Method suitable for steel rail hardening layer depth test

Abstract

The invention discloses a method suitable for a steel rail hardening layer depth test, and belongs to the technical field of heat treatment detection methods. By combining the sampling position, the sampling size and the experimental method of the steel rail, the hardenability and the hardenability of the steel rails with different components, different materials and different sections can be rapidly and accurately measured according to the end quenching experimental thought, and an important reference basis is provided for formulating a hot working process for process production. Based on the method, the hardenability and hardenability of steel rails with different components, different materials and different sections can be measured, and the method is suitable for rapidly and simply judging the change of microscopic structures and mechanical properties at different positions and under different processes in the heat treatment process of the steel rails.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment detection, and in particular relates to a method suitable for testing the depth of a hardened layer of a rail. Background Art

[0002] With the rapid development of heavy-load lines, large-axle-weight and large-capacity freight trains have been put into service on heavy-load lines one after another. The requirements for rail hardness are getting higher and higher. The wear resistance of rails is becoming more and more important to the safety of train operation. The replacement cycle of ordinary rails is short, which affects the line transportation efficiency and increases the transportation cost. Therefore, more wear-resistant rails are needed to meet the service requirements of heavy-load lines.

[0003] At present, the common method at home and abroad is to control the cooling of the rails, that is, to accelerate the cooling of the rail head to refine the structure, thereby increasing the hardness of the rails. The relationship between the cold hardenability, hardened layer depth and structure of the rails cannot be determined. It is particularly important to select a suitable cooling medium and cooling rate to achieve excellent hardenability and hardened layer depth of the rails, so as to achieve the best combination of structure and performance. Combined with the sampling position, sampling size and experimental method of the rails, based on the idea of ​​end quenching experiments, the hardenability and hardenability of rails with different compositions, different materials and different sections can be quickly and accurately determined, providing an important reference for the formulation of hot processing technology for process production. Summary of the invention

[0004] The purpose of the present invention is to provide a method suitable for testing the depth of the hardened layer of a rail. By combining the rail sampling position, sampling size and experimental method, and based on the idea of ​​end quenching experiment, the hardenability and hardenability of rails with different compositions, different materials and different cross-sections can be quickly and accurately determined, providing an important reference basis for formulating hot working technology for process production.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for testing the depth of a rail hardened layer, comprising:

[0007] (1) Sampling is carried out at the rail head position, which should be the A line position of the rail head cross-section hardness. The test surface coincides with the rail head tread, and the fixed surface is at the intersection of the rail head and the rail waist;

[0008] (2) Process the rail head into a round bar with a flange, where the flange diameter is Between, thickness is 3mm; round rod diameter is The total height of the specimen is between 40-50mm;

[0009] (3) Heating the rail hardened layer depth sample, and adjusting the heating temperature and holding time according to different steel qualities and different process requirements;

[0010] (4) After the sample heating process meets the experimental requirements, The cooling medium is sprayed on the lower end of the round rod to control the cooling of the sample. The cooling time is ≥10min. The selection of cooling medium and the control of cooling speed are adjusted according to different steel qualities and different process requirements.

[0011] (5) After the experiment, the sample is milled and finely ground to produce two parallel planes along the axis of the sample for hardness measurement; the grinding depth is between 0.4 and 0.5 mm.

[0012] (6) Perform hardness test on a hardness testing machine. The hardness test lines are located on two parallel lines of the ground surface. The distance between the two lines is ≥3mm. The first measuring point starts at 1mm from the end face, and the distance between the remaining measuring points can be between 1-5mm.

[0013] (7) The hardness is tested at different positions inside the sample at a certain interval from the end of the sample to form a curve of the relationship between hardness and heat treatment depth. At the same time, combined with the microstructural morphology at the hardness position, the changes in microstructure and mechanical properties at different positions and under different processes during the heat treatment of the rail are evaluated.

[0014] Furthermore, it is applicable to heat-treated rails of all materials and rails of all cross-sections.

[0015] Furthermore, the cooling medium is air, water mist or water.

[0016] Furthermore, the grinding depth is between 0.4-0.5 mm.

[0017] Furthermore, hardness tests were performed using Rockwell hardness and Vickers hardness.

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

[0019] The selection of cooling medium and the control of cooling speed of the present invention can be adjusted according to different steel qualities and different process requirements. Based on this method, the hardenability and hardenability of rails with different compositions, different materials and different cross-sections can be measured. It is suitable for quickly and easily judging the changes in microstructure and mechanical properties at different positions and under different processes during the heat treatment of rails, and provides an important reference basis for formulating hot processing technology for rail process production.

[0020] Based on this method, the hardenability and hardenability of rails with different compositions, materials and sections can be determined. It is suitable for quickly and easily evaluating the changes in microstructure and mechanical properties at different positions and under different processes during the heat treatment of rails. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below in conjunction with the accompanying drawings.

[0022] Figure 1 Schematic diagram of sampling location;

[0023] Figure 2 Sampling size for rail hardened layer depth test;

[0024] Figure 3 It is the cooling position for rail hardened layer depth test;

[0025] Figure 4 It is the hardness test position for rail hardened layer depth test. DETAILED DESCRIPTION

[0026] A method for testing the depth of a rail hardened layer, comprising:

[0027] 1. The present invention is applicable to heat-treated rails of all materials and rails of all cross-sections.

[0028] 2. The hardened layer depth test of the present invention is carried out by sampling at the rail head position, which should be the position of the A line of the cross-sectional hardness of the rail head. The test surface coincides with the tread of the rail head, and the fixed surface is at the intersection of the rail head and the rail waist. The schematic diagram of the sampling position is shown in Figure 1 .

[0029] 3. The method for testing the depth of the hardened layer of a rail of the present invention is to process the rail head into a round bar with a flange, wherein: the diameter of the flange is Between, thickness is 3mm; round rod diameter is The total height of the sample is between 40-50mm. The sampling and processing dimensions of the rail hardened layer depth test are shown in Figure 2 .

[0030] 4. Heat the rail hardened layer depth sample. The heating temperature and insulation time can be adjusted according to different steel qualities and different process requirements.

[0031] 5. After the sample heating process meets the experimental requirements, The cooling medium is sprayed on the lower end of the round rod to control the cooling of the sample. The cooling time is ≥10min. The cooling medium can be air, water mist and water. The selection of cooling medium and the control of cooling speed can be adjusted according to different steel qualities and different process requirements. The cooling position of the rail hardened layer depth test is shown in Figure 3 .

[0032] 6. After the experiment is completed, the sample is milled and finely ground to grind two parallel planes in the axis direction of the sample for hardness measurement. The grinding depth is between 0.4-0.5mm. The test grinding depth of the rail hardened layer is shown in the following figure. Figure 4 .

[0033] 7. Carry out hardness test on hardness testing machine. Hardness test can be carried out by Rockwell hardness and Vickers hardness. The hardness test line is located on two parallel lines of the grinding surface. The distance between the two lines is ≥3mm. The first measuring point starts at 1mm from the end face. The distance between the other measuring points can be between 1-5mm. The location of hardness test for rail hardened layer depth test is shown in Figure 4 .

[0034] 8. Test the hardness at different positions inside the sample at a certain interval from the end of the sample to form a curve of the relationship between hardness and heat treatment depth. Combined with the microstructure morphology at the hardness position, the changes in microstructure and mechanical properties at different positions and under different processes during the heat treatment of the rail can be judged.

[0035] The present invention provides a method suitable for testing the depth of a hardened layer of a rail. The selection of a cooling medium and the control of a cooling speed can be adjusted according to different steel qualities and different process requirements. Based on the method, the hardenability and hardenability of rails with different compositions, different materials and different cross-sections can be measured. The method is suitable for quickly and easily judging changes in microstructure and mechanical properties at different positions and under different processes during the heat treatment of the rail, and provides an important reference basis for formulating a heat processing process for the process production of the rail.

[0036] Implementation process comparison:

[0037] During the implementation of the invention, U75V rails were used to test and illustrate the depth of the hardened layer. Water mist was used as the cooling medium. The Rockwell hardness of the rails is shown in Table 1.

[0038] Table 1 Depth and hardness of hardened layer of U75V rail / HRC

[0039]

[0040] It can be seen from Table 1 that with the increase of the distance between the test points, the hardness of the rail tends to decrease. When the test point is at the 14th point, the hardness of the sample is equivalent to the hardness of the rail base material.

[0041] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for testing the depth of a rail hardened layer, characterized in that: include: (1) Sampling is carried out at the rail head position, which should be the A line position of the rail head cross-section hardness. The test surface coincides with the rail head tread, and the fixed surface is at the intersection of the rail head and the rail waist; (2) Process the rail head into a round bar with a flange, where the flange diameter is Between, thickness is 3mm; round rod diameter is The total height of the specimen is between 40-50mm; (3) Heating the rail hardened layer depth sample, and adjusting the heating temperature and holding time according to different steel qualities and different process requirements; (4) After the sample heating process meets the experimental requirements, The cooling medium is sprayed on the lower end of the round rod to control the cooling of the sample. The cooling time is ≥10min. The selection of cooling medium and the control of cooling speed are adjusted according to different steel qualities and different process requirements. (5) After the experiment is completed, the sample is milled and finely ground to produce two parallel planes along the axis of the sample for hardness measurement; (6) Perform hardness test on a hardness testing machine. The hardness test lines are located on two parallel lines of the ground surface. The distance between the two lines is ≥3mm. The first measuring point starts at 1mm from the end face, and the distance between the remaining measuring points can be between 1-5mm. (7) The hardness is tested at different positions inside the sample at a certain interval from the end of the sample to form a curve of the relationship between hardness and heat treatment depth. At the same time, combined with the microstructural morphology at the hardness position, the changes in microstructure and mechanical properties at different positions and under different processes during the heat treatment of the rail are evaluated.

2. The method for testing the depth of the rail hardened layer according to claim 1, characterized in that: Applicable to heat-treated rails of all materials and rails of all sections.

3. The method for testing the depth of rail hardened layer according to claim 1, characterized in that: The cooling medium is air, water mist or water.

4. The method for testing the depth of rail hardened layer according to claim 1, characterized in that: In (5), the grinding depth is between 0.4-0.5 mm.

5. The method for testing the depth of rail hardened layer according to claim 1, characterized in that: The hardness test is carried out using Rockwell hardness and Vickers hardness.

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