CN112063825A - A post-weld heat treatment method for 1100MPa low-alloy heat-treated rails - Google Patents

Abstract

The invention relates to the technical field of railway steel rail manufacturing, and discloses a postweld heat treatment method for a 1100 MPa-level low-alloy heat-treated steel rail. The method comprises the following steps: (1) cooling a welded steel rail welding joint with the residual temperature of 1150-1300 ℃ to a first stage, so that the surface temperature of the steel rail welding joint is reduced to 580-640 ℃; (2) cooling the steel rail welding joint in the second stage to reduce the surface temperature of the steel rail welding joint to 410-470 ℃; (3) and cooling the welded joint of the steel rail in the third stage to reduce the surface temperature of the welded joint of the steel rail to 10-30 ℃. The invention carries out heat treatment by using the welding waste heat without reheating, thereby simplifying the heat treatment process and reducing the cost; the percentage content of martensite structures possibly appearing in the metallographic structure of the steel rail welded joint can be controlled within the range of less than or equal to 3%, and meanwhile, the physical fatigue life of the steel rail joint can reach 250 ten thousand times.

Description

A post-weld heat treatment method for 1100MPa grade low alloy heat treated rail

technical field

The invention relates to the technical field of railway steel rail manufacturing, in particular to a post-weld heat treatment method for a 1100 MPa low-alloy heat-treated steel rail.

Background technique

With the continuous improvement of my country's high-speed railway network, the existing passenger and freight trunk lines will gradually undergo heavy-duty transformation. Large capacity, large axle load, and high density are the future development directions of heavy-duty railways. The rapid development of railways has put forward higher requirements for the service performance of steel rails, and ordinary carbon steel rails have been unable to meet the needs of railway speed-up and heavy-duty transportation.

There are usually two ways to strengthen rails: heat treatment and alloying. Heat treatment is the most economical and effective way to improve the performance of rails. The advantage of alloying is that the production process is simple, and it is generally delivered in a hot-rolled state, saving heat energy. Studies have shown that the use of alloy strengthening alone can produce rails with higher strength, but lower plasticity and toughness. The combination of low alloy and heat treatment can produce high-strength rails with higher strength grades and better plasticity and toughness. Based on the rail on-line heat treatment technology, with low content of alloying elements, a low-alloy heat-treated rail with a tensile strength of 1100 MPa can be produced. Medium axle load freight and mixed passenger and freight railways.

The addition of alloying elements in the rail steel increases the stability of the supercooled austenite, shifts the CCT curve to the right, and improves the hardenability significantly. Therefore, when the production process is not strictly controlled or the cooling rate is not controlled properly, when cooling at the usual cooling rate or even air cooling, the critical cooling rate for the component segregation region also exceeds the critical cooling rate to form martensite, which cannot be ignored in the production of alloy rails. The problem. Limited by the steelmaking process, steel homogeneity, cleanliness and other factors, local segregation of rail steel is inevitable. Due to segregation, the chemical composition of each microscopic region is different, resulting in different Ms points, resulting in different synchronicity of martensite transformation, and martensite is formed in some regions. At the same time, these segregation will lead to the formation of martensite due to segregation in the rail under the action of welding thermal cycle. Even though the final cooling temperature during the rapid cooling of rail post-weld heat treatment is higher than the Ms (martensitic transformation start temperature) temperature of the rail steel, the CCT curve is shifted to the right due to the existence of local segregation, resulting in the formation of martensite. Therefore, for rails with component segregation, reasonable control of the cooling rate and final cooling temperature during the post-weld heat treatment cooling process can help reduce or even avoid the influence of segregated martensite on the service performance of rail joints.

At this stage, mobile flash welding of rails has become the mainstream rail on-line welding technology in railway construction sites at home and abroad. For two rails with different strength grades and materials, the difference between the performance of the base metal brings great challenges to the welding. . At the same time, after the rail is subjected to the welding thermal cycle, the hardened layer in the welded area disappears and a wide low-hardness area is formed on both sides of the weld, resulting in the hardness of the weld and the heat-affected zone being lower than that of the rail base metal. During the service process of the rail, it is easy to preferentially form "saddle" wear on the rail head tread of the welded joint, which not only increases the wheel-rail impact, but also seriously affects the service life of the rail, and even endangers the driving safety. Therefore, how to restore the mechanical properties of the rails reduced by welding has become the premise for the application of the rails.

Chinese patent CN106544933A discloses a post-weld heat treatment method for a hypereutectoid rail and a PG4 heat-treated eutectoid pearlitic rail welded joint. The method includes first cooling the welded joint to be cooled to below 400°C, and then The rail welded joint after the first cooling is heated to 860-930°C, and then the second cooling is performed until the tread temperature of the rail welded joint is 410-450°C. The dissimilar rail welded joints obtained by this method can meet the test requirements for fatigue, tensile, impact and static bending tests in the current domestic railway industry standard TB/T1632.2-2014 "Rail Welding Part 2: Flash Welding"; but The above invention involves the post-weld normalizing heat treatment process of the rail, and it is necessary to use the rail post-weld heat treatment equipment to locally heat the rail welded joint, which is not only complicated in operation and implementation, but also high in cost. It should be pointed out that this patent involves the post-weld normalizing heat treatment process of the rail. Since the welding area of the rail is reheated to above the austenitizing temperature during the heating process, it is not necessary to consider the influence of the welding process on the microstructure and properties of the rail joint. . However, it is necessary to use the rail post-weld heat treatment equipment to locally heat the rail welded joints, and the operation and implementation process is complicated and the cost is high.

Chinese patent CN103898310A discloses a method for heat treatment of bainitic rail welded joints, the method includes first cooling the welded joints of bainitic rails to be cooled to a first temperature not higher than 450°C, The first cooled welded joint is then heated to a second temperature, which is higher than the first temperature and not higher than 510°C, followed by a second cooling. The method is mainly a post-weld heat treatment process for welded joints of bainitic steel rails, wherein the cooling starting temperature of the bainitic steel rail is 1300-1380° C., and the cooling ending temperature after the second cooling is room temperature. However, it should be noted that the bainitic steel rails involved in the above patents and the hypoeutectoid steel rails involved in the present application have different composition systems, and have completely different metallographic structure and mechanical properties. In addition, the above-mentioned patent also involves the post-weld normalizing heat treatment process of the rail. It is necessary to use the rail post-weld heat treatment equipment to locally heat and cool the welded joint of the rail, which is not only complicated in the operation and implementation process, but also high in cost.

Therefore, in the field of railway engineering, there is an urgent need for a post-weld heat treatment method that can effectively improve the longitudinal section hardness of low-alloy heat-treated rail welded joints, so as to improve the service performance of rail welded joints and ensure the safety of railway operation.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the problems existing in the prior art that the heat treatment method for rail welded joints has complicated operation process, high cost, poor mechanical properties of welded joints after heat treatment, and short physical fatigue life of rail joints. The post-weld heat treatment method for 1100MPa low-alloy heat-treated rail is heat-treated for 1100MPa-grade low-alloy heat-treated rail welded joints. The heat treatment cost is low, and the mechanical properties of the welded joints after heat treatment are good.

In order to achieve the above purpose, the present invention provides a post-weld heat treatment method for a 1100MPa-level low-alloy heat-treated rail, the method comprising the following steps:

(1) The first-stage cooling is performed on the rail welded joints formed by welding with a residual temperature of 1150-1300 °C, so that the surface temperature of the rail welded joints is reduced to 580-640 °C. The first-stage cooling method is natural in the air. Cooling, the cooling rate is 6.5-8.0℃/s;

(2) The second-stage cooling of the rail welded joint is carried out to reduce the surface temperature of the rail welded joint to 410-470°C. The second-stage cooling adopts the rail head profiling cooling device for cooling, and the cooling medium is compressed air or Water mist mixture, the cooling rate is 1.2-2.8℃/s;

(3) The rail welded joint is cooled in the third stage, so that the surface temperature of the rail welded joint is reduced to 10-30°C. The third stage cooling is to use the rail head profiling cooling device for cooling, and the cooling medium is compressed air. Or water mist mixture, the cooling rate is 0.2-0.6℃/s;

Wherein, the tensile strength of the rail base material of the rail welded joint is 1100MPa, and the chemical composition of the rail base material includes 0.65-0.72 wt % C, 0.9-1.1 wt % Si, 1.05-1.2 wt % % Mn, 0.5-0.7 wt% Cr, ≤0.02 wt% P, ≤0.02 wt% S, ≤0.01 wt% V, balance Fe and inevitable impurities.

Preferably, in step (1), the rail welding joint is formed by welding with a rail moving flash welder.

Preferably, in step (1), the first-stage cooling is performed on the welded joint of the rail with a residual temperature of 1200-1250° C. obtained by welding.

Preferably, in step (1), the cooling rate of the first stage cooling is 7-7.5°C/s.

Preferably, when the second stage cooling is performed in step (2), the distance between the profile cooling device of the rail head and the tread surface of the rail head is 20-30 mm.

Preferably, when the second stage cooling is performed in step (2), the pressure of the compressed air or water-mist mixture sprayed by the rail head profile cooling device is 0.2-0.4 MPa.

Preferably, in step (2), the cooling rate of the second stage cooling is 2-2.5°C/s.

Preferably, in step (3), the rail welded joint is cooled in the third stage to reduce the surface temperature of the rail welded joint to 20-25°C.

Preferably, when the third stage cooling is performed in step (3), the distance between the profile cooling device of the rail head and the tread surface of the rail head is 20-30 mm.

Preferably, when the third stage cooling is performed in step (3), the pressure of the compressed air or water-mist mixture sprayed by the rail head profile cooling device is 0.04-0.15MPa.

More preferably, when the third stage cooling is performed in step (3), the pressure of the compressed air or water-mist mixture sprayed by the rail head profile cooling device is 0.06-0.1 MPa.

Compared with the current technology, the present invention has the following advantages:

(1) The present invention utilizes the welding residual heat of the welded joint to perform heat treatment, and does not require reheating during the heat treatment process, thus simplifying the heat treatment process and reducing the cost.

(2) The present invention can ensure that the longitudinal average hardness of the rail joint within the range of ±20mm from the center of the weld meets the range of ±30HV of the average hardness of the corresponding rail base metal (excluding the centerline of the decarburized weld: affected by the high temperature of the rail welding , the center of the weld is decarburized and the element is burnt, resulting in low hardness), and the width of the softening zone on both sides of the joint weld is not greater than 15mm, which can improve the rail in the line service process due to the low hardness of the welded area. Rail joint "saddle" wear. At the same time, the percentage content of martensite structure that may appear in the metallographic structure of the rail welded joint can be controlled within the range of ≤3%, which is helpful to control the martensite formed due to the segregation of alloy elements. At the same time, the physical fatigue life of rail joints can reach 2.5 million times, which helps to ensure the safety of railway operation.

In addition, both the present invention and Chinese patent CN110016544A involve a cooling method of three-step cooling after rail flash welding. However, it should be pointed out that the present invention is significantly different from the Chinese patent CN110016544A, and the specific comparison is shown in Table A.

Table A Comparison of this application and Chinese patent CN110016544A

As can be seen from the results of Table A, the present invention and Chinese patent CN110016544A are both the process of performing heat treatment on the rail joint with the welding residual heat as the heat source for the rail joint with higher welding residual temperature, but the rail materials in the two documents are different, and the cooling process is different. , resulting in different microstructure changes and performance of rail joints, that is, different implementation effects. Therefore, the present invention is significantly different from the Chinese patent CN110016544A.

Description of drawings

Fig. 1 is the longitudinal hardness effect diagram of the position 3-5mm below the rail head tread of the low-alloy heat-treated steel rail welded joint obtained by the method in Example 1;

Fig. 2 is the longitudinal hardness effect diagram of the position 3-5mm below the rail head tread of the low-alloy heat-treated steel rail welded joint under the post-weld heat treatment condition obtained by the method in Example 2;

Fig. 3 is the longitudinal hardness effect diagram at the position 3-5mm below the rail head tread of the low-alloy heat-treated steel rail welded joint obtained by the method in Comparative Example 1 under the condition of air cooling after welding;

Fig. 4 is the longitudinal hardness effect diagram at the position 3-5mm below the rail head tread of the low-alloy heat-treated steel rail welded joint under the post-weld heat treatment condition obtained by the method in Comparative Example 2;

Fig. 5 is the longitudinal hardness effect diagram at the position 3-5mm below the rail head tread of the low-alloy heat-treated steel rail welded joint under the post-weld heat treatment condition obtained by the method in Comparative Example 3;

Fig. 6 is the longitudinal hardness effect diagram at the position 3-5mm below the rail head tread of the low-alloy heat-treated steel rail welded joint under the post-weld heat treatment condition obtained by the method in Comparative Example 4;

Fig. 7 is the longitudinal hardness effect diagram of the position 3-5mm below the rail head tread of the low-alloy heat-treated steel rail welded joint under the post-weld heat treatment condition obtained by the method in Comparative Example 5;

8 is a schematic diagram of the position of the longitudinal hardness detection point at a position 3-5 mm below the rail head tread of the rail welded joint according to the present invention;

9 is a schematic diagram of the sampling position of the metallographic sample of the rail head tread of the rail welded joint according to the present invention;

Fig. 10 is the schematic diagram of the profile cooling device of the rail head according to the present invention;

Fig. 11 is the bottom schematic diagram of the profile cooling device of the rail head used in the present invention.

Description of reference numerals

1 medium channel; 2 top nozzle; 3 medium channel; 4 side nozzle; a recrystallization zone; b rail head tread; c welding seam; d metallographic test inspection surface.

Detailed ways

The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, but not to limit the present invention.

The endpoints of ranges and any values disclosed herein are not limited to the precise ranges or values, which are to be understood to encompass values proximate to those ranges or values. For ranges of values, the endpoints of each range, the endpoints of each range and the individual point values, and the individual point values can be combined with each other to yield one or more new ranges of values that Ranges should be considered as specifically disclosed herein.

In the previous research, the inventor found that the critical cooling rate of martensitic transformation during continuous cooling and transformation of a 1100MPa grade low-alloy heat-treated rail steel involved in the present invention is about 1.5-2.5°C/s, and the Ms temperature (the martensitic structure begins forming temperature) about 230-280°C. Usually, in order to avoid abnormal structures such as martensite and bainite in rail welded joints, when post-weld heat treatment is performed on rail welded joints, the final cooling temperature in the rapid cooling process of rail post-weld heat treatment should be controlled above the Ms temperature of the rail. Including the use of a cooling rate higher than the critical cooling rate of the martensitic transformation of the rail steel to rapidly cool the rail joints above the austenitizing temperature, the final cooling temperature should be controlled above the Ms temperature of the rail steel, and the subsequent cooling rate should be low. Critical cooling rate for martensitic transformation of rail steel. Otherwise, the joint will suffer premature fatigue fracture due to a large amount of hardened martensite. Without considering the composition segregation of the rail, when the rail joint above the austenitizing temperature is rapidly cooled to the temperature below Ms using a cooling rate lower than the critical cooling rate of the martensitic transformation of the rail steel, the rail joint still does not contain Martensite will be formed. Therefore, the rail welding standard, such as the Australian Rail Welding Standard AS1085.20-2012, stipulates that for some high-strength grades, high carbon content and high alloy content rails, under the observation magnification of metallographic microscope 100X, for rail welded joints In the most serious area where middle martensite appears, the percentage of martensite structure should not be higher than 5%, otherwise the joint will cause premature fatigue fracture due to a large amount of hardened martensite structure, which will seriously affect the safety of railway operation. Therefore, strictly controlling the martensite content in the welded structure of the rail is very important for the stable operation of the railway line. Based on the above findings, the inventors have completed the present invention.

It should be noted that the thickness of the rail waist and the bottom of the rail is relatively thin, and the temperature drops rapidly during the cooling process. At the same time, the rail waist region is usually the region with the most serious rail segregation, and the martensitic structure is also the easiest to form in the rail waist. In order to avoid the deterioration of the service performance of the rail welded joint due to a large amount of brittle and hard martensite structure, the post-weld heat treatment of the rail is only carried out on the rail head tread of the rail joint and the side of the rail head adjacent to it, while the rail waist and rail bottom of the rail joint are not treated. Implement natural cooling.

The post-weld heat treatment method for a 1100MPa-level low-alloy heat-treated rail provided by the present invention includes the following steps:

(1) The first-stage cooling is performed on the rail welded joints formed by welding with a residual temperature of 1150-1300 °C, so that the surface temperature of the rail welded joints is reduced to 580-640 °C. The first-stage cooling method is natural in the air. Cooling, the cooling rate is 6.5-8.0℃/s;

(2) The second-stage cooling of the rail welded joint is carried out to reduce the surface temperature of the rail welded joint to 410-470°C. The second-stage cooling adopts the rail head profiling cooling device for cooling, and the cooling medium is compressed air or Water mist mixture, the cooling rate is 1.2-2.8℃/s;

(3) The rail welded joint is cooled in the third stage, so that the surface temperature of the rail welded joint is reduced to 10-30°C. The third stage cooling is to use the rail head profiling cooling device for cooling, and the cooling medium is compressed air. Or water mist mixture, the cooling rate is 0.2-0.6℃/s.

In the present invention, the tensile strength of the rail base material of the rail welded joint is 1100 MPa, and the chemical composition of the rail base material includes 0.65-0.72 wt% C, 0.9-1.1 wt% Si, 1.05- 1.2 wt% Mn, 0.5-0.7 wt% Cr, ≤0.02 wt% P, ≤0.02 wt% S, ≤0.01 wt% V, balance Fe and inevitable impurities.

In the method of the present invention, the structure of the rail head profiling cooling device described in steps (2) and (3) is shown in Figures 10-11, including a medium channel 1, a top nozzle 2, a medium channel 3 and side nozzle 4, the medium channel 1 is connected with the top nozzle 2, and the medium channel 3 is connected with the side nozzle 4. The device only cools the rail head tread and the side surface of the rail head, and the shape and size of the aperture can be designed, processed and modified according to actual needs, so as to achieve different cooling intensities. The pressure of the medium flowing through the medium channel 1 and the medium channel 3 can be monitored by relevant pressure detection devices, and the medium pressure can be adjusted according to actual needs.

In the present invention, an infrared thermometer is used to collect the temperature signal of the tread of the rail head, and the tread of the rail head is the contact part between the wheel and the rail; the hardness value corresponding to the softening zone width measurement line in the longitudinal hardness curve of the rail joint is the hardness value The hardness after subtracting 25HV from the average hardness Hp of the rail base metal; the softening zone width in the hardness curve is the intercept of the hardness curve and the softening zone width measurement line.

In the present invention, unless otherwise stated, the "rail welded joint" is a region with a length of 60-80 mm including the weld and/or the heat-affected zone obtained by welding, and the center of the region is Welds for rails.

The method of the invention heat-treats the welded joints of 1100MPa grade low-alloy heat-treated rails. The method adopts a three-stage cooling process to treat the welded joints, and reduces the surface temperature of the welded joints of the rails to a suitable temperature during each stage of cooling. Reasonably control the cooling rate of each stage of the cooling process, and adopt appropriate cooling devices and appropriate cooling methods, so as to effectively improve the longitudinal section hardness of low-alloy heat-treated rail welded joints, improve the service performance of rail welded joints, and ensure the safety of railway operation.

The invention implements accelerated cooling after welding for the rail joints with high residual temperature obtained by welding, so as to reduce the phase transition temperature of the joint rail head from austenite to pearlite and improve the hardness of the austenite recrystallization zone. Based on the principle of metallology, there is a certain degree of dynamic undercooling of rail joints under the condition of rapid cooling at high temperature after welding, which causes the phase transition temperature of austenite to pearlite to move down in the non-equilibrium state, and with the increase of the degree of undercooling large, the phase transition temperature gradually decreases. It should be pointed out that the temperature measurement process of the infrared thermometer is only carried out on the surface of the rail head tread, and the temperature of the rail core is usually 50-80°C higher than the surface under the action of rapid cooling. Even when the rail surface temperature is lower than the transformation temperature, since the core temperature is still high, the transformation process can still occur. Therefore, the microstructure transformation from austenite to pearlite can still occur in the joint rail head even in the second stage cooling with relatively low cooling temperature. In the present invention, the first cooling is natural cooling in the air, and the cooling speed of the first stage can be controlled by adjusting the temperature of the test environment (such as using a central air conditioner to control the temperature), and the setting of the welding machine can be adjusted. Or manual operation to control the final cooling temperature of the first cooling of the rail welded joint at 580-640°C. The cooling temperature of the second cooling is 580-640°C. In the present invention, the final cooling temperature of the second cooling is 410-470° C. above the Ms temperature of the rail steel. When the rail joint is cooled in the third stage, in order to avoid a large amount of hardened martensite in the joint, the present invention selects a cooling rate of 0.2-0.6°C/s lower than the critical cooling rate of martensitic transformation of the rail steel. cool down.

In the metallographic principle, the martensitic structure of the steel is the steel above the austenitizing temperature, and the cooling rate is higher than the critical cooling rate of the martensitic transformation to (the starting temperature of the martensitic structure) The temperature below Ms. product. In the present invention, in order to avoid the generation of a large amount of brittle and hard martensite in the rail joint, when the post-weld heat treatment is performed on the rail joint, the final cooling temperature in the rapid cooling process of the post-weld heat treatment is controlled at the Ms temperature of the rail steel in the second cooling stage. above. When the joint is heat treated with a cooling rate higher than the critical cooling rate for martensite formation of the rail steel in the second cooling stage, since the final cooling temperature in this stage is higher than the Ms temperature of the rail steel and the cooling rate in the third cooling stage is in the The rail steel martensite is formed below the critical cooling rate. Although there is inevitable element segregation during rail welding, due to the high final cooling temperature in the post-weld heat treatment cooling process, only a small amount of martensite is generated. When the percentage of martensite is less than 5% and the distribution is dispersed (under the observation condition of metallographic microscope at 100X), it will not significantly affect the fatigue life of rail joints. At the same time, the cooling rate of the second cooling stage of the post-weld heat treatment is relatively large, and the large degree of undercooling helps to improve the toughness of the joint, so the fatigue life of the rail joint in the present invention is high.

In the method of the present invention, in step (1), the rail welding joint is formed by welding with a rail moving flash welder.

The present invention utilizes the welding residual heat of the welded joint for heat treatment. In a specific embodiment, the first stage cooling can be performed on the rail welded joints formed by welding with residual temperatures of 1150°C, 1170°C, 1190°C, 1200°C, 1230°C, 1250°C, 1170°C or 1300°C.

In a preferred embodiment, in step (1), the first-stage cooling is performed on the welded joint of the rail with a residual temperature of 1200-1250°C.

In the method of the present invention, it is necessary to reasonably control the cooling temperature and cooling rate during each stage of cooling, so as to improve the longitudinal section hardness of the welded joint of the 1100MPa low-alloy heat-treated rail, and to reduce the possible occurrence of the metallographic structure of the welded joint of the rail. The percentage of martensitic structure is controlled within the range of ≤3%, and at the same time, the fatigue life of rail joints can reach 2.5 million times.

In a specific embodiment, after the first stage cooling, the surface temperature of the rail welded joint can be reduced to 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C and any two of these points. any value in the range that constitutes it.

In a preferred embodiment, after the first stage cooling, the surface temperature of the rail welded joint can be reduced to 600°C-640°C.

In a specific embodiment, in step (1), the cooling rate of the first stage cooling may be 6.5°C/s, 6.7°C/s, 6.9°C/s, 7°C/s, 7.2°C/s, 7.4°C/s °C/s, 7.6 °C/s, 7.8 °C/s or 8.0 °C/s.

In a preferred embodiment, in step (1), the cooling rate of the first stage cooling is 7-7.5°C/s.

In the method of the present invention, in step (2), when the rail welded joint is cooled in the second stage, the surface temperature of the rail welded joint can be reduced to 410° C., 420° C., 430° C., 440° C., 450° C. °C, 460°C, 470°C, and any value in the range formed by any two of these point values.

In a specific embodiment, when the second stage cooling is performed in step (2), the distance between the rail head profile cooling device and the rail head tread can be 20mm, 22mm, 24mm, 26mm, 28mm or 30mm.

In the method of the present invention, when the second-stage cooling is performed in step (2), the pressure of the compressed air or water-mist mixture sprayed by the profiling cooling device is 0.2-0.4MPa; specifically, for example, it can be 0.2 MPa, 0.3MPa, 0.4MPa; preferably, when the second-stage cooling is performed in step (2), the pressure of the compressed air or water-mist mixture sprayed by the profiling cooling device is 0.3MPa.

In a specific embodiment, in step (2), the cooling rate of the second stage cooling may be 1.2°C/s, 1.4°C/s, 1.6°C/s, 1.8°C/s, 2°C/s, 2.2°C/s °C/s, 2.4 °C/s, 2.6 °C/s or 2.8 °C/s.

In a preferred embodiment, in step (2), the cooling rate of the second stage cooling is 2-2.5°C/s.

In a specific embodiment, in step (3), when the rail welded joint is cooled in the third stage, the surface temperature of the rail welded joint can be reduced to 10°C, 14°C, 18°C, 22°C, 24°C, 26°C ℃ or 30℃.

In a preferred embodiment, in step (3), when the rail welded joint is cooled in the third stage, the surface temperature of the rail welded joint is lowered to 20-25°C.

In the method of the present invention, when the third stage cooling is performed in step (3), the distance between the profile cooling device of the rail head and the tread of the rail head can be 20mm, 22mm, 24mm, 26mm, 28mm or 30mm.

In the method of the present invention, when the third stage cooling is performed in step (3), the pressure of the compressed air or water mist mixture sprayed by the rail head profile cooling device is 0.04-0.15MPa; specifically, for example It can be 0.04MPa, 0.06MPa, 0.08MPa, 0.1MPa, 0.12MPa, 0.14MPa or 0.15MPa; preferably, when the third stage cooling is performed in step (3), the compression pressure sprayed by the rail head profiling cooling device The pressure of air or water mist mixture is 0.06-0.1MPa.

Regarding the present invention, it should be noted that the heat treatment technology itself is a process of controlling various factors in the heating and cooling process, and the steps in the heat treatment technology are interrelated and affect each other. This application may unavoidably overlap with other patent documents in process parameters, but the applicable objects and heat treatment implementation equipment are different between each patent, so it is impossible to simply apply and compare data. The chemical composition and heat treatment process of rails developed by various countries in the world inevitably overlap and overlap. Influenced by factors such as smelting capacity, heat treatment equipment, personnel operation level, etc., the applicable objects of each invention patent are different (including the mechanical properties of rails, temperature distribution, etc.) , the adopted cooling device and implementation process are also different, resulting in essential differences, resulting in these processes cannot be simply applied. In addition, according to the continuous cooling characteristics of low-alloy heat-treated rail steel, this application adopts a three-step cooling cooling method (no need for post-weld normalizing heat treatment) to limit the cooling rate and cooling temperature of each cooling stage, and improve the rail in the line service process. The "saddle-type" wear of rail joints is caused by the low hardness of the area, so this application has a significant improvement compared with other patent applications.

The present invention will be described in detail through the following examples, but the protection scope of the present invention is not limited thereto.

In the embodiment of the present invention and the comparative example, the sampling position of the metallographic sample of the rail head tread of the rail welded joint is shown in FIG. 9 . The position of the longitudinal hardness test point 3-5mm below the rail head tread of the rail welded joint is shown in Figure 8. In the figure, a is the recrystallization area, b is the rail head tread, c is the weld seam, and d is the metallographic test inspection surface .

In the embodiment of the present invention and the comparative example, the specification of the 1100MPa grade low-alloy heat-treated steel rail used for welding is 60-75kg/m, and the rail welded joint is a welded joint welded by a rail mobile flash welder using the same welding process. .

The present invention adopts the pulsating bending fatigue test, the load frequency is 5Hz, and the load ratio is 0.2. Determine the maximum and minimum loads according to TB/T 1632.1-2014. The MTS-FT310 fatigue testing machine was used to conduct three-point bending fatigue tests on the welded joints of the rails. The test goal was that the welded joints did not experience fatigue fracture when the cyclic load was loaded for 2.5 million times.

Example 1

After the rail with a specification of 68kg/m has completed the upsetting and push-out during the mobile flash welding process, the welded joint is subjected to post-weld heat treatment. First, the rail joint obtained by welding with a residual temperature of 1250 °C was subjected to the first stage cooling at a first cooling rate of 7.5 °C/s to reduce the surface temperature of the rail head of the rail joint to 640 °C, and then the rail joint was cooled at 2.5 °C. At the second cooling rate of 0.40°C/s, the second-stage cooling was performed to reduce the surface temperature of the rail head of the rail joint to 450°C, and finally the rail joint was subjected to the third-stage cooling at the third cooling rate of 0.40°C/s to reduce the temperature of the rail joint to 450°C. The surface temperature of the rail head is lowered to a room temperature of 25° C., thereby obtaining a rail welded joint that has undergone post-weld heat treatment. In the post-weld heat treatment process, the first stage of cooling is natural cooling in the air; during the second stage of cooling and the third stage of third cooling, the rail head profile cooling device is used to use compressed air as the cooling medium to cool the rail head tread and the rail head of the rail joint. The side of the rail head is cooled, and the cooling device is 30mm away from the rail head tread; in the second stage of cooling, the gas pressure of the compressed air injected by the cooling device is 0.32MPa; in the third stage of cooling, the gas pressure of the compressed air injected by the cooling device The pressure is 0.1MPa. An infrared thermometer is used to monitor the temperature of the rail head tread.

The post-weld heat-treated rail joints obtained in this example were machined into longitudinal hardness specimens. The vertical Vickers hardness test was carried out on the hardness sample by using a Bouvet hardness tester (Shandong Laizhou Testing Machine General Factory, model HBV-30A) at a position 4mm below the rail head tread, with a distance of 2mm as the measuring point. The center is symmetrically arranged to the left and right sides. The Vickers hardness test method is carried out with reference to GB/T4340.1-2009 "Metal Vickers Hardness Test Part 1: Test Method", and the HV scale is used. The hardness test data are shown in Table 1, and the distribution effect of the longitudinal hardness of the joint is shown in Figure 1.

Table 1

It can be seen from Table 1 and Figure 1 that the average hardness of the rail base metal is 411HV. For the rail welded joint treated by the present invention, the longitudinal average hardness of the rail joint within the range of ±20mm from the center of the weld is 387HV, which satisfies the range of ±30HV of the average hardness of the rail base metal (excluding the decarburized weld centerline: subject to Affected by the high temperature of rail welding, the center of the weld is decarburized and the elements are burned, resulting in low hardness). The width of the softening zone on the left side of the joint weld is 8.0mm, the width of the softening zone on the right side of the joint weld is 8.0mm, and the width of the softening zone on both sides of the joint weld is not more than 15.0mm.

Referring to the sampling method shown in Figure 9, in accordance with GB/T13298-2015 "Metal Microstructure Inspection Method", the metallographic structure of the rail joint metallographic sample is tested, and 3% nitric acid alcohol solution is used to carry out the metallographic examination of the rail joint metallographic sample. The metallographic structure of the rail joint was observed with a German Leica MeF3 optical microscope. The results show that under the observation magnification of metallographic microscope at 100X, only a small amount of point-like martensite is produced and the percentage of martensite is 2.0% for the area with the most serious martensite in the heat-affected zone of the joint. At the same time, the fatigue life of rail joints can reach 2.5 million times, which helps to ensure the safety of railway operation.

Example 2

After the upsetting and push-out during the mobile flash welding process of the 60kg/m rail, the welded joints are subjected to post-weld heat treatment. First, the rail joint obtained by welding with a residual temperature of 1200°C was subjected to first-stage cooling at a first cooling rate of 7°C/s to reduce the surface temperature of the rail head of the rail joint to 600°C, and then the rail joint was cooled to 2°C. At the second cooling rate of 0.2°C/s, the second-stage cooling was performed to reduce the surface temperature of the rail head of the rail joint to 430°C, and finally the rail joint was subjected to the third-stage cooling at the third cooling rate of 0.2°C/s to reduce the temperature of the rail joint to 430°C. The surface temperature of the rail head is lowered to a room temperature of 20° C., thereby obtaining a rail welded joint that has undergone post-weld heat treatment. In the post-weld heat treatment process, the first stage cooling is natural cooling in the air; during the second stage cooling and the third stage cooling process, the rail head profiling cooling device is used to use the water mist mixture as the cooling medium to cool the rail of the rail joint. The head tread and the side of the rail head are cooled, and the cooling device is 20mm away from the rail head tread; in the second stage of cooling, the gas pressure of the water mist mixture sprayed by the cooling device is 0.26MPa; in the third stage of cooling, the cooling device sprays The gas pressure of the water mist mixture is 0.04MPa. An infrared thermometer is used to monitor the temperature of the rail head tread.

The post-weld heat-treated rail joints obtained in this example were machined into longitudinal hardness specimens. The vertical Vickers hardness test was carried out on the hardness sample by using a Bouvet hardness tester (Shandong Laizhou Testing Machine General Factory, model HBV-30A) at a position 4mm below the rail head tread, with a distance of 2mm as the measuring point. The center is symmetrically arranged to the left and right sides. The Vickers hardness test method is carried out with reference to GB/T 4340.1-2009 "Metal Vickers Hardness Test Part 1: Test Method", and the HV scale is used. The hardness test data are shown in Table 2, and the distribution effect of the longitudinal hardness of the joint is shown in Figure 2.

Table 2

It can be seen from Table 2 and Figure 2 that the average hardness of the rail base metal is 411HV. For the rail welded joint treated by the present invention, the longitudinal average hardness of the rail joint within the range of ±20mm from the center of the weld is 389HV, which meets the range of ±30HV of the average hardness of the rail base metal (excluding the decarburized weld centerline: subject to Affected by the high temperature of rail welding, the center of the weld is decarburized and the elements are burned, resulting in low hardness). The width of the softening zone on the left side of the joint is 8.0mm, the width of the softening zone on the right side is 8.0mm, and the width of the softening zone on both sides of the joint weld is not more than 15.0mm.

Referring to the sampling method shown in Figure 9, in accordance with GB/T 13298-2015 "Metal Microstructure Test Method", the metallographic structure of the rail joint sample is tested, and 3% nitric acid alcohol solution is used for the metallographic sample of the rail joint. Etching was carried out, and the metallographic structure of the rail joint was observed with a German Leica MeF3 optical microscope. The results show that under the observation magnification of metallographic microscope at 100X, only a small amount of point-like martensite is produced and the percentage of martensite is only 2.5% for the area with the most serious martensite in the heat-affected zone of the joint. At the same time, the fatigue life of rail joints can reach 2.5 million times, which helps to ensure the safety of railway operation.

Comparative Example 1

After the rail with a specification of 68kg/m completes the upsetting and push-out during the mobile flash welding process, the rail joint with a residual temperature of 1100°C is directly air-cooled to room temperature (about 25°C), so as to obtain the air-cooled (natural cooling) condition. Rail welded joints.

Take the rail joints obtained in this comparative example under the condition of air cooling after welding and process them into longitudinal hardness samples. The vertical Vickers hardness test was carried out on the hardness samples with a Bwe hardness tester (Shandong Laizhou Testing Machine General Factory, model HBV-30A) at a position 5mm below the rail head tread, and the distance between the measuring points was 2mm. The center is symmetrically arranged to the left and right sides. The Vickers hardness test method is carried out with reference to GB/T4340.1-2009 "Metal Vickers Hardness Test Part 1: Test Method", and the HV scale is used. The hardness test data is shown in Table 3, and the distribution effect of the longitudinal hardness of the joint is shown in Figure 3.

table 3

As can be seen from Table 3 and Fig. 3, the average hardness of the base metal is 411HV. For the rail welded joint not treated by the post-weld heat treatment method provided by the present invention, compared with the hardness of the rail base metal on both sides of the weld, the entire welded area is in a softened state. The average longitudinal hardness of the rail joint within the range of ±20mm from the center of the weld is 356HV, which cannot meet the range of ±30HV of the average hardness of the corresponding rail base metal (excluding the centerline of the decarburized weld: affected by the high temperature of the rail welding, welding Decarburization in the center of the seam and element burning, resulting in low hardness). The width of the softening zone on the left side of the joint weld is 18.0mm, and the width of the softening zone on the right side of the joint weld is 18.0mm. During the service process of the line, the welded joint obtained from this comparative example is prone to preferentially form a low-sloughing of the rail head tread in the softening area of the joint, resulting in "saddle-shaped" wear and affecting the smoothness of the line and the driving safety.

Referring to the sampling method shown in Figure 9, in accordance with GB/T13298-2015 "Metal Microstructure Inspection Method", the metallographic structure of the rail joint metallographic sample is tested, and 3% nitric acid alcohol solution is used to carry out the metallographic examination of the rail joint metallographic sample. The metallographic structure of the rail joint was observed with a German Leica MeF3 optical microscope. The results show that the metallographic structure of the joint is normal, and there is no abnormal structure such as martensite and bainite. In this comparative example, the fatigue life of the rail joint is only 1.5 million times.

Comparative Example 2

After the upsetting and push-out during the mobile flash welding process of the 75kg/m rail, the welded joints are subjected to post-weld heat treatment. First, the rail joint obtained by welding with a residual temperature of 1200°C was subjected to first-stage cooling at a first cooling rate of 6°C/s to reduce the surface temperature of the rail head of the rail joint to 720°C, and then the rail joint was cooled to 2.8°C. At the second cooling rate of 0.2°C/s, the second-stage cooling was performed to reduce the surface temperature of the rail head of the rail joint to 180°C, and finally the rail joint was subjected to the third-stage cooling at the third cooling rate of 0.2°C/s to reduce the temperature of the rail joint to 180°C. The surface temperature of the rail head is lowered to a room temperature of 30° C., thereby obtaining the rail welded joint of the present invention that has undergone post-weld heat treatment. During the post-weld heat treatment, the first stage cooling is natural cooling in the air; during the second stage cooling and the third stage cooling process, the rail head profile cooling device is used to use compressed air as the cooling medium to the rail head tread of the rail joint. and the side of the rail head for cooling, and the cooling device is 30mm away from the rail head tread; in the second stage of cooling, the gas pressure of the compressed air injected by the cooling device is 0.4MPa; in the third stage of cooling, the compressed air injected by the cooling device The gas pressure was 0.04MPa. An infrared thermometer is used to monitor the temperature of the rail head tread.

Take the rail joints obtained in this comparative example under the condition of air cooling after welding and process them into longitudinal hardness samples. The vertical Vickers hardness test was carried out on the hardness sample by using a Bouvet hardness tester (Shandong Laizhou Testing Machine General Factory, model HBV-30A) at a position 4mm below the rail head tread, with a distance of 2mm as the measuring point. The center is symmetrically arranged to the left and right sides. The Vickers hardness test method is carried out with reference to GB/T4340.1-2009 "Metal Vickers Hardness Test Part 1: Test Method", and the HV scale is used. The hardness test data are shown in Table 4, and the distribution effect of the longitudinal hardness of the joint is shown in Figure 4.

Table 4

It can be seen from Table 4 and Figure 4 that for the rail welded joints not treated by the post-weld heat treatment method provided by the present invention, the width of the softening zone on the left side of the obtained joint is 9.0mm, and the width of the softening zone on the right side is 9.0mm. The width of the softening zone on both sides of the weld shall not be greater than 15.0mm.

Referring to the sampling method shown in Figure 9, in accordance with GB/T 13298-2015 "Metal Microstructure Test Method", the metallographic structure of the rail joint sample is tested, and 3% nitric acid alcohol solution is used for the metallographic sample of the rail joint. Etching was carried out, and the metallographic structure of the rail joint was observed with a German Leica MeF3 optical microscope. Metallographic examination showed that a large amount of hardened martensitic structure appeared in the heat affected zone on the left and right sides of the joint weld. The results show that under the observation magnification of metallographic microscope at 100X, the percentage of martensite structure reaches 8% for the most serious area where martensite structure appears. In this comparative example, the fatigue life of the rail joint is only 1.8 million times, which is not conducive to the safety of railway operation.

Comparative Example 3

After the upsetting and push-out during the mobile flash welding process of the 75kg/m rail, the welded joints are subjected to post-weld heat treatment. First, the rail joint obtained by welding with a residual temperature of 1200°C was subjected to first-stage cooling at a first cooling rate of 7.0°C/s to reduce the surface temperature of the rail head of the rail joint to 680°C, and then the rail joint was cooled at 4°C. At the second cooling rate of 3°C/s, the second stage cooling is performed to reduce the surface temperature of the rail head of the rail joint to 350°C, and finally the rail joint is subjected to the third stage cooling at the third cooling rate of 3°C/s to reduce the temperature of the rail joint to 350°C. The surface temperature of the rail head is lowered to a room temperature of 25° C., thereby obtaining the rail welded joint of the present invention that has undergone post-weld heat treatment. In the post-weld heat treatment process, the first cooling is natural cooling in the air; during the second and third stages of cooling, the rail head profile cooling device is used to use compressed air as the cooling medium to cool the rail head tread and the rail head of the rail joint. The side of the rail head is cooled, and the cooling device is 30mm away from the rail head tread; in the second stage of cooling, the gas pressure of the compressed air injected by the cooling device is 0.6MPa; in the third stage of cooling, the gas pressure of the compressed air injected by the cooling device The pressure was 0.44MPa. An infrared thermometer is used to monitor the temperature of the rail head tread.

Take the rail joints obtained in this comparative example under the condition of air cooling after welding and process them into longitudinal hardness samples. The vertical Vickers hardness test was carried out on the hardness sample by using a Bouvet hardness tester (Shandong Laizhou Testing Machine General Factory, model HBV-30A) at a position 4mm below the rail head tread, with a distance of 2mm as the measuring point. The center is symmetrically arranged to the left and right sides. The Vickers hardness test method is carried out with reference to GB/T4340.1-2009 "Metal Vickers Hardness Test Part 1: Test Method", and the HV scale is used. The hardness test data are shown in Table 5, and the distribution effect of the longitudinal hardness of the joint is shown in Figure 5.

table 5

It can be seen from Table 5 and Figure 5 that the average hardness of the rail base metal is 411HV. For the rail welded joint not treated by the post-weld heat treatment method provided by the present invention, the width of the softening zone on the left side of the obtained joint weld is 14.0mm, and the width of the softening zone on the left side of the joint weld is 14.0mm. The width of the softening zone on the side is not more than 15.0mm.

Referring to the sampling method shown in Figure 9, in accordance with GB/T 13298-2015 "Metal Microstructure Test Method", the metallographic structure of the rail joint sample is tested, and 3% nitric acid alcohol solution is used for the metallographic sample of the rail joint. Etching was carried out, and the metallographic structure of the rail joint was observed with a German Leica MeF3 optical microscope. Metallographic examination showed that a large amount of hardened martensitic structure appeared in the heat affected zone on the left and right sides of the joint weld. The results show that under the observation magnification of metallographic microscope at 100X, the percentage of martensite structure reaches 10% for the most serious area where martensite structure appears. In this comparative example, the fatigue life of the rail joint is only 800,000 times, which is not conducive to the safety of railway operation.

Comparative Example 4

According to the method of Example 1, the difference is that the second-stage cooling reduces the surface temperature of the rail head of the rail joint to 350°C.

Take the rail joints obtained in this comparative example under the condition of air cooling after welding and process them into longitudinal hardness samples. The vertical Vickers hardness test was carried out on the hardness sample by using a Bouvet hardness tester (Shandong Laizhou Testing Machine General Factory, model HBV-30A) at a position 4mm below the rail head tread, with a distance of 2mm as the measuring point. The center is symmetrically arranged to the left and right sides. The Vickers hardness test method is carried out with reference to GB/T4340.1-2009 "Metal Vickers Hardness Test Part 1: Test Method", and the HV scale is used. The hardness test data is shown in Table 6, and the distribution effect of the longitudinal hardness of the joint is shown in Figure 6.

Table 6

It can be seen from Table 6 and Figure 6 that the average hardness of the rail base metal is 411HV. For the rail welded joint treated by the post-weld heat treatment method provided in this comparative example, the width of the softening zone on the left side of the obtained joint weld is 8.0mm, and the width of the softening zone on the left side of the joint weld is 8.0mm. The width of the softening zone on the side is not more than 15.0mm.

Referring to the sampling method shown in Figure 9, in accordance with GB/T 13298-2015 "Metal Microstructure Test Method", the metallographic structure of the rail joint sample is tested, and 3% nitric acid alcohol solution is used for the metallographic sample of the rail joint. Etching was carried out, and the metallographic structure of the rail joint was observed with a German Leica MeF3 optical microscope. Metallographic examination showed that a large amount of hardened martensitic structure appeared in the heat affected zone on the left and right sides of the joint weld. The results show that under the observation magnification of metallographic microscope at 100X, the percentage of martensite structure reaches 8% for the most serious area where martensite structure appears. In this comparative example, the fatigue life of the rail joint is only 1.6 million times, which is not conducive to the safety of railway operation.

Comparative Example 5

According to the method of Example 1, the difference is that the cooling rate of the first stage cooling is 5.5°C/s.

Take the rail joints obtained in this comparative example under the condition of air cooling after welding and process them into longitudinal hardness samples. The vertical Vickers hardness test was carried out on the hardness sample by using a Bouvet hardness tester (Shandong Laizhou Testing Machine General Factory, model HBV-30A) at a position 4mm below the rail head tread, with a distance of 2mm as the measuring point. The center is symmetrically arranged to the left and right sides. The Vickers hardness test method is carried out with reference to GB/T4340.1-2009 "Metal Vickers Hardness Test Part 1: Test Method", and the HV scale is used. The hardness test data are shown in Table 7, and the distribution effect of the longitudinal hardness of the joint is shown in Figure 7.

Table 7

It can be seen from Table 7 and Fig. 7 that the average hardness of the rail base metal is 411HV. For the rail welded joints treated in this comparative example, the longitudinal average hardness of the rail joints within ±20mm from the center of the weld is 378HV, which cannot meet the range of ±30HV of the average hardness of the rail base metal (excluding the decarburized weld centerline : Affected by the high temperature of rail welding, the center of the weld is decarburized and the element is burned, resulting in low hardness). The width of the softening zone on the left side of the joint weld is 12.0mm, the width of the softening zone on the right side of the joint weld is 12.0mm, and the width of the softening zone on both sides of the joint weld is not greater than 15.0mm.

Referring to the sampling method shown in Figure 9, in accordance with GB/T13298-2015 "Metal Microstructure Inspection Method", the metallographic structure of the rail joint metallographic sample is tested, and 3% nitric acid alcohol solution is used to carry out the metallographic examination of the rail joint metallographic sample. The metallographic structure of the rail joint was observed with a German Leica MeF3 optical microscope. The results show that under the observation magnification of metallographic microscope at 100X, only a small amount of point-like martensite is produced and the percentage of martensite is 2.0% for the area with the most serious martensite in the heat-affected zone of the joint. Meanwhile, the fatigue life of the rail joint is 1.8 million cycles. In this comparative example, the hardness and fatigue life of the rail joint within ±20mm from the center of the weld are low.

By comparing the longitudinal hardness of the rail head tread of the welded joint and the width of the joint softening zone in Fig. 1 to Fig. 7 and Table 1 to Table 7, it can be seen that the post-weld heat treatment method for the hypoeutectoid rail joint is carried out by using the post-weld heat treatment method provided by the present invention. , the longitudinal average hardness of the rail joint in the area of ±20mm from the center of the weld can meet the range of ±30HV of the average hardness of the corresponding rail base metal (excluding the centerline of the decarburized weld: affected by the high temperature of the rail welding, the center of the weld is removed carbon and element burning loss, resulting in low hardness), and the width of the softening zone on both sides of the joint weld is not more than 15.0mm. At the same time, the percentage content of martensitic structure that may appear in the metallographic structure of the rail welded joint can be controlled within the range of ≤3%. At the same time, the fatigue life of rail joints can reach 2.5 million times, which helps to ensure the safety of railway operation.

The preferred embodiments of the present invention have been described above in detail, however, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, a variety of simple modifications can be made to the technical solutions of the present invention, including combining various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as the content disclosed in the present invention. All belong to the protection scope of the present invention.

Claims (10)

1. a 1100MPa grade low-alloy heat treatment rail post-weld heat treatment method, is characterized in that, the method comprises the following steps: (1) The first-stage cooling is performed on the rail welded joints formed by welding with a residual temperature of 1150-1300 °C, so that the surface temperature of the rail welded joints is reduced to 580-640 °C. The first-stage cooling method is natural in the air. Cooling, the cooling rate is 6.5-8.0℃/s; (2) The second-stage cooling of the rail welded joint is carried out to reduce the surface temperature of the rail welded joint to 410-470°C. The second-stage cooling adopts the rail head profiling cooling device for cooling, and the cooling medium is compressed air or Water mist mixture, the cooling rate is 1.2-2.8℃/s; (3) The rail welded joint is cooled in the third stage, so that the surface temperature of the rail welded joint is reduced to 10-30°C. The third stage cooling is to use the rail head profiling cooling device for cooling, and the cooling medium is compressed air. Or water mist mixture, the cooling rate is 0.2-0.6℃/s; Wherein, the tensile strength of the rail base material of the rail welded joint is 1100MPa, and the chemical composition of the rail base material includes 0.65-0.72 wt % C, 0.9-1.1 wt % Si, 1.05-1.2 wt % % Mn, 0.5-0.7 wt% Cr, ≤0.02 wt% P, ≤0.02 wt% S, ≤0.01 wt% V, balance Fe and inevitable impurities. 2 . The method according to claim 1 , wherein, in step (1), the rail welded joint is formed by welding with a rail moving flash welder. 3 . 3 . The method according to claim 2 , wherein in step (1), the first-stage cooling is performed on the welded joint of the rail with a residual temperature of 1200-1250° C. 3 . 4 . The method according to claim 3 , wherein, in step (1), the cooling rate of the first stage cooling is 7-7.5° C./s. 5 . 5 . The method according to claim 1 , wherein when the second stage cooling is performed in step (2), the distance between the rail head profile cooling device and the rail head tread is 20-30 mm. 6 . 6. method according to claim 5, is characterized in that, when carrying out the second stage cooling in step (2), the pressure of the compressed air or the water-mist mixture sprayed out by the rail head profiling cooling device is 0.2-0.4 MPa. 7. The method according to claim 5, characterized in that, in step (2), the cooling rate of the second-stage cooling is 2-2.5°C/s. 8. The method according to claim 1, characterized in that, in step (3), the rail welded joint is cooled in a third stage to reduce the surface temperature of the rail welded joint to 20-25°C. 9 . The method according to claim 7 , wherein, when the third stage cooling is performed in step (3), the distance between the rail head profile cooling device and the rail head tread is 20-30 mm. 10 . 10. The method according to claim 9, characterized in that, when the third stage cooling is carried out in step (3), the pressure of the compressed air or the water-mist mixture sprayed by the rail head profile cooling device is 0.04-0.15 MPa, preferably 0.06-0.1 MPa.

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