Heat treatment method for fixed flash welding joint of 400HB-grade hypereutectoid rare earth heat treatment steel rail

Abstract

The invention discloses a heat treatment method for a fixed flash welding joint of a 400HB-level hypereutectoid rare earth heat treatment steel rail, the steel rail, C, S i, Mn, Cr, Nb, N i, V and RE are used as main composition elements, and the problems of low strength and hardness of a high-strength steel rail joint are solved through control of a welding state air spraying process and a normalizing air spraying process of the steel rail. And the requirement of heavy haul railways on the smoothness of high-strength steel rail joints can be met. Meanwhile, it can be guaranteed that a 400 HB-level hypereutectoid steel rail fixed flash welding head is of a normal pearlite structure, and bainite, martensite, secondary cementite and other abnormal structures do not exist; the problems that a high-strength and high-hardness hypereutectoid steel rail joint is low in hardness, poor in joint drop hammer performance and low in joint collapse are solved, performance matching of the steel rail joint and base metal can be effectively improved, the comprehensive mechanical performance and the contact fatigue performance of the joint are improved, and therefore the service performance of the joint is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of rail welding, and in particular relates to a heat treatment method for a fixed flash welding joint of a 400HB-level hypereutectoid rare earth heat-treated rail. Background Art

[0002] Pearlite rails at home and abroad all belong to the high-carbon, low-alloy composition system, with a carbon content between 0.70-1.00% and an alloy element content between 1.30-2.50%. Combined with online heat treatment production, the resulting rails have higher strength, hardness and wear resistance, and can meet the service requirements of mixed passenger and freight lines, heavy-load lines and lines with small curve radius.

[0003] The 400HB grade hypereutectoid rare earth heat-treated rails for heavy-duty railways developed by Baotou Steel have the characteristics of high strength and high hardness. The carbon content of the rails can reach about 1%, and its alloy content is also high, which makes its welding performance very poor, mainly manifested as: there are many defects in the welding overheating zone, abnormal microstructures such as bainite or martensite are prone to appear in the joints, the strength, hardness and toughness of the joints are poor, the drop hammer fracture and the gray spots on the fracture exceed the standard, and saddle wear and joint peeling will occur during the service of the line, seriously affecting the smoothness of the seamless line. The poor welding performance of hypereutectoid rails seriously restricts the large-scale application of rails in seamless and heavy-duty lines. Summary of the invention

[0004] The purpose of the present invention is to provide a heat treatment method for a fixed flash welded joint of a 400HB grade hypereutectoid rare earth heat-treated rail, which can ensure that the rail flash welded joints are all normal pearlite structures without abnormal structures such as bainite, martensite and secondary cementite, and solve the problems of low hardness, poor drop hammer performance and low collapse of 380HB grade high-strength heat-treated rail joints, thereby obtaining an excellent joint that matches the performance of the parent material.

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

[0006] The present invention discloses a heat treatment method for a 400HB grade hypereutectoid rare earth heat-treated rail fixed flash welding joint, comprising:

[0007] 1) The 400HB grade hypereutectoid rare earth heat-treated rail flash welded by the present invention has C, Si, Mn, Cr, Nb, Ni, V and RE as main components, and the weight percentage of the chemical composition of the rail is C: 0.95-1.10%, Si: 0.40-0.90%, Mn: 0.85-1.20%, (Cr, Nb+Ni+V): 0.40-1.20%, RE: 0.0005-0.0020%, P≤0.025%, S≤0.025%, Al: ≤0.010%, and the rest is Fe; and impurities

[0008] 2) Derust and polish the welding end faces and electrode clamping ends of two 400HB grade hypereutectoid rare earth heat-treated rails with the same cross-section and material, and perform fixed flash welding;

[0009] 3) The high-temperature flash welded joint is cooled by air jet to 420±20℃, the cooling rate is controlled at 3-6℃ / s, and then the joint is air-cooled to below 300℃;

[0010] 4) Use normalizing induction heating equipment to normalize the joint, the joint heating target temperature is 900±20℃, and the heating speed is controlled at 4-7℃ / s;

[0011] 5) After the joint normalizing heating temperature reaches the target temperature of 900±20℃, stop heating and immediately perform air jet accelerated cooling on the rail head, rail waist and rail bottom of the joint. The final air jet cooling temperature of the joint rail top surface should be controlled between 350 and 420℃, then stop air jet cooling and air cool the joint to room temperature.

[0012] Furthermore, the welding air jet cooling rate is controlled at 5.5°C / s.

[0013] Furthermore, the final cooling temperature should be controlled at 400°C.

[0014] Furthermore, the joint is heated to a target temperature of 900°C.

[0015] Furthermore, the normalizing air jet cooling rate is controlled at 4.0°C / s.

[0016] Furthermore, the method ensures that the rail flash weld joints are all normal pearlite structures without the presence of abnormal bainite, martensite and secondary cementite structures.

[0017] Furthermore, the method solves the problems of low hardness of 380HB grade high-strength heat-treated rail joints, poor drop hammer performance of joints and low collapse of joints.

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

[0019] The invention provides a heat treatment method for a fixed flash weld joint of a 400HB grade hypereutectoid rare earth heat-treated rail, which can ensure that the rail flash weld joints all have normal pearlite structures without abnormal structures such as bainite, martensite and secondary cementite, and solves the problems of low hardness, poor drop hammer performance and low collapse of 380HB grade high-strength heat-treated rail joints, thereby obtaining an excellent joint that matches the performance of a parent material, and making the joint performance meet the inspection requirements for joint mechanical properties and drop hammer in "TB / T 1632.2-2014 Rail Welding Part 2: Flash Welding". DETAILED DESCRIPTION

[0020] A heat treatment method for a 400HB grade hypereutectoid rare earth heat-treated rail fixed flash welded joint, comprising:

[0021] 1) The 400HB grade hypereutectoid rare earth heat-treated rail flash welded by the present invention has C, Si, Mn, Cr, Nb, Ni, V and RE as main components, and the weight percentage of the chemical composition of the rail is C: 0.95-1.10%, Si: 0.40-0.90%, Mn: 0.85-1.20%, (Cr, Nb+Ni+V): 0.40-1.20%, RE: 0.0005-0.0020%, P≤0.025%, S≤0.025%, Al: ≤0.010%, and the rest is Fe.

[0022] 2) Derust and polish the welding end faces and electrode clamping ends of two 400HB grade hypereutectoid rare earth heat-treated rails (60kg / m or 75kg / m) with the same cross-section and material, and perform fixed flash welding.

[0023] 3) The high-temperature flash welded joint is cooled by air jet to 420±20℃, the cooling rate is controlled at 3-6℃ / s, and then the joint is air-cooled to below 300℃.

[0024] 4) Use normalizing induction heating equipment to normalize the joint. The joint heating target temperature is 900±20℃, and the heating speed is controlled at 4-7℃ / s.

[0025] 5) After the joint normalizing heating temperature reaches the target temperature of 900±20℃, stop heating and immediately perform air jet accelerated cooling on the rail head, rail waist and rail bottom of the joint. The final air jet cooling temperature of the joint rail top surface should be controlled between 350 and 420℃, then stop air jet cooling and air cool the joint to room temperature.

[0026] Process comparison during implementation:

[0027] During the implementation process, the focus was on combining different 400HB grade hypereutectoid rare earth heat-treated rail fixed flash welded joint heat treatment methods, and the corresponding joint mechanical properties were compared and analyzed. The comparison scheme of different joint heat treatment processes during the implementation process is shown in Table 1.

[0028] Table 1 Comparison of different heat treatment processes for joints during implementation

[0029]

[0030] The flash welded joints after normalizing in Example 1 to Example 3 were subjected to comparative analysis of Rockwell hardness performance of the rail head longitudinal section according to "TB / T 1632.2-2014 Rail Welding Part 2: Flash Welding". The comparative analysis results are shown in Table 2 to Table 4.

[0031] Table 2 Test results of joint longitudinal section (test line 1) of Example 1

[0032]

[0033]

[0034] It can be seen from Table 2 that the ratio of the average hardness HJ of the welded joint in Example 1 to the average hardness HP of the base material is: HJ / HP=0.81, the ratio of the average hardness HJ1 of the joint soft spot to the average hardness HP of the base material is: HJ1 / HP=0.73, and the widths W1 and W2 of the softening zone are 31 mm and 28 mm respectively. Both the joint hardness and the softening zone width do not meet the standard requirements of the heat-treated rail.

[0035] Table 3 Test results of joint longitudinal section (test line 1) of Example 2

[0036]

[0037] As shown in Table 3, the ratio of the average hardness HJ of the welded joint of Example 2 to the average hardness HP of the base material is: HJ / HP=0.90, the ratio of the average hardness HJ1 of the joint soft spot to the average hardness HP of the base material is: HJ1 / HP=0.79, and the widths W1 and W2 of the softening zone are: 21 mm and 17 mm, respectively. Compared with Example 1, the joint hardness of Example 2 is improved to a certain extent, but the average hardness of the joint soft spot and the width of the softening zone still do not meet the standard requirements of heat-treated rails.

[0038] Table 4 Test results of joint longitudinal section (test line 1) of Example 3

[0039]

[0040] As shown in Table 4, the ratio of the average hardness HJ of the welded joint of Example 3 to the average hardness HP of the base material is: HJ / HP=0.90, the ratio of the average hardness HJ1 of the joint soft spot to the average hardness HP of the base material is: HJ1 / HP=0.80, and the widths W1 and W2 of the softening zone are: 18 mm and 15 mm, respectively. Compared with Examples 1 and 2, the joint hardness of Example 3 is significantly improved, and the joint hardness and softening zone width of Example 3 meet the standard requirements of heat-treated rails. The joint hardness of Example 3 is well matched with the base material hardness.

[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 heat treatment method for a 400HB grade hypereutectoid rare earth heat-treated rail fixed flash welding joint, characterized in that: include: 1) The 400HB grade hypereutectoid rare earth heat-treated rail flash welded by the present invention has C, Si, Mn, Cr, Nb, Ni, V and RE as main components, and the weight percentage of the chemical composition of the rail is C: 0.95-1.10%, Si: 0.40-0.90%, Mn: 0.85-1.20%, (Cr, Nb+Ni+V): 0.40-1.20%, RE: 0.0005-0.0020%, P≤0.025%, S≤0.025%, Al: ≤0.010%, and the rest is Fe; and impurities 2) Derust and polish the welding end faces and electrode clamping ends of two 400HB grade hypereutectoid rare earth heat-treated rails with the same cross-section and material, and perform fixed flash welding; 3) The flash welded joint in high temperature state is cooled by air jet to 420±20℃, the cooling rate is controlled at 3-6℃ / s, and then the joint is air cooled to below 300℃; 4) Use normalizing induction heating equipment to normalize the joint, the joint heating target temperature is 900±20℃, and the heating speed is controlled at 4-7℃ / s; 5) After the joint normalizing heating temperature reaches the target temperature of 900±20℃, stop heating and immediately perform air jet accelerated cooling on the rail head, rail waist and rail bottom of the joint. The final air jet cooling temperature of the joint rail top surface should be controlled between 350 and 420℃, then stop air jet cooling and air cool the joint to room temperature.

2. The heat treatment method for the 400HB grade hypereutectoid rare earth heat-treated rail fixed flash welding joint according to claim 1, characterized in that: The welding air jet cooling rate is controlled at 5.5℃ / s.

3. The heat treatment method for the 400HB grade hypereutectoid rare earth heat-treated rail fixed flash welding joint according to claim 1, characterized in that: The final cooling temperature should be controlled at 400℃.

4. The heat treatment method for the 400HB grade hypereutectoid rare earth heat-treated rail fixed flash welding joint according to claim 1, characterized in that: The joint heating target temperature is 900°C.

5. The heat treatment method for the 400HB grade hypereutectoid rare earth heat-treated rail fixed flash welding joint according to claim 1, characterized in that: The normalizing air jet cooling rate is controlled at 4.0℃ / s.

6. The heat treatment method for the 400HB grade hypereutectoid rare earth heat-treated rail fixed flash welding joint according to claim 1, characterized in that: The method ensures that the rail flash weld joints all have normal pearlite structures without abnormal structures such as bainite, martensite and secondary cementite.

7. The heat treatment method for the 400HB grade hypereutectoid rare earth heat-treated rail fixed flash welding joint according to claim 1, characterized in that: The method solves the problems of low hardness of 380HB grade high-strength heat-treated rail joints, poor drop hammer performance of the joints and low collapse of the joints.

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