CN112171125A - Method for improving microstructure of steel rail welded joint - Google Patents
Method for improving microstructure of steel rail welded joint Download PDFInfo
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- CN112171125A CN112171125A CN202011131777.3A CN202011131777A CN112171125A CN 112171125 A CN112171125 A CN 112171125A CN 202011131777 A CN202011131777 A CN 202011131777A CN 112171125 A CN112171125 A CN 112171125A
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 88
- 239000010959 steel Substances 0.000 title claims abstract description 88
- 238000000034 method Methods 0.000 title claims abstract description 52
- 238000003466 welding Methods 0.000 claims abstract description 139
- 238000001816 cooling Methods 0.000 claims abstract description 129
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 22
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 21
- 239000003595 mist Substances 0.000 claims abstract description 17
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 17
- 238000012544 monitoring process Methods 0.000 claims abstract description 11
- 239000002826 coolant Substances 0.000 claims description 24
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- 229910001567 cementite Inorganic materials 0.000 abstract description 39
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 abstract description 38
- 238000005452 bending Methods 0.000 abstract description 18
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K37/00—Auxiliary devices or processes, not specially adapted to a procedure covered by only one of the preceding main groups
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K31/00—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K37/00—Auxiliary devices or processes, not specially adapted to a procedure covered by only one of the preceding main groups
- B23K37/003—Cooling means
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2101/00—Articles made by soldering, welding or cutting
- B23K2101/26—Railway- or like rails
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Machines For Laying And Maintaining Railways (AREA)
Abstract
The invention relates to the field of steel rail welding, and discloses a method for improving a steel rail joint microstructure. The method comprises the following steps: the method comprises the following steps: using an accelerated cooling device, adopting water mist and compressed air as cooling media, carrying out accelerated cooling on a rail waist part of a welding joint to be cooled, which is obtained by flash welding, and simultaneously measuring the temperature of the central position of a welding seam of the rail waist of the welding joint and monitoring the temperature; step two: when the temperature of the central position of the welding seam is reduced to a preset temperature, stopping accelerated cooling, and then placing the welding joint in air for natural cooling to room temperature; wherein the steel rail is a pearlitic steel rail with a carbon content of 0.6-0.9 wt%. The method utilizes the waste heat of the steel rail welding joint, does not need to heat the joint again, can effectively ensure that abnormal structures such as intercrystalline cementite and the like in the pearlite steel rail flash welding joint are normal, and simultaneously ensures that the properties such as the hardness and the static bending of the joint meet the use requirements.
Description
Technical Field
The invention relates to the field of steel rail welding, in particular to a method for improving the microstructure of a steel rail joint.
Background
With the rapid development of the seamless track technology in the fields of passenger transport, freight transport, high-speed and heavy-load railway construction in the world, the quality of the steel rail joint attracts more and more attention of related departments. The railway line is used as a direct carrier for train operation, and the reliability of the quality of the railway line is the key of the safe operation of the train. The flash welded joint for steel rail belongs to the weak link of the whole line, the quality of the flash welded joint can directly affect the safety of the railway, and the microscopic structure of the steel rail joint directly determines the service performance of the joint.
At present, the mainstream steel rails at home and abroad are pearlite steel rails. All the existing flash welding standards and enterprise technical conditions suitable for pearlitic steel rails make specific provisions on the microstructure of joints. Standard series standard TB/T1632.2-2014 in China railway industry part2 of rail welding: in the flash welding, the microstructure of a welding seam and a heat affected zone of a steel rail joint is defined to be pearlite, a small amount of ferrite can appear, and harmful structures such as martensite, bainite and the like do not exist; the american society for railroad engineering standards (amama) states that the weld and heat affected zone of a rail joint are desirably 100% pearlite structures, which can affect the results of static bending tests once the joint develops an untempered martensite structure; the European standard BS EN 14587-3:2012, the Rail way applications-Rack-Flash but Welding of rails, part 3: Welding in association with the cross structuring, observed with an optical microscope at a magnification of 100 x, does not show acicular carbides and intergranular continuous network carbides with signs of embrittlement, allowing the appearance of granular martensite structures; australian Standard AS1085.20-2012, Railway track Material Part 20: the Welding of steel rail standards stipulate that the rail joint microstructure should be a pearlite structure substantially free of intergranular cementite and untempered martensite, allowing for the presence of a small amount of martensite if the requirements of other tests can be met; the location and size of intergranular carbides that are allowed to occur in rail joints are also well defined in many foreign well-known technical conditions for heavy haul lines.
From the above standards and technical conditions, it is obvious that the requirements for the morphology and content of the intergranular cementite structure of the flash welded pearlitic rail joint in various countries of the world are extremely high, and even strictly in the allowable range of the harmful structures such as martensite, bainite and the like. How to inhibit or eliminate the precipitation of the intergranular carbide structure of the welded joint of the pearlitic steel rail through a welding process and a post-welding treatment process is an important factor for obtaining the high-quality pearlitic steel rail flash welding joint.
Intercrystalline cementite, i.e., cementite between grains distributed along grain boundaries, is generally in the form of a network. The cementite being a Fe-C interstitial compound Fe3C, the carbon content is 6.99 weight percent. Cementite belongs to an orthorhombic system, the crystal structure is very complex, and a unit cell contains 12 iron atoms and 4 carbon atoms. Cementite has a very high hardness of about 800HBW, but has poor plasticity and an elongation close to zero. Cementite has some ferromagnetism at low temperatures, but is the magnetic transition temperature of cementite at 230 ℃. The melting point of the cementite is 1227 ℃ according to theoretical calculation. Cementite with a complex structure is the most common and very important carbide in steel and is one of the precipitated phases in steel. The form and state of presence of cementite in the steel, whether as a product of eutectoid or eutectic transformation (e.g. valence changes of Fe and C, Fe3C crystalline and amorphous, geometry, size, quantity and distribution) directly affect the properties of the steel. Depending on the position of precipitation, cementite can be classified into primary cementite precipitated from the liquid phase, secondary cementite precipitated from austenite, and tertiary cementite precipitated from ferrite. The primary cementite is distributed among ledeburite in a white strip shape; secondary cementite is usually precipitated along the original austenite grain boundary, and after the austenite is transformed into pearlite, the secondary cementite is distributed on the pearlite boundary in a continuous net shape; the tertiary cementite is distributed in the ferrite grain boundary, but is not generally seen because of a small amount and extremely dispersed.
In the steel of the existing steel rail component system, cementite mainly exists in the form of a sheet and a net. Lamellar cementite is the main form of cementite in steel and generally is transformed by eutectoid transformation, and lamellar pearlite consists of both lamellar cementite and lamellar ferrite. The network cementite is also called as proeutectoid cementite, and is precipitated from austenite higher than eutectoid components along intergranular regions due to the change of the carbon content during temperature reduction, and is usually in a network shape in eutectoid steel or hypereutectoid steel, so the network cementite is also called as network cementite. The presence of reticulated cementite greatly increases the brittleness of the steel. At present, the carbon content of steel of the steel rail widely used by common lines such as domestic and overseas passenger transport, subway and the like is generally 0.61-0.82%, the carbon content of a eutectoid point is 0.77% under the state close to equilibrium, but the carbon content of the eutectoid point can be reduced to about 0.71% under the action of certain alloy elements; meanwhile, the center position of the rail web of the steel rail produced by continuous casting and rolling is usually a component positive segregation region, has higher carbon content, is easy to precipitate intercrystalline cementite which is in net distribution in the welding process, and reduces the welding quality of the joint in serious cases.
At present, the technical literature and invention patents aiming at the technology research for inhibiting the precipitation of the intercrystalline cementite of the steel rail welding joint are less.
Disclosure of Invention
The invention aims to overcome the problems in the prior art and provide a method for improving the microstructure of a steel rail joint.
In order to achieve the above object, the present invention provides a method for improving a microstructure of a welded joint for a steel rail, the method comprising the steps of:
the method comprises the following steps: using an accelerated cooling device, adopting water mist and compressed air as cooling media, carrying out accelerated cooling on a rail waist part of a welding joint to be cooled, which is obtained by flash welding, and simultaneously measuring the temperature of the central position of a welding seam of the rail waist of the welding joint and monitoring the temperature;
step two: when the temperature of the center position of the rail web welding line is reduced to a preset temperature, stopping accelerated cooling, and then placing the welding joint in air to naturally cool to room temperature;
wherein the steel rail is a pearlitic steel rail with a carbon content of 0.6-0.9 wt%.
Preferably, in the step one, the pressure of the water mist is 1-2 bar; the pressure of the compressed air is 0.2-0.4 MPa.
Preferably, the rail is a hot rolled pearlitic rail and/or a heat treated pearlitic rail.
Preferably, in the first step, the accelerated cooling device is a box-shaped hollow cavity structure and comprises a cooling medium inlet surface and a cooling surface, the cooling medium enters the accelerated cooling device through the cooling medium inlet surface, and the cooling medium is sprayed out through the cooling surface.
Preferably, a plurality of conical narrow-angle nozzles are equidistantly distributed on the cooling surface;
preferably, the injection angle of the tapered narrow-angle nozzle is 40-45 °.
Preferably, in the first step, in the step (1), the rail web part of the welded joint comprises a region with a height direction being two thirds of the height of the steel rail web and a region with a width direction being 40mm outwards of the heat affected zone of the welded joint.
Further preferably, the web portion of the welded joint comprises a region in which the weld extends 20 to 30mm in height from the center line in the rail height direction to each side, and a region in which the weld extends 40 to 60mm in width from the center line in the weld width direction to each side.
Preferably, in the step one, the distance between the cooling surface of the accelerated cooling device and the rail web surface is 15-35 mm.
Preferably, in the step one, the cooling rate of the central position of the rail web welding seam is more than 18 ℃/s in the accelerated cooling process;
further preferably, the cooling rate of the central position of the rail web welding seam is 19-35 ℃/s.
Preferably, in the second step, the preset temperature is 900-.
The method provided by the invention aims at the pearlitic steel rail with the carbon mass fraction of 0.6-0.9%, and utilizes the waste heat of the steel rail welding joint, so that the joint does not need to be heated again, the normal abnormal structures such as intercrystalline cementite and the like in the pearlitic steel rail flash welding joint can be effectively ensured, and the properties such as the hardness and the static bending of the joint can be ensured to meet the use requirements. The invention has the advantages of obvious effect, simple process flow and convenient operation, and is suitable for both fixed flash welding and movable flash welding.
Drawings
FIG. 1 is a schematic view of the installation of the accelerated cooling device of the present invention;
FIG. 2 is a schematic view showing the microstructure sampling positions of welded joint for steel rails of examples and comparative examples in test example 1;
FIG. 3 is a microstructure diagram of a sampling test of comparative example 1 in test example 1;
FIG. 4 is a microstructure diagram of a sampling test of comparative example 2 in test example 1;
FIG. 5 is a microstructure diagram of a sampling test of comparative example 3 in test example 1.
Description of the reference numerals
1 cooling medium inlet surface 2 accelerated cooling device
3 cooling surface of conical narrow-leg nozzle 4
5 fixer 6 pipeline
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a method for improving the microstructure of a steel rail welded joint, which comprises the following steps:
the method comprises the following steps: using an accelerated cooling device 2, adopting water mist and compressed air as cooling media, carrying out accelerated cooling on a rail waist part of a welding joint to be cooled obtained by flash welding, and simultaneously measuring the temperature of the central position of a welding seam of the rail waist of the welding joint and monitoring the temperature;
step two: when the temperature of the center position of the rail web welding line is reduced to a preset temperature, stopping accelerated cooling, and then placing the welding joint in air to naturally cool to room temperature;
wherein the steel rail is a pearlitic steel rail with a carbon content of 0.6-0.9 wt%.
In the invention, the accelerated cooling of the rail waist part of the welding joint to be cooled obtained by flash welding means that the rail waist part is immediately accelerated and cooled at the same time of finishing the flash welding so as to fully utilize the waste heat of the steel rail welding joint.
In the invention, the steel rail flash welding is a welding method which clamps the steel rails on two sides by a clamping device such as a conductive electrode, contacts the end faces of the steel rails after electrification, generates resistance heat at the contact point by conducting current, rapidly melts the contact point to form flash and strong splashing, and applies a certain upsetting force after a certain flash allowance so as to recrystallize and form the steel rails at high temperature. Mainly comprises two types of fixed flash welding and movable flash welding.
In the present invention, there is no particular requirement for the equipment used for flash welding, and various flash welders conventionally used in the art may be used.
In the invention, a mixed medium of water mist and compressed air is used as a cooling medium, and the pressure of the water mist is 1-2bar under the optimal condition; the pressure of the compressed air is 0.2-0.4 MPa. Specifically, the pressure of the water mist may be 1bar, 1.1bar, 1.2bar, 1.3bar, 1.4bar, 1.5bar, 1.6bar, 1.7bar, 1.8bar, 1.9bar, or 2 bar; the pressure of the compressed air may be 0.2MPa, 0.21MPa, 0.22MPa, 0.23MPa, 0.24MPa, 0.25MPa, 0.26MPa, 0.27MPa, 0.28MPa, 0.29MPa, 0.3MPa, 0.31MPa, 0.32MPa, 0.33MPa, 0.34MPa, 0.35MPa, 0.36MPa, 0.37MPa, 0.38MPa, 0.39MPa or 0.4 MPa.
In the present invention, the pressure is an absolute pressure.
In the method of the present invention, the rail is a hot rolled pearlitic rail and/or a heat treated pearlitic rail.
In the present invention, the pearlite rail is a rail in which the entire microstructure of the rail is pearlite in a supplied state.
In the method of the invention, preferably, in the step one, an infrared thermometer is used for measuring the temperature of the central position of the welding joint web welding seam and monitoring the temperature.
In the invention, the rail web welding seam center position refers to the welding seam center of the rail web area subjected to accelerated cooling.
In the method of the present invention, in the step one, there is no particular requirement for the selection of the device for performing accelerated cooling, and various accelerated cooling devices conventionally used in the art may be used. In a preferred case, the accelerated cooling device 2 is a box-shaped hollow cavity structure, and mainly functions to disperse and concentrate columnar cooling media, and comprises a cooling medium inlet surface 1 and a cooling surface 4. The cooling medium enters the accelerated cooling device through the cooling medium inlet surface 1, and the cooling medium is sprayed out through the cooling surface 4.
More preferably, a plurality of conical narrow-angle nozzles 3 are equidistantly distributed on the cooling surface 4, and the conical narrow-angle nozzles 3 are used for spraying cooling media.
Further preferably, the injection angle of the tapered narrow-angle nozzle 3 is 40 to 45 °.
In a preferred embodiment, in the first step, the cooling surface 4 of the accelerated cooling device 2 is a surface facing the rail web surface and is a surface closest to the rail web surface of the rail joint, and the distance between the cooling surface 4 and the rail web surface may be set according to the magnitude of the pressure of the cooling medium. In a more preferred embodiment, the cooling surface 4 is at a distance of 15-35mm from the rail web surface. In particular embodiments, the distance may be 15mm, 20mm, 25mm, 30mm or 35 mm.
In a preferred embodiment, the accelerated cooling device 2 is schematically installed as shown in fig. 1. The two accelerated cooling devices 2 are fixed on two sides of a rail joint by a fixer 5 arranged above a rail through a pipeline 6, the cooling surface 4 is kept to face the surface of the rail web, and the pipeline 6 is connected with the cooling medium inlet surface 1 of the accelerated cooling device 2. When the device is used, a cooling medium enters the accelerated cooling device 2 sequentially through the fixer 5, the pipeline 6 and the cooling medium inlet surface 1 and then is sprayed out from the conical narrow-angle nozzle 3 of the cooling surface 4, and the spraying angle is 40-45 degrees.
In a preferred embodiment, in the first step, the rail web part of the welded joint comprises a region with the height direction being two thirds of the height of the steel rail web plate and a region with the width direction being 40mm outwards of the heat-affected zone of the welded joint.
More preferably, the web portion of the welded joint includes a region in which the weld extends 20 to 30mm in height from the center line in the rail height direction to each of both sides, and a region in which the weld extends 40 to 60mm in width from the center line in the weld width direction to each of both sides.
In a preferred embodiment, in the step one, the cooling rate of the central position of the rail web welding seam is more than 18 ℃/s in the accelerated cooling process. In a more preferred embodiment, the cooling rate of the rail web weld center position is 19-35 ℃/s.
In a preferred embodiment, in the second step, the preset temperature may be set according to the profile and material grade of the steel rail. In a preferred embodiment, the preset temperature is 900-. Specifically, the preset temperature may be 900 ℃, 950 ℃, 1000 ℃, 1050 ℃, 1100 ℃, 1150 ℃ or 1200 ℃.
In the present invention, the performance of the rail weld joint is also related to rail joint hardness, static bending load and static bending deflection. The post-welding treatment process can improve the joint structure, reduce the softening degree and meet the requirement of the wear resistance of the joint.
The method of the invention utilizes the waste heat of the steel rail welding joint, does not need to heat the joint again, can effectively ensure that the abnormal structures such as intercrystalline cementite and the like in the hot-rolled or heat-treated pearlite steel rail flash welding joint with the carbon mass fraction of 0.6-0.9% are normal, and simultaneously ensures that the properties such as the hardness, the static bending and the like of the joint meet the use requirements. The invention has the advantages of obvious effect, simple process flow and convenient operation, and is suitable for both fixed flash welding and movable flash welding.
The present invention will be described in detail below by way of examples, but the scope of the present invention is not limited thereto.
The accelerated cooling device 2 used in the examples and comparative examples is a box-like hollow cavity structure, and mainly functions to disperse and concentrate columnar cooling media, including a cooling medium inlet face 1 and a cooling face 4. The installation schematic is shown in fig. 1. The two accelerated cooling devices 2 are fixed on two sides of a rail joint by a fixer 5 arranged above a rail through a pipeline 6, the cooling surface 4 is kept to face the surface of the rail web, and the pipeline 6 is connected with the cooling medium inlet surface 1 of the accelerated cooling device 2. When the device is used, a cooling medium enters the accelerated cooling device 2 through the fixer 5, the pipeline 6 and the cooling medium inlet surface 1 in sequence, and then is sprayed out from a plurality of conical narrow-angle nozzles 3 distributed at equal intervals on the cooling surface 4.
The web portions of the welded joints in the examples and comparative examples included regions having a height direction in which the weld extended 20 to 30mm to each side along the center line in the height direction of the rail and regions having a width direction in which the weld extended 40 to 60mm to each side along the center line in the width direction of the weld.
Example 1
The experimental material of this example was a 68kg rail profile, head hardened (heat treated) pearlitic rail AS specified in AS 1085.1, Rail track materials, Part 1, Steel rails Standard, with a solid chemical composition of 0.8% by weight carbon content. 5 parallel experiments are carried out, and the specific experimental process comprises the following steps: a GAAS80/580 steel rail fixed flash welding machine is adopted to carry out welding experiments, an accelerated cooling device 2 (the cooling surface 4 is 25mm away from the rail waist surface, the spraying angle is 45 degrees) is used, water mist (the pressure is 1.5bar) and compressed air (the pressure is 0.3MPa) are adopted as cooling media, the rail waist part of a welding joint to be cooled obtained by flash welding is subjected to accelerated cooling, meanwhile, an infrared thermometer is adopted to measure the temperature of the central position of the rail waist welding seam of the welding joint and continuously monitor the temperature, the cooling rate of the central position of the rail waist welding seam is 19-35 ℃/s, when the temperature is reduced to 1050 ℃, a control system automatically closes the cooling media, the accelerated cooling is immediately stopped, and then the joint is placed in air to be naturally cooled to the room temperature. Rail weld joints a11, a12, a13, a14 and a15 were obtained.
Example 2
The experimental material of this example was a 68kg rail profile, head hardened (heat treated) pearlitic rail AS specified in AS 1085.1, Rail track materials, Part 1, Steel rails Standard, with a solid chemical composition of 0.8% by weight carbon content. 5 parallel experiments are carried out, and the specific experimental process comprises the following steps: a steel rail mobile flash welding machine is adopted to carry out welding experiments, an accelerated cooling device 2 (the cooling surface is 4 mm away from the rail waist surface, the spraying angle is 45 degrees) is used, water mist (the pressure is 1.5bar) and compressed air (the pressure is 0.3MPa) are used as cooling media, the rail waist part of a welding joint to be cooled obtained by flash welding is subjected to accelerated cooling, meanwhile, an infrared thermometer is used for measuring the temperature of the central position of the rail waist welding line of the welding joint and continuously monitoring the temperature, the cooling rate of the central position of the rail waist welding line is 19-35 ℃/s, when the temperature is reduced to 1050 ℃, a control system automatically closes the cooling media, the accelerated cooling is immediately stopped, and the joint is placed in the air to be naturally cooled to the room temperature. Rail weld joints a21, a22, a23, a24 and a25 were obtained.
Comparative example 1
The procedure is as described in example 1, except that the pressure of the compressed air is 0.5MPa and the control system automatically shuts off the cooling medium when the temperature drops to 880 ℃. Rail weld joints D11, D12, D13, D14 and D15 were obtained.
Comparative example 2
The procedure is as described in example 1, except that the cooling surface 4 is 15mm from the rail web surface, the pressure of the compressed air is 0.1MPa, and the control system automatically shuts off the cooling medium when the temperature drops to 1250 ℃. Rail joints D21, D22, D23, D24 and D25 were obtained.
Comparative example 3
The experimental material of this comparative example was a 68kg rail profile, nose hardened (heat treated) pearlitic rail specified in AS 1085.1: Rail track materials, Part 1: Steel rails Standard, with a solid chemical composition of the rail having a measured carbon content of 0.8% by weight. 5 parallel experiments are carried out, and the specific experimental process comprises the following steps: a GAAS80/580 steel rail fixed flash welding machine is adopted to carry out welding experiments, and a welding joint to be cooled obtained by flash welding is placed in air to be naturally cooled to room temperature. Rail weld joints D31, D32, D33, D34 and D35 were obtained.
Example 3
The experimental material of this example is a 60E1 Rail profile, R260 hot rolled pearlitic Rail specified in BS EN 13674-1: Rail applications-Track-Rail, Part 1: Vignole Rail rails 46kg/m and above standard, with a solid chemical composition of the Rail having a measured carbon content of 0.6% by weight. 5 parallel experiments are carried out, and the specific experimental process comprises the following steps: a steel rail mobile flash welding machine is adopted to carry out welding experiments, an accelerated cooling device 2 (the cooling surface is 4 mm away from the rail waist surface, the spraying angle is 40 degrees) is used, water mist (the pressure is 1bar) and compressed air (the pressure is 0.4MPa) are used as cooling media, the rail waist part of a welding joint to be cooled obtained by flash welding is subjected to accelerated cooling, meanwhile, an infrared thermometer is used for measuring the temperature of the central position of the rail waist welding line of the welding joint and continuously monitoring the temperature, the cooling rate of the center of the rail waist welding line is 19-35 ℃/s, when the temperature is reduced to 950 ℃, a control system automatically closes the cooling media, the accelerated cooling is immediately stopped, and the joint is placed in the air to be naturally cooled to the room temperature. Rail weld joints a31, a32, a33, a34 and a35 were obtained.
Example 4
The experimental material of this example is a 60E1 Rail profile, R260 hot rolled pearlitic Rail specified in BS EN 13674-1: Rail applications-Track-Rail, Part 1: Vignole Rail rails 46kg/m and above standard, with a solid chemical composition of the Rail having a measured carbon content of 0.6% by weight. 5 parallel experiments are carried out, and the specific experimental process comprises the following steps: a steel rail mobile flash welding machine is adopted to carry out welding experiments, an accelerated cooling device 2 (the cooling surface is 4 mm away from the rail waist surface, the spraying angle is 40 degrees) is used, water mist (the pressure is 1.0bar) and compressed air (the pressure is 0.4MPa) are used as cooling media, the rail waist part of a welding joint to be cooled obtained by flash welding is subjected to accelerated cooling, meanwhile, an infrared thermometer is used for measuring the temperature of the central position of the rail waist welding line of the welding joint and continuously monitoring the temperature, the cooling rate of the central position of the rail waist welding line is 19-35 ℃/s, when the temperature is reduced to 900 ℃, a control system automatically closes the cooling media, the accelerated cooling is immediately stopped, and then the joint is placed in the air to be naturally cooled to the room temperature. Rail weld joints a41, a42, a43, a44 and a45 were obtained.
Example 5
The experimental material of this example is a 60E1 Rail profile, R260 hot rolled pearlitic Rail specified in BS EN 13674-1: Rail applications-Track-Rail, Part 1: Vignole Rail rails 46kg/m and above standard, with a solid chemical composition of the Rail having a measured carbon content of 0.6% by weight. 5 parallel experiments are carried out, and the specific experimental process comprises the following steps: a steel rail mobile flash welding machine is adopted to carry out welding experiments, an accelerated cooling device 2 (the cooling surface is 4 mm away from the rail waist surface, the spraying angle is 45 degrees) is used, water mist (the pressure is 1.0bar) and compressed air (the pressure is 0.4MPa) are used as cooling media, the rail waist part of a welding joint to be cooled obtained by flash welding is subjected to accelerated cooling, meanwhile, an infrared thermometer is used for measuring the temperature of the central position of the rail waist welding line of the welding joint and continuously monitoring the temperature, the cooling rate of the central position of the rail waist welding line is 19-35 ℃/s, when the temperature is reduced to 1200 ℃, a control system automatically closes the cooling media, the accelerated cooling is immediately stopped, and then the joint is placed in the air to be naturally cooled to the room temperature. Rail weld joints a51, a52, a53, a54 and a55 were obtained.
Example 6
The experimental materials of this example are BS EN 13674-1: Rail applications-Track-Rail, Part 1: Vignole Rail 46kg/m and above standard specified 60E2 Rail profile, R400HT heat treated pearlitic Rail, with a solid chemical composition of the Rail of 0.9% by weight carbon content. 5 parallel experiments are carried out, and the specific experimental process comprises the following steps: a steel rail mobile flash welding machine is adopted to carry out welding experiments, an accelerated cooling device 2 (the cooling surface is 4 mm away from the rail waist surface, the spraying angle is 43 degrees) is used, water mist (the pressure is 2.0bar) and compressed air (the pressure is 0.3MPa) are used as cooling media, the rail waist part of a welding joint to be cooled obtained by flash welding is subjected to accelerated cooling, meanwhile, an infrared thermometer is used for measuring the temperature of the central position of the rail waist welding line of the welding joint and continuously monitoring the temperature, the cooling rate of the central position of the rail waist welding line is 19-35 ℃/s, when the temperature is reduced to 1000 ℃, a control system automatically closes the cooling media, the accelerated cooling is immediately stopped, and then the joint is placed in the air to be naturally cooled to the room temperature. Rail weld joints a61, a62, a63, a64 and a65 were obtained.
Example 7
The experimental material used in this example was a 136RE Rail profile and HH head hardened (heat treated) pearlite Rail as specified in the American society for railway engineering handbook AMERICAN RARILWAYENGINEERING AND MAINTENANCE-OF-WAY Association (AREMA), Part 1: Design OF Rail Standard, and the steel Rail had a solid chemical composition OF measured carbon content OF 0.86 wt%. 5 parallel experiments are carried out, and the specific experimental process comprises the following steps: a GAAS80/580 steel rail fixed flash welding machine is adopted to carry out welding experiments, an accelerated cooling device 2 (the cooling surface 4 is 15mm away from the rail waist surface, the spraying angle is 40 degrees) is used, water mist (the pressure is 2.0bar) and compressed air (the pressure is 0.2MPa) are adopted as cooling media, the rail waist part of a welding joint to be cooled obtained by flash welding is subjected to accelerated cooling, meanwhile, an infrared thermometer is adopted to measure the temperature of the central position of the rail waist welding line of the welding joint and continuously monitor the temperature, the cooling rate of the central position of the rail waist welding line is 19-35 ℃/s, when the temperature is reduced to 950 ℃, a control system automatically closes the cooling media, the accelerated cooling is immediately stopped, and the joint is placed in air to be naturally cooled to the room temperature. Rail weld joints a71, a72, a73, a74 and a75 were obtained.
Example 8
The experimental material used in this example was a 136RE Rail profile and HH head hardened (heat treated) pearlite Rail as specified in the American society for railway engineering handbook AMERICAN RARILWAY ENGINEERING AND MAINTENANCE-OF-WAY Association (AREMA), Part 1: Design OF Rail Standard, and the steel Rail had a solid chemical composition OF measured carbon content OF 0.86 wt%. 5 parallel experiments are carried out, and the specific experimental process comprises the following steps: a GAAS80/580 steel rail fixed flash welding machine is adopted to carry out welding experiments, an accelerated cooling device 2 is used (the cooling surface 4 is 20mm away from the rail web surface, the spraying angle is 40 degrees, the spraying angle is 45 degrees), water mist (the pressure is 1.5bar) and compressed air (the pressure is 0.3MPa) are used as cooling media, the rail web part of a welding joint to be cooled obtained by flash welding is subjected to accelerated cooling, meanwhile, an infrared thermometer is used for measuring the temperature of the central position of the rail web welding seam of the welding joint and continuously monitoring the temperature, the cooling rate of the central position of the rail web welding seam is 19-35 ℃/s, when the temperature is reduced to 1000 ℃, a control system automatically closes the cooling media, the accelerated cooling is immediately stopped, and the joint is placed in the air to be naturally cooled to the room temperature. Rail weld joints a81, a82, a83, a84 and a85 were obtained.
Test example 1
1 steel rail welded joint obtained from the examples and the comparative examples is respectively selected and numbered as A11, A21, A31, A41, A51, A61, A71, A81, D11, D21 and D31. Sampling is carried out at the center of the welding line of the rail web by adopting a wire cut electrical discharge machining mode, and the sampling position is shown in figure 2. And adopting a microscopic structure inspection method, namely dissolving nitric acid alcohol prepared from 3-5 volume percent of nitric acid and 95-97 volume percent of absolute ethyl alcohol in a polished state, corroding the solution for about 15s at normal temperature, and observing the solution by adopting an optical electron microscope.
No apparent intercrystalline cementite microstructure was examined on the observation face of the steel welded rail joint sampling sites described in examples 1-8.
Although no obvious intercrystalline cementite microstructure is detected on the observation surface of the steel rail welding joint sampling position in the comparative example 1, a large amount of martensite structures are detected, and the microstructure is shown in figure 3 and does not meet the requirements.
The microscopic structure of the obvious intercrystalline cementite is detected on the observation surface of the sampling position of the steel rail welding joint in the comparative example 2, and the microscopic structure is shown in figure 4 and can not meet the requirements.
The microscopic structure of the obvious intercrystalline cementite is detected on the observation surface of the sampling position of the steel rail welding joint in the comparative example 3, and the microscopic structure is shown in figure 5 and can not meet the requirements.
Test example 2
4 of the rail joints obtained in examples 1-2 and comparative examples 1-3 were selected, wherein 1 of the 4 joints was subjected to a hardness test and was numbered a12, a22, D12, D22 and D32; 3 branches were used for static bending tests, numbered A13, A14, A15, A23, A24, A25, D13, D14, D15, D23, D24, D25, D33, D34, D35. The hardness test and the static bending test were carried out using AS1085.20, the road track material, Part 20: Welding of steel rail. The test results of the lowest value and the highest value of the hardness of the longitudinal section of the joint are shown in table 1, and the test results of the maximum deflection value and whether the fracture occurs when the maximum stress of the rail base in the static bending test is 910MPa are shown in table 1.
As can be seen from the results shown in Table 1, the hardness test and the static bending test results of the rail joints obtained in examples 1 to 2 and comparative examples 1 to 3 meet the standard requirements.
TABLE 1
| Numbering | Minimum value (HV) | Maximum value (HV) | Maximum deflection value (mm) | Whether or not to break |
| Example 1 | 379 | 424 | 14.2 | Whether or not |
| Example 2 | 376 | 428 | 14.1 | Whether or not |
| Comparative example 1 | 374 | 425 | 13.3 | Whether or not |
| Comparative example 2 | 377 | 422 | 14.2 | Whether or not |
| Comparative example 3 | 372 | 421 | 13.5 | Whether or not |
Test example 2
4 of the rail weld joints obtained in examples 3 to 6 were selected, wherein 1 of the joints was subjected to a hardness test and was numbered a32, a42, a52 and a 62; the 3 branches are used for static bending test and are numbered as A33, A34, A35, A43, A44, A45, A53, A54, A55, A63, A64 and A65. The hardness test and the static bending test were both performed using the BS EN 14587-2: Rail-Flash debug welding of rails, Part 2: New R220, R260, R260Mn and R350HT grade rails by mobile welding machines at sites other than a fixed plant standard. The test results of the lowest and highest values of the stiffness of the joint longitudinal section are shown in table 2, and the test results of the maximum deflection value and the occurrence of fracture when the maximum load of the static bending test is 1610kN are shown in table 2.
As can be seen from the results shown in Table 2, the hardness test and static bending test results of the rail joints obtained in examples 3 to 6 meet the standard requirements.
TABLE 2
| Numbering | Minimum value (HV) | Maximum value (HV) | Maximum deflection value (mm) | Whether or not to break |
| Example 3 | 256 | 340 | 23.5 | Whether or not |
| Example 4 | 256 | 338 | 22.6 | Whether or not |
| Example 5 | 257 | 338 | 23.2 | Whether or not |
| Example 6 | 409 | 446 | 21.3 | Whether or not |
Test example 3
4 of the rail weld joints obtained in examples 7 to 8 were selected, 1 for hardness testing, and numbered a72 and a 82; the 3 branches are used for static bending tests and are numbered A73, A74, A75, A83, A84 and A85. The hardness test and the static bending test were conducted according to the American society for railway engineering Manual AMERICAN RARILWAY ENGINEERING AND MAINTENANCE-OF-WAY Association (AREMA), CHAPTER 4, Part 3: Joining OF Rail standards. The test results of the lowest and highest values of the longitudinal section hardness of the joint are shown in Table 3, and the maximum rail base stress of the static bending test joint is 125000lbs/in2The maximum deflection values and the results of the test for the occurrence of fracture are shown in Table 3.
As can be seen from the results shown in Table 3, the hardness test and static bending test results of the welded steel rail joints obtained in examples 7 to 8 meet the standard requirements.
TABLE 3
| Numbering | Minimum value (BHN) | Maximum value (BHN) | Maximum deflection value (inch) | Whether or not to break |
| Example 7 | 355 | 409 | 0.77 | Whether or not |
| Example 8 | 354 | 397 | 0.8 | Whether or not |
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (10)
1. A method of improving the microstructure of a rail weld joint, the method comprising the steps of:
the method comprises the following steps: using an accelerated cooling device (2), adopting water mist and compressed air as cooling media, carrying out accelerated cooling on a rail web part of a welding joint to be cooled, which is obtained by flash welding, and simultaneously measuring the temperature of the central position of a welding seam of the rail web of the welding joint and monitoring the temperature;
step two: when the temperature of the center position of the rail web welding line is reduced to a preset temperature, stopping accelerated cooling, and then placing the welding joint in air to naturally cool to room temperature;
wherein the steel rail is a pearlitic steel rail with a carbon content of 0.6-0.9 wt%.
2. A method for improving the microstructure of a steel rail welded joint according to claim 1, wherein in the first step, the pressure of the water mist is 1-2 bar; the pressure of the compressed air is 0.2-0.4 MPa.
3. A method of improving the microstructure of a steel rail weld joint according to claim 1, wherein the steel rail is a hot rolled pearlitic rail and/or a heat treated pearlitic rail.
4. A method for improving the microstructure of a steel rail welded joint according to claim 1, wherein in the first step, the accelerated cooling device (2) is a box-shaped hollow cavity structure and comprises a cooling medium inlet surface (1) and a cooling surface (4), the cooling medium enters the accelerated cooling device (2) through the cooling medium inlet surface (1), and the cooling medium is sprayed out through the cooling surface (4).
5. A method for improving the microstructure of a steel rail welding joint according to claim 4, characterized in that a plurality of conical narrow-angle nozzles (3) are equidistantly distributed on the cooling surface (4);
preferably, the spray angle of the conical narrow-angle nozzle (3) is 40-45 degrees.
6. A method for improving the microstructure of a welded joint on a steel rail according to claim 1 or 2, wherein in the first step, the web part of the welded joint comprises a region with a height of two thirds of the height of a web of the steel rail and a region with a width of 40mm extending outwards from a heat-affected zone of the welded joint.
7. A method according to claim 6, wherein the web portion of the weld joint comprises a region of the weld seam extending 20-30mm in height from the rail height direction centre line to each side and a region of the weld seam extending 40-60mm in width from the rail width direction centre line to each side.
8. A method for improving the microstructure of a steel rail welding joint according to claim 4 or 5, characterized in that in the first step, the distance between the cooling surface (4) of the accelerated cooling device (2) and the surface of the rail web is 15-35 mm.
9. A method for improving the microstructure of a steel rail welding joint according to claim 1 or 2, characterized in that, in the step one, the cooling rate of the central position of the rail web welding seam is more than 18 ℃/s in the accelerated cooling process;
preferably, the cooling rate of the central position of the rail web welding seam is 19-35 ℃/s.
10. The method for improving the microstructure of the steel rail welding joint as recited in claim 1 or 2, wherein in the second step, the preset temperature is 900-1200 ℃.
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