Method for eliminating martensite structure of hypereutectoid steel rail flash welded joint

Abstract

The present application relates to the technical field of rail welding, and particularly relates to a method for eliminating martensite structure of hypereutectoid rail flash butt joint. The method comprises the following steps: S10, normalizing the hypereutectoid rail flash butt joint with martensite structure by using medium-frequency induction heating, wherein the peak heating temperature of the joint is 20-30 DEG C higher than the normal heating temperature during normalizing, and the peak heating temperature is kept for 10-15 s; S20, air cooling the top surface of the rail and the two sides of the rail head, so that the air cooling is stopped after the top surface of the rail is cooled to the set temperature, and the air cooling is continued until the room temperature is reached. The peak heating temperature is kept for 10-15 s, and then the top surface of the rail and the two sides of the rail head are air cooled by spraying, so that the martensite structure of the hypereutectoid rail joint is eliminated, the hardness, grain size, strength and toughness of the joint meet the standard requirements, and a large amount of manpower and material resources are saved, and valuable construction time is saved.

Description

Technical Field

[0001] This invention relates to the field of rail welding technology, and in particular to a method for eliminating martensitic structure in flash welded joints of hypereutectoid rails. Background Technology

[0002] To meet the needs of heavy-haul railways with high axle loads and high-density transportation, existing rails require a hardness of at least 420 HB. Currently, even with special manufacturing processes such as alloying, controlled rolling, and controlled cooling, the surface hardness of existing all-pearlitic rails can only reach a maximum of around 410 HB. Therefore, both domestic and international heavy-haul railways are focusing on hypereutectoid rails.

[0003] With the rapid development of seamless track technology in passenger, freight, and high-speed / heavy-haul railway construction worldwide, the quality of rail joints is increasingly attracting the attention of relevant departments. Rail welded joints are among the weakest links in the entire railway line, and their quality directly affects railway safety. The microstructure of the rail joint directly determines its performance.

[0004] Existing technologies still produce martensitic structures in the welded joints of hypereutectoid rails after heat treatment, which seriously affects the welding quality. To solve this technical problem, a method for eliminating martensitic structures in the flash welded joints of hypereutectoid rails is proposed. Summary of the Invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides a method for eliminating the martensitic structure of the flash weld joint of hypereutectoid rail.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0007] In a first aspect, in one embodiment of the present invention, a method for eliminating martensitic structure in a flash weld joint of a hypereutectoid rail is provided, the method comprising the following steps:

[0008] S10. For the flash welded joints of hypereutectoid rails that have already produced martensitic structure, medium-frequency induction heating is used for normalizing. During normalizing, the peak heating temperature of the joint is 20-30°C higher than the normal heating temperature, and the peak heating temperature is held for 10-15 seconds.

[0009] S20. Air-cool the top surface of the rail and both sides of the rail head until the top surface of the rail is cooled to the set temperature, then stop the air cooling and allow it to cool to room temperature.

[0010] As a further aspect of the present invention, S10, the hypereutectoid steel rail flash weld joint that has produced martensitic structure is normalized by medium frequency induction heating, wherein the peak heating temperature of the joint during normalization is 25-28°C higher than the normal heating temperature; and the peak heating temperature is held for 12-13 seconds.

[0011] S20. Air-cool the top surface of the rail and both sides of the rail head until the top surface of the rail is cooled to the set temperature, then stop the air cooling and allow it to cool to room temperature.

[0012] As a further aspect of the present invention, step S20, air cooling of the top surface of the rail and both sides of the rail head, so that the top surface of the rail can be cooled to a set temperature and then the air cooling is stopped, and the rail is air-cooled to room temperature, includes:

[0013] The air cooling process is stopped after the area within 0mm to 15mm below the top surface of the rail is rapidly cooled to a final cooling temperature of 440℃ to 470℃.

[0014] As a further aspect of the present invention, step S20, air cooling of the top surface of the rail and both sides of the rail head, so that the top surface of the rail can be cooled to a set temperature and then the air cooling is stopped, and the rail is air-cooled to room temperature, includes:

[0015] The air cooling process is stopped after the area within 0mm to 15mm below the top surface of the rail is rapidly cooled to a final cooling temperature of 452℃ to 460℃.

[0016] As a further aspect of the present invention, step S20, air cooling of the top surface of the rail and both sides of the rail head, so that the top surface of the rail can be cooled to a set temperature and then the air cooling is stopped, and the rail is air-cooled to room temperature, includes:

[0017] The air cooling process is stopped after the area within 0mm to 15mm below the top surface of the rail is rapidly cooled to the final cooling temperature of 455℃.

[0018] As a further embodiment of the present invention, the air-cooled spray pressure is 0.25MPa to 0.30MPa, and the spray distance is 30 to 45mm.

[0019] As a further aspect of the present invention, the air-cooled jet pressure is 0.27MPa to 0.28MPa, and the jet distance is 35 to 40mm.

[0020] As a further aspect of the present invention, the air-cooling spray time is 90s to 110s.

[0021] As a further aspect of the present invention, the air-cooling spray time is 95s to 105s.

[0022] As a further aspect of the present invention, the air-cooled spray time is 100s.

[0023] The technical solution provided by this invention has the following beneficial effects:

[0024] This invention provides a method for eliminating martensitic structure in hypereutectoid rail flash welded joints. The method includes the following steps: S10, normalizing the hypereutectoid rail flash welded joint with martensitic structure using medium-frequency induction heating, wherein the peak heating temperature of the joint during normalizing is 20-30°C higher than the normal heating temperature; and holding at the peak heating temperature for 10-15 seconds; S20, air cooling the top surface of the rail and both sides of the rail head, stopping the air cooling after the top surface of the rail has cooled to a set temperature, and then air cooling to room temperature. This invention, by heating to the peak temperature and holding at that temperature for 10-15 seconds before air cooling the top surface and both sides of the rail head, can eliminate the martensitic structure in the hypereutectoid rail joint, while ensuring that the joint's hardness, grain size, strength, and toughness meet standard requirements, saving significant manpower, material resources, and valuable construction time.

[0025] These or other aspects of the invention will become more apparent from the following description of embodiments. It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a metallographic inspection sampling location diagram of the flash welded head according to an embodiment of the present invention.

[0028] Figure 2 The martensitic structure at the weld is due to the excessively rapid cooling rate after welding.

[0029] Figure 3 The martensitic structure at the weld is due to the excessively rapid cooling rate after welding.

[0030] Figure 4 The microstructure of the weld and heat-affected zone after normalizing of the joint in Example 1 is shown.

[0031] Figure 5 This is a comparison of the martensitic structure "inherited" from the heat-affected zone of welding in Example 1. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The flowchart shown in the attached diagram is for illustrative purposes only and does not necessarily include all content and operations / steps, nor does it necessarily have to be performed in the order described. For example, some operations / steps can be broken down, combined, or partially merged, so the actual execution order may change depending on the actual situation.

[0034] Hypereutectoid rails have a tensile strength ≥1380MPa and a tread hardness ≥420HB. The base metal chemical composition includes: C: 0.90–1.10%, Si: 0.30–0.80%, Mn: 0.40–1.20%, Cr: 0.2–0.60%, V: 0.01–0.12%, P≤0.020%, S≤0.025%, with the remainder being Fe and unavoidable impurities. Hypereutectoid rails have a high carbon content and contain certain alloying elements. Due to segregation, the chemical composition varies in different micro-regions, leading to different Ms points and causing asynchronous martensitic transformation. Even if the final cooling temperature during the post-weld cooling process is higher than the Ms (martensitic transformation start temperature) of the rail steel, the presence of local segregation shifts the CCT curve to the right, and martensitic structures may still form in flash weld joints. To address this technical problem, the present invention provides a method for eliminating martensite structure in flash welded joints of hypereutectoid steel rails. This method for eliminating martensite structure in flash welded joints of hypereutectoid steel rails includes the following steps:

[0035] S10. For the flash welded joints of hypereutectoid rails that have already produced martensitic structure, medium-frequency induction heating is used for normalizing. During normalizing, the peak heating temperature of the joint is 20-30°C higher than the normal heating temperature, and the peak heating temperature is held for 10-15 seconds.

[0036] S20. Air-cool the top surface of the rail and both sides of the rail head until the top surface of the rail is cooled to the set temperature, then stop the air cooling and allow it to cool to room temperature.

[0037] S20, air cooling of the top surface of the rail and both sides of the rail head, so that the top surface of the rail can be cooled to the set temperature, and then air cooling is stopped and the rail is air-cooled to room temperature, including:

[0038] The air cooling process is stopped after the area within 0mm to 15mm below the top surface of the rail is rapidly cooled to a final cooling temperature of 440℃ to 470℃.

[0039] The air-cooled system has a spray pressure of 0.25MPa to 0.30MPa and a spray distance of 30 to 45mm.

[0040] The air-cooled spray time is 90s to 110s.

[0041] This invention heats the rail to its peak temperature and holds it at that temperature for 10-15 seconds before applying air cooling to the top surface and both sides of the rail head. This eliminates the martensitic structure in the hypereutectoid rail joint while ensuring that the joint's hardness, grain size, strength, and toughness meet the standard requirements. This saves a significant amount of manpower and resources, as well as valuable construction time.

[0042] Example 1

[0043] A method for eliminating martensitic structure in flash welded joints of hypereutectoid rails includes the following steps:

[0044] S10. For the flash welded joints of hypereutectoid rails that have already produced martensitic structure, medium-frequency induction heating is used for normalizing. During normalizing, the peak heating temperature of the joint is 20°C higher than the normal heating temperature, and the peak heating temperature is held for 15 seconds.

[0045] S20. Air-cool the top surface of the rail and both sides of the rail head until the top surface of the rail is cooled to the set temperature, then stop the air cooling and allow it to cool to room temperature.

[0046] S20, air cooling of the top surface of the rail and both sides of the rail head, so that the top surface of the rail can be cooled to the set temperature, and then air cooling is stopped and the rail is air-cooled to room temperature, including:

[0047] The air cooling process is stopped after the area within 0mm to 15mm below the top surface of the rail is rapidly cooled to a final cooling temperature of 470℃.

[0048] The air-cooled system has a spray pressure of 0.30 MPa and a spray distance of 30 mm.

[0049] The air-cooled spray time is 90 seconds.

[0050] Example 2

[0051] A method for eliminating martensitic structure in flash welded joints of hypereutectoid rails includes the following steps:

[0052] S10. For the flash welded joints of hypereutectoid rails that have already produced martensitic structure, medium-frequency induction heating is used for normalizing. During normalizing, the peak heating temperature of the joint is 30°C higher than the normal heating temperature, and the peak heating temperature is held for 10 seconds.

[0053] S20. Air-cool the top surface of the rail and both sides of the rail head until the top surface of the rail is cooled to the set temperature, then stop the air cooling and allow it to cool to room temperature.

[0054] S20, air cooling of the top surface of the rail and both sides of the rail head, so that the top surface of the rail can be cooled to the set temperature, and then air cooling is stopped and the rail is air-cooled to room temperature, including:

[0055] The air cooling process is stopped after the area within 0mm to 15mm below the top surface of the rail is rapidly cooled to the final cooling temperature of 452℃.

[0056] The air-cooled system has a spray pressure of 0.25 MPaa and a spray distance of 45 mm.

[0057] The air-cooled spray time is 110 seconds.

[0058] Example 3

[0059] A method for eliminating martensitic structure in flash welded joints of hypereutectoid rails includes the following steps:

[0060] S10. For the flash welded joints of hypereutectoid rails that have already produced martensitic structure, medium-frequency induction heating is used for normalizing. During normalizing, the peak heating temperature of the joint is 25°C higher than the normal heating temperature, and the peak heating temperature is held for 12 seconds.

[0061] S20. Air-cool the top surface of the rail and both sides of the rail head until the top surface of the rail is cooled to the set temperature, then stop the air cooling and allow it to cool to room temperature.

[0062] S20, air cooling of the top surface of the rail and both sides of the rail head, so that the top surface of the rail can be cooled to the set temperature, and then air cooling is stopped and the rail is air-cooled to room temperature, including:

[0063] The air cooling process is stopped after the area within 0mm to 15mm below the top surface of the rail is rapidly cooled to the final cooling temperature of 460℃.

[0064] The air-cooled system has a spray pressure of 0.25 MPa and a spray distance of 40 mm.

[0065] The air-cooled spray time is 100 seconds.

[0066] Example 4

[0067] A method for eliminating martensitic structure in flash welded joints of hypereutectoid rails includes the following steps:

[0068] S10. For the flash welded joints of hypereutectoid rails that have already produced martensitic structure, medium-frequency induction heating is used for normalizing. During normalizing, the peak heating temperature of the joint is 25°C higher than the normal heating temperature, and the peak heating temperature is held for 13 seconds.

[0069] S20. Air-cool the top surface of the rail and both sides of the rail head until the top surface of the rail is cooled to the set temperature, then stop the air cooling and allow it to cool to room temperature.

[0070] S20, air cooling of the top surface of the rail and both sides of the rail head, so that the top surface of the rail can be cooled to the set temperature, and then air cooling is stopped and the rail is air-cooled to room temperature, including:

[0071] The air cooling process is stopped after the area within 0mm to 15mm below the top surface of the rail is rapidly cooled to a final cooling temperature of 450℃.

[0072] The air-cooled system has a spray pressure of 0.28 MPa and a spray distance of 40 mm.

[0073] The air-cooled jetting time is 105 seconds.

[0074] Example 5

[0075] A method for eliminating martensitic structure in flash welded joints of hypereutectoid rails includes the following steps:

[0076] S10. For the flash welded joints of hypereutectoid rails that have already produced martensitic structure, medium-frequency induction heating is used for normalizing. During normalizing, the peak heating temperature of the joint is 28°C higher than the normal heating temperature, and the peak heating temperature is held for 12 seconds.

[0077] S20. Air-cool the top surface of the rail and both sides of the rail head until the top surface of the rail is cooled to the set temperature, then stop the air cooling and allow it to cool to room temperature.

[0078] S20, air cooling of the top surface of the rail and both sides of the rail head, so that the top surface of the rail can be cooled to the set temperature, and then air cooling is stopped and the rail is air-cooled to room temperature, including:

[0079] The air cooling process is stopped after the area within 0mm to 15mm below the top surface of the rail is rapidly cooled to the final cooling temperature of 455℃.

[0080] The air-cooled system has a spray pressure of 0.27 MPa and a spray distance of 35 mm.

[0081] The air-cooled spray time is 95 seconds.

[0082] Comparative Example 1

[0083] For the flash welded joint of hypereutectoid rail with existing martensitic structure, the rail is heated to the normal normalizing temperature using medium frequency induction heating. After heating to the normalizing temperature, the rail top surface and both sides of the rail head are immediately cooled by air spraying. The air spraying pressure is 0.30 MPa, the air spraying distance is 40 mm, the air spraying time is 100 s, and the air spraying cooling is stopped after the final cooling temperature of 450℃. The rail is then air-cooled to room temperature.

[0084] Comparative Example 2

[0085] For the flash welded joint of hypereutectoid rail with existing martensitic structure, the rail is heated to the normal normalizing temperature using medium frequency induction heating. The temperature is held at the normalizing peak temperature for 10 seconds. Then, the top surface of the rail and both sides of the rail head are cooled by air spraying. The air spraying pressure is 0.25 MPa, the air spraying distance is 30 mm, the air spraying time is 105 seconds, and the air spraying cooling is stopped after the final cooling temperature reaches 460℃. The rail is then air-cooled to room temperature.

[0086] Comparative Example 3

[0087] For the flash welded joint of hypereutectoid rail with existing martensitic structure, medium-frequency induction heating is used. During normalizing, the peak heating temperature of the joint is 10℃ higher than the normal heating temperature. After holding at the peak heating temperature for 5 seconds, air cooling is applied to the top surface of the rail and both sides of the rail head. The air pressure is 0.30MPa, the air distance is 30mm, and the air cooling time is 90s. This allows the area within 0mm to 15mm below the top surface of the rail to be rapidly cooled to the final cooling temperature of 470℃. After that, the air cooling is stopped, and the rail is air-cooled to room temperature.

[0088] The joint microstructure was inspected according to the TB / T1632.2-2014 standard. Metallographic samples of the rail head, rail foot, and rail bottom triangular areas of Examples 1-4 and Comparative Examples 1-3 were taken to inspect the joint microstructure and grain size.

[0089]

[0090]

[0091]

[0092] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method of eliminating the martensitic structure of a transus steel rail flash welded joint, characterized in that, The method comprises the following steps: S10, the flash butt welded joint of the hypereutectoid steel rail with generated martensite structure is normalized by using medium frequency induction heating, wherein the peak temperature of the joint during the normalizing is 25-28 DEG C higher than the normal heating temperature; and the peak temperature is kept for 12-13 s; S20, the top surface of the rail and the two sides of the rail head are air-cooled, so that the top surface of the rail can be cooled to a set temperature and then the air-cooling is stopped, and the air-cooling is continued to room temperature, comprising: the region within 0 mm-15 mm below the top surface of the rail is rapidly cooled to a final cooling temperature of 440 DEG C-470 DEG C, and then the air-cooling is stopped; the air-cooling pressure is 0.25 MPa-0.30 MPa, and the air-cooling distance is 30-45 mm; the air-cooling time is 90 s-110 s.

2. The method of eliminating the martensite structure of a transus steel rail flash welded joint according to claim 1, characterized in that, S20, the top surface of the rail and the two sides of the rail head are air-cooled, so that the top surface of the rail can be cooled to a set temperature and then the air-cooling is stopped, and the air-cooling is continued to room temperature, comprising: the region within 0 mm-15 mm below the top surface of the rail is rapidly cooled to a final cooling temperature of 452 DEG C-460 DEG C, and then the air-cooling is stopped.

3. The method of eliminating the martensite structure of a transus steel rail flash welded joint according to claim 1, characterized in that, S20, the top surface of the rail and the two sides of the rail head are air-cooled, so that the top surface of the rail can be cooled to a set temperature and then the air-cooling is stopped, and the air-cooling is continued to room temperature, comprising: the region within 0 mm-15 mm below the top surface of the rail is rapidly cooled to a final cooling temperature of 455 DEG C, and then the air-cooling is stopped.

4. The method of eliminating the martensite structure of a trans-critical steel rail flash welded joint according to claim 1, characterized in that, the air-cooling pressure is 0.27 MPa-0.28 MPa, and the air-cooling distance is 35-40 mm.

5. The method of eliminating the martensite structure of a trans-critical steel rail flash welded joint according to claim 1, characterized in that, the air-cooling time is 95 s-105 s.

6. The method of eliminating the martensite structure of a trans-critical steel rail flash welded joint according to claim 1, characterized in that, the air-cooling time is 100 s.

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