Method for reducing abrasion rate of softening area of flash welding joint of steel rail
By heating, accelerated cooling and constant temperature treatment of rail flash welded joints, the problem of fast wear rate in the joint softening zone is solved, and the wear resistance and service life are significantly improved.
Patent Information
- Application Number
- CN202510291164.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-12
- Publication Date
- 2025-05-23
AI Technical Summary
The wear rate of the softening zone of the rail flash welded joint is faster, resulting in the joint life being lower than that of the rail base material, affecting the service life.
By optimizing the heat treatment process of welded joints, including heating and accelerated cooling of the rail flash welded joint area, and constant temperature treatment of the joint parent material area on both sides of the welded joint area, the heating and cooling process is controlled to slow wear in the softening zone.
It significantly improves the wear resistance of welded joints, enhances wear resistance and impact resistance, extends the service life of the rail, and narrows the range of softening zones, improving overall strength and stability.
Smart Images
Figure CN120023443A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of rail welding, and in particular to a method for slowing down the wear rate of a softening zone of a rail flash welding joint. Background Art
[0002] In recent years, with the continuous increase in heavy-duty railway transportation volume, axle load and maximum load of a single train, the wear and damage problems of rails and their welded joints have become increasingly serious. Whether it is thermite welding or flash welding, the hardness of the welded joint in the heat-affected zone is usually lower than that of the parent material, resulting in a significant reduction in its mechanical properties such as tensile strength, hardness and fatigue strength. Under high-volume conditions, the softening zone of the welded joint wears faster, the collapse phenomenon is very serious, and the joint life is much lower than that of the rail parent material. Studies have shown that impact wear and rolling contact fatigue wear in the softening zone of the welded joint are important causes of joint damage.
[0003] The softening zone of the rail flash weld refers to the area where the hardness of the weld joint is significantly lower than that of the base material. The metal in this area does not undergo austenite transformation during the heating process, and its temperature range is usually in the annealing range of metal heat treatment, so the softening zone is also called the annealing zone. Since rail welding mainly heats the end locally, there is always a transition zone between the heated part and the unheated base material. The area with lower hardness in this transition zone is the softening zone. The existence of the softening zone is the weak link of the rail weld joint, and its tensile and impact properties are poor, which seriously affects the service life of the rail.
[0004] At present, the heat treatment technology for rail welded joints has made certain progress at home and abroad. For example, my country's railway base flash welding adopts medium-frequency induction heating and air jet cooling process solutions to improve the performance of welded joints by controlling heating temperature and cooling rate. However, with the development of heavy load and high speed of railway transportation, the existing technology is still difficult to completely solve the problem of accelerated wear of the softening zone of welded joints. Therefore, reducing the wear rate of the softening zone of welded joints and extending the life of rail welded joints have become important issues that need to be solved urgently.
[0005] However, the existing processing technology still has the following shortcomings: the hardness and toughness and plasticity of the softening zone of the welded joint are lower than those of the parent material, which leads to faster wear and serious collapse during service. Although the existing post-weld heat treatment technology can improve some performance, it still has shortcomings in controlling the width of the softening zone and matching the hardness. At present, the wheel-rail contact relationship is mainly improved by reasonable lubrication, damage grinding and other means, but these measures are difficult to fundamentally improve the wear resistance of the welded joint. Based on this, the existing technology still needs to be improved. Summary of the invention
[0006] In view of this, the present invention proposes a method for slowing down the wear rate of the softening zone of a rail flash weld joint, by optimizing the heat treatment process of the weld joint, improving the strength and toughness and plasticity of the softening zone, and reducing the width of the softening zone, thereby significantly improving the wear resistance of the weld joint.
[0007] A method for slowing down the wear rate of a softening zone of a rail flash weld joint of the present invention comprises: Heating the rail flash weld joint area; Accelerate cooling of the heated weld joint area; Before heating the rail flash welding joint area, during heating, during cooling, and after cooling, the joint base material areas on both sides of the rail flash welding joint area are subjected to constant temperature treatment.
[0008] In some embodiments, during the heating and accelerated cooling of the rail flash weld joint region, the constant temperature treatment maintains the temperature of the joint base material region between 20°C and 50°C.
[0009] In some embodiments, the start time of the constant temperature treatment is more than 30 seconds earlier than the start time of heating the rail flash welding joint area, and the end time of the constant temperature treatment is more than 30 seconds later than the end time of accelerated cooling of the heated welding joint area.
[0010] In some embodiments, accelerated cooling of the heated welding joint area includes: using compressed air for accelerated cooling, the starting temperature of the center of the top surface of the rail welding joint area during accelerated cooling is 850℃~980℃, the pressure of the compressed air is 0.05MPa~0.70MPa, the average cooling rate of the accelerated cooling is 5℃ / s~25℃ / s, and at the end of the accelerated cooling, the temperature of the center of the top surface of the rail welding joint area is 350℃~550℃.
[0011] In some embodiments, the joint parent material regions on both sides of the rail flash weld joint region are the entire rail head and rail waist regions including the rail top surface, rail head fillet, rail head side and rail waist web.
[0012] In some embodiments, the constant temperature treatment is implemented using a contact heat conduction device that imitates the profile of a rail. The contact heat conduction device is a hollow structure, and heat exchange is performed inside through a cooling medium. The contact heat conduction device and the contact surface of the rail are coupled using a flexible heat conductive material.
[0013] In some embodiments, the contact heat conduction device includes a first heat conduction component in contact with the rail top surface, the rail head fillet, and the rail head side surface, and a second heat conduction component in contact with both sides of the rail waist web. The thickness of the first heat conduction component is 15mm to 30mm, and the length along the extension direction of the rail is 20mm to 40mm. The length of the second heat conduction component along the extension direction of the rail is 20mm to 40mm, the height is equal to the height of the rail waist web, and the thickness is 45mm to 60mm.
[0014] In some embodiments, the heating process is to perform secondary heating on the flash welded joint area of the rail that has been cooled to a certain temperature after welding, the starting temperature of the heating process is less than 300°C, and the ending temperature of the heating process is 800°C to 1000°C.
[0015] In some embodiments, the heating process uses an induction coil that simulates the profile of a rail. The distance between the induction coil and the surface of the rail is 5 mm to 50 mm. The length of the induction coil along the extension direction of the rail is 60 mm to 150 mm. During the heating process, the induction coil controls the temperature rise rate of the welding joint area to be 1.0°C / s to 20.0°C / s.
[0016] In some embodiments, the working position of the contact heat conduction device is adjacent to the electric induction coil during the heating process, with a gap of ≤2 mm.
[0017] The beneficial effects of the present invention are as follows: the method for slowing down the wear rate of the softening zone of the rail flash weld joint provided by the present invention effectively solves the technical problem of failure of the rail flash weld joint due to impact and fatigue wear in the softening zone during service by heating and accelerating cooling in the weld joint area and performing constant temperature treatment on the parent material areas on both sides of the weld joint area, and has significant innovation and practicality. Specifically, the present application improves the average hardness of the softening zone of the rail flash weld joint by ≥95% compared with the air-cooled joint after welding by heating and accelerating cooling the joint area, which can effectively enhance the wear resistance and impact resistance of the weld joint, reduce the wear caused by the impact of train operation and long-term friction, and extend the service life of the rail. The present invention controls the width of the softening zone on one side of the joint to ≤5mm by precisely controlling the heating and cooling process. Compared with the traditional welding process, the softening zone range is greatly reduced, the problem of performance degradation of the weld joint caused by the excessive softening zone is reduced, and the overall strength and stability of the weld joint are further improved. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying creative work.
[0019] Figure 1 A schematic front view of the heating, cooling and constant temperature treatment areas for a rail flash weld joint provided by one embodiment of the present invention; Figure 2 A left schematic diagram of the heating, cooling and constant temperature treatment areas for a rail flash weld joint provided by an embodiment of the present invention. DETAILED DESCRIPTION
[0020] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.
[0021] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two non-identical entities with the same name or non-identical parameters. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. The subsequent embodiments will not explain this one by one.
[0022] An embodiment of the present invention provides a method for slowing down the wear rate of a softening zone of a rail flash weld joint, comprising: Heating the rail flash weld joint area; Accelerate cooling of the heated weld joint area; Before heating the rail flash welding joint area, during heating, during cooling, and after cooling, the joint base material areas on both sides of the rail flash welding joint area are subjected to constant temperature treatment.
[0023] The above-mentioned rail flash welding joint area mainly refers to the welded joint formed after the flash welding is completed, which mainly includes three main areas: fusion line, heat affected zone and parent material. Among them, the welded joint is centered on the fusion line, and the width of the fusion line is 0.5mm~2.0mm. The fusion line is the area formed by the melting and re-solidification of the materials at both ends of the rail during the welding process, which ensures the physical connection between the two ends of the rail. The heat affected zone is the area affected by the welding heat during the welding process. The single-side width of the heat affected zone on both sides of the joint fusion line is 5.0mm~30.0mm. The heat affected zone is the area that is affected by heat but not melted during the welding process. It is located on both sides of the fusion line, and the width of the heat affected zone on each side is 5.0mm~30.0mm. The parent material area is the area that is not affected by heat during the welding process. It is located on the side of the heat affected zone away from the fusion line. The width of the parent material area on each side is 5.0mm~20.0mm. The parent material area of the joint is the area that is not affected by the heat affected zone during the welding process. The width of the single-sided joint parent material area referred to in this patent is 5.0mm~40.0mm.
[0024] In the present application, the microstructure of the rail is pearlite. In the chemical composition of the rail, the mass fraction of the C element is 0.35% to 1.20%, the mass fraction of the Si element is 0.10% to 1.20%, the mass fraction of the Mn element is 0.60% to 1.40%, the mass fraction of the Cr element does not exceed 0.25%, the mass fraction of the V element does not exceed 0.20%, the mass fractions of the P and S elements do not exceed 0.040%, the mass fraction of the Al element does not exceed 0.004%, and the rest are iron and unavoidable impurities.
[0025] Flash welding mainly refers to a method of using resistance heat to heat the part of the rail to be welded until it reaches a predetermined temperature, and then quickly applying a forging force to achieve atomic bonding between the rails. The flash welding process includes four stages: electrode clamping, power heating, pressure forging, and rapid nodule pushing. During the welding process, the temperature of the rails on both sides of the rails 0mm to 25mm away from the end face of the rail to be welded is 900℃ to 1800℃, and the welding duration is 50s to 300s. Specifically, the electrode clamping stage: through electrode clamping, it can ensure that the end of the rail to be welded remains stable during the welding process to avoid welding defects caused by vibration or displacement. The power heating stage: the end of the rail is heated to 900℃ to 1800℃, and the time is controlled at 50s to 300s, which can make the end of the rail reach sufficient plasticity and provide good conditions for subsequent forging. The pressure forging stage: the forging force is applied at high temperature to cause plastic deformation of the rail end and achieve atomic bonding to form a firm welded joint. Rapid nodule removal stage: After welding is completed, excess weld nodules are removed by rapid nodule removal to ensure a smooth surface of the weld joint, reduce stress concentration points, and improve fatigue performance of the weld joint.
[0026] The method for slowing down the wear rate of the softening zone of the rail flash weld joint provided by the present invention effectively solves the technical problem of failure of the rail flash weld joint due to impact and fatigue wear in the softening zone during service by heating and accelerating cooling in the weld joint area and performing constant temperature treatment on the parent material areas on both sides of the weld joint area, and has significant innovation and practicality. Specifically, the present application improves the average hardness of the softening zone of the rail flash weld joint by ≥95% compared with the air-cooled joint after welding by heating and accelerating cooling the joint area, which can effectively enhance the wear resistance and impact resistance of the weld joint, reduce the wear caused by the impact of train operation and long-term friction, and extend the service life of the rail. The present invention controls the width of the softening zone on one side of the joint to ≤5mm by precisely controlling the heating and cooling process. Compared with the traditional welding process, the softening zone range is greatly reduced, the problem of performance degradation of the weld joint caused by the excessive softening zone is reduced, and the overall strength and stability of the weld joint are further improved.
[0027] In some embodiments, during the heating and accelerated cooling of the rail flash weld joint area, the temperature of the joint parent material area is maintained between 20° C. and 50° C. by constant temperature treatment. The constant temperature treatment can keep the joint parent material area at a relatively stable temperature during the welding process, avoiding stress concentration caused by excessive temperature gradient, thereby effectively slowing down the wear rate of the softening area of the rail flash weld joint.
[0028] In some embodiments, the start time of the constant temperature treatment is more than 30 seconds earlier than the start time of heating the rail flash weld joint area, and the end time of the constant temperature treatment is more than 30 seconds later than the end time of the accelerated cooling of the heated weld joint area, so as to ensure that the temperature of the joint base material area is maintained between 20°C and 50°C during the heating and accelerated cooling of the rail flash weld joint area.
[0029] In some embodiments, the accelerated cooling of the heated weld joint area includes: using compressed air for accelerated cooling, the starting temperature of the center of the rail top surface of the rail weld joint area during accelerated cooling is 850℃~980℃, the pressure of the compressed air is 0.05MPa~0.70MPa, the average cooling rate of the accelerated cooling is 5℃ / s~25℃ / s, and at the end of the accelerated cooling, the temperature of the center of the rail top surface of the rail weld joint area is 350℃~550℃. Compressed air is a clean cooling medium, and no liquid residue is produced during the cooling process. The pressure and flow rate of the compressed air can be precisely adjusted according to the specific requirements of the weld joint, thereby achieving precise control of the cooling rate and cooling effect. Specifically, by precisely controlling the starting temperature (850℃~980℃) and the ending temperature (350℃~550℃) of the accelerated cooling, as well as the cooling rate (5℃ / s~25℃ / s), the width of the softening zone of the weld joint can be effectively controlled, which helps to reduce the softening zone of the weld joint and improve its overall performance.
[0030] In some embodiments, the joint parent material area on both sides of the rail flash weld joint area is the entire rail head and rail waist area including the rail top surface, rail head fillet, rail head side and rail waist web. During the heat treatment process of the rail weld joint, the rail head and rail waist area are the parts with the most significant stress concentration and temperature change. By performing constant temperature treatment on the entire rail head and rail waist area of the joint parent material area, it can be ensured that the temperature changes of these key parts during the welding process are more uniform, avoiding thermal stress concentration caused by local temperature differences, thereby improving the overall toughness and fatigue resistance of the welded joint, and slowing down the wear rate of the softening zone of the rail flash welded joint.
[0031] In some embodiments, the constant temperature treatment is implemented using a contact heat-conducting device that imitates the profile of a steel rail. The contact heat-conducting device is a hollow structure, and heat exchange is carried out inside through a cooling medium. The contact heat-conducting device and the contact surface of the rail are coupled with a flexible heat-conducting material. Specifically, the cooling device is provided with a cooling medium inlet and outlet to allow the cooling medium to circulate inside the device. This circulation system can continuously take away the heat of the welded joint and ensure the stability and efficiency of the cooling process. In addition, the contact heat-conducting device and the contact surface of the rail are coupled with a flexible heat-conducting material, which can fill the tiny gaps on the contact surface and increase the actual contact area, thereby improving the heat transfer efficiency. Flexible heat-conducting materials (such as thermal grease, graphite sheets, etc.) can effectively reduce the contact thermal resistance and ensure that the temperature distribution of the joint parent material area is more uniform during the constant temperature treatment process.
[0032] In some embodiments, Figure 1 and Figure 2As shown, the contact heat-conducting device includes a first heat-conducting component in contact with the rail top surface, the rail head fillet, and the rail head side surface, and a second heat-conducting component in contact with both sides of the rail waist web. The thickness d of the first heat-conducting component is 15mm-30mm, and the length b along the extension direction of the rail is 20mm-40mm, that is, the width c1 of the first heat-conducting component perpendicular to the extension direction of the rail = the rail head width + 2d, and the height c2 of the first heat-conducting component = the rail head height + d; the length b of the second heat-conducting component along the extension direction of the rail is 20mm-40mm, the height e is equal to the height of the rail waist web, and the thickness e is 45mm-60mm, so as to be able to completely cover the entire rail head and rail waist area including the rail top surface, the rail head fillet, the rail head side surface and the rail waist web in the joint base material area.
[0033] In some embodiments, the heating process is to perform secondary heating on the flash welded joint area of the rail that has been cooled to a certain temperature (such as less than 300°C) after welding. The starting temperature of the heating process is less than 300°C, and the termination temperature of the heating process is 800°C to 1000°C. Through secondary heating, the austenite grains in the welded joint area can be reorganized and refined. During the welding process, the austenite grains in the joint area tend to coarsen due to high temperature, resulting in a significant decrease in toughness and plasticity. After secondary heating to 800°C to 1000°C, the grain size is refined, thereby significantly improving the microstructure of the welded joint. The impact energy of the welded joint that has not been normalized is only 30% to 40% of that of the parent material, but after secondary heating treatment, its performance is significantly improved. In addition, secondary heating can also effectively control the width of the softening zone of the welded joint, thereby reducing the low joint phenomenon caused by local softening.
[0034] In some embodiments, the heating process uses an induction coil that simulates the profile of a rail, and the induction coil covers the entire cross-section of the rail flash weld joint. The distance between the induction coil and the surface of the rail is 5mm to 50mm, and the length a of the induction coil along the extension direction of the rail is 60mm to 150mm. During the heating process, the induction coil controls the temperature rise rate of the weld joint area to be 1.0℃ / s to 20.0℃ / s. The heating area of the induction coil covers the entire weld joint area, including the fusion line, heat-affected zone, and parent material area, to effectively refine the grains in the weld joint area, reduce the residual stress of the weld joint, and ensure that the temperature distribution of the entire cross-section of the weld joint is more uniform.
[0035] In some embodiments, the working position of the contact heat conduction device is adjacent to the electric induction coil during the heating process, with a gap of ≤2mm, which can ensure that the heat generated during the induction heating process is quickly transferred to the heat conduction device to reduce heat loss. This close layout can improve the overall efficiency of the heat treatment and ensure that the temperature distribution of the weld joint area during the heating process is more uniform.
[0036] The method for slowing down the wear rate of the softening zone of the rail flash weld joint provided by the present application will be further described below in conjunction with specific embodiments: Example 1 In this embodiment, the pearlite rail used has a C mass fraction of 0.80%, a Si mass fraction of 1.20%, a Mn mass fraction of 1.10%, a Cr mass fraction of 0.12%, a V mass fraction of 0.05%, a P mass fraction of 0.005% for both S and Al. The flash welding process mainly consists of four stages: electrode clamping, power heating, pressurized upsetting, and rapid nodule pushing. The duration of the entire welding process is 130 seconds. After the welding process is completed and the joint is cooled to below 300°C, a contact heat conduction device imitating the rail profile is used to perform constant temperature treatment on the joint base material area on both sides of the rail flash welding joint area, including the rail top surface, rail head fillet, rail head side and rail waist web. The appearance dimensions b, d, and e of the constant temperature treatment device are 20 mm, 15 mm, and 45 mm, respectively. Its working position is adjacent to the heating process induction coil and the gap is ≤2 mm. After the constant temperature treatment time of the parent material area is 40s, the electric induction coil imitating the rail profile is used to reheat the rail flash welding joint area. The distance between the electric induction coil and the rail surface is 5mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 60mm. The temperature rise rate of the rail flash welding joint area during the heating process is 1.0℃ / s. When the heating temperature reaches 850℃, compressed air is used to accelerate the cooling of the area covered by the heating induction coil. The pressure of the compressed air is 0.05MPa, and the average cooling rate of the accelerated cooling is 5℃ / s. When the temperature of the center of the top surface of the rail is 350℃, the air compression cooling is stopped. During the heating and cooling process of the joint area, the constant temperature treatment of the joint parent material area is maintained continuously, and the temperature is maintained at 20℃. And the termination time of the constant temperature treatment is delayed by 40s compared with the termination time of the accelerated cooling of the joint area. The average hardness of the softening zone of the rail flash welded joint treated by this method is increased by 98% compared with the air-cooled joint after welding. The width of the softening zone on one side of the joint is 4mm, which greatly slows down the wear rate of the softening zone of the rail flash welded joint.
[0037] Example 2 In this embodiment, the pearlite rail used has a C mass fraction of 0.80%, a Si mass fraction of 1.20%, a Mn mass fraction of 1.10%, a Cr mass fraction of 0.12%, a V mass fraction of 0.05%, a P mass fraction of 0.005% and a S mass fraction of 0.001%. The flash welding process mainly includes four stages: electrode clamping, power heating, pressurized upsetting and rapid nodule pushing. The duration of the entire welding process is 130s. After the welding process is completed and the joint is cooled to below 300°C, a contact heat conduction device imitating the rail profile is used to perform constant temperature treatment on the joint base material area on both sides of the rail flash welding joint area, including the rail top surface, rail head fillet, rail head side and rail waist web. The appearance dimensions b, d and e of the constant temperature treatment device are 40mm, 30mm and 60mm respectively, and its working position is adjacent to the heating process induction coil with a gap of ≤2mm. After the constant temperature treatment time of the parent material area is 50s, the electric induction coil imitating the rail profile is used to reheat the rail flash welding joint area. The distance between the electric induction coil and the rail surface is 50mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 150mm. The temperature rise rate of the rail flash welding joint area during the heating process is 20.0℃ / s. When the heating temperature reaches 980℃, compressed air is used to accelerate the cooling of the area covered by the heating induction coil. The pressure of the compressed air is 0.70MPa, and the average cooling rate of the accelerated cooling is 25℃ / s. When the temperature of the center of the top surface of the rail is 550℃, the air compression cooling is stopped. During the heating and cooling process of the joint area, the constant temperature treatment of the joint parent material area is maintained continuously, and the temperature is maintained at 50℃. And the termination time of the constant temperature treatment is delayed by 70s compared with the termination time of the accelerated cooling of the joint area. The average hardness of the softening zone of the rail flash welded joint treated by this method is increased by 97% compared with the air-cooled joint after welding. The width of the softening zone on one side of the joint is 3mm, which greatly slows down the wear rate of the softening zone of the rail flash welded joint.
[0038] Example 3 In this embodiment, the pearlite rail used has a C mass fraction of 0.80%, a Si mass fraction of 1.20%, a Mn mass fraction of 1.10%, a Cr mass fraction of 0.12%, a V mass fraction of 0.05%, a P mass fraction of 0.005% for each of the S elements, and an Al mass fraction of 0.001%. The flash welding process mainly includes four stages: electrode clamping, power heating, pressurized upsetting, and rapid nodule pushing. The duration of the entire welding process is 130 seconds. After the welding process is completed and the joint is cooled to below 300°C, a contact heat conduction device imitating the rail profile is used to perform constant temperature treatment on the joint base material area on both sides of the rail flash welding joint area, including the rail top surface, rail head fillet, rail head side, and rail waist web. The appearance dimensions b, d, and e of the constant temperature treatment device are 30 mm, 25 mm, and 50 mm, respectively. Its working position is adjacent to the heating process induction coil and the gap is ≤2 mm. After the constant temperature treatment time of the parent material area is 60s, the electric induction coil imitating the rail profile is used to reheat the rail flash welding joint area. The distance between the electric induction coil and the rail surface is 30mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 100mm. The temperature rise rate of the rail flash welding joint area during the heating process is 10.0℃ / s. When the heating temperature reaches 900℃, compressed air is used to accelerate the cooling of the area covered by the heating induction coil. The pressure of the compressed air is 0.3MPa, and the average cooling rate of the accelerated cooling is 15℃ / s. When the temperature of the center of the top surface of the rail is 400℃, the air compression cooling is stopped. During the heating and cooling process of the joint area, the constant temperature treatment of the joint parent material area is maintained continuously, and the temperature is maintained at 40℃. And the termination time of the constant temperature treatment is delayed by 60s compared with the termination time of the accelerated cooling of the joint area. The average hardness of the softening zone of the rail flash welded joint treated by this method is increased by 97% compared with the air-cooled joint after welding. The width of the softening zone on one side of the joint is 4mm, which greatly slows down the wear rate of the softening zone of the rail flash welded joint.
[0039] Example 4 In this embodiment, the pearlite rail used has a C mass fraction of 0.80%, a Si mass fraction of 1.20%, a Mn mass fraction of 1.10%, a Cr mass fraction of 0.12%, a V mass fraction of 0.05%, a P mass fraction of 0.005% for both S and Al. The flash welding process mainly consists of four stages: electrode clamping, power heating, pressurized upsetting, and rapid nodule pushing. The duration of the entire welding process is 130 seconds. After the welding process is completed and the joint is cooled to below 300°C, a contact heat conduction device imitating the rail profile is used to perform constant temperature treatment on the joint base material area on both sides of the rail flash welding joint area, including the rail top surface, rail head fillet, rail head side and rail waist web. The appearance dimensions b, d, and e of the constant temperature treatment device are 20 mm, 15 mm, and 45 mm, respectively. Its working position is adjacent to the heating process induction coil and the gap is ≤2 mm. After the constant temperature treatment time of the parent material area is 50s, the electric induction coil imitating the rail profile is used to reheat the rail flash welding joint area. The distance between the electric induction coil and the rail surface is 5mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 60mm. The temperature rise rate of the rail flash welding joint area during the heating process is 1.0℃ / s. When the heating temperature reaches 850℃, compressed air is used to accelerate the cooling of the area covered by the heating induction coil. The pressure of the compressed air is 0.70MPa, and the average cooling rate of the accelerated cooling is 25℃ / s. When the temperature of the center of the top surface of the rail is 550℃, the air compression cooling is stopped. During the heating and cooling process of the joint area, the constant temperature treatment of the joint parent material area is maintained continuously, and the temperature is maintained at 40℃. And the termination time of the constant temperature treatment is delayed by 60s compared with the termination time of the accelerated cooling of the joint area. The average hardness of the softening zone of the rail flash welded joint treated by this method is increased by 97% compared with the air-cooled joint after welding. The width of the softening zone on one side of the joint is 3mm, which greatly slows down the wear rate of the softening zone of the rail flash welded joint.
[0040] Example 5 In this embodiment, the pearlite rail used has a C mass fraction of 0.80%, a Si mass fraction of 1.20%, a Mn mass fraction of 1.10%, a Cr mass fraction of 0.12%, a V mass fraction of 0.05%, a P mass fraction of 0.005% for both S and Al. The flash welding process mainly consists of four stages: electrode clamping, power heating, pressurized upsetting, and rapid nodule pushing. The duration of the entire welding process is 130 seconds. After the welding process is completed and the joint is cooled to below 300°C, a contact heat conduction device imitating the rail profile is used to perform constant temperature treatment on the joint base material area on both sides of the rail flash welding joint area, including the rail top surface, rail head fillet, rail head side and rail waist web. The appearance dimensions b, d, and e of the constant temperature treatment device are 20 mm, 15 mm, and 45 mm, respectively. Its working position is adjacent to the heating process induction coil and the gap is ≤2 mm. After the constant temperature treatment time of the parent material area is 50s, the electric induction coil imitating the rail profile is used to perform secondary heating on the flash welding joint area of the rail. The distance between the electric induction coil and the rail surface is 50mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 150mm. The temperature rise rate of the flash welding joint area of the rail during the heating process is 20.0℃ / s. When the heating temperature reaches 980℃, compressed air is used to accelerate the cooling of the area covered by the heating induction coil. The pressure of the compressed air is 0.05MPa~0.70MPa, and the average cooling rate of the accelerated cooling is 5℃ / s. When the temperature of the center of the top surface of the rail is 350℃, the air compression cooling is stopped. During the heating and cooling process of the joint area, the constant temperature treatment of the parent material area of the joint is maintained continuously, and the temperature is maintained at 40℃. And the termination time of the constant temperature treatment is delayed by 50s compared with the termination time of the accelerated cooling of the joint area. The average hardness of the softening zone of the rail flash welded joint treated by this method is increased by 98% compared with the air-cooled joint after welding. The width of the softening zone on one side of the joint is 3mm, which greatly slows down the wear rate of the softening zone of the rail flash welded joint.
[0041] Comparative Example 1 In this comparative example, the pearlite rail used has a C mass fraction of 0.80%, a Si mass fraction of 1.20%, a Mn mass fraction of 1.10%, a Cr mass fraction of 0.12%, a V mass fraction of 0.05%, a P mass fraction of 0.005% for both S and Al. The flash welding process mainly consists of four stages: electrode clamping, power heating, pressurized upsetting, and rapid nodule pushing. The duration of the entire welding process is 130s. After the welding process is completed and the joint is cooled to below 300°C, a contact heat conduction device imitating the rail profile is used to perform constant temperature treatment on the joint base material area on both sides of the rail flash welding joint area, including the rail top surface, rail head fillet, rail head side, and rail waist web. The appearance dimensions b, d, and e of the constant temperature treatment device are 10mm, 10mm, and 30mm, respectively. Its working position is adjacent to the heating process induction coil and the gap is ≤2mm. After the constant temperature treatment time of the parent material area is 20s, the electric induction coil imitating the rail profile is used to reheat the rail flash welding joint area. The distance between the electric induction coil and the rail surface is 4mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 50mm. The temperature rise rate of the rail flash welding joint area during the heating process is 0.5℃ / s. When the heating temperature reaches 800℃, compressed air is used to accelerate the cooling of the area covered by the heating induction coil. The pressure of the compressed air is 0.04MPa, and the average cooling rate of the accelerated cooling is 4℃ / s. When the temperature of the center of the top surface of the rail is 300℃, the air compression cooling is stopped. During the heating and cooling process of the joint area, the constant temperature treatment of the joint parent material area is maintained continuously, and the temperature is maintained at 10℃. And the termination time of the constant temperature treatment is delayed by 10s compared with the termination time of the accelerated cooling of the joint area. The average hardness of the softening zone of the rail flash welded joint treated by this method is only 20% higher than that of the air-cooled joint after welding, and the width of the softening zone on one side of the joint is 30mm, which cannot meet the use requirements.
[0042] Comparative Example 2 In this comparative example, the pearlite rail used has a C mass fraction of 0.80%, a Si mass fraction of 1.20%, a Mn mass fraction of 1.10%, a Cr mass fraction of 0.12%, a V mass fraction of 0.05%, a P mass fraction of 0.005% for both S and Al. The flash welding process mainly consists of four stages: electrode clamping, power heating, pressurized upsetting, and rapid nodule pushing. The duration of the entire welding process is 130s. After the welding process is completed and the joint is cooled to below 300°C, a contact heat conduction device imitating the rail profile is used to perform constant temperature treatment on the joint base material area on both sides of the rail flash welding joint area, including the rail top surface, rail head fillet, rail head side, and rail waist web. The appearance dimensions b, d, and e of the constant temperature treatment device are 45mm, 35mm, and 65mm, respectively. Its working position is adjacent to the electric induction coil of the heating process and the gap is ≤2mm. After the constant temperature treatment time of the parent material area is 20s, the electric induction coil imitating the rail profile is used to reheat the rail flash welding joint area. The distance between the electric induction coil and the rail surface is 55mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 200mm. The temperature rise rate of the rail flash welding joint area during the heating process is 25.0℃ / s. When the heating temperature reaches 1000℃, compressed air is used to accelerate the cooling of the area covered by the heating induction coil. The pressure of the compressed air is 0.80MPa, and the average cooling rate of the accelerated cooling is 30℃ / s. When the temperature of the center of the top surface of the rail is 600℃, the air compression cooling is stopped. During the heating and cooling process of the joint area, the constant temperature treatment of the joint parent material area is maintained continuously, and the temperature is maintained at 40℃. And the termination time of the constant temperature treatment is delayed by 10s compared with the termination time of the accelerated cooling of the joint area. The average hardness of the softening zone of the rail flash welded joint treated by this method is only 40% higher than that of the air-cooled joint after welding, and the width of the softening zone on one side of the joint is 35mm, which cannot meet the use requirements.
[0043] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0044] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.
Claims
1. A method for slowing down the wear rate of the softening zone of a rail flash weld joint, characterized in that: include: Heating the rail flash weld joint area; Accelerate cooling of the heated weld joint area; Before heating the rail flash welding joint area, during heating, during cooling, and after cooling, the joint base material areas on both sides of the rail flash welding joint area are subjected to constant temperature treatment.
2. The method for slowing down the wear rate of the softening zone of the rail flash weld joint according to claim 1, characterized in that: During the heating and accelerated cooling of the rail flash welded joint region, the constant temperature treatment maintains the temperature of the joint base material region between 20°C and 50°C.
3. The method for slowing down the wear rate of the softening zone of the rail flash welded joint according to claim 2, characterized in that: The start time of the constant temperature treatment is more than 30 seconds earlier than the start time of heating the rail flash welding joint area, and the end time of the constant temperature treatment is more than 30 seconds later than the end time of accelerated cooling of the heated welding joint area.
4. The method for slowing down the wear rate of the softening zone of the rail flash welded joint according to claim 1, characterized in that: The accelerated cooling of the heated welding joint area includes: using compressed air for accelerated cooling, the starting temperature of the center of the rail top surface of the rail welding joint area during accelerated cooling is 850°C to 980°C, the pressure of the compressed air is 0.05MPa to 0.70MPa, the average cooling rate of the accelerated cooling is 5°C / s to 25°C / s, and at the end of the accelerated cooling, the temperature of the center of the rail top surface of the rail welding joint area is 350°C to 550°C.
5. The method for slowing down the wear rate of the softening zone of the rail flash weld joint according to claim 1, characterized in that: The joint parent material areas on both sides of the rail flash welding joint area are the entire rail head and rail waist area including the rail top surface, rail head fillet, rail head side surface and rail waist web.
6. The method for slowing down the wear rate of the softening zone of the rail flash weld joint according to claim 5, characterized in that: The constant temperature treatment is implemented by using a contact heat conduction device imitating the profile of a rail. The contact heat conduction device is a hollow structure, and heat exchange is performed inside through a cooling medium. The contact heat conduction device and the contact surface of the rail are coupled by a flexible heat conducting material.
7. The method for slowing down the wear rate of the softening zone of the rail flash welded joint according to claim 6, characterized in that: The contact heat-conducting device includes a first heat-conducting component in contact with the rail top surface, the rail head fillet, and the rail head side surface, and a second heat-conducting component in contact with both sides of the rail waist web. The thickness of the first heat-conducting component is 15mm to 30mm, and the length along the extension direction of the rail is 20mm to 40mm; the length of the second heat-conducting component along the extension direction of the rail is 20mm to 40mm, the height is equal to the height of the rail waist web, and the thickness is 45mm to 60mm.
8. The method for slowing down the wear rate of the softening zone of the rail flash welded joint according to claim 7, characterized in that: The heating process is to perform secondary heating on the rail flash welding joint area cooled to a certain temperature after welding. The starting temperature of the heating process is less than 300°C, and the ending temperature of the heating process is 800°C to 1000°C.
9. The method for slowing down the wear rate of the softening zone of the rail flash weld joint according to claim 8, characterized in that: The heating process uses an electric induction coil that simulates the profile of a rail. The distance between the electric induction coil and the surface of the rail is 5 mm to 50 mm. The length of the electric induction coil along the extension direction of the rail is 60 mm to 150 mm. During the heating process, the electric induction coil controls the temperature rise rate of the welding joint area to be 1.0°C / s to 20.0°C / s.
10. The method for slowing down the wear rate of the softening zone of the rail flash weld joint according to claim 9, characterized in that: The working position of the contact heat conduction device is adjacent to the electric induction coil during the heating process, with a gap of ≤2mm.