A quenching method for reducing the heat-affected zone of local heat treatment of rails

Abstract

The present application relates to a quenching method for reducing the heat-affected zone of a local heat treatment of a rail, comprising the following steps in sequence: quenching preparation, setting the sensor of the quenching machine tool at a position close to the raw material at the forging heel end of the rail and maintaining a gap with the top surface of the rail; initial quenching, controlling the quenching machine tool to move from the inside to the outside on the top surface of the rail at a quenching speed lower than the quenching speed required by the target rail material, and controlling the quenching power to be lower than the quenching process parameter value required by the target rail material for quenching; mid-term quenching, quenching according to the quenching process parameter value required by the target rail material. Low-frequency quenching can prevent the rail end from heating up too quickly and causing overheating and overburning due to the sharp corner effect, reduce the heat-affected zone, avoid saddle wear, and maintain a low speed so that the part of the rail close to the raw material can be fully quenched. Mid-term quenching ensures the quenching depth of the heel end of the rail, so that the rail is fully quenched.

Description

Technical Field

[0001] The present application relates to the field of heat treatment of rails, and in particular to a quenching method for reducing a heat-affected zone of a local heat treatment of a rail. Background Art

[0002] The strength and toughness of the turnout rail heel end decreases after forging, and the forged heel end (the forged heel end is the area from the forged end of the rail to 1.5 meters near the end of the rail) needs to be re-heat treated to improve the performance of the forged heel end of the rail to the strength and toughness level of the original material.

[0003] At present, the medium frequency induction quenching method is usually used. When the forging and end of the rail are quenched, there is a transition area between the quenched area and the raw material that is not affected by the quenching. Due to the temperature gradient, there will inevitably be a heat-affected zone with a lower hardness than the raw material in this transition area. When the heat-affected zone is wide, saddle-shaped wear is prone to occur during long-term railway driving, that is, the area with relatively high hardness is the saddle peak, and the area with relatively low hardness is the saddle valley, which will cause the rail surface to be short, sharp and uneven, affecting driving safety. Summary of the invention

[0004] In order to improve the product quality of quenched rail heel ends, the present application provides a quenching method for reducing the heat affected zone of the rail during local heat treatment.

[0005] The present application provides a method for reducing the quenching of the heat-affected zone of a local heat treatment of a rail, which adopts the following technical solution:

[0006] A quenching method for reducing the heat-affected zone of a local heat treatment of a rail, comprising the following steps performed in sequence:

[0007] In preparation for quenching, place the front and rear guide wheels of the quenching machine on the rails. The sensor of the quenching machine is located at the forging end of the rail close to the raw material. The sensor and air jet of the quenching machine are controlled to maintain a gap with the top surface of the rail.

[0008] In the initial quenching, the quenching machine is controlled to move from the inside to the outside on the top surface of the rail at a quenching speed lower than the quenching speed required by the target rail material, and the quenching power is controlled to be lower than the quenching process parameter value required by the target rail material to ensure that the quenching time is 10-90s;

[0009] During mid-term quenching, the quenching machine speed and quenching power are adjusted to the quenching process parameter values ​​required by the target rail material for quenching.

[0010] By adopting the above technical solution, low-frequency quenching is first performed on the forged heel end of the rail near the raw material, which can reduce the heat-affected area, avoid saddle wear, and extend the service life of the rail. At the same time, the vehicle speed is kept low so that the part of the rail close to the raw material can be fully quenched. When gradually moving away from the raw material part, the quenching power and vehicle speed are adjusted to the quenching process parameter value of the target steel to ensure the quenching depth of the heel end of the rail and make the rail fully quenched.

[0011] Preferably, the quenching preparation step is specifically as follows: the front and rear guide wheels of the quenching machine are placed on the rail, the sensor of the quenching machine is located at the forging heel end of the rail close to the raw material, and the gap between the sensor of the quenching machine and the two sides of the rail fillet is adjusted to be the same, and the centers of the front and rear guide wheels, the sensor and the air jet are located on the same straight line, the sensor of the quenching machine is controlled to maintain a gap of 5-15mm with the top surface of the rail, and the gap between the air jet and the top surface of the rail is maintained at 10-40mm.

[0012] By adopting the above technical solution and controlling the gap size, the heating and cooling effects of the rails are improved, thereby improving the quenching quality of the rails.

[0013] Preferably, it also includes rail end quenching after mid-term quenching. When the sensor of the quenching machine heats the rail heel end, the vehicle speed is reduced by one-fifth to one-half and the quenching power is reduced by one-fifth to two-thirds.

[0014] By adopting the above technical solution, the quenching machine gradually approaches the heel end of the rail. Due to the sharp corner effect, the heel end of the rail has a "crescent-shaped" high-temperature area with a temperature significantly higher than other positions. This high-temperature area is prone to overheating and overburning, which in turn causes the entire rail to be scrapped. Under the premise of ensuring that the heel end of the rail is fully quenched, the quenching power and vehicle speed are reduced to avoid overheating and overburning in this high-temperature area as much as possible to ensure the quality of the entire rail.

[0015] Preferably, the step of quenching the rail end further comprises: observing the heated color of the fillet of the rail end rail top, and controlling the heated color to remain orange, light orange or yellow.

[0016] By adopting the above technical solution, the quenching degree is monitored by manually observing the heating color, and the quenching process parameters are adjusted in time according to abnormal heating color.

[0017] Preferably, when the heated color is yellowish, the quenching power is reduced, and when the heated color is orange-yellow, the quenching power is increased, while avoiding the appearance of light yellow, white with a slight yellowish color, bright white, orange with a slight red, cherry red, etc. on the end.

[0018] By adopting the above technical solution, the quenching power is specifically adjusted so that the rail heel end will present the required heating color, avoiding the appearance of light yellow, white with a slight yellow, bright white, orange with a slight red, cherry red, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the quenching machine tool of the embodiment of the present application for quenching the forged heel end of the rail.

[0020] Explanation of the accompanying reference numerals: 1. Rail; 2. Front guide wheel; 3. Sensor; 4. Rear guide wheel; 5. Air jet. DETAILED DESCRIPTION

[0021] The following is combined with Figure 1 This application is described in further detail.

[0022] Reference Figure 1 The present application discloses a method for reducing the quenching of the heat-affected zone of a rail in a local heat treatment, comprising the following steps performed in sequence:

[0023] (In this embodiment, commonly used steels such as U71MnH and U75VH are mainly quenched, and corresponding specific quenching process parameter values ​​are set.)

[0024] Quenching preparation: place the front and rear guide wheels of the quenching machine on the rail, the sensor of the quenching machine is located at 1.5 meters from the forging heel of the rail, and adjust the gap between the sensor of the quenching machine and the two sides of the fillet of the rail to be the same, and make the centers of the front and rear guide wheels, sensors and air jets on the same straight line, control the sensor of the quenching machine to maintain a gap of 10mm with the top surface of the rail, and the air jet to maintain a gap of 25mm with the top surface of the rail. In this embodiment, the length of the forged rail is adopted, in which the sum of the length of the forming section and the transition section of the commonly used forged rail is 600mm. In other embodiments, the starting position of the quenching of the lengthened rail heel is adjusted accordingly according to the length of the forging heel of the rail, specifically: the starting position of the sensor is located 800-1000mm after the transition section of the forging heel, that is, the distance between the starting position of the quenching and the end of the forging heel is the length of the forming section + the length of the transition section + (any value in the range of 800-1000mm).

[0025] Initial quenching: Control the quenching machine to move from the inside to the outside on the top surface of the rail at a quenching speed of 5-15cm / min ( Figure 1 The arrow A in the middle indicates the direction), the quenching power is controlled to be 50-150kw for quenching, and the quenching time is ensured to be 10-90s. In this embodiment, a quenching speed of 10cm / min and a quenching power of 100kw are specifically adopted.

[0026] Mid-term quenching: The quenching machine speed and quenching power are adjusted to the quenching process parameter values ​​required by the target rail material for quenching. In this embodiment, a quenching speed of 45 cm / min and a quenching power of 160 kW are used for U71MnH rails; a quenching speed of 45 cm / min and a quenching power of 180 kW are used for U75VH rails.

[0027] Rail end quenching: when the sensor of the quenching machine moves to heat the rail heel end, the vehicle speed is reduced by one third and the quenching power is reduced by one quarter. In the present embodiment, specifically for U71MnH rails, the vehicle speed is reduced to 30 cm / min and the quenching power is reduced to 120 kW; for U75VH rails, the vehicle speed is reduced to 30 cm / min and the quenching power is reduced to 135 kW; at the same time, observe the heating color of the fillet of the rail end, reduce the quenching power when the heating color is yellowish, increase the quenching power when the heating color is orange-yellow, and avoid the appearance of light yellow, white slightly yellow, bright white, orange-yellow slightly red, cherry red, etc. on the end.

[0028] Comparative example: The entire quenching process is always quenched according to the quenching process parameter values ​​required by the target rail material (such as U71MnH material rail: quenching speed 45cm / min, quenching power 160kw; U75VH material rail: quenching speed 45cm / min, quenching power 180kw).

[0029] Performance test experiment: the quenched heel end of the rail is sampled and processed, the top surface of the rail head is ground off 0.5mm, and the Brinell hardness is tested according to the HBW10 / 3000 test method. In the forming section and transition section, the distance between the measuring points is 100mm, and in the parent material section, the distance between the measuring points is 10mm (the heat affected zone is in the parent material section). The test results are shown in Table 1 below.

[0030] Table 1 Brinell hardness test results of quenched rail heel

[0031]

[0032] It can be seen from Table 1 that the quenching method of the present invention can significantly reduce the width of the heat affected zone (heat affected zone width = number of soft spots × spacing between measuring points in the parent material section, where the soft spot is a detection point in the heat affected zone whose hardness value is lower than the hardness standard), increase the hardness of the heat affected zone, improve the local quenching quality of the rail, thereby avoiding saddle wear, extending the service life of the rail, and improving the smoothness and safety of line driving.

[0033] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A quenching method for reducing the heat-affected zone of a rail in a local heat treatment, characterized in that: The method comprises the following steps in sequence: In preparation for quenching, place the front and rear guide wheels of the quenching machine on the rails. The sensor of the quenching machine is located at the forging end of the rail close to the raw material. The sensor and air jet of the quenching machine are controlled to maintain a gap with the top surface of the rail. In the initial quenching, the quenching machine is controlled to move from the inside to the outside on the top surface of the rail at a quenching speed lower than the quenching speed required by the target rail material, and the quenching power is controlled to be lower than the quenching process parameter value required by the target rail material to ensure that the quenching time is 10-90s; Mid-term quenching: adjust the quenching machine speed and quenching power to the quenching process parameter values ​​required by the target rail material for quenching; It also includes the rail end quenching after the mid-term quenching. When the sensor of the quenching machine heats the rail end, the vehicle speed is reduced by one-fifth to one-half and the quenching power is reduced by one-fifth to two-thirds.

2. A quenching method for reducing the heat affected zone of a rail in a local heat treatment according to claim 1, characterized in that: The specific steps of quenching preparation are: place the front and rear guide wheels of the quenching machine on the rail, the sensor of the quenching machine is located at the forging end of the rail close to the raw material, and the gap between the sensor of the quenching machine and the two sides of the rail fillet is adjusted to be the same, and the centers of the front and rear guide wheels, sensors and air jets are located on the same straight line, and the sensor of the quenching machine is controlled to maintain a gap of 5-15mm with the top surface of the rail, and the gap between the air jet and the top surface of the rail is maintained at 10-40mm.

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