Heat treatment method for flash welding joint of 340HB-grade steel rail and 380HB-grade steel rail

Abstract

The invention discloses a heat treatment method for a flash welding joint of a 340HB-grade steel rail and a 380HB-grade steel rail, which is characterized in that the hardness of the mixed welding joint of the 340HB-grade steel rail and the 380HB-grade steel rail is improved by controlling the heating temperature, the air spraying pressure and the final cooling temperature of the mixed welding joint, and the average hardness value of the joint and the average hardness value of a base material HJ / HP are greater than or equal to 0.90; and the average hardness value HJ1 / HP of the joint soft point and the average hardness value of the base metal are greater than or equal to 0.80, the softening area W is less than or equal to 20mm, and the standard requirements are met. The mechanical property of the obtained joint can be well matched with that of two different steel base materials, and the problem of mixed welding between steel rails of different steel rail materials and different hardness levels is solved, so that the service performance of the mixed welding 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 flash welded joint of a 340HB grade rail and a 380HB grade rail. Background Art

[0002] At present, the domestic railway rail standards are divided into four hardness grades: H320, H340, H350, and H370. The strength, hardness, and wear resistance of the rails can meet the needs of most domestic heavy-duty lines, high-speed railways, mixed passenger and freight lines, speed-up lines, urban rail and subways, etc. With the continuous improvement of the heavy-duty railway transportation capacity, the rails within the current standard range can no longer meet the line service requirements for heavy-duty lines with an axle weight of more than 27 tons and an annual transportation volume of more than 300 million tons and lines with a small curve radius of less than 800m. At present, various railway bureaus and engineering sections select rails of different materials and strength levels according to the axle weight, freight volume, different transportation conditions, and different curve radii of the train to meet the service requirements of different lines. Reasonable rail matching can effectively improve the service performance of the line rails and the cost-effectiveness of rail application, and reduce the cost of rail replacement and maintenance. Therefore, different rail materials have gradually begun to be mixed on a large scale on railway lines, and it is urgent to solve the welding problem between different rail materials.

[0003] Flash welding of rails of different steels is a difficult problem in the industry. Welding between different materials is affected by composition, performance, organization, standard requirements, service requirements and other aspects. The composition of different rails is different, and the mechanical properties and physical and chemical constants are different, and the welding process parameters are also different. At present, the 340HB grade rails in the standard and the 380HB grade heat-treated rails developed by Baosteel are both high-carbon and low-alloy composition systems, which show poor weldability. During the welding or heat treatment of the joints, defects such as abnormal microstructure, gray spots, and microcracks are prone to occur, which affects the quality of the joints. In addition, the strength and hardness of the joints after welding are low. During the service of the line, the joints will collapse, have poor wear resistance, and horseshoe saddle joints, which seriously affect the smoothness of the joints and the safety of seamless line train operation. With the development of domestic heavy-duty lines, high-strength heat-treated rails are gradually mixed on a large scale on existing lines. It is urgent to solve the problem of mixed welding between rails of different rail materials and different hardness levels. It is of great significance to promote the batch application of heavy-duty railway rails and improve the safe operation of the line, and the application prospects are broad. Summary of the invention

[0004] The purpose of the present invention is to provide a heat treatment method for flash welded joints of 340HB grade rails and 380HB grade rails. The mixed welded joints of 340HB grade rails and 380HB grade rails produced by the heat treatment method of the present invention take into account the mechanical properties of the two types of rails, effectively improve the stability of the joint structure and performance, and make them meet the standard requirements.

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

[0006] The invention discloses a heat treatment method for flash welding joints of 340HB grade rails and 380HB grade rails, wherein the end faces and electrode clamping ends of the 340HB grade rails and 380HB grade rails with the same cross-sections are rust-removed and polished, and flash welding is completed at the same time; the joints of the 340HB grade rails and 380HB grade rails after welding are air-cooled, and the joints are cooled to below 300° C. before the next heat treatment can be performed;

[0007] For the welded joints of 340HB grade rails and 380HB grade rails, heating is stopped after heating to 890-910℃, and air jet cooling is adopted. After the tread temperature of the rail joint drops to 400-450℃, air jet cooling is stopped, and the rail joint is naturally cooled to room temperature.

[0008] Further, the cross section is 60kg / m or 75kg / m rail.

[0009] Furthermore, a dual-frequency normalizing machine is used to perform induction heating treatment on the joint in the welded state, wherein the low-frequency power heats the joint to between 800-840°C, and the high-frequency power heats the joint to between 890-910°C.

[0010] Furthermore, after the induction heating of the joint reaches a temperature of 890-910°C, the heating is stopped, and the joint is immediately subjected to air spray cooling treatment. The air spray pressure on one side of the 340HB grade rail is between 0.10-0.30MPa, and the air spray pressure on one side of the 380HB grade rail is between 0.30-0.45MPa. The air spray time of the joint is controlled between 100-180s, and the joint is cooled from 890-910°C to between 400-450°C; after cooling to the target temperature, it is naturally cooled to room temperature.

[0011] Furthermore, the performance of the treated joint meets the following requirements: the average hardness of the joint and the average hardness of the base material HJ / HP≥0.90; the average hardness of the joint soft spot and the average hardness of the base material HJ1 / HP≥0.80, and the softening area W≤20mm.

[0012] Furthermore, the method improves the hardness of the mixed weld joint and solves the welding problem between different rail materials. The mixed weld joint takes into account the mechanical properties of the two rails and effectively improves the stability of the joint structure and performance.

[0013] Compared with the prior art, the beneficial technical effects of the present invention are:

[0014] The method of the present invention improves the hardness of the mixed welded joint of 340HB grade rail and 380HB grade rail by controlling the heating temperature, the air jet pressure and the final cooling temperature of the mixed welded joint. The average hardness of the joint and the average hardness of the base material HJ / HP are ≥0.90; the average hardness of the joint soft spot and the average hardness of the base material HJ1 / HP are ≥0.80, and the softening area W is ≤20mm, which meets the standard requirements.

[0015] The mechanical properties of the joint obtained by the present invention can achieve excellent matching with two different steel base materials, effectively control the hardness of the rail joint, ensure the normal structure and morphology of the rail joint, and improve the mechanical properties of the joint in the welded state. The heat treatment method of the joint of the 340HB grade rail and the 380HB grade rail provided by the present invention takes into account the mechanical properties of the two rails, effectively improves the stability of the joint structure and performance, makes them meet the standard requirements, solves the problem of mixed welding between different rail materials and different hardness levels for heavy-duty railways, and effectively improves the service performance of the mixed welded joint. DETAILED DESCRIPTION

[0016] In the present invention, the welded joints of 340HB grade rails and 380HB grade rails with the same cross section (60kg / m or 75kg / m) are normalized. Re-normalizing heat treatment of the welded joints can effectively refine the joint structure, increase the joint hardness, reduce the joint stress, and improve the service performance of the joints.

[0017] In the present invention, heating the joint to 890-910°C can ensure that the welded joint structure is completely austenitized, which is beneficial to the next step of joint structure transformation. If the heating temperature is too low, the phase change temperature requirement and the joint hardness depth requirement cannot be met. If the heating temperature is too high, the joint has the risk of overheating structure and excessive grain growth.

[0018] In the present invention, the cooling method of the welded joint of the 340HB grade rail and the 380HB grade rail adopts the rail head and rail waist air jet cooling treatment, the air jet pressure on one side of the 340HB grade rail is between 0.10-0.30MPa, the air jet pressure on one side of the 380HB grade rail is between 0.30-0.45MPa, and the joint air jet time is controlled between 100-180s. According to the hardness of different rail base materials, different air jet pressures and cooling speeds can be used to ensure the grain refinement of the heat affected zone on both sides of the joint, and further improve the hardness of the heat affected zone.

[0019] In the present invention, the joint is cooled from 890-910°C to between 400-450°C, and after reaching the target temperature, it is naturally cooled to room temperature. If the final cooling temperature of the joint is too high, the hardness requirement cannot be met; if the final cooling temperature is too low, the rail joint will produce abnormal bainite or martensite structures.

[0020] Example 1

[0021] A dual-frequency normalizing machine is used to heat the welded joint area of ​​340HB grade rails and 380HB grade rails in the welded state: the low-frequency power heats the joint to 810℃, and the high-frequency power heats the joint to 890℃. After stopping heating, spray cooling is carried out. The spray pressure on the joint surface is 0.15MPa, and the spray time is 90s. When the joint tread temperature drops to the final cooling temperature of 500℃, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature. Referring to the requirements of TB / T 1632.2-2014 standard, the LC-200RB Rockwell hardness tester is used to test the Rockwell hardness of 5mm below the rail head tread on the longitudinal section. In Example 1, the ratio of the average hardness HJ of the mixed welded joint to the average hardness HP of the base material is 0.82, the ratio of the average soft spot hardness HJ1 of the joint to the average hardness HP of the base material is 0.71, the width of the softening zone on the left side of the joint is 30 mm, and the width of the softening zone on the right side is 25 mm. Both the joint hardness and the softening zone width do not meet the standard requirements.

[0022] Example 1: Rockwell hardness test data and results of welded joint longitudinal section

[0023]

[0024] Example 2

[0025] A dual-frequency normalizing machine is used to heat the welded joint area of ​​340HB grade rails and 380HB grade rails in the welded state: the low-frequency power heats the joint to 815℃, and the high-frequency power heats the joint to 890℃. After stopping heating, spray cooling is carried out. The spray pressure on the joint surface is 0.25MPa, and the spray time is 100s. When the joint tread temperature drops to the final cooling temperature of 470℃, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature. Referring to the requirements of TB / T 1632.2-2014 standard, the LC-200RB Rockwell hardness tester is used to test the Rockwell hardness of 5mm below the rail head tread on the longitudinal section. In Example 2, the ratio of the average hardness HJ of the mixed welded joint to the average hardness HP of the base material is 0.87, the ratio of the average soft spot hardness HJ1 of the joint to the average hardness HP of the base material is 0.76, the width of the softening zone on the left side of the joint is 25 mm, and the width of the softening zone on the right side is 19 mm. Both the joint hardness and the softening zone width do not meet the standard requirements.

[0026] Example 2: Rockwell hardness test data and results of welded joint longitudinal section

[0027]

[0028] Example 3

[0029] A dual-frequency normalizing machine is used to heat the welded joint area of ​​340HB-grade rails and 380HB-grade rails in the welded state: the low-frequency power heats the joint to 820℃, and the high-frequency power heats the joint to 900℃. After stopping heating, spray cooling is carried out. The spray pressure on one side of the 340HB-grade rail is 0.25MPa, and the spray pressure on one side of the 380HB-grade rail is 0.40MPa. The spray time is 120s. When the joint tread temperature is cooled to the final cooling temperature of 440℃, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature. Referring to the requirements of TB / T 1632.2-2014 standard, the LC-200RB Rockwell hardness tester is used to test the Rockwell hardness of 5mm below the rail head tread on the longitudinal section. In Example 3, the ratio of the average hardness HJ of the mixed welded joint to the average hardness HP of the base material is 0.82, the ratio of the average soft spot hardness HJ1 of the joint to the average hardness HP of the base material is 0.71, the width of the softening zone on the left side of the joint is 17 mm, and the width of the softening zone on the right side is 13 mm. The joint hardness and softening zone width meet the standard requirements.

[0030] Example 3: Rockwell hardness test data and results of welded joint longitudinal section

[0031]

[0032] Example 4

[0033] A dual-frequency normalizing machine is used to heat the welded joint area of ​​340HB-grade rails and 380HB-grade rails in the welded state: the low-frequency power heats the joint to 825℃, and the high-frequency power heats the joint to 905℃. After stopping heating, spray cooling is carried out. The spray pressure on one side of the 340HB-grade rail is 0.30MPa, and the spray pressure on one side of the 380HB-grade rail is 0.45MPa. The spray time is 135s. When the joint tread temperature is cooled to the final cooling temperature of 400℃, the spray cooling is stopped, and then the rail joint is naturally cooled to room temperature. Referring to the requirements of TB / T 1632.2-2014 standard, the LC-200RB Rockwell hardness tester is used to test the Rockwell hardness of 5mm below the rail head tread on the longitudinal section. In Example 4, the ratio of the average hardness HJ of the mixed welded joint to the average hardness HP of the base material is 0.95, the ratio of the average soft spot hardness HJ1 of the joint to the average hardness HP of the base material is 0.83, the width of the softening zone on the left side of the joint is 11 mm, and the width of the softening zone on the right side is 9 mm. The joint hardness and softening zone width meet the standard requirements.

[0034] Example 4: Rockwell hardness test data and results of welded joint longitudinal section

[0035]

[0036] It can be seen from different embodiments that the welded joints of 340HB grade rails and 380HB grade rails obtained in Example 3 and Example 4 have good hardness, and the average hardness of the joints and the average hardness of the base material HJ / HP≥0.90; the average hardness of the joint soft spot and the average hardness of the base material HJ1 / HP≥0.80, and the softening area W≤20mm meet the standard requirements. The method of the present invention improves the hardness of the mixed welded joint by controlling the normalizing heating temperature, cooling temperature, air jet pressure and final cooling temperature of the welded joints of 340HB grade rails and 380HB grade rails, solves the welding problem between different rail materials, and the mixed welded joint takes into account the mechanical properties of the two rails, effectively improves the stability of the joint organization and performance, and makes them meet the standard requirements.

[0037] 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 flash welded joints of 340HB rails and 380HB rails, characterized in that: The end faces and electrode clamping ends of 340HB and 380HB rails with the same cross-section are derusted and polished, and flash welding is completed at the same time; the joints of 340HB and 380HB rails are air-cooled after welding, and the next step of heat treatment can be carried out only after the joints are cooled to below 300℃; After the welding joint of 340HB grade rail and 380HB grade rail is heated to 890-910℃, heating is stopped and air jet cooling is adopted. After the tread temperature of the rail joint drops to 400-450℃, air jet cooling is stopped and the rail joint is naturally cooled to room temperature.

2. The heat treatment method for flash welded joints of 340HB rail and 380HB rail according to claim 1, characterized in that: The cross section is 60kg / m or 75kg / m rail.

3. The heat treatment method for flash welded joints of 340HB rail and 380HB rail according to claim 1, characterized in that: A dual-frequency normalizing machine is used to perform induction heating on the welded joint, wherein the low-frequency power heats the joint to between 800-840°C, and the high-frequency power heats the joint to between 890-910°C.

4. The heat treatment method for flash welded joints of 340HB rail and 380HB rail according to claim 1 or 3, characterized in that: After the induction heating of the joint reaches the temperature of 890-910℃, the heating is stopped and the joint is immediately cooled by air spray. The air spray pressure on one side of the 340HB grade rail is between 0.10-0.30MPa, and the air spray pressure on one side of the 380HB grade rail is between 0.30-0.45MPa. The air spray time of the joint is controlled between 100-180s, and the joint is cooled from 890-910℃ to between 400-450℃; after cooling to the target temperature, it is naturally cooled to room temperature.

5. The heat treatment method for flash welded joints of 340HB rail and 380HB rail according to claim 1, characterized in that: The performance of the treated joint meets the following requirements: the average hardness of the joint and the average hardness of the base material HJ / HP≥0.90; the average hardness of the joint soft spot and the average hardness of the base material HJ1 / HP≥0.80, and the softening area W≤20mm.

6. The heat treatment method for flash welded joints of 340HB rail and 380HB rail according to claim 1, characterized in that: This method improves the hardness of the mixed weld joint and solves the welding problem between different rail materials. The mixed weld joint takes into account the mechanical properties of the two rails and effectively improves the stability of the joint structure and performance.

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