Heat treatment method for double-frequency induction heating of high-weldability U71MnG steel rail joint

Abstract

The invention discloses a heat treatment method for double-frequency induction heating of a high-weldability U71MnG steel rail joint. The heat treatment method comprises the following steps that the welded high-weldability U71MnG steel rail welded joint is air-cooled to a first temperature; the temperature of a welding seam area of a welding joint is heated to 900-960 DEG C through double-frequency induction; the method specifically comprises the steps that heating is conducted for 100-130 s at the low frequency of 1200-1600 Hz till the tread temperature of a weld joint reaches 800-850 DEG C, then heating is conducted for 50-90 s at the high frequency of 2200-3000 Hz, and heating is stopped till the tread temperature of the weld joint reaches 900-960 DEG C; blowing air to quickly cool, and stopping blowing air to cool after the temperature of the welding seam range area of the joint quickly rises to 400-430 DEG C; and the welded joint is air-cooled to the room temperature. The longitudinal hardness HJ / HP of the steel rail joint can be controlled to reach 0.95-1.05, and the width lt of left and right softening areas of the joint can be controlled; and the thickness is 20 mm.

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 high-weldability U71MnG rail joint using dual-frequency induction heating. Background Art

[0002] The performance of rail flash welding joints is not only affected by welding defects, welding machine conditions and rail base materials, but also by post-weld heat treatment. After heat treatment, the metal microstructure of the weld is significantly refined, and the grain size is increased from level 1 to more than level 9, which greatly improves the toughness of the weld. In addition, heat treatment also significantly improves the plasticity of the weld. Therefore, the post-weld heat treatment process is extremely important in improving the quality of high-speed rails.

[0003] For example, patent document CN109022748A (hereinafter referred to as document 1) discloses a heat treatment method for U71MnH rail welded joints, which heats the weld area of ​​the U71MnH rail welded joint that has been cooled to below 300°C after welding to 915-935°C and then stops heating, adopts air jet cooling when it is cooled to 710-810°C, stops air jet cooling when the tread temperature of the rail joint drops to 405-432°C, and naturally cools to room temperature, so that the ratio of the average hardness J of the treated joint to the average hardness HP of the base material is ≥0.90, the ratio of the average hardness HJ1 of the joint soft spot to the average hardness HP of the base material is >0.80, and the softening areas on the left and right sides are less than 20 mm, meeting the standard requirements. However, this document 1 can only make the ratio of the average hardness value of the treated joint HJ to the average hardness value HP of the base material ≥ 0.90, and the ratio of the average hardness value HJ1 of the joint soft spot to the average hardness value HP of the base material be in the range of 0.80-0.85. Although both meet the standard requirements, the heat treatment effect is still not ideal. Summary of the invention

[0004] The purpose of the present invention is to provide a dual-frequency induction heating heat treatment method for high-weldability U71MnG rail joints, which can control the longitudinal hardness H of the rail joints. J / H P , reaching 0.95-1.05, and the width of the softening zone on the left and right sides of the joint is <20mm.

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

[0006] The present invention provides a heat treatment method for high weldability U71MnG rail joints by dual-frequency induction heating, comprising the following steps:

[0007] Air-cooling the welded high-weldability U71MnG rail weld joint to a first temperature;

[0008] The temperature of the weld area of ​​the welding joint reaches 900℃-960℃ by using dual-frequency induction heating; specifically, it includes: using 1200-1600Hz low-frequency heating for 100-130s until the weld surface temperature reaches 800-850℃, and then switching to 2200-3000Hz high-frequency heating for 50-90s until the weld surface temperature reaches 900℃-960℃ and then stopping heating;

[0009] The welded joint is cooled quickly by air jet, so that the temperature of the weld area of ​​the joint quickly rises to 400-430℃, and then the air jet cooling is stopped;

[0010] Air cool the welded joint to room temperature;

[0011] Wherein, the base material of the high weldability U71MnG rail joint includes the following chemical components by mass percentage:

[0012] C 0.65-0.73; Si 0.35-0.55; Mn 0.80-0.90; P<0.020; S<0.006, the balance is Fe and unavoidable impurities.

[0013] Furthermore, the first temperature is from room temperature to 400°C.

[0014] Furthermore, the air jet pressure is controlled to be 0.20MPa±0.05MPa, the air jet outlet is 20±6mm away from the tread, 40-50mm away from the side of the rail head, 50-60mm away from the rail waist, and 50-70mm away from the rail bottom.

[0015] Furthermore, the start-up temperature of the air jet rapid cooling is controlled at 800±30°C.

[0016] Furthermore, the joint weld area refers to the area of ​​20 mm on both sides of the fusion line.

[0017] Further, it includes: using a dual-frequency heating method to heat the weld area of ​​the high-weldability U71MnG rail weld joint, first using a low frequency of 1300Hz, 350℃ for heating, heating time 110s, to 810℃, and then using a high frequency of 2600Hz, heating time 60s, to 940℃ and then stop heating; after stopping heating, when the tread temperature of the rail joint drops to 820℃, spray cooling is performed, the spray air pressure is controlled to be 0.22MPa, the air nozzle is 23mm away from the tread, the air nozzle is 21mm away from the tread, 40mm away from the side of the rail head, 52mm away from the rail waist, and 59mm away from the rail bottom; when the tread temperature of the joint is cooled to the final cooling temperature of 420℃ by air cooling, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature;

[0018] The chemical composition of the high weldability U71Mn rail base material used includes: C content 0.70%; Si content 0.36%; Mn content 0.85%; P content 0.013%; S content 0.010%, and the balance is Fe and unavoidable impurities.

[0019] Further, it includes: using a dual-frequency heating method to heat the weld area of ​​the high-weldability U71MnG rail weld joint, first using a low frequency of 1400Hz, 300℃ for heating, heating time 130s, to 800℃, and then using a high frequency of 2400Hz, heating time 80s, to 920℃ and then stop heating; after stopping heating, when the tread temperature of the rail joint drops to 800℃, spray cooling is performed, the spray air pressure is controlled to be 0.24MPa, the air nozzle is 21mm away from the tread, the air nozzle is 23mm away from the tread, 42mm away from the side of the rail head, 50mm away from the rail waist, and 55mm away from the rail bottom; when the tread temperature of the joint drops to the final cooling temperature of 400℃ by air cooling, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature;

[0020] The chemical composition of the high weldability U71Mn rail base material used includes: C content 0.72%; Si content 0.35%; Mn content 0.86%; P content 0.011%; S content 0.015%, and the balance is Fe and unavoidable impurities.

[0021] Further, it includes: using a dual-frequency heating method to heat the weld area of ​​the high-weldability U71MnG rail welding joint, first using a low frequency of 1500Hz, 380℃ for heating, heating time, 90s, to 830℃, and then using a high frequency of 2300Hz, heating time 85s, to 950℃ and then stop heating; after stopping heating, when the tread temperature of the rail joint drops to 780℃, spray cooling is performed, the spray air pressure is controlled to be 0.24MPa, the air nozzle is 23mm away from the tread, the air nozzle is 25mm away from the tread, 41mm away from the side of the rail head, 50mm away from the rail waist, and 60mm away from the rail bottom; when the tread temperature of the joint is cooled to the final cooling temperature of 410℃ by air cooling, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature;

[0022] The chemical composition of the high weldability U71Mn rail base material used includes: C content 0.70%; Si content 0.38%; Mn content 0.84%; P content 0.010%; S content 0.018%, and the balance is Fe and unavoidable impurities.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are:

[0024] The dual-frequency induction heating post-weld heat treatment method for high-weldability U71MnG rail weld joints provided by the above technical solution improves the hardness of high-weldability U71MnG rail weld joints by controlling the heating temperature, air jet pressure and final cooling temperature, so that the ratio K1 of the average hardness HJ of the weld joint to the average hardness HP of the base material satisfies 1.10>K1≥0.95; the ratio K2 of the average hardness HJ1 of the weld joint soft spot to the average hardness HP of the base material ≥0.80; the softening area is less than 20mm, meeting the standard requirements. In addition, while effectively controlling the hardness of the rail weld joint, the method of the present invention also ensures that the microstructure of the rail weld joint is normal and improves the reduced performance state. The method of the present invention has a good prospect for promotion and application, and can be promoted and used in domestic high-speed rail welding bases or online welding construction units. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below in conjunction with the accompanying drawings.

[0026] Figure 1 This is the longitudinal section hardness curve of the high weldability U71MnG rail after weld heat treatment in Example 3. DETAILED DESCRIPTION

[0027] A heat treatment method for high weldability U71MnG rail joints by dual-frequency induction heating, the technical solution adopted to solve the technical problem is to obtain a welding joint that meets the requirements by optimizing the heating temperature, the rail joint tread temperature during air jet cooling, and the final cooling temperature of the rail joint tread. The specific steps are as follows;

[0028] The high-temperature welded joint is air-cooled to a temperature between room temperature and 400°C to ensure complete phase change at every position of the joint.

[0029] Use a dual-frequency normalizing machine to normalize the welded joints. First, use low-frequency induction heating: use 1200-1600Hz low-frequency heating for 100-130s to heat the joints from 0-400℃ to 800-850℃.

[0030] After the low-frequency induction heating of the joint reaches the target temperature, turn off the low-frequency heating and immediately perform high-frequency induction heating on the joint. Adjust the normalizing machine to 2200-3000Hz high-frequency power for 50-90s to heat the joint from 800-850℃ to 920-960℃.

[0031] When the joint of normalizing heat treatment reaches the target temperature of 900-960℃, stop heating and control the opening temperature of rapid cooling by air jet at 800±30℃. Immediately after reaching the temperature, the rail head tread, rail waist and rail bottom in the heating zone and the heating zone within a length of 160mm on both sides are subjected to rapid forced cooling by air jet. The air jet pressure is controlled at 0.20MPa±0.05MPa, the air jet port is 20mm-30mm away from the tread, 20±6mm away from the tread, 40-50mm away from the side of the rail head, 50-60mm away from the rail waist and 50-70mm away from the rail bottom.

[0032] The final air-jet cooling temperature of the joint should be controlled between 400-430℃, then the air-jet cooling is stopped and the joint is cooled naturally to air temperature.

[0033] The high weldability U71Mn rail weld joint base material may include the following chemical components by mass percentage: C content 0.65-0.73; Si content 0.35-0.55; Mn content 0.80-0.90; P<0.020; S<0.006, and the remainder is Fe and unavoidable impurities.

[0034] In the present invention, the weld area of ​​the joint whose cooling temperature after welding is less than 430°C is heated to 920-960°C. This process adopts a normalizing process, which changes the joint structure morphology and refines the grain size, thereby increasing the weld hardness and improving the performance state.

[0035] When the surface of the rail head reaches the required range, it cannot be guaranteed that the temperature inside the rail, especially the core, can reach the required temperature. In order to ensure that the core temperature can reach the required temperature, the temperature cannot be too low. When the temperature is too high, on the one hand, the temperature at the bottom of the relatively thin rail is higher than the actual measured temperature, and there is a risk of tissue overheating. On the other hand, the heating coil is the source of heat, and the heat is conducted to the two ends of the rail with the heating coil as the center. The width of the heat affected zone will become wider, and may even fail to meet the standard requirements.

[0036] The content of the present invention is described in detail below through specific examples. The examples are intended to help understand the present invention but are not intended to limit the content of the present invention.

[0037] Example 1

[0038] The chemical composition of the high weldability U71Mn rail base material used in this embodiment includes: C content 0.70; Si content 0.36; Mn content 0.85; P content 0.013; S content 0.010, and the balance is Fe and unavoidable impurities.

[0039] The dual-frequency heating method is used to heat the weld area of ​​the high-weldability U71MnG rail welded joint. First, a low frequency of 1300Hz is used to heat at 350℃ for 110s to 810℃, and then a high frequency of 2600Hz is used for 60s to heat to 940℃ before stopping heating. After stopping heating, when the tread temperature of the rail joint drops to 820℃, spray cooling is carried out. The spray pressure is controlled to be 0.22MPa, and the distance between the spray port and the tread is 23mm, 21mm, 40mm from the side of the rail head, 52mm from the rail waist, and 59mm from the rail bottom. When the tread temperature of the joint drops to the final cooling temperature of 420℃, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature.

[0040] The results are shown in Table 1 below. The above method can control the longitudinal hardness of the rail joint Hj / Hp to 0.98, Hj1 / Hp=0.90, and the width of the softening zone is 13mm, which meets the standard requirements.

[0041] Table 1

[0042]

[0043]

[0044] Example 2

[0045] The chemical composition of the high weldability U71Mn rail base material used in this embodiment includes: C content 0.72; Si content 0.35; Mn content 0.86; P content 0.011; S content 0.015, and the balance is Fe and unavoidable impurities.

[0046] The dual-frequency heating method is used to heat the weld area of ​​the high-weldability U71MnG rail welded joint. First, a low frequency of 1400Hz is used to heat at 300℃ for 130s to 800℃, and then a high frequency of 2400Hz is used for 80s to heat to 920℃ before stopping heating. After stopping heating, when the tread temperature of the rail joint drops to 800℃, spray cooling is carried out. The spray pressure is controlled to be 0.24MPa, and the distance between the spray port and the tread is 21mm, 23mm, 42mm from the side of the rail head, 50mm from the rail waist, and 55mm from the rail bottom. When the tread temperature of the joint drops to the final cooling temperature of 400℃, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature.

[0047] The results are shown in Table 2 below. The above method can control the longitudinal hardness of the rail joint Hj / Hp to 0.99, Hj1 / Hp=0.86, and the width of the softening zone is 15mm, which meets the standard requirements.

[0048] Table 2

[0049]

[0050]

[0051] Example 3

[0052] The chemical composition of the high weldability U71Mn rail base material used in this embodiment includes: C content 0.70; Si content 0.38; Mn content 0.84; P content 0.010; S content 0.018, and the balance is Fe and unavoidable impurities.

[0053] The dual-frequency heating method is used to heat the weld area of ​​the high-weldability U71MnG rail welding joint. First, a low frequency of 1500Hz is used to heat at 380℃ for 90s to 830℃, and then a high frequency of 2300Hz is used for 85s to heat to 950℃ and then stop heating. After stopping heating, when the tread temperature of the rail joint drops to 780℃, spray cooling is carried out. The spray pressure is controlled to be 0.24MPa, and the distance between the nozzle and the tread is 23mm, 25mm, 41mm from the side of the rail head, 50mm from the rail waist, and 60mm from the rail bottom. When the joint tread temperature drops to the final cooling temperature of 410℃, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature.

[0054] The results are shown in Table 3 below. The above method can control the longitudinal hardness of the rail joint Hj / Hp to 1.03, Hj1 / Hp=0.87, and the width of the softening zone is 12mm, which meets the standard requirements.

[0055] Table 3

[0056]

[0057]

[0058] 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 dual-frequency induction heating heat treatment method for high weldability U71MnG rail joints, characterized in that: The following steps are involved: Air-cooling the welded high-weldability U71MnG rail weld joint to a first temperature; The temperature of the weld area of ​​the welding joint reaches 900℃-960℃ by using dual-frequency induction heating; specifically, it includes: using 1200-1600Hz low-frequency heating for 100-130s until the weld surface temperature reaches 800-850℃, and then switching to 2200-3000Hz high-frequency heating for 50-90s until the weld surface temperature reaches 900℃-960℃ and then stopping heating; The welded joint is cooled quickly by air jet, so that the temperature of the weld area of ​​the joint quickly rises to 400-430℃, and then the air jet cooling is stopped; Air cool the welded joint to room temperature; Wherein, the base material of the high weldability U71MnG rail joint includes the following chemical components by mass percentage: C 0.65-0.73; Si 0.35-0.55; Mn 0.80-0.90; P<0.020; S<0.006, the balance is Fe and unavoidable impurities.

2. The heat treatment method of high weldability U71MnG rail joint dual-frequency induction heating according to claim 1 is characterized in that: The first temperature is from room temperature to 400°C.

3. The heat treatment method of high weldability U71MnG rail joint dual-frequency induction heating according to claim 1 is characterized in that: The air jet pressure is controlled at 0.20MPa±0.05MPa, the air jet outlet is 20±6mm away from the tread, 40-50mm away from the side of the rail head, 50-60mm away from the rail waist, and 50-70mm away from the rail bottom.

4. The heat treatment method of high weldability U71MnG rail joint dual-frequency induction heating according to claim 1 is characterized in that: The start-up temperature of the air jet rapid cooling is controlled at 800±30°C.

5. The heat treatment method of high weldability U71MnG rail joints by dual-frequency induction heating according to claim 1, characterized in that: The joint weld area refers to the area of ​​20 mm on both sides of the fusion line.

6. The heat treatment method of high weldability U71MnG rail joints by dual-frequency induction heating according to claim 1, characterized in that: include: The dual-frequency heating method is used to heat the weld area of ​​the high-weldability U71MnG rail welding joint. First, a low frequency of 1300Hz is used to heat at 350℃ for 110s to 810℃, and then a high frequency of 2600Hz is used for 60s to heat to 940℃ and then stop heating. After stopping heating, when the tread temperature of the rail joint drops to 820℃, spray cooling is carried out. The spray pressure is controlled to be 0.22MPa, and the distance between the spray port and the tread is 23mm, 21mm, 40mm from the side of the rail head, 52mm from the rail waist, and 59mm from the rail bottom. When the tread temperature of the joint drops to the final cooling temperature of 420℃, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature. The chemical composition of the high weldability U71Mn rail base material used includes: C content 0.70%; Si content 0.36%; Mn content 0.85%; P content 0.013%; S content 0.010%, and the balance is Fe and unavoidable impurities.

7. The heat treatment method of high weldability U71MnG rail joints by dual-frequency induction heating according to claim 1, characterized in that: include: The dual-frequency heating method is used to heat the weld area of ​​the high-weldability U71MnG rail welding joint. First, a low frequency of 1400Hz is used to heat at 300℃ for 130s to 800℃, and then a high frequency of 2400Hz is used for 80s to heat to 920℃ and then stop heating. After stopping heating, when the tread temperature of the rail joint drops to 800℃, spray cooling is carried out. The spray pressure is controlled to be 0.24MPa, and the distance between the spray port and the tread is 21mm, 23mm, 42mm from the side of the rail head, 50mm from the rail waist, and 55mm from the rail bottom. When the tread temperature of the joint drops to the final cooling temperature of 400℃, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature. The chemical composition of the high weldability U71Mn rail base material used includes: C content 0.72%; Si content 0.35%; Mn content 0.86%; P content 0.011%; S content 0.015%, and the balance is Fe and unavoidable impurities.

8. The heat treatment method of high weldability U71MnG rail joints by dual-frequency induction heating according to claim 1, characterized in that: include: The dual-frequency heating method is used to heat the weld area of ​​the high-weldability U71MnG rail welding joint. First, a low frequency of 1500Hz is used to heat at 380℃ for 90s to 830℃, and then a high frequency of 2300Hz is used for 85s to heat to 950℃ and then stop heating. After stopping heating, when the tread temperature of the rail joint drops to 780℃, spray cooling is carried out. The spray pressure is controlled to be 0.24MPa, and the distance between the spray port and the tread is 23mm, 25mm, 41mm from the side of the rail head, 50mm from the rail waist, and 60mm from the rail bottom. When the tread temperature of the joint drops to the final cooling temperature of 410℃, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature. The chemical composition of the high weldability U71Mn rail base material used includes: C content 0.70%; Si content 0.38%; Mn content 0.84%; P content 0.010%; S content 0.018%, and the balance is Fe and unavoidable impurities.

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