A method for eliminating martensite structure of flash welded joint of hypereutectoid steel rail

Abstract

The present invention relates to the technical field of steel rail welding, in particular to a method for eliminating a martensitic structure of a flash-welded joint of a hypereutectoid steel rail. The method comprises the following steps: S10, for a hypereutectoid steel rail flash-welded joint where a martensitic structure has already been generated, carrying out normalizing by means of using medium-frequency induction heating, the heating peak temperature of the joint during the normalizing being 20-30℃ higher than a normal heating temperature, and performing heat preservation for 10-15s at the heating peak temperature; and S20, performing air cooling on the top surface of the steel rail and two sides of a steel rail head to allow the top surface of the steel rail to be cooled to a set temperature, then stop air cooling, and allowing same to cool naturally to room temperature. In the present invention, heating is performed to the peak temperature, heat preservation is performed for 10-15s at the peak temperature, and then air blast cooling is performed on the top surface of the rail and the two sides of the rail head, such that martensitic structures of hypereutectoid steel rail joints can be eliminated, and simultaneously it is ensured that the hardness, grain size, strength and toughness of joints meet standard requirements, saving a large amount of manpower and material resources, and saving precious construction time.

Description

Technical Field The present invention relates to the technical field of rail welding, in particular to a method for eliminating martensite structure of flash welded joint of hypereutectoid steel rail. Background Art In order to meet the needs of the development of heavy-haul railway with large axle load and high density transportation mode, the hardness of existing rails needs to reach above 420 HB. The existing all-pearlite rails need to adopt special production processes such as alloying+controlled rolling+controlled cooling, and the highest tread hardness can only reach about 410 HB. Therefore, heavy-haul lines at home and abroad focus on hypereutectoid steel rails. With the rapid development of jointless track technology in passenger transport, freight transport, high-speed and heavy-haul railway construction around the world, the quality of rail joints has attracted more and more attention from relevant departments. The welded joint of rail belongs to the weak link of the whole line, and its quality directly affects the safety of railway, while the microstructure of rail joint directly determines the service performance of the joint. In the prior art, martensite structure still exists in the welded joint of hypereutectoid steel rail after heat treatment, which seriously affects the welding quality. In order to solve this technical problem, a method for eliminating martensite structure of flash welded joint of hypereutectoid steel rail is proposed. Summary In order to solve the technical problems in the prior art, the present invention provides a method for eliminating martensite structure of flash welded joint of hypereutectoid steel rail. In order to achieve the above purpose, the embodiment of the present invention provides the following technical scheme: In a first aspect, in an embodiment provided by the present invention, there is provided a method for eliminating martensite structure of flash welded joint of a hypereutectoid steel rail, which comprises the following steps: S10, normalizing the flash welded joint of hypereutectoid steel rail with martensite structure by medium frequency induction heating, wherein the joint is heated to a peak heating temperature which is 20-30°C higher than the normal heating temperature during the normalizing; and the joint is heated over a dwell time of 10-15s at the peak heating temperature; and S20, cooling a top surface of the rail and both sides of a rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, stopping the cooling by the compressed air and cooling the joint to room temperature naturally. As a further scheme of the present invention, in S10, normalizing the flash welded joint of hypereutectoid steel rail with martensite structure by medium-frequency induction heating, wherein the joint is heated to the peak heating temperature which is 25-28°C higher than the normal heating temperature during the normalizing; and the joint is heated over a dwell time of 12-13s at the peak heating temperature; and in S20, cooling the top surface of the rail and both sides of the rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, stopping the cooling by the compressed air and cooling the joint to room temperature naturally. As a further scheme of the present invention, in S20, the step that cooling a top surface of the rail and both sides of a rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, stopping the cooling by the compressed air and cooling the joint to room temperature naturally further includes: cooling an area within a range of 0 mm to 15 mm below the top surface of the rail rapidly to a final cooling temperature of 440°C to 470°C, and stopping the cooling by the compressed air. As a further scheme of the present invention, in S20, the step that cooling a top surface of the rail and both sides of a rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, stopping the cooling by the compressed air and cooling the joint to room temperature naturally further includes: cooling an area within a range of 0 mm to 15 mm below the top surface of the rail rapidly to a final cooling temperature of 452°C to 460°C, and stopping the cooling by the compressed air. As a further scheme of the present invention, in S20, the step that cooling a top surface of the rail and both sides of a rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, stopping the cooling by the compressed air and cooling the joint to room temperature naturally further includes: cooling an area within a range of 0 mm-15 mm below the top surface of the rail rapidly to a final cooling temperature of 455°C, and stopping the cooling by the compressed air. As a further scheme of the present invention, the compressed air is sprayed at a pressure of 0.25 MPa-0.30 MPa with a distance of 30-45 mm. As a further scheme of the present invention, the compressed air is sprayed at a pressure of 0.27 MPa to 0.28 MPa with a distance of 35-40 mm. As a further scheme of the present invention, the compressed air is sprayed for 90s-110s. As a further scheme of the present invention, the compressed air is sprayed for 95s-105s. As a further scheme of the present invention, the compressed air is sprayed for 100s. The technical scheme provided by the present invention has the following beneficial effects: The present invention provides a method for eliminating martensite structure of flash welded joint of hypereutectoid steel rail, which comprises the following steps: S10, normalizing the flash welded joint of hypereutectoid steel rail with martensite structure by adopting medium-frequency induction heating, wherein the joint is heated to a peak heating temperature 20-30°C higher than normal heating temperature during the normalizing; and the joint is heated over a dwell time of 10-15s at the peak heating temperature; S20, cooling a top surface of the rail and both sides of a rail head by air, so that the top surface of the rail can be cooled to a set temperature, and then the air cooling is stopped and cooled to room temperature. The present invention heats the joint to the peak temperature, keeps the joint at the peak temperature for 1015s, and then sprays air to cool the rail top surface and both sides of the rail head, which can eliminate the martensite structure of the hypereutectoid steel rail joint, ensure that the hardness, grain size, strength and toughness of the joint meet the standard requirements, and save a lot of manpower and material resources and valuable construction time. These or other aspects of the present invention will be more concise and easy to understand in the following description of the embodiment. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present invention. Description of Drawings In order to more clearly explain the embodiment of the present invention or the technical scheme in the prior art, the attached drawings needed in the description of the embodiment or the prior art will be briefly introduced below. Obviously, the attached drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other embodiments can be obtained according to these drawings without creative labor. Figure 1 is a sampling position diagram of metallographic examination of flash welded joint according to the embodiments of the present invention. Figure 2 shows martensite structure I in the weld where the cooling rate after welding is too fast. Figure 3 shows martensite structure II in the weld where the cooling rate after welding is too fast. Figure 4 shows the structure of weld and the heat affected zone of the joint after normalization according to the operation of embodiment 1. Figure 5 shows the martensite structure inherited from the welding heat affected zone of the joint obtained by comparative example 1. Embodiments In the following, the technical scheme in the embodiment of the present invention will be clearly and completely described with reference to the attached drawings. Obviously, the described embodiment is a part of the embodiment of the present invention, but not the whole embodiment. Based on the embodiment in the present invention, all other embodiments obtained by ordinary technicians in the field without creative labor belong to the protection scope of the present invention. The flow chart shown in the attached drawings is only for illustration, and it is not necessary to include all the contents and operations / steps, nor to execute them in the described order. For example, some operations / steps can be decomposed, combined or partially merged, so the actual execution order may change according to the actual situation. The tensile strength of hypereutectoid steel rail is ^ 1380 MPa, and the tread hardness is ^420 HB. The chemical composition of the base material contains: C: 0.90-1.10%, Si: 0.300.80%, Mn: 0.40-1.20%, Cr: 0.2-0.60%, V: 0.01-0.12%, P ^ 0.020% and S ^ 0.025%. The balance is Fe and inevitable impurities. Hypereutectoid steel rail contains high carbon content and certain alloying elements. Due to segregation, the chemical composition of each microscopic region is different, which leads to different Ms points and martensite transformation at different temperatures. Even if the final cooling temperature of rail after welding is higher than the Ms temperature (martensite transformation start temperature) of rail steel, the CCT curve shifts to the right due to local segregation, and the flash welded joint may produce martensite structure. In order to solve this technical problem, the present invention provides a method for eliminating martensite structure of flash welded joint of hypereutectoid steel rail, which comprises the following steps: S10, normalizing the flash welded joint of hypereutectoid steel rail with martensite structure by medium frequency induction heating, wherein the joint is heated to a peak heating temperature which is 20-30°C higher than normal heating temperature during the normalizing; and the joint is heated over a dwell time of 10-15s at the peak heating temperature; S20, cooling a top surface of the rail and both sides of a rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, and then stopping the cooling by the compressed air and cooling the joint to room temperature naturally. In S20, the step that cooling a top surface of the rail and both sides of a rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, and then stopping the cooling by the compressed air and cooling the joint to room temperature naturally further including: cooling an area within a range of 0 mm to 15 mm below the top surface of the rail rapidly to a final cooling temperature of 440°C to 470°C, and then stopping the cooling by the compressed air. The compressed air is sprayed at a pressure of 0.25 MPa-0.30 MPa with a distance of 3045 mm. The compressed air is sprayed for 90s to 110s. The present invention heats the joint to the peak temperature over a dwell time of 10-15s, and then sprays compressed air to cool the rail top surface and both sides of the rail head, which can eliminate the martensite structure of the joint of the hypereutectoid steel rail, ensure that the hardness, grain size, strength and toughness of the joint meet the standard requirements, and save a lot of manpower and material resources and valuable construction time. Embodiment 1 The present invention relates to a method for eliminating martensite structure of a flash welded joint of hypereutectoid steel rail, which comprises the following steps: S10, normalizing the flash welded joint of hypereutectoid steel rail with martensite structure by medium frequency induction heating, wherein the joint is heated to the peak heating temperature which is 20°C higher than the normal heating temperature during the normalizing; and the joint is heated over a dwell time of 15s at the peak heating temperature; S20, cooling the top surface of the rail and both sides of the rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, and then stopping the cooling by the compressed air and cooling the joint to room temperature naturally. In S20, the step that cooling the top surface of the rail and both sides of the rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, and then stopping the cooling by the compressed air and cooling the joint to room temperature naturally further including: cooling the area within a range of 0 mm-15 mm below the top surface of the rail rapidly to the final cooling temperature of 470°C, and stopping the cooling by the compressed air. The compressed air is sprayed at a pressure of 0.30 MPa with a distance of 30 mm. The compressed air is sprayed for 90s. Embodiment 2 The present invention relates to a method for eliminating martensite structure of a flash welded joint of hypereutectoid steel rail, which comprises the following steps: S10, normalizing the flash welded joint of hypereutectoid steel rail with martensite structure by medium frequency induction heating, wherein the joint is heated to the peak heating temperature which is 30°C higher than the normal heating temperature during the normalizing; and the joint is heated over a dwell time of 10s; S20, cooling the top surface of the rail and both sides of the rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, and then stopping the cooling by the compressed air and cooling the joint to room temperature naturally. In S20, the step that cooling the top surface of the rail and both sides of the rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, and then stopping the cooling by the compressed air and cooling the joint to room temperature naturally further including: cooling the area within a range of 0 mm-15 mm below the top surface of the rail rapidly to the final cooling temperature of 452°C, and then stopping the cooling by the compressed air. The compressed air is sprayed at a pressure of 0.25 MPa with a distance of 45 mm. The compressed air is sprayed for 110s. Embodiment 3 The present invention relates to a method for eliminating martensite structure of a flash welded joint of hypereutectoid steel rail, which comprises the following steps: S10, normalizing the flash welded joint of hypereutectoid steel rail with martensite structure by medium frequency induction heating, wherein the joint is heated to the peak heating temperature which is 25°C higher than the normal heating temperature during normalizing; and the joint is heated over a dwell time of 12s; S20, cooling the top surface of the rail and both sides of the rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, and then stopping the cooling by the compressed air and cooling the joint to room temperature naturally. In S20, the step that cooling the top surface of the rail and both sides of the rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, and then stopping the cooling by the compressed air and cooling the joint to room temperature naturally further including: cooling the area within a range of 0 mm-15 mm below the top surface of the rail rapidly to the final cooling temperature of 460°C, and then stopping the cooling by the compressed air. The compressed air is sprayed at a pressure of 0.25 MPa with a distance of 40 mm. The compressed air is sprayed for 100s. Embodiment 4 The present invention relates to a method for eliminating martensite structure of a flash welded joint of hypereutectoid steel rail, which comprises the following steps: S10, normalizing the flash welded joint of hypereutectoid steel rail with martensite structure by medium frequency induction heating, wherein the joint is heated to the peak heating temperature which is 25°C higher than the normal heating temperature during normalizing; and the joint is heated over a dwell time of 13s at the peak heating temperature; S20, cooling the top surface of the rail and both sides of the rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, and then stopping the cooling by the compressed air and cooling the joint to room temperature naturally. In S20, the step that cooling the top surface of the rail and both sides of the rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, and then stopping the cooling by the compressed air and cooling the joint to room temperature naturally further including: cooling the area within a range of 0 mm-15 mm below the top surface of the rail rapidly to the final cooling temperature of 450°C, and then stopping the cooling by the compressed air. The compressed air is sprayed at a pressure of 0.28 MPa with a distance of 40 mm. The compressed air is sprayed for 105s. Embodiment 5 The present invention relates to a method for eliminating martensite structure of a flash welded joint of hypereutectoid steel rail, which comprises the following steps: S10, normalizing the flash welded joint of hypereutectoid steel rail with martensite structure by medium frequency induction heating, wherein the joint is heated to the peak heating temperature which is 28°C higher than the normal heating temperature during normalizing; and the joint is heated over a dwell time of 12s at the peak heating temperature; S20, cooling the top surface of the rail and both sides of the rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, and then stopping the cooling by the compressed air and cooling the joint to room temperature. In S20, the step that cooling the top surface of the rail and both sides of the rail head by compressed air, so that the top surface of the rail can be cooled to a set temperature, and then stopping the cooling by the compressed air and cooling the joint to room temperature naturally further including: cooling the area within a range of 0 mm-15 mm below the top surface of the rail rapidly to the final cooling temperature of 455°C, and then stopping the cooling by the compressed air. The compressed air is sprayed at a pressure of 0.27 MPa with a distance of 35 mm. The compressed air is sprayed for 95s. Comparative Example 1 Heating the flash welded joint of hypereutectoid steel rail with martensite structure to the normal normalizing heating temperature by medium frequency induction without holding the temperature. Cooling the top surface of the rail and both sides of the rail head immediately by compressed air, wherein the air pressure is 0.30 MPa, the distance between the air port and the surface of the rail is 40 mm, and the air is sprayed for 100s. Stopping the cooling by the compressed air when the final cooling temperature of 450°C is reached. And then cooling the joint to room temperature naturally. Comparative Example 2 Heating the flash welded joint of hypereutectoid steel rail with martensite structure to the normal normalizing heating temperature by medium frequency induction, and heating the joint to the normalized peak temperature for 10s. And then cooling the rail top surface and both sides of the rail head by compressed air, wherein the air pressure is 0.25 MPa, the distance between the air port and the surface of the rail is 30 mm, and the air is sprayed for 105s. Stopping the cooling by the compressed air when the final cooling temperature of 460°C is reached. And then cooling the joint to room temperature naturally. Comparative Example 3 Heating the flash welded joint of hypereutectoid steel rail with martensite structure by medium frequency induction heating, and the peak heating temperature of the joint is 10°C higher than the normal heating temperature when normalizing. Cooling the top surface of the rail and both sides of the rail head by compressed air, wherein the air pressure is 0.30 MPa, the distance between the air port and the surface of the rail is 30 mm, and the air is sprayed for 90s, so that the area below the top surface of the rail is rapidly cooled to a final cooling temperature of 470°C, and then stopping the cooling by the compressed air. Cooling the joint to room temperature naturally. Inspection of joint structure according to TB / T1632.2-2014 standard, metallographic samples were taken from the rail head, rail foot and rail bottom triangle area of embodiments 1-4 and comparative examples 1-3, respectively, to inspect the joint structure and grain size. Item Grain size grade of rail head weld Grain size grade of rail foot weld Grain size grade of weld in triangle area of rail bottom Microstructure of the joint Embodiment 1 Grade 9 Grade 9 Grade 7 The microstructure of the weld in the triangle area of rail head, rail foot and rail bottom       is ferrite+pearlite, and         the microstructure of heat affected zone is pearlite. Embodiment 2 Grade 8.5 Grade 8.5 Grade 7 The microstructure of the weld in triangle area of rail head, rail foot and rail bottom       is ferrite+pearlite, and         the microstructure of heat affected zone is pearlite. Embodiment 3 Grade 8.5 Grade 8.5 Grade 6.5 The microstructure of the weld in triangle area of rail head, rail foot and rail bottom       is ferrite+pearlite, and         the microstructure of heat affected zone is pearlite. Embodiment 4 Grade 9 Grade 9 Grade 6.5 The microstructure of the weld in triangle area of rail head, rail foot and rail bottom       is ferrite+pearlite, and         the microstructure of heat affected zone is pearlite. Comparative Example 1 Martensite structure exists in the heat affected zone of rail foot and rail head weld. Comparative Example 2 Martensite structure exists in the heat affected zone of rail foot and rail head weld. Comparative Example 3 There is a small amount      of martensite in the heat affected zone of weld at the distance of 10 mm-15 mm from the rail head to the tread. The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the present invention.

Claims

1. A method for eliminating martensite structure of flash welded joint of hypereutectoid steel rail characterized by comprising the following steps:S10, normalizing the flash welded joint of hypereutectoid steel rail with martensite structure by medium frequency induction heating, wherein the joint is heated to a peak heating temperature which is 25-28°C higher than a normal heating temperature during the normalizing; and the joint is heated over a dwell time of 12-13s at the peak heating temperature; andS20, cooling a top surface of the rail and both sides of a rail head by compressed air, so that an area within a range of 0 mm to 15 mm below the top surface of the rail can be cooled rapidly to a final cooling temperature of 440°C to 470°C, stopping the cooling by the compressed air and cooling the joint to room temperature naturally;wherein, the compressed air is sprayed at a pressure of 0.25 MPa-0.30 MPa with a distance of 30-45 mm;wherein, the compressed air is sprayed for 90s to 110s.

2. The method for eliminating martensite structure of flash welded joint of hypereutectoid steel rail according to claim 1, characterized in that:in S20, cooling an area within a range of 0 mm to 15 mm below the top surface of the rail rapidly to a final cooling temperature of 452°C to 460°C, and then stopping the cooling by the compressed air.

3. The method for eliminating martensite structure of flash welded joint of hypereutectoid steel rail according to claim 1, characterized in that:in S20,cooling an area within a range of 0 mm-15 mm below the top surface of the rail rapidly to a final cooling temperature of 455°C, and then stopping the cooling by the compressed air.

4. The method for eliminating martensite structure of flash welded joint of hypereutectoid steel rail according to claim 1, characterized in that the compressed air is sprayed at a pressure2024227062   28 Sep 2026of 0.27 MPa-0.28 MPa with a distance of 35-40 mm.

5. The method for eliminating martensite structure of flash welded joint of hypereutectoid steel rail according to claim 1, characterized in that the compressed air is sprayed for 95s-105s.

6. The method for eliminating martensite structure of flash welded joint of hypereutectoid steel rail according to claim 1, characterized in that the compressed air is sprayed for 100s.

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