A heat treatment method for flash welding joint of 340HB grade rail and 380HB grade rail

Abstract

The application discloses a kind of 340HB grade rail and 380HB grade rail flash welding joint heat treatment method, by controlling the heating temperature of mixed welding joint, air pressure and final cooling temperature, improve the hardness of 340HB grade rail and 380HB grade rail mixed welding joint, the average value of the hardness of its joint and the average value of the hardness of base material HJ / HP≥0.90;Joint soft point hardness average value and the average value of the hardness of base material HJ1 / HP≥0.80, softening area W≤20mm, meet standard requirements.The mechanical properties of the joint obtained by the application can be matched with two different steel base materials to achieve excellent, solve the mixed welding problem between different rail materials and different hardness levels, thereby effectively improving the service performance of mixed welding joint.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of rail welding, and particularly relates to a heat treatment method for a flash welding joint of 340HB-grade rail and 380HB-grade rail. BACKGROUND

[0002] At present, the domestic railway rail standards are divided into four hardness levels of H320, H340, H350 and H370, and the rail strength, hardness and wear resistance can meet the requirements of most heavy-load lines, high-speed railways, passenger and freight mixed lines, speed-up lines, urban and subway lines, etc. With the continuous improvement of heavy-load railway transportation capacity, the current standard range of rails cannot meet the service requirements of lines on heavy-load lines with an axle load of more than 27 tons and an annual traffic volume of more than 300 million tons, and small curve radius lines below 800m. At present, different rail materials and strength levels are selected by various railway bureaus and maintenance sections according to train axle load, traffic volume, different transportation conditions and different curve radii to meet the service requirements of different lines. Reasonable rail matching can effectively improve the service performance and cost performance of rail application, and reduce rail replacement and maintenance costs. Therefore, different rail materials are gradually mixed in a large range on railway lines, and the welding problem between different rail materials needs to be solved urgently.

[0003] The flash welding of rails of different materials is difficult in the industry, and the welding between different materials is affected by composition, performance, organization, standard requirements, service requirements, etc. The composition of the rail is different, the mechanical properties and physical and chemical constants are different, and the welding process parameters are also different. The current standard 340HB-grade rail and the 380HB-grade heat-treated rail developed by Baotou Steel belong to high-carbon and low-alloy composition systems, which exhibit poor weldability, and abnormal microstructure, gray spots, micro-cracks and other defects are prone to occur during welding or heat treatment of the joint, affecting the quality of the joint. Moreover, the joint strength and hardness after welding are low, and during the service process of the line, the joint may appear to be low, poor wear resistance, horseshoe saddle joint, etc., which seriously affects the smoothness of the joint and the safety of train operation on the seamless line. With the development of domestic heavy-load lines, high-strength heat-treated rails are gradually mixed in a large range on existing lines, and the mixed welding problem between different rail materials and different hardness levels of rails needs to be solved urgently, which is of great significance to promote the batch application of heavy-load railway rails and improve the safe operation of the line, and has a wide application prospect. SUMMARY

[0004] The purpose of the present application is to provide a heat treatment method for a flash welding joint of 340HB-grade rail and 380HB-grade rail. The mixed welding joint of 340HB-grade rail and 380HB-grade rail produced by the heat treatment method of the present application takes into account the mechanical properties of the two rails, effectively improves the stability of the joint organization and performance, and meets the standard requirements.

[0005] To solve the above technical problems, the application adopts the following technical solutions:

[0006] The method for heat treatment of the flash-welded joint of the 340HB-grade rail and the 380HB-grade rail comprises the following steps: rust removal and polishing of the end faces of the 340HB-grade rail and the 380HB-grade rail and the electrode clamping end with the same cross section, and simultaneous flash welding; air cooling treatment of the welded joint of the 340HB-grade rail and the 380HB-grade rail, and cooling of the joint to below 300 DEG C before the next heat treatment.

[0007] The welded joint of the 340HB-grade rail and the 380HB-grade rail is heated to 890-910 DEG C, and then the heating is stopped, air cooling is adopted, and the air cooling is stopped when the temperature of the rail joint tread surface is reduced to 400-450 DEG C, and then the natural cooling is performed to room temperature.

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

[0009] Further, a double-frequency normalizing machine is used for induction heating treatment of the joint in the welded state, wherein the low-frequency power heats the joint to 800-840 DEG C, and the high-frequency power heats the joint to 890-910 DEG C.

[0010] Further, the joint is heated to 890-910 DEG C, and then the heating is stopped, and immediately air cooling treatment is performed on the joint, the air blowing pressure on one side of the 340HB-grade rail is 0.10-0.30 MPa, the air blowing pressure on one side of the 380HB-grade rail is 0.30-0.45 MPa, the air blowing time of the joint is controlled to 100-180 s, and the joint is cooled from 890-910 DEG C to 400-450 DEG C; after the target temperature is reached, the natural cooling is performed to room temperature.

[0011] Further, the performance of the treated joint meets the following conditions: the average hardness of the joint and the average hardness of the base material HJ / HP is greater than or equal to 0.90; the average hardness of the soft point of the joint and the average hardness of the base material HJ1 / HP is greater than or equal to 0.80, and the softening area W is less than or equal to 20 mm.

[0012] Further, the method improves the hardness of the mixed-welded joint, solves the welding problem between different rail materials, and 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 application has the following beneficial technical effects:

[0014] The method improves the hardness of the mixed welding joint of the 340HB grade rail and the 380HB grade rail by controlling the heating temperature, the air blowing pressure and the final cooling temperature of the mixed welding joint, the average value of the hardness of the joint and the average value of the hardness of the base material HJ / HP is greater than or equal to 0.90, the average value of the hardness of the joint soft point and the average value of the hardness of the base material HJ1 / HP is greater than or equal to 0.80, the softening area W is less than or equal to 20 mm, and the standard requirements are met.

[0015] The mechanical properties of the joint obtained by the method can be matched with the two different steel base materials, the hardness of the rail joint is effectively controlled, the normal joint organization form is ensured, and the mechanical property state of the joint in the as-welded state is improved. The heat treatment method of the 340HB grade rail and the 380HB grade rail joint provided by the application takes into account the mechanical properties of the two rails, effectively improves the stability of the joint organization and performance, and makes the joint meet the standard requirements, thereby solving the mixed welding problem between different rail materials and different hardness grades of rails for heavy haul railways, and effectively improving the service performance of the mixed welding joint. DETAILED DESCRIPTION

[0016] In the application, the 340HB grade rail and the 380HB grade rail welded joint with the same cross section (60 kg / m or 75 kg / m) are normalized. Re-normalizing the joint in the as-welded state can effectively refine the joint organization, improve the joint hardness, reduce the joint stress, and improve the service performance of the joint.

[0017] In the application, the joint is heated to 890-910 DEG C, which can ensure that the as-welded joint organization is completely austenitized, which is beneficial to the next step of joint organization transformation. If the heating temperature is too low, the phase change temperature requirement and the joint hardness depth requirement cannot be met, and if the heating temperature is too high, the joint has the risk of overheated organization and excessive growth of grain size.

[0018] In the application, the cooling method of the joint is air blowing cooling treatment of the rail head and the rail waist, the air blowing pressure of the 340HB grade rail on one side is between 0.10-0.30 MPa, the air blowing pressure of the 380HB grade rail on one side is between 0.30-0.45 MPa, and the joint air blowing time is controlled between 100-180 s. Different air blowing pressures and cooling speeds are adopted according to the hardness of different rail base materials 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 application, the joint is cooled from 890-910 DEG C to 400-450 DEG C, and after the target temperature is reached, it is naturally cooled to room temperature. If the final cooling temperature of the joint is too high, the hardness requirement cannot be met, and if the final cooling temperature is too low, the rail joint will produce bainite or martensite abnormal organization.

[0020] Example 1

[0021] The 340HB grade rail and 380HB grade rail welded joint area in the as-welded state was heated by a double-frequency normalizing machine: the joint was heated to 810°C by low-frequency power and to 890°C by high-frequency power. After stopping heating, air blast cooling was performed, the air blast pressure on the joint surface was 0.15 MPa, the air blast time was 90 s, when the joint tread temperature was reduced to the final cooling temperature of 500°C, the air blast cooling was stopped, and then the rail joint was naturally cooled to room temperature. According to the standard requirement of TB / T 1632.2-2014, the Rockwell hardness of the longitudinal section at 5 mm below the rail head tread was tested by LC-200RB Rockwell hardness tester. In Example 1, the ratio of the hardness average value HJ of the mixed welding joint to the hardness average value HP of the base material was 0.82, the ratio of the hardness average value HJ1 of the joint soft point to the hardness average value HP of the base material was 0.71, the left side softening zone width of the joint was 30 mm, the right side softening zone width of the joint was 25 mm, and the joint hardness and softening zone width did not meet the standard requirements.

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

[0023]

[0024] Example 2

[0025] The 340HB grade rail and 380HB grade rail welded joint area in the as-welded state was heated by a double-frequency normalizing machine: the joint was heated to 815°C by low-frequency power and to 890°C by high-frequency power. After stopping heating, air blast cooling was performed, the air blast pressure on the joint surface was 0.25 MPa, the air blast time was 100 s, when the joint tread temperature was reduced to the final cooling temperature of 470°C, the air blast cooling was stopped, and then the rail joint was naturally cooled to room temperature. According to the standard requirement of TB / T 1632.2-2014, the Rockwell hardness of the longitudinal section at 5 mm below the rail head tread was tested by LC-200RB Rockwell hardness tester. In Example 2, the ratio of the hardness average value HJ of the mixed welding joint to the hardness average value HP of the base material was 0.87, the ratio of the hardness average value HJ1 of the joint soft point to the hardness average value HP of the base material was 0.76, the left side softening zone width of the joint was 25 mm, the right side softening zone width of the joint was 19 mm, and the joint hardness and softening zone width did not meet the standard requirements.

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

[0027]

[0028] Example 3

[0029] The 340HB grade rail and the 380HB grade rail welded joint area in butt-welded state was heated by using a double-frequency normalizing machine: the joint was heated to 820°C by low-frequency power and to 900°C by high-frequency power. After stopping heating, air blast cooling was carried out, the air blast pressure on one side of the 340HB grade rail was 0.25 MPa, the air blast pressure on one side of the 380HB grade rail was 0.40 MPa, the air blast time was 120 s, when the joint tread temperature was reduced to the final cooling temperature of 440°C, the air blast cooling was stopped, and then the rail joint was naturally cooled to room temperature. According to the standard requirement of TB / T 1632.2-2014, the Rockwell hardness of the longitudinal section at 5 mm below the rail head tread was tested by using an LC-200RB Rockwell hardness tester. In Example 3, the ratio of the hardness average value HJ of the mixed welding joint to the hardness average value HP of the base material was 0.82, the ratio of the hardness average value HJ1 of the joint soft point to the hardness average value HP of the base material was 0.71, the left side softening zone width of the joint was 17 mm, the right side softening zone width of the joint was 13 mm, and the joint hardness and the softening zone width met the standard requirement.

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

[0031]

[0032] Example 4

[0033] The 340HB grade rail and the 380HB grade rail welded joint area in butt-welded state was heated by using a double-frequency normalizing machine: the joint was heated to 825°C by low-frequency power and to 905°C by high-frequency power. After stopping heating, air blast cooling was carried out, the air blast pressure on one side of the 340HB grade rail was 0.30 MPa, the air blast pressure on one side of the 380HB grade rail was 0.45 MPa, the air blast time was 135 s, when the joint tread temperature was reduced to the final cooling temperature of 400°C, the air blast cooling was stopped, and then the rail joint was naturally cooled to room temperature. According to the standard requirement of TB / T 1632.2-2014, the Rockwell hardness of the longitudinal section at 5 mm below the rail head tread was tested by using an LC-200RB Rockwell hardness tester. In Example 4, the ratio of the hardness average value HJ of the mixed welding joint to the hardness average value HP of the base material was 0.95, the ratio of the hardness average value HJ1 of the joint soft point to the hardness average value HP of the base material was 0.83, the left side softening zone width of the joint was 11 mm, the right side softening zone width of the joint was 9 mm, and the joint hardness and the softening zone width met the standard requirement.

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

[0035]

[0036] As can be seen from different embodiments, the 340HB grade rail and the 380HB grade rail welding joint obtained by example 3 and example 4 have good hardness, the average hardness of the joint and the average hardness of the base material HJ / HP is greater than or equal to 0.90, the average hardness of the soft point of the joint and the average hardness of the base material HJ1 / HP is greater than or equal to 0.80, the softening area W is less than or equal to 20mm, and the requirements of the standard are met. The method of the present application improves the hardness of the mixed welding joint by controlling the heating temperature, the cooling temperature, the air blowing pressure and the final cooling temperature of the normalizing treatment of the 340HB grade rail and the 380HB grade rail welding joint, solves the welding problem between different rail materials, and the mixed welding joint takes into account the mechanical properties of the two rails, effectively improves the stability of the joint structure and performance, and makes them meet the standard requirements.

[0037] The above-described embodiments are only used to describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements of the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method of heat treatment of flash welded joints of 340 HB grade rail and 380 HB grade rail, characterized in that: The same cross-section of 340HB grade rail and 380HB grade rail end face and electrode clamping end are rusted and polished, and at the same time, flash welding is completed; the joint of 340HB grade rail and 380HB grade rail after welding is air-cooled, and the joint is cooled to below 300 DEG C before the next heat treatment is carried out; After the welded joint of 340HB grade rail and 380HB grade rail is inductively heated to a temperature of 890-910 DEG C, the heating is stopped, and immediately, the joint is subjected to air cooling treatment, the air blowing pressure on one side of the 340HB grade rail is between 0.10-0.30 MPa, the air blowing pressure on one side of the 380HB grade rail is between 0.30-0.45 MPa, the joint air blowing time is controlled between 100-180 s, and the joint is cooled from 890-910 DEG C to 400-450 DEG C; after the cooling reaches the target temperature, the joint is naturally cooled to room temperature.

2. The method of heat treatment of flash welded joints of 340 HB grade rail to 380 HB grade rail as claimed in claim 1 wherein: The cross-section of the rail is 60 kg / m or 75 kg / m.

3. The method of heat treatment of flash welded joints of 340 HB grade rail to 380 HB grade rail as claimed in claim 1 wherein: The joint in the butt-welded state is inductively heated using a double-frequency normalizing machine, wherein the low-frequency power heats the joint to 800-840 DEG C, and the high-frequency power heats the joint to 890-910 DEG C.

4. The method of heat treatment of flash welded joints of 340 HB grade rail to 380 HB grade rail as claimed in claim 1 wherein: The performance of the treated joint satisfies: the average value of the hardness of the joint and the average value of the hardness of the base material HJ / HP is greater than or equal to 0.90; the average value of the hardness of the soft point of the joint and the average value of the hardness of the base material HJ1 / HP is greater than or equal to 0.80, and the softening area W is less than or equal to 20 mm.

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