the V content in the present disclosure is limited within a range of 0.002
0.20%.
[0044] In a preferred embodiment, the steel rail comprises the following
chemical components in percentage by weight: at least one of 0.68-0.82%
of C, 0.2-0.7% of Si, 0.6-1.2% of Mn, less than or equal to 0.025% of P,
less than or equal to 0.02% of S, 0.05-0.15% of Cr, 0.005-0.1% of Ni,
0.001-0.2% ofMoand0.02-0.1% ofV, and the balance of Fe and inevitable
impurities.
[0045] The inventors of the present disclosure have found through a large
amount of researches that:
[0046] (1) In regard to the first stage cooling: when the temperature of the
running surface of the steel rail is within a range of 760-900°C, the steel
rail shall be subjected to an accelerated cooling at a high temperature stage
so as to inhibit precipitation of proeutectoid ferrite or proeutectoid
cementite in the steel rail and obtain the steel rail with uniform hardness
gradient; in addition, because the starting temperature of the cooling
process is high, a larger cooling rate is required to ensure the stable
performance of the interior of the rail head, and the cooling rate needs to
be controlled within a range of 2.0-6.0°C/s;
[0047] (2) In regard to the second stage cooling: after the steel rail is
subjected to the first-stage accelerated cooling for 50-150 seconds, the
internal temperature of the rail running surface of the steel rail is still within
a range of 500-600°C, the phase change of the steel rail is still performed
in the temperature range, if the accelerated cooling is stopped, the heat of the part of steel rail, which is not subjected to the accelerated cooling, can be quickly diffused to the rail head, the phase change cooling rate is reduced, such that the hardness of the final product steel rail is reduced, the hardness gradient is adversely affected, and the effect of a heat treatment process is insufficient; in the meanwhile, it is required to carry out the accelerated cooling of the second stage, and considering that the cooling rate of the central part of the rail head is lower than that of the surface at this time, if the cooling rate is adopted continuously at the same level as that of the first stage, the risk of abnormal structures on the surface is high, and it is difficult to obtain the uniform hardness gradient, so that the cooling intensity and the cooling time shall be reduced to obtain the pearlite steel rail with an uniform hardness gradient.
[0048] (3) In regard to the third stage cooling: after the first two cooling
stages are finished, the internal temperature of the rail head of the steel rail
shall be within a range of 400-450°C, the phase change of the steel rail has
been completed at the moment, there is not obvious significance to
continue the accelerated cooling process, the steel rail can be subjected to
an air cooling to room temperature to facilitate the subsequent process
treatment.
[0049] In a specific embodiment, a first stage accelerated cooling in step
(1) may be performed when the temperature of the running surface of the
steel rail after the finish final rolling is 760°C, 780°C, 800°C, 820°C,
840°C,860°C,880°C,or900°C.
[0050] In a specific embodiment, the cooling rate of the accelerated
cooling in step (1) may be 2°C/s, 3C/s, 4°C/s, 5°C or 6°C/s.
[0051] In a specific embodiment, the time for the accelerated cooling in
step (1) may be 50s, 60s, 70s, 80s, 90s, 100s, 10s, 120s, 130s, 140s or 150
s.
[0052] In a specific embodiment, the cooling rate of the accelerated
cooling in step (2) may be 1C, 2°C, 3C, 4C, or 5°C.
[0053] In a specific embodiment, the time for accelerated cooling in step
(2) may be 20s, 30s, 40s, 50s or 60s.
[0054] In a preferred embodiment, the cooling medium used in the heat
treatment is water mist and/or compressed air.
[0055] In a preferred embodiment, the continuous casting is a bloom billet
protection continuous casting.
[0056] In a preferred embodiment, the steel billet is descaled by using high
pressure water before subjecting the steel billet to rolling.
[0057] In a preferred embodiment, the rolling is carried out in an universal
rolling mill.
[0058] In a preferred embodiment, the air cooling is performed on a
walking beam cooling bed.
[0059] In a preferred embodiment, the processing course comprises:
straightening the steel rails by using a horizontal and vertical composite straightening machine.
[0060] In a specific embodiment, the method for preparing a pearlite steel
rail with a rail head hardened layer having an uniform hardness gradient
comprises the successively performed steps on low-sulfur molten steel of
smelting with a revolving furnace or an electric furnace, refining with a LF
furnace, RH or VD vacuum treatment, bloom billet protection continuous
casting, heating the steel billet with a heating furnace, descaling the steel
billet by using high pressure water before subjecting the steel billet to
rolling, carrying out rolling with an universal rolling mill, subjecting the
steel rail to an online heat treatment, air cooling with a walking beam
cooling bed at room temperature, straightening the steel rails by using a
horizontal and vertical composite straightening machine, inspecting
specification of the steel rails, treating the steel rails on a processing line,
surface inspection, and transporting the steel rails to a warehouse.
[0061] A second aspect of the present disclosure provides a pearlite steel
rail with a rail head hardened layer having an uniform hardness gradient
prepared with the aforementioned method, wherein the running surface of
the steel rail has a Brinell hardness within a range of 360-400 HB; the rail
head part of the steel rail has a hardened layer with a depth more than
mm, and the deep hardened layer has an uniform hardness gradient;
when an inner depth of the rail head increases for every 5mm, the Brinell
hardness of the hardened layer decreases by 3 ~ 6 HB; namely the Brinell hardness of the hardened layer at an inner depth of 5mm in the rail head is within a range of 355-397HB, the Brinell hardness of the hardened layer at an inner depth of 10mm in the rail head is within a range of 350-393HB, the Brinell hardness of the hardened layer at an inner depth of 15mm in the rail head is within a range of 345-390HB, the Brinell hardness of the hardened layer at an inner depth of 20mm in the rail head is within a range of 340-387HB, the Brinell hardness of the hardened layer at an inner depth of 25mm in the rail head is within a range of 335-383HB.
[0062] Preferably, the steel rail has a tensile strength larger than 1,200MPa
and an elongation rate greater than or equal to 10%.
[0063] The present disclosure will be described in detail below with
reference to examples, but the scope of the present disclosure is not limited
thereto.
[0064] Example 1
[0065] The specific process for preparing the steel rail comprised the
following steps:
[0066] smelting with an electric furnace, refining with a LF furnace, RH
vacuum treatment, performing a bloom billet protection continuous casting
to obtain steel billets, descaling the steel billets by using high pressure
water before subjecting the steel billets to rolling, rolling the steel billets in
an universal rolling mill, heat treatment and processing of the steel rail
were sequentially carried out;
[0067] wherein the cooling medium for heat treatment was compressed air,
and the heat treatment specifically comprised the following steps:
[00681 (1) First stage cooling: when the temperature of the running surface
of the steel rail after the finish final rolling was 855°C, the running surface
of the steel rail, gauge corner and field corner of the rail head, gauge face
and field face of the rail head and two rail head comers of the rail head
were subjected to an accelerated cooling treatment for 150 seconds at a
cooling rate of 2.1°C/s;
[0069] (2) Second stage cooling: the running surface of the steel rail, gauge
corner and field comer of the rail head, gauge face and field face of the rail
head and two rail head comers of the rail head of the cooled steel rail
obtained after step (1) were subjected to an accelerated cooling treatment
for 50 seconds at a cooling rate of 1.6°C/s;
[0070] (3) Third stage cooling: the cooled steel rail obtained after step (2)
was placed on a walking beam cooling bed and subjected to an air cooling
to room temperature;
[0071] The chemical components of the steel rail were as shown in Table
1.
[0072] Example 2
[0073] The specific process for preparing the steel rail comprised the
following steps:
[0074] smelting with an electric furnace, refining with a LF furnace, RH vacuum treatment, performing a bloom billet protection continuous casting to obtain steel billets, descaling the steel billets by using high pressure water before subjecting the steel billets to rolling, rolling the steel billets in an universal rolling mill, heat treatment and processing of the steel rail were sequentially carried out;
[0075] wherein the cooling medium for heat treatment was compressed air,
and the heat treatment specifically comprised the following steps:
[0076] (1) First stage cooling: when the temperature of the running surface
of the steel rail after the finish final rolling was 792°C, the running surface
of the steel rail, gauge corner and field corner of the rail head, gauge face
and field face of the rail head and two rail head comers of the rail head
were subjected to an accelerated cooling treatment for 85 seconds at a
cooling rate of 3.9°C/s;
[0077] (2) Second stage cooling: the running surface of the steel rail, gauge
corner and field comer of the rail head, gauge face and field face of the rail
head and two rail head comers of the rail head of the cooled steel rail
obtained after step (1) were subjected to an accelerated cooling treatment
for 35 seconds at a cooling rate of 2.7°C/s;
[0078] (3) Third stage cooling: the cooled steel rail obtained after step (2)
was placed on a walking beam cooling bed and subjected to an air cooling
to room temperature;
[0079] The chemical components of the steel rail were as shown in Table
1.
[0080] Example 3
[0081] The specific process for preparing the steel rail comprised the
following steps:
[0082] smelting with an electric furnace, refining with a LF furnace, RH
vacuum treatment, performing a bloom billet protection continuous casting
to obtain steel billets, descaling the steel billets by using high pressure
water before subjecting the steel billets to rolling, rolling the steel billets in
an universal rolling mill, heat treatment and processing of the steel rail
were sequentially carried out;
[0083] wherein the cooling medium for heat treatment was compressed air
and water mist, and the heat treatment specifically comprised the following
steps:
[0084] (1) First stage cooling: when the temperature of the running surface
of the steel rail after the finish final rolling was 846°C, the running surface
of the steel rail, gauge corner and field corner of the rail head, gauge face
and field face of the rail head and two rail head comers of the rail head
were subjected to an accelerated cooling treatment for 150 seconds at a
cooling rate of 5.6°C/s;
[0085] (2) Second stage cooling: the running surface of the steel rail, gauge
corner and field comer of the rail head, gauge face and field face of the rail
head and two rail head comers of the rail head of the cooled steel rail obtained after step (1) were subjected to an accelerated cooling treatment for 25 seconds at a cooling rate of 4°C/s;
[0086] (3) Third stage cooling: the cooled steel rail obtained after step (2)
was placed on a walking beam cooling bed and subjected to an air cooling
to room temperature;
[0087] The chemical components of the steel rail were as shown in Table
1.
[0088] Example 4
[0089] The steel rail was prepared according to the same method in
Example 1, except that the chemical components of the steel rail were
different, as shown in Table 1.
[0090] Example 5
[0091] The steel rail was prepared according to the same method in
Example 2, except that the starting temperature of the accelerated cooling
in step (1) is 760°C.
[0092] Comparative Example 1
[0093] The steel rail was prepared according to the same method in
Example 1, except that the heat treatment specifically comprised the
following steps:
[0094] (1) First stage cooling: when the temperature of the running surface
of the steel rail after the finish final rolling was 860°C, the running surface
of the steel rail, gauge corner and field corner of the rail head, gauge face and field face of the rail head and two rail head comers of the rail head were subjected to an accelerated cooling treatment for 210 seconds at a cooling rate of 1.8°C/s;
[0095] (2) Third stage cooling: the cooled steel rail obtained after step (1)
was placed on a walking beam cooling bed and subjected to an air cooling
to room temperature.
[0096] Comparative Example 2
[0097] The steel rail was prepared according to the same method in
Example 2, except that the heat treatment specifically comprised the
following steps:
[0098] (1) First stage cooling: when the temperature of the running surface
of the steel rail after the finish final rolling was 775°C, the running surface
of the steel rail, gauge corner and field corner of the rail head, gauge face
and field face of the rail head and two rail head comers of the rail head
were subjected to an accelerated cooling treatment for 190 seconds at a
cooling rate of 2°C/s;
[0099] (2) Third stage cooling: the cooled steel rail obtained after step (1)
was placed on a walking beam cooling bed and subjected to an air cooling
to room temperature.
[00100] Comparative Example 3
[00101] The steel rail was prepared according to the same method in
Example 3, except that the heat treatment specifically comprised the following steps:
[001021 (1) First stage cooling: when the temperature of the running
surface of the steel rail after the finish final rolling was 838°C, the running
surface of the steel rail, gauge corner and field corner of the rail head,
gauge face and field face of the rail head and two rail head corners of the
rail head were subjected to an accelerated cooling treatment for 170
seconds at a cooling rate of 2.4°C/s;
[001031 (2) Third stage cooling: the cooled steel rail obtained after step
(1) was placed on a walking beam cooling bed and subjected to an air
cooling to room temperature.
[001041 Table 1
Example 1 Example 2 Example 3 Example 4
C(%) 0.78 0.76 0.8 0.81
Si(%) 0.47 0.5 0.46 0.55
Mn(%) 1.11 1.13 1.08 0.74
Cr(%) 0.12 0.1 0.14 0.08
P(%) 0.012 0.02 0.01 0.012
S(%) 0.014 0.008 0.013 0.004
Ni(%) - - 0.02 0.01
Mo(%) - 0.01 -
V(%) 0.01 - -
Fe + Balance Balance Balance Balance inevitable impurities (%)
[001051 Test Example
[00106] The tensile properties and the section hardness of the rail head
of the Examples and Comparative Examples were tested according to the
HBW 2.5/187.5 test force scheme of the Standard CB/T231.1-2018
"Brinell hardness Test of Metal Material, Part I: Test Method", wherein the
measurement position of section hardness of the rail head were shown in
FIG. 1, the Brinell hardness measurement was carried out on three lines A,
B and C, the distance between measurement points of hardness was 5mm,
the first point was 5mm away from the rail surface, and the measurement
depth was up to 25 mm. The results were shown in Table 2.
[001071 Table 2 Fracture section hardness /HB Hardness Tensile Elongat of rail Numbers strength ionrate running Sites 5mm10mm15mm20mm25mm /MPa /% surface /HB A 360 357 351 348 344 Example B 362 357 355 351 347 1237 10.5 366 C 360 363 357 353 350 A 379 374 369 363 359 Example B 378 367 365 356 351 1290 10.0 379 2 C 380 373 369 364 357 A 382 379 373 369 362 Example B 381 375 376 367 364 1287 10.0 383 C 386 383 378 375 367 Comparati A 358 365 364 351 341 1228 10.5 362 ve B 351 359 350 336 328
Example C 362 364 359 347 339 1 Comparati A 373 374 375 363 361 ve B 368 376 368 357 350 1281 10.5 375 Example 2 C 369 377 369 364 359 Comparati A 373 380 369 372 367 ve B 374 374 370 367 356 1274 10.5 381 Example 3 C 373 386 380 375 366
[00108] The detection results in Table 2 demonstrates that the Brinell
hardness of the running surface of the steel rail prepared with the method
of the present disclosure is within a range of 360-400HB, the rail head part
of the steel rail is provided with a deep hardened layer with a depth more
than 25mm, the deep hardened layer of the steel rail has a more uniform
hardness gradient than the steel rail prepared in the Comparative Examples.
[00109] The above content describes in detail the preferred embodiment
of the present disclosure, but the present disclosure is not limited thereto.
A variety of simple modifications can be made in regard to the technical
solutions of the present disclosure within the scope of the technical concept
of the present disclosure, including a combination of individual technical
features in any other suitable manner, such simple modifications and
combinations thereof shall also be regarded as the content disclosed by the
present disclosure, each of them falls into the protection scope of the
present disclosure.
Claims (10)
- Claims 1. A method for preparing a pearlite steel rail with a rail head hardenedlayer having an uniform hardness gradient, the method comprises thesuccessively performed steps of smelting with a revolving furnace or anelectric furnace, refining with a LF furnace, RH or VD vacuum treatment,continuous casting to obtain steel billets, subjecting the steel billets torolling, heat treatment and processing the steel rail;wherein the heat treatment is a multi-stage cooling process, andspecifically comprises the following steps:(1) first stage cooling: when the temperature of the running surface of thesteel rail after the finish final rolling is within a range of 760-900°C,subjecting the running surface of the steel rail, gauge corner and fieldcorner of the rail head, gauge face and field face of the rail head and tworail head comers of the rail head to an accelerated cooling treatment for 50150 seconds at a cooling rate of 2-6°C/s;(2) second stage cooling: subjecting the running surface of the steel rail,gauge corner and field corner of the rail head, gauge face and field face ofthe rail head and two rail head corners of the rail head of the cooled steelrail obtained after step (1) to an accelerated cooling treatment for 20-60seconds at a cooling rate of 1-5°C/s;(3) third stage cooling: subjecting the cooled steel rail obtained after step(2) to an air cooling to room temperature;controlling the chemical components of the steel rail, the steel railcomprises the following chemical components in percentage by weight: atleast one of 0.65-0.85% of C, 0.1-1% of Si, 0.1-1.5% of Mn, less than orequal to 0.03% of P, less than or equal to 0.03% of S, 0.01-0.2% of Cr,0.005-0.15% of Ni, 0.001-0.3% of Mo and 0.002-0.2% of V, and thebalance of Fe and inevitable impurities.
- 2. The method of claim 1, wherein the steel rail comprises the followingchemical components in percentage by weight: at least one of 0.68-0.82%of C, 0.2-0.7% of Si, 0.6-1.2% of Mn, less than or equal to 0.025% of P,less than or equal to 0.02% of S, 0.05-0.15% of Cr, 0.005-0.1% of Ni,0.001-0.2% ofMoand0.02-0.1% ofV, and the balance of Fe and inevitableimpurities.
- 3. The method of claim 1 or 2, wherein the cooling medium used in theheat treatment is water mist and/or compressed air.
- 4. The method of claim 1 or 2, wherein the continuous casting is a bloombillet protection continuous casting.
- 5. The method of claim 1 or 2, wherein the steel billet is descaled by usinghigh pressure water before subjecting the steel billet to rolling.
- 6. The method of claim 1 or 2, wherein the rolling is carried out in anuniversal rolling mill.
- 7. The method of claim 1 or 2, wherein the air cooling is performed on a walking beam cooling bed.
- 8. The method of claim orclaim 2, wherein the processing coursecomprises: straightening the steel rails by using a horizontal and verticalcomposite straightening machine.
- 9. A pearlite steel rail with a rail head hardened layer having an uniformhardness gradient prepared with the method of any one of claims 1 to 8,wherein the running surface of the steel rail has a Brinell hardness withina range of 360-400 HB; the rail head part of the steel rail has a hardenedlayer with a depth more than 25mm, and when an inner depth of the railhead increases for every 5mm, the Brinell hardness of the hardened layerdecreases by 3 - 6 HB.
- 10. The pearlite steel rail of claim 9, wherein the steel rail has a tensilestrength larger than 1,200MPa and an elongation rate greater than or equalto 10%.
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CN114058824B (en) * | 2021-11-26 | 2023-12-08 | 武汉钢铁有限公司 | Production method for improving hardness uniformity of heat-treated steel rail tread and steel rail obtained by production method |
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