A method for fixed flash welding of a 60N390 HB grade high-hardness rail joint

Abstract

The application discloses a fixed flash welding method for 60N 390HB-grade high-hardness rail joints, which comprises the following steps: using a fixed flash welding machine to weld a rail joint with the chemical components of C: 0.80-0.84%, Si: 0.70-0.80%, Mn: 0.70-0.75%, Cr: 0.30-0.45%, Nb: 0.04-0.05%, RE: 0.0010-0.0020%, P≤0.010%, S≤0.005% and Al≤0.004% without needing to perform heat treatment after welding, and the mechanical properties of the welded joint meet the following conditions: the average hardness of the joint is H J , the average hardness of the base material is H P , the ratio H J / H P ≥0.92, the average hardness of the soft point of the joint is H J1 , the average hardness of the base material is H P , the ratio H J1 / H P ≥0.84, and the softening area W≤15 mm.

Description

Technical Field

[0001] This invention belongs to the field of rail welding technology, specifically relating to a fixed flash welding method for 60N 390HB grade high hardness rail joints. Background Technology

[0002] The research and development of pearlitic steel rails in my country is characterized by "high carbon, low silicon, and medium manganese" as the main elements, with chromium and vanadium added as alloying strengthening elements according to different strength and hardness requirements. Due to the high strength and high hardness of high-hardness pearlitic steel rails used in heavy-haul railways, the carbon content of these rails can reach about 1%, and their alloy content is also relatively high, resulting in very poor weldability. This is mainly manifested in the following ways: ① Numerous defects in the overheated weld zone. In flash welding, carbon and manganese segregation along the austenite grain boundaries occurs in the overheated zone, causing abnormal microstructures such as bainite or martensite to appear in the joint under undercooled conditions. Secondary cementite is also prone to appear near the heat-affected zone, leading to increased joint brittleness. ② Due to the cyclic heating in the heat-affected zone, the grain size increases significantly, and the unbalanced process of rapid heating and cooling of the joint reduces the toughness of the flash weld joint. The impact strength of the joint is only about 50% of that of the base material, increasing the risk of rail breakage at the joint during rail line service. ③ Due to the burning loss of carbon and alloys during welding, the mechanical properties of the joint are significantly reduced, especially the joint hardness. The performance matching between the joint and the base material is poor, resulting in saddle-shaped wear and joint peeling during track service, which seriously affects the smoothness of seamless tracks. The poor welding performance of high-hardness rails severely restricts the widespread application of rails in seamless, heavy-load tracks.

[0003] The flash welding process for rails directly affects the microstructure and service condition of the joint. Improper flash welding can cause defects such as overheating, incomplete welding, excessive ash spots, and liquefaction cracks. In the welded state, the metallographic grain size of the joint is relatively coarse, only about level 1-2, resulting in very poor joint performance. Summary of the Invention

[0004] To address one or more problems existing in the prior art, this invention provides a fixed flash welding method for 60N 390HB grade high-hardness rail joints, wherein the mechanical properties of the 60N 390HB grade high-hardness rail joints welded by the fixed flash welding method meet the following requirements: tensile strength Rm≥1150MPa, joint elongation A≥10.5%, joint impact KU2≥19.1J, and average joint hardness H. J Compared with the average hardness H of the base material P The ratio of H satisfies: J / H P ≥0.92, average hardness H of joint soft spots J1 Compared with the average hardness H of the base material P The ratio of: H J1 / H P≥0.84, softened area W≤15mm;

[0005] The chemical composition of the 60N 390HB grade high-hardness steel rail, by weight percentage, is: C: 0.80-0.84%, Si: 0.70-0.80%, Mn: 0.70-0.75%, Cr: 0.30-0.45%, Nb: 0.04-0.05%, RE: 0.0010-0.0020%, P≤0.010%, S≤0.005%, Al≤0.004%, with the remainder being Fe and unavoidable impurities.

[0006] The fixed flash welding method includes the following steps:

[0007] 1) Grind and remove rust from the end face of the 60N 390HB grade high hardness steel rail and the electrode clamping end;

[0008] 2) Use a fixed flash welding machine for rail joint welding; control the oil temperature of the welding machine at 38-42℃, the water temperature at 18-22℃, and the mains voltage at 427-430V.

[0009] 3) Flash welding process for joint fixing: The weld seam of the rail is controlled between 10-12mm, the camber is controlled between 0.35-0.55mm, the number of flash welding preheating times is controlled between 10-12, the secondary preheating current is controlled between 63-66kA, the flash welding upsetting amount is controlled between 10-13mm, the upsetting force is controlled between 580-600kN, the welding time is controlled between 130-140s, and the final melting speed is controlled between 2.20-2.30mm / s;

[0010] 4) Air cool the high-temperature welded joint to below 200°C to ensure that each part of the joint undergoes a complete phase transformation. When the joint temperature is below 300°C, the cooling can be accelerated appropriately.

[0011] In some embodiments, the fixed flash welder is a GAAS80 / 580 fixed flash welder.

[0012] In some embodiments, the 60N 390HB grade high-hardness steel rail is produced by smelting, continuous casting, slow cooling of the cast billet, and rolling process, wherein the size of the cast billet is controlled to be 280mm×380mm.

[0013] The fixed flash welding method for 60N 390HB grade high-hardness rail joints provided by the above technical solution improves the rail welding performance by optimizing and controlling the fixed flash welding process parameters and the chemical composition of the rail. The rail achieves a hardness similar to the base material, solving the problems of low hardness and joint collapse in existing 60N 390HB grade high-hardness rail welded joints. Furthermore, this welding method eliminates the need for post-weld heat treatment, effectively improving the mechanical properties of the rail joint and meeting the following requirements: tensile strength Rm ≥ 1150 MPa, joint elongation A ≥ 10.5%, and joint impact KU2 ≥ 19.1 J. Moreover, it yields excellent joints with properties matching the base material, with an average hardness H of the welded joint. J Compared with the average hardness H of the base material P The ratio of H satisfies: J / H P ≥0.92, average hardness H of joint soft spots J1 Compared with the average hardness H of the base material P The ratio of: H J1 / H P ≥0.84, softened area W≤15mm. Detailed Implementation

[0014] The present invention aims to provide a fixed flash welding method that can improve the performance of welded joints of 60N 390HB grade high hardness steel rails.

[0015] The technical solution adopted by this invention to solve its technical problem is to optimize and control the fixed flash welding process parameters and the chemical composition of 60N390HB grade high-hardness steel rails. Specifically, it includes the following steps: 1) 60N 390HB grade high-hardness steel rails (chemical composition by weight percentage: C: 0.80-0.84%, Si: 0.70-0.80%, Mn: 0.70-0.75%, Cr: 0.30-0.45%, Nb: 0.04-0.05%, RE: 0.0010-0.0020%, P≤0.010%, S≤0.005%, Al≤0.004%, with the remainder being Fe and unavoidable impurities) are smelted... The steel rails are produced using a continuous casting, billet slow cooling, and rolling process, with the billet size controlled at 280mm×380mm. The end faces are ground and rust removed, and the electrode clamping ends are also ground and rusted. 2) Rail welding is performed using a GAAS80 / 580 fixed flash welding machine. The welding machine oil temperature is controlled at 38-42℃ (e.g., 40℃), the water temperature at 18-22℃ (e.g., 20℃), and the mains voltage between 427-430V (e.g., 428V). 3) The joint is fixed using a flash welding machine. Welding process: The weld seam allowance for rails should be controlled between 10-12 mm, the camber allowance between 0.35-0.55 mm, the number of preheating cycles for flash welding between 10-12, the secondary preheating current between 63-66 kA, the upsetting allowance for flash welding between 10-13 mm, the upsetting force between 580-600 kN, the welding time between 130-140 s, and the final melting velocity between 2.20 and 2.3 kN. Between 0 mm / s; and 4) air cool the high-temperature welded joint to below 200℃ to ensure that each position of the joint undergoes a complete phase transformation. When the joint temperature is less than 300℃, the cooling can be accelerated appropriately. After the joint is cooled, grind the weld bead of the joint flat, that is, grind the protrusion allowance at the rail head and rail bottom (the maximum allowable protrusion allowance for the rail head is 2.0mm, the maximum allowable protrusion allowance for the lower jaw of the rail head and the rail web is 2.0mm, and the maximum allowable protrusion allowance for the rail bottom is 1.5mm).

[0016] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0017] Example:

[0018] In this embodiment, the high-hardness 60N 390HB grade steel rail of this invention is first produced by rolling a 280mm×380mm billet to produce 60kg / m steel rails using the existing method (including smelting, continuous casting, slow cooling of the billet, and rolling process). Table 1 below shows the chemical composition and percentage content of the billets of the rolled steel rails 1-3, and also shows the hardness of the 60N 390HB grade steel rails of 1-3. It can be seen that the chemical composition and content of the steel rails 1-3 can ensure that the hardness of the resulting steel rails reaches above 390HB.

[0019] Table 1: Chemical composition and content (by weight percentage) of the billets for rails 1-3, and hardness of each actual rail.

[0020] 1 0.80 0.70 0.70 0.30 0.04 0.001 0.008 0.004 0.004 392 2 0.82 0.75 0.73 0.37 0.04 0.002 0.009 0.005 0.003 401 3 0.84 0.80 0.75 0.45 0.05 0.002 0.008 0.004 0.003 402

[0021] Fixed flash welding was performed on the cross-sections of rails 1-3. By adjusting parameters such as preheating current, preheating cycles, upsetting amount, welding time, and final melting speed of the fixed flash welding process, and by comparing and analyzing the joint mechanical properties and drop hammer test results, the fixed flash welding process for high-hardness 60N 390HB grade rails was determined. Table 2 below lists the main adjustment parameters for the welding process of rails 1-3 (in each example, the high-temperature welded joint was air-cooled to approximately 190℃). Table 3 below shows the mechanical property indices and drop hammer test results of the rail welded joints for each example.

[0022] Table 2: Main Adjustment Parameters for Welding Process of Rails 1-3

[0023] 1 1 10 10 63 130 580 2.20 2 2 11 11 65 135 590 2.25 3 3 12 13 66 140 600 2.30 4 1 10 10 63 130 580 2.50 5 1 10 10 61 130 620 2.60

[0024] Table 3: Test results of mechanical properties and drop hammer test results of rail welded joints in Examples 1-5 of Table 2

[0025]

[0026]

[0027] As shown in Tables 2 and 3 above, the welding processes for rail sections 1-3 in Examples 1-3 all ensured that the welded joints of the rails had good mechanical properties, satisfying the following requirements: tensile strength Rm ≥ 1150 MPa, joint elongation A ≥ 10.5%, and joint impact KU2 ≥ 19.1 J. Furthermore, the drop hammer pass rate of the rails welded using the welding processes in Examples 1-3 all reached 100%. However, when the welding processes in Examples 4-5 differed from those in Example 1, specifically, a higher melting velocity in Example 4 led to a significant decrease in the impact KU2 of the rail welded joints and the drop hammer pass rate. Similarly, when the preheating current, upsetting force, and melting velocity in Example 5 differed from those in Example 1, not only did the impact KU2 of the rail welded joints and the drop hammer pass rate decrease significantly, but the tensile strength of the rail welded joints also decreased significantly. Therefore, the welding process of Examples 1-3 is determined as the fixed flash welding process for high hardness 60N 390HB grade steel rails.

[0028] According to the requirements of TB / T 1632.2-2014 standard, for heat-treated rails: the ratio of the average hardness HJ of the joint to the average hardness HP of the base material, and the ratio of the average hardness HJ1 of the soft spot of the joint to the average hardness HP of the base material should meet the following requirements: Hj≥0.90Hp, Hj1≥0.8Hp, and the softened area W≤20mm). The Rockwell hardness of the rail joint 5mm below the rail head tread on the longitudinal section obtained in Example 1-3 was tested using an HR-150A Rockwell hardness tester. The test results are shown in Table 4-6 below.

[0029] Table 4: Rockwell hardness test results 5mm below the rail head tread on the longitudinal section of the rail joint obtained in Example 1

[0030]

[0031] Table 5: Rockwell hardness test results 5mm below the rail head tread on the longitudinal section of the rail joint obtained in Example 2

[0032]

[0033] Table 6: Rockwell hardness test results 5mm below the rail head tread on the longitudinal section of the rail joint obtained in Example 3

[0034]

[0035]

[0036] Based on the results in Tables 4-6 above, it can be seen that the joints treated by the fixed flash welding process provided by this invention in each example all have good welding performance, and the ratio of the average hardness HJ of the joint to the average hardness HP of the base material satisfies H... J / HP ≥0.92, average hardness H of joint soft spots J1 Compared with the average hardness H of the base material P The ratio of: H J1 / H P The hardness index is ≥0.84, and the softened area W≤15mm, meeting the standard requirements. The fixed flash welding method for 60N 390HB grade high-hardness rail joints provided by this invention allows the hardness index of the welded joint of the high-hardness 60N 390HB grade rail to match the properties of the rail base material, resulting in excellent mechanical properties and drop hammer performance of the rail joint. This meets the requirements for rail joint smoothness, ensures normal microstructure of the rail joint, and improves the performance state of the rail weld.

[0037] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fixed flash welding method for a 60N 390HB grade high-hardness steel rail joint, characterized in that, The mechanical properties of the 60N 390HB grade high-hardness steel rail joint welded by the aforementioned fixed flash welding method, without any post-weld heat treatment, meet the following requirements: tensile strength Rm ≥ 1150 MPa, joint elongation A ≥ 10.5%, joint impact KU2 ≥ 19.1 J, and average joint hardness H. J Compared with the average hardness H of the base material P The ratio of H satisfies: J / H P ≥0.92, average hardness H of joint soft spots J1 Compared with the average hardness H of the base material P The ratio of: H J1 / H P ≥0.84, softened area W≤15 mm; The chemical composition of the 60N 390HB grade high-hardness steel rail, by weight percentage, is C: 0.80-0.84%, Si: 0.70-0.80%, Mn: 0.70-0.75%, Cr: 0.30-0.45%, Nb: 0.04-0.05%, RE: 0.0010-0.0020%, P≤0.010%, S≤0.005%, Al≤0.004%, with the remainder being Fe and unavoidable impurities; The fixed flash welding method includes the following steps: 1) Grind and remove rust from the end face of the 60N 390HB grade high hardness steel rail and the electrode clamping end; 2) Use a fixed flash welding machine for rail joint welding; control the oil temperature of the welding machine at 38-42℃, the water temperature at 18-22℃, and the mains voltage at 427-430V. 3) Joint fixing flash welding process: The weld seam of the rail is controlled between 10-12 mm, the camber is controlled between 0.35-0.55 mm, the number of flash welding preheating times is controlled between 10-12, the secondary preheating current is controlled between 63-66 kA, the flash welding upsetting amount is controlled between 10-13 mm, the upsetting force is controlled between 580-600 kN, the welding time is controlled between 130-140 s, and the final melting speed is controlled between 2.20-2.30 mm / s; 4) Air cool the high-temperature welded joint to below 200°C to ensure that each part of the joint undergoes a complete phase transformation. When the joint temperature is below 300°C, accelerate the cooling appropriately and do not perform any post-weld heat treatment after air cooling.

2. The fixed flash welding method according to claim 1, characterized in that, The fixed flash welding machine is a GAAS80 / 580 fixed flash welding machine.

3. The fixed flash welding method according to claim 1 or 2, characterized in that, The 60N 390HB grade high-hardness steel rail is produced through smelting, continuous casting, slow cooling of the cast billet, and rolling processes, wherein the size of the cast billet is controlled to be 280mm×380mm.

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