Heat treatment method and equipment for improving performance stability of end-quenched steel rail

Abstract

The invention relates to the technical field of steel rail production processes, in particular to a heat treatment method and equipment for improving the performance stability of an end-quenched steel rail, the method is completed by adopting a combined cooling quenching unit, and the combined cooling quenching unit comprises a combined cooling nozzle; the combined cooling nozzles are arranged on the rail head tread and the rail head side face of the steel rail, the combined cooling nozzles comprise air cooling nozzles and water cooling nozzles, the air cooling nozzles are arranged in the centers of the combined cooling nozzles, and the multiple water cooling nozzles are arranged on the air cooling nozzles in a circle surrounding mode at equal angles and equal distances. By adopting a water cooling and air cooling combined cooling mode and optimizing a heat treatment method, the method disclosed by the invention has the beneficial effects that the quenching cooling speed can be flexibly adjusted and controlled, so that the mechanical property and the performance stability of the steel rail with the quenched end part are improved.

Description

Technical Field

[0001] The invention relates to the technical field of rail production technology, and in particular to a heat treatment method and equipment for improving the performance stability of end-quenched rails. Background Art

[0002] Railways are the main arteries of the world's economy, and their safe transportation is very important. In order to meet the needs of high-speed railway transportation, high axle load and high freight density, in addition to using large-end rails, rails are required to have higher strength and toughness, that is, higher wear resistance, compression resistance and brittle fracture resistance. There are two ways to improve the strength and toughness of steel, alloying and heat treatment. At present, my country mainly adopts heat treatment, that is, full-length quenching of 100-meter rails and quenching of rail ends.

[0003] End-quenched rails have long occupied a large share of usage due to their economical and practical nature, and are widely used in mines and dedicated lines. Rails are used when there is no welding, and the rails are connected by connecting plates. When the train runs to the joint, the wheels will inevitably press over the joint between the rails, and the ends of the rails are often flattened or crushed. At this time, the height of the rail ends will be lower than the rail body. When the train runs at the joint, the unevenness causes the forces on the rail ends to be complex and severe, and they usually wear out. In severe cases, the rails will break. Usually, the ends of the rails wear 3-5 times faster than the rail body, and sometimes up to 7 times. An effective way to increase the service life of the rail ends is to quench the ends. For this reason, stable control of the heat treatment process of the rail ends is the guarantee for the rails to meet high strength and toughness.

[0004] The Chinese invention with authorization announcement number CN105177242B "A movable rail head after heating air jet cooling device" discloses a movable rail head after heating air jet cooling device, which relates to the field of air jet cooling equipment, and a plurality of air inlets are distributed on the top surfaces of the front end bellows, the middle end bellows and the rear end bellows, and the front end bellows, the middle end bellows and the rear end bellows are all provided with bellows cover plates, and the middle end bellows and the rear end bellows are connected by a connecting rotating device, and the increase in the distance between the lower surface of the bellows body and the rail tread caused by the bending and sagging of the rail head due to heat is reduced by the mutually connected rotating structure, and the cooling speed of the rail head is further stabilized and increased, the hardening effect of the rail head is improved, the dead weight of the device is reduced, the load on the lead screw of the quenching machine tool is reduced, the service life of the rail parts is extended, and the needs of the turnout rail parts market are better met. However, the patent adopts a heat treatment method of air jet cooling, and the cooling nozzle is designed as a simple cylindrical spray hole structure, the heat treatment cooling speed is slow, the cooling effect is poor, and the mechanical properties of the quenched rail end are low. Summary of the invention

[0005] To overcome the deficiencies of the prior art, the present invention provides a heat treatment method and equipment for improving the performance stability of end-quenched rails. The method is completed by a combined cooling and quenching unit, and the combined cooling and quenching unit uses a combined cooling nozzle of air-cooling nozzles and water-cooling nozzles, adopting a combined cooling method of water-cooling and air-cooling to improve the heat treatment cooling rate, the quenching cooling speed and the hardening depth of the end-quenched rails, thereby ensuring the performance stability of the end-quenched rails.

[0006] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0007] A heat treatment method for improving the performance stability of end-quenched rails, which is completed by a combined cooling and quenching unit. The combined cooling and quenching unit includes a combined cooling nozzle; the combined cooling nozzle is arranged on the tread surface and the side surface of the rail head. The combined cooling nozzle includes an air-cooling nozzle and a water-cooling nozzle. The heat treatment method specifically includes the following steps:

[0008] S1. Push 100-140 mm of the rail end into the induction heating unit. The induction coil of the induction unit is connected to an alternating current with a medium frequency of 1.0-2.0 kHz to generate a large amount of resistance heat. During the production process, the heating temperature of the rail end is set to 900-1000 °C to enable the rail to be fully austenitized.

[0009] S2. Immediately push 100-140 mm of the rail end heated to austenitization into the combined cooling and quenching unit. First, turn on the air-cooling nozzle and control the cooling speed to be 7-9 °C / s, and the cooling time to be 10-20 s.

[0010] S3. When the surface temperature of the rail end drops to 700-800 °C, on the basis of maintaining the air-cooling nozzle for air-cooling, turn on the water-cooling nozzle, and control the cooling speed to be increased to 9-11 °C / s, and the cooling time to be 15-20 s.

[0011] S4. When the surface temperature of the rail drops to 450-550 °C, turn off the combined cooling and quenching unit; at the same time, immediately push 100-140 mm of the rail end out of the combined cooling and quenching unit, and then push the rail into the cooling bed for air-cooling.

[0012] Further, after quenching, the depth of the hardened layer on the tread surface of the rail end ≥ 14 mm; the length of the stable hardening zone ≥ 60 mm; the length of the transition zone ≤ 30 mm.

[0013] Further, the microstructure of the hardened layer is fine lamellar pearlite.

[0014] Further, an air-cooling nozzle is arranged at the central position of the combined cooling nozzle, and a plurality of water-cooling nozzles are arranged in a circular shape at equal angles and equal distances around the air-cooling nozzle for one week. The air-cooling nozzle and the water-cooling nozzles are connected by threads; the structure of the air-cooling nozzle is a Laval nozzle, and the structure of the water-cooling nozzle is a straight tube nozzle.

[0015] Further, the inlet diameter of the air-cooling nozzle is 5.5 - 7.5 mm; the throat diameter of the air-cooling nozzle is 2.5 - 4.5 mm; the outlet diameter of the air-cooling nozzle is 4.5 - 6.5 mm.

[0016] Further, the diameter of the water-cooling nozzle is 1.5 - 3.5 mm, the number of water-cooling nozzles is 12 - 16, and the included angle between adjacent water-cooling nozzles is 22.5° - 30°.

[0017] Further, the distance between the water-cooling nozzle and the air-cooling nozzle is 4 - 6 mm.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] (1) By using the traditional air-cooling nozzle and its process, the performance of the end-quenched rail is unstable, and the first-pass qualification rate of the end-quenched rail inspection is 90%. By using the newly designed combined cooling nozzle and its process, the quenching cooling rate can be flexibly adjusted and controlled, thereby significantly improving the performance stability of the end-quenched rail, and the first-pass qualification rate of the end-quenched rail inspection is 100%.

[0020] (2) Through the structural design of the combined cooling nozzle, the spraying area is increased to expand the effective cooling area of the rail surface, ensuring the shape and size of the hardened layer of the head part of the end-quenched rail. The depth of the hardened layer on the tread is ≥14 mm; the length of the stable hardened area is ≥60 mm; the length of the transition area is ≤30 mm, and the performance of the end quenching of the rail is stable.

[0021] (3) By adopting the combined cooling method of air cooling combined with water cooling to increase the cooling rate of the end-quenched rail, as the cooling rate increases, the pearlite lamellar spacing gradually decreases, thereby improving the mechanical properties of the end-quenched rail. The hardness and wear resistance of the rail end are significantly improved, avoiding the potential accident hazard of rail head fracture caused by unevenness at the connection.

[0022] (4) By using the newly designed combined cooling nozzle and its process, not only can the quenching cooling rate be flexibly adjusted and controlled, but also the process of single air blowing cooling or water spraying cooling can be adopted to produce the end-quenched rail, thereby improving the production stability of the end-quenched rail and the service life of the equipment. Description of the Drawings

[0023] Figure 1It is the hardness distribution diagram of the hardened layer from the surface to the core of the cross-section of the end-quenched rail in Embodiment 1 of the present invention.

[0024] Figure 2 It is the hardness distribution diagram of the hardened layer from the surface to the core of the longitudinal section of the end-quenched rail in Embodiment 1 of the present invention.

[0025] Figure 3 It is the photo diagram of the shape and depth of the hardened layer of the cross-section of the end-quenched rail in Embodiment 1 of the present invention.

[0026] Figure 4 It is the photo diagram of the shape and length of the hardened layer of the longitudinal section of the end-quenched rail in Embodiment 1 of the present invention.

[0027] Figure 5 It is the hardness distribution diagram of the hardened layer from the surface to the core of the cross-section of the end-quenched rail in Embodiment 2 of the present invention.

[0028] Figure 6 It is the hardness distribution diagram of the hardened layer from the surface to the core of the longitudinal section of the end-quenched rail in Embodiment 2 of the present invention.

[0029] Figure 7 It is the photo diagram of the shape and depth of the hardened layer of the cross-section of the end-quenched rail in Embodiment 2 of the present invention.

[0030] Figure 8 It is the photo diagram of the shape and length of the hardened layer of the longitudinal section of the end-quenched rail in Embodiment 2 of the present invention.

[0031] Figure 9 It is the hardness distribution diagram of the hardened layer from the surface to the core of the cross-section of the end-quenched rail in the comparative example of the present invention.

[0032] Figure 10 It is the hardness distribution diagram of the hardened layer from the surface to the core of the longitudinal section of the end-quenched rail in the comparative example of the present invention.

[0033] Figure 11 It is the photo diagram of the shape and depth of the hardened layer of the cross-section of the end-quenched rail in the comparative example of the present invention.

[0034] Figure 12 It is the photo diagram of the shape and length of the hardened layer of the longitudinal section of the end-quenched rail in the comparative example of the present invention.

[0035] Figure 13 It is the photo diagram of the 100x, 200x, and 500x microstructures of the hardened layer in the comparative example of the present invention.

[0036] Figure 14 It is the photo diagram of the 100x, 200x, and 500x microstructures of the hardened layer in Embodiment 1 of the present invention.

[0037] Figure 15 They are the micrographs of the hardened layer of the second embodiment of the present invention at 100 times, 200 times, and 500 times.

[0038] Figure 16 It is a front view structural sectional view of the combined cooling nozzle of the present invention.

[0039] Figure 17 It is a side view structural sectional view of the combined cooling nozzle of the present invention.

[0040] Figure 18 It is a front view structural sectional view of the air-cooling nozzle of the combined cooling nozzle of the present invention.

[0041] Figure 19 It is a side view structural sectional view of the air-cooling nozzle of the combined cooling nozzle of the present invention.

[0042] Figure 20 It is a front view structural sectional view of the water-cooling nozzle of the combined cooling nozzle of the present invention.

[0043] Figure 21 It is a side view structural sectional view of the water-cooling nozzle of the combined cooling nozzle of the present invention.

[0044] In the figure: 1. Air-cooling nozzle; 2. Water-cooling nozzle; 3. Air inlet of the air-cooling nozzle; 4. Air outlet of the air-cooling nozzle; 5. External thread; 6. Thread connection; ③. Maximum hardening depth; ④. Hardening zone length; ⑤. 0.8 times the maximum hardening depth; ⑥. Stable hardening zone length. Specific embodiments

[0045] The following further describes the specific embodiments of the present invention with reference to the accompanying drawings of the specification:

[0046] As Figures 16 - 21As shown in the figure, a combined cooling nozzle for a heat treatment method to improve the performance stability of end-quenched rails includes an air-cooling nozzle 1 and a water-cooling nozzle 2. The air-cooling nozzle 1 is arranged at the central position of the combined cooling nozzle. Sixteen water-cooling nozzles 2 are arranged in a circular pattern at equal angles and equal distances around the air-cooling nozzle 1. The included angle between adjacent water-cooling nozzles 2 is 22.5°. The air-cooling nozzle 1 and the water-cooling nozzle 2 are connected by a thread 6. Threads are machined on the outer wall of the structure of the air-cooling nozzle 1, and a through-hole is provided in the center of the structure of the water-cooling nozzle 2, and threads are machined on the inner wall of the through-hole. The air-cooling nozzle 1 is arranged in the central through-hole of the water-cooling nozzle 2 through the thread connection 6. The distance between the water-cooling nozzle 2 and the air-cooling nozzle 1 is 5 mm. The structure of the air-cooling nozzle 1 is a Laval nozzle. The diameter of the air inlet 3 of the air-cooling nozzle is 6 mm, the diameter of the throat of the air-cooling nozzle is 3 mm, and the diameter of the air outlet 4 of the air-cooling nozzle is 5 mm. The structure of the water-cooling nozzle 2 is a straight-tube nozzle, and the diameter of the water-cooling nozzle 2 is 2 mm. An external thread 5 is provided on the outside of the combined cooling nozzle on the side of the air inlet, and it is installed on the end-quenching unit of the rail through the thread. The combined cooling nozzle is arranged on the tread and the side of the rail head.

[0047] In the embodiment, tests were carried out on U71Mn end-quenched rails with a weight of 50 kg / m. Comparative tests were carried out using traditional air-cooling nozzles and newly designed combined cooling nozzles respectively. The diameter of the traditional air-cooling nozzle is 2 mm.

[0048] Table 1 Main process parameters of end-quenched rails:

[0049]

[0050] As Figure 12 shown, for the comparative example, the maximum hardening depth ③ at the end of the quenched rail is 12 mm; the hardening zone length ④ is 90 mm; 0.8 times the maximum hardening depth ⑤ is 9.6 mm; the stable hardening zone length ⑥ is 64 mm; the hardening depth is shallow, and the hardness at the end of the quenched rail is low.

[0051] As Figure 4 、 Figure 8 shown, for Example 1, the maximum hardening depth ③ at the end of the quenched rail is 14 mm; the hardening zone length ④ is 90 mm; 0.8 times the maximum hardening depth ⑤ is 11.2 mm; the stable hardening zone length ⑥ is 64 mm; for Example 2, the maximum hardening depth ③ at the end of the quenched rail is 15 mm; the hardening zone length ④ is 120 mm; 0.8 times the maximum hardening depth ⑤ is 12 mm; the stable hardening zone length ⑥ is 97 mm; the maximum depth of the hardening zone is stable ≥ 14 mm, the length of the stable hardness zone is stable ≥ 60 mm, the length of the transition zone ≤ 30 mm, the hardening depth at the end of the rail is stable, and the hardness at the end of the quenched rail is high.

[0052] As Figures 1 - 15As shown, by detecting the hardened layer shape and size, metallographic structure, cross-sectional and longitudinal hardness of Examples 1-2 and the comparative example, it can be obtained that with the traditional air-cooled nozzle and its process, the performance of the end-quenched rail is unstable. There is no hardened layer coating at the gauge corners on both sides of the rail head cross-section, and the hardened layer shape and size of the end-quenched rail do not meet the standard requirements. After Vickers hardness testing, the hardness at the gauge corner is closer to the matrix and the quenching transition zone, which is judged to be caused by insufficient cooling intensity. With the newly designed combined cooling nozzle and its process, the quenching cooling rate can be flexibly adjusted and controlled, and the performance of the end-quenched rail is stable. There is a hardened layer coating at the gauge corners on both sides of the rail head cross-section. The end-quenched rail produced by the above quenching process has the following characteristics: the depth of the tread hardened layer ≥ 14 mm; the length of the stable hardened zone ≥ 60 mm; the length of the transition zone ≤ 30 mm.

[0053] As Figures 13 - 15 shown, the hardened layer microstructure of the comparative example is pearlite, and the hardened layer microstructures of Examples 1-2 are fine flaky pearlite. The pearlite lamellar spacing is reduced, thereby improving the mechanical properties of the end-quenched rail.

[0054] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and its concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A heat treatment method for improving the performance stability of end-quenched rail, which is completed by a combined cooling and quenching unit, characterized in that The described combined cooling and quenching unit includes a combined cooling nozzle; the combined cooling nozzle is arranged on the tread surface and the side surface of the rail head. The combined cooling nozzle includes an air-cooling nozzle and a water-cooling nozzle. The heat treatment method specifically includes the following steps: S1. Push the 100 - 140 mm end of the rail into the induction heating unit. The induction coil of the induction unit is connected to an alternating current with a medium frequency of 1.0 - 2.0 kHz, generating a large amount of resistance heat. During the production process, set the heating temperature of the rail end to 900 - 1000 °C to enable the rail to be fully austenitized; S2. Immediately push the 100 - 140 mm end of the rail heated to austenitization into the combined cooling and quenching unit. First, turn on the air-cooling nozzle, control the cooling rate to be 7 - 9 °C / s, and the cooling time to be 10 - 20 s; S3. When the surface temperature of the rail end drops to 700 - 800 °C, while maintaining the air-cooling nozzle for air-cooling, then turn on the water-cooling nozzle, control the cooling rate to increase to 9 - 11 °C / s, and the cooling time to be 15 - 20 s; S4. When the surface temperature of the rail drops to 450 - 550 °C, turn off the combined cooling and quenching unit; at the same time, immediately push the 100 - 140 mm end of the rail out of the combined cooling and quenching unit, and then push the rail into the cooling bed for air-cooling.

2. The heat treatment method for improving the performance stability of end-quenched rails according to claim 1, characterized in that, After quenching, the depth of the hardened layer on the tread of the rail end is ≥14 mm; the length of the stable hardened zone is ≥60 mm; the length of the transition zone is ≤30 mm.

3. The heat treatment method for improving the performance stability of end-quenched rail according to claim 2, characterized in that The microstructure of the hardened layer is fine lamellar pearlite.

4. A combined cooling nozzle for the heat treatment method of improving the performance stability of end-quenched rails according to claim 1, characterized in that, An air-cooling nozzle is arranged at the central position of the combined cooling nozzle, and a number of water-cooling nozzles are arranged in a circular shape with equal angles and equal distances around the air-cooling nozzle for one week. The air-cooling nozzle and the water-cooling nozzle are connected by threads; the structure of the air-cooling nozzle is a Laval nozzle, and the structure of the water-cooling nozzle is a straight tube nozzle.

5. The combined cooling nozzle of the heat treatment method for improving the performance stability of end-quenched rails according to claim 4, characterized in that, The inlet diameter of the air-cooling nozzle is 5.5 - 7.5 mm; the throat diameter of the air-cooling nozzle is 2.5 - 4.5 mm; the outlet diameter of the air-cooling nozzle is 4.5 - 6.5 mm.

6. The combined cooling nozzle of the heat treatment method for improving the performance stability of end-quenched rails according to claim 4, characterized in that, The diameter of the water-cooling nozzle is 1.5 - 3.5 mm, the number of water-cooling nozzles is 12 - 16, and the included angle between adjacent water-cooling nozzles is 22.5° - 30°.

7. The combined cooling nozzle of the heat treatment method for improving the performance stability of end-quenched rails according to claim 4, characterized in that, The distance between the water-cooling nozzle and the air-cooling nozzle is 4 - 6 mm.

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