Method for improving hardness of flash welded joint of medium carbon low alloy steel rail

Abstract

The application discloses a method for improving the hardness of a flash-welded joint of a medium-carbon low-alloy steel rail, and comprises the following steps: sequentially performing pre-flashing, flashing, accelerated sintering and top forging on the rail; performing forging; and performing air spraying cooling on the welded joint of the rail, wherein the starting air spraying temperature is greater than or equal to 650 DEG C, the air spraying distance is 20-50 mm, and the air spraying pressure is 0.30-0.50 MPa. The method can obtain a high-quality medium-carbon low-alloy steel rail welded joint with high strength and stable quality by adding a forging stage after flash welding and performing forced air spraying cooling after flash welding.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, and specifically relates to a method for improving the hardness of flash welded joints of medium carbon low alloy steel rails. Background Technology

[0002] Pearlitic steel rails typically have a carbon content of 0.70%–0.84%. Hot-rolled rails have a strength range of 880–1080 MPa and a hardness of 260–350 HBW; heat-treated rails have a strength of 1080–1280 MPa and a hardness of 320–400 HB. Representative rail grades include U71Mn, U75V, and U78CrV. These rails are mainly used in domestic high-speed railways, mixed passenger and freight lines, and heavy-haul lines. They have high carbon content, high alloy element content, high strength, high hardness, and good wear resistance. Normalizing is necessary after welding to ensure joint quality. For high-altitude and frigid regions with large annual and diurnal temperature variations, higher requirements are placed on the impact toughness of the rails. Currently, no single type of rail can fully meet the service requirements of railway lines in high-altitude and frigid regions with large annual and diurnal temperature variations and complex track conditions. Therefore, the rail treads laid on extremely long downhill sections in high-altitude and cold regions are prone to abrasion of martensite structure, which can lead to rail breakage and seriously affect service safety.

[0003] To ensure the joint toughness meets standard requirements, existing high-carbon steel rails must be reheated and normalized after welding. Reheating consumes a large amount of fuel gas, resulting in high overall costs.

[0004] Therefore, the railway engineering field urgently needs a rail welding method that is low in cost and has good overall weld performance. Summary of the Invention

[0005] This invention discloses a method for improving the hardness of flash welded joints of medium carbon low alloy steel rails. By adding a forging stage after flash welding and performing forced air cooling after flash welding, high-strength and high-quality medium carbon low alloy steel rail welded joints are obtained.

[0006] To solve at least one of the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] According to the present invention, a method for improving the hardness of a flash welded joint of medium carbon low alloy steel rail is provided, comprising the following steps: performing forging on the rail in sequence through pre-flash, flash, accelerated burning, and upsetting stages; and cooling the welded joint of the rail by air spraying, wherein the initial air spraying temperature is ≥650℃, the air spraying distance is 20~50mm, and the air spraying pressure is 0.30~0.50MPa.

[0008] According to one embodiment of the present invention, air cooling of the welded joint of a rail includes: air cooling of the rail head weld, wherein the initial air cooling temperature is the temperature at the center of the rail head weld.

[0009] According to one embodiment of the present invention, air cooling of the welded joint of the rail includes stopping air cooling when the temperature at the center of the rail head weld drops to 300-350°C.

[0010] According to one embodiment of the present invention, the medium carbon low alloy steel rail comprises the following components by mass fraction: C: 0.50% to 0.70%, Si: 0.30% to 0.60%, Mn: 0.50% to 0.80%, Cr+Ni+Cu+V: 0.30% to 1.0%, P, S≤0.025%, with the balance being Fe and unavoidable impurities.

[0011] According to one embodiment of the present invention, the pre-flash stage includes: a set time of 15s to 30s, a voltage of 370V to 400V, a set current 1 of 180A to 220A, a set current 2 of 270A to 400A, a set current 3 of 350A to 450A, a pre-flash displacement of 3mm to 7mm, a forward speed of 1mm / s to 1.5mm / s, and a backward speed of 0.5mm / s to 1.2mm / s.

[0012] According to one embodiment of the present invention, the flash phase includes: Flash sub-phase 1: set time of 10s to 25s, voltage of 330V to 360V, set current 1 of 200A to 280A, current 2 of 350A to 500A, current 3 of 450A to 550A, pre-flash displacement of 6mm to 12mm, forward speed of 1.2mm / s to 1.7mm / s, and backward speed of 0.5mm / s to 1.2mm / s; Flash sub-phase 2: set time of 10s to 25s, voltage of 300V to 340V, set current 1 of 220A to 250A, current 2 of 310A to 460A, current 3 of 400A to 530A, pre-flash displacement of 6mm to 10mm, forward speed of 1.5mm / s to 2.5mm / s, and backward speed of 0.5m. m / s~1.2mm / s; Flash sub-stage 3: set time 5s~15s, voltage 300V~330V, set current 1 230A~300A, current 2 300A~450A, current 3 380A~520A, pre-flash displacement 3mm~6mm, forward speed 1.3mm / s~2.3mm / s, backward speed 0.5mm / s~1.5mm / s; Flash sub-stage 4: set time 5s~15s, voltage 320V~360V, set current 1 150A~300A, current 2 300A~400A, current 3 350A~500A, pre-flash displacement 3mm~5mm, forward speed 0.6mm / s~1.3mm / s, backward speed 0.3mm / s~1.0mm / s.

[0013] According to one embodiment of the present invention, the accelerated burning stage includes: accelerated burning sub-stage 1: set time of 3s to 8s, voltage of 350V to 380V, set current 1 of 150A to 300A, current 2 of 350A to 500A, current 3 of 450A to 550A, pre-flash displacement of 5mm to 10mm, forward speed of 0.6mm / s to 1.3mm / s, and backward speed of 0.3mm / s to 0.8mm / s; accelerated burning sub-stage 2: set time of 1s to 5s, voltage of 360V to 400V, set current 1 of 200A to 300A, current 2 of 350A to 500A, current 3 of 450A to 550A, pre-flash displacement of 5mm to 10mm, forward speed of 0.6mm / s to 1.3mm / s, and backward speed of 0.1mm / s to 0.4mm / s.

[0014] According to one embodiment of the present invention, the upsetting stage includes: setting the electric upsetting time to 0.1s to 2.0s and the upsetting amount to 12mm to 15.0mm.

[0015] According to one embodiment of the present invention, the rail consumption during the forging stage is 2.0 mm to 4.0 mm, the forging time is 2.0 s to 3.0 s, the average speed is 1.0 mm / s to 2.0 mm / s, and the forging pressure is 50 T to 80 T.

[0016] By adopting the above technical solution, the present invention has at least one of the following advantages compared with the prior art:

[0017] 1. The method according to the present invention eliminates the need for post-weld normalizing, effectively simplifying the welding and post-weld heat treatment processes and reducing welding costs;

[0018] 2. According to the method of the present invention, the welded joint is cooled by air spraying after welding, and the air spraying part is the rail head, which greatly improves the hardness of the rail head;

[0019] 3. Using the technical solution of this invention, flash welding can be used to successfully complete the welding of medium carbon low alloy steel rails, resulting in fewer internal defects in the rail joints, high weld joint strength, and stable quality. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart of a method for improving the hardness of a flash welded joint of medium carbon low alloy steel rail according to the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] Flash welding is divided into two types: fixed flash welding and mobile flash welding. Mobile flash welding, due to its small equipment and ease of movement, is often used for on-site rail laying welding. Fixed flash welding of rails typically involves fixing the welding equipment inside the factory building, hence it is also commonly referred to as factory welding or base welding. Mobile flash welding heats the rail through intermittent pulsed flash explosions or continuous flash explosions; therefore, mobile flash welding is further divided into pulsed flash and continuous flash. Continuous flash welding has a low welding current and low heat input, resulting in a small heat-affected zone and a narrow softening zone in the weld joint. Pulsed flash welding has a high welding current and high heat input, resulting in good stability of the joint under static bending and drop hammer tests.

[0024] Figure 1 The flowchart illustrates a method for improving the hardness of flash welded joints of medium-carbon low-alloy steel rails according to the present invention. This method is applicable to medium-carbon low-alloy steel rails, and the preferred chemical composition and weight percentages of the base metal are: C: 0.50%–0.70%, Si: 0.30%–0.60%, Mn: 0.50%–0.80%, Cr+Ni+Cu+V: 0.30%–1.0%, P, S ≤ 0.025%, with the balance being Fe and unavoidable impurities. The method generally includes the following steps:

[0025] Step S1 involves sequentially performing pre-brightening, brightening, accelerated melting, and upsetting on the rail;

[0026] Step S2, perform forging;

[0027] Step S3: Cool the welded joint of the rail with air spray. The initial air spray temperature is ≥650℃, the air spray distance is 20-50mm, and the air spray pressure is 0.30-0.50MPa.

[0028] The main function of the pre-flash stage is to make the weldable section of the rail flat and clean through flash explosion, providing favorable conditions and basic heat for the subsequent flash. To achieve the above objective, the pulsed flash process of this invention is controlled by setting eight variables: pre-flash time, voltage, current 1, 2, 3, pre-flash displacement, and forward and backward speeds. In the embodiment of this invention, the pre-flash stage of step S1 can be set to a time of 15s to 30s, a voltage of 370V to 400V, a current 1 of 180A to 220A, a current 2 of 270A to 400A, a current 3 of 350A to 450A, a pre-flash displacement of 3mm to 7mm, a forward speed of 1mm / s to 1.5mm / s, and a backward speed of 0.5mm / s to 1.2mm / s.

[0029] The main function of the flashing stage is to continue heating the rail surface to be welded through pulsating flashes, building upon the heat accumulated in the pre-flash stage. This creates a temperature gradient along the longitudinal direction of the rail, heating the rail end face to a sufficient temperature and laying the groundwork for accelerated burning. In the initial flashing stage, the rail end face temperature is relatively low, requiring higher voltage and current for the flashing process to function properly. However, as the rail end face temperature rises, higher voltage and current would lead to excessively rapid burning, removing too much heat and hindering heat accumulation. Therefore, the flashing stage is divided into four sub-stages, with each subsequent sub-stage using lower voltage and current to ensure sufficient heating of the rail end face and accelerate the burning process. Each of the four sub-stages requires setting eight variables: flash time, voltage, current (1, 2, 3), pre-flash displacement, and forward and backward speeds. In this embodiment of the invention, the flashing sub-stage in step S1 is divided into four sub-stages. The flash sub-stage 1 has the following settings: set time 10s–25s, voltage 330V–360V, set current 1 200A–280A, current 2 350A–500A, current 3 450A–550A, pre-flash displacement 6mm–12mm, forward speed 1.2mm / s–1.7mm / s, and backward speed 0.5mm / s–1.2mm / s. The flash sub-stage 2 has the following settings: set time 10s–25s, voltage 300V–340V, set current 1 220A–250A, current 2 310A–460A, current 3 400A–530A, pre-flash displacement 6mm–10mm, forward speed 1.5mm / s–2.5mm / s, and backward speed 0.5mm / s–1.2m. m / s; Flash sub-stage 3: Set time 5s~15s, voltage 300V~330V, set current 1 230A~300A, current 2 300A~450A, current 3 380A~520A, pre-flash displacement 3mm~6mm, forward speed 1.3mm / s~2.3mm / s, backward speed 0.5mm / s~1.5mm / s; Flash sub-stage 4: Set time 5s~15s, voltage 320V~360V, set current 1 150A~300A, current 2 300A~400A, current 3 350A~500A, pre-flash displacement 3mm~5mm, forward speed 0.6mm / s~1.3mm / s, backward speed 0.3mm / s~1.0mm / s.

[0030] The main function of the accelerated burning stage is to create a protective atmosphere throughout the welding area to prevent end-face oxidation, ultimately forming a suitable temperature field distribution to provide conditions for upsetting. The accelerated burning stage is characterized by intense flashes and rapid burning speed. It is further divided into two sub-stages, with current and voltage gradually increasing. Each sub-stage requires setting eight variables: flash time, voltage, currents 1, 2, and 3, pre-flash displacement, and forward and backward speeds. In an embodiment of the invention, the accelerated burning sub-stage of step S1 is divided into two stages. The accelerated burning stage 1 has the following settings: time set to 3s-8s, voltage set to 350V-380V, current set to 150A-300A, current set to 350A-500A, current set to 450A-550A, pre-flash displacement set to 5mm-10mm, forward speed set to 0.6mm / s-1.3mm / s, and backward speed set to 0.3mm / s-0.8mm / s. The accelerated burning stage 2 has the following settings: time set to 1s-5s, voltage set to 360V-400V, current set to 200A-300A, current set to 350A-500A, current set to 450A-550A, pre-flash displacement set to 5mm-10mm, forward speed set to 0.6mm / s-1.3mm / s, and backward speed set to 0.1mm / s-0.4mm / s.

[0031] In the upsetting stage of step S1, the upsetting time can be set to 0.1s to 2.0s, and the upsetting amount can be set to 12mm to 15.0mm.

[0032] The forging stage in step S2 aims to continuously apply load to the rail joint during the metal solidification process after upsetting, thereby enhancing the joint quality. To achieve this objective, the rail consumption during the forging stage is 2.0 mm to 4.0 mm, the forging time is 2 to 3.0 s, the average speed is 1.0 mm / s to 2.0 mm / s, and the forging pressure is T50T to T80T.

[0033] After flash welding is completed, in step S3, the residual heat generated during rail welding is used to cool the welded joint of the rail using a dedicated air-blasting device. In this embodiment of the invention, the air-blasting point is the rail head, which greatly improves the hardness of the rail head. When the temperature at the center of the rail head weld drops to 300-350°C, the air-blasting cooling is stopped, and the welded joint is left to cool naturally to room temperature in the air.

[0034] The welded joint obtained by the method of the present invention has a longitudinal hardness HJ / HP of 0.90 to 0.95, a softening zone width of ≤20mm on both sides, and a microstructure of pearlite + proeutectoid ferrite, exhibiting good service performance.

[0035] The following are specific embodiments of a method for improving the hardness of flash welded joints of medium carbon low alloy steel rails according to the present invention.

[0036] Example 1

[0037] In this embodiment, the measured chemical composition of the rail showed that the mass fraction of carbon was 0.59%, the mass fraction of Si was 0.55%, the mass fraction of Mn was 0.7%, the mass fraction of Cr+Ni+Cu+V was 0.6%, and P and S ≤ 0.025%.

[0038] The rails were subjected to a series of processes including pre-brightening, brightening, accelerated melting, upsetting, and forging. Specific operating parameters for the pre-brightening, brightening, and accelerated melting stages are shown in Table 1.

[0039] Table 1. Operating parameters for the pre-flash stage, flash stage, and accelerated burning stage.

[0040]

[0041]

[0042] During the upsetting stage, the upsetting time is 1.0s and the upsetting amount is 13.6mm.

[0043] The main function of the forging stage is to continuously apply load to the rail joint during the metal crystallization process after the rail is upset, thereby increasing the joint hardness. To achieve this purpose, the rail consumption during the forging stage is 4.0 mm, the forging time is 2 seconds, the average speed is 2 mm / s, and the forging pressure is T80T.

[0044] After flash welding, the residual heat generated during rail welding is used to spray air onto the rail head using a special air spraying device to accelerate its cooling. At the start of air spraying, the rail head temperature is 700℃, the spraying distance is 20mm, and the spraying pressure is 0.30MPa. When the temperature at the center of the rail head weld drops to 300℃, the air spraying is stopped, and the welded joint is left to cool naturally to room temperature in the air.

[0045] The rail flash welded joint described in this embodiment has a longitudinal hardness HJ / HP of 0.91, a softening zone width of ≤15mm on both sides of the joint, and a microstructure of pearlite + proeutectoid ferrite, exhibiting good service performance.

[0046] Example 2

[0047] In this embodiment, the measured carbon mass fraction of the rail is 0.60%, the Si mass fraction is 0.55%, the Mn mass fraction is 0.67%, the Cr+Ni+Cu+V mass fraction is 0.58%, and P and S ≤ 0.025%.

[0048] The rails were subjected to a series of processes including pre-brightening, brightening, accelerated melting, upsetting, and forging. Specific operating parameters for the pre-brightening, brightening, and accelerated melting stages are shown in Table 2.

[0049] Table 2 Operating parameters for the pre-flash stage, flash stage, and accelerated burning stage

[0050]

[0051]

[0052] During the upsetting stage, the upsetting time was 1.0s and the upsetting amount was 13.8mm.

[0053] The main function of the forging stage is to continuously apply load to the rail joint during the metal crystallization process after the rail is upsetting, thereby increasing the joint hardness. To achieve the above objective, the rail consumption during the forging stage is 3.6 mm, the forging time is 2 seconds, the average speed is 1.8 mm / s, and the forging pressure is 75 T.

[0054] After flash welding, the residual heat generated during rail welding is used to spray air onto the rail head using a special air spraying device to accelerate its cooling. At the start of air spraying, the rail head temperature is 710℃, the spraying distance is 50mm, and the spraying pressure is 0.5MPa. When the temperature at the center of the rail head weld drops to 350℃, the air spraying is stopped, and the welded joint is left to cool naturally to room temperature in the air.

[0055] The rail flash welded joint described in this embodiment has a longitudinal hardness HJ / HP of 0.93, a softening zone width of ≤13mm on both sides of the joint, and a microstructure of pearlite + proeutectoid ferrite, exhibiting good service performance.

[0056] Example 3

[0057] In this embodiment, the measured chemical composition of the rail showed that the mass fraction of carbon was 0.60%, the mass fraction of Si was 0.55%, the mass fraction of Mn was 0.67%, the mass fraction of Cr+Ni+Cu+V was 0.58%, and P and S ≤ 0.025%.

[0058] The rails were subjected to a series of processes including pre-flaming, flashing, accelerated melting, upsetting, and forging. Specific operating parameters for the pre-flaming, flashing, and accelerated melting stages are shown in Table 3.

[0059] Table 3. Operating parameters for the pre-flash stage, flash stage, and accelerated burning stage.

[0060]

[0061]

[0062] During the upsetting stage, the upsetting time is 1.0s and the upsetting amount is 14.8mm.

[0063] The main function of the forging stage is to continuously apply load to the rail joint during the metal crystallization process after the rail is upsetting, thereby increasing the joint hardness. To achieve the above objective, the rail consumption during the forging stage is 2.8 mm, the forging time is 2.3 s, the average speed is 1.2 mm / s, and the forging pressure is 78 T.

[0064] After flash welding, the residual heat generated during rail welding is used to spray air onto the rail head using a special air spraying device to accelerate its cooling. At the start of air spraying, the rail head temperature is 690℃, the spraying distance is 40mm, and the spraying pressure is 0.4MPa. When the temperature at the center of the rail head weld drops to 320℃, the air spraying is stopped, and the welded joint is left to cool naturally to room temperature in the air.

[0065] The rail flash welded joint described in this embodiment has a longitudinal hardness HJ / HP of 0.94, a softening zone width of ≤16mm on both sides of the joint, and a microstructure of pearlite + proeutectoid ferrite, exhibiting good service performance.

[0066] Example 4

[0067] In this embodiment, the measured chemical composition of the rail showed that the mass fraction of carbon was 0.60%, the mass fraction of Si was 0.55%, the mass fraction of Mn was 0.67%, the mass fraction of Cr+Ni+Cu+V was 0.58%, and P and S ≤ 0.025%.

[0068] The rails were subjected to a series of processes including pre-flaming, flashing, accelerated melting, upsetting, and forging. Specific operating parameters for the pre-flaming, flashing, and accelerated melting stages are shown in Table 4.

[0069] Table 4. Operating parameters for the pre-flash stage, flash stage, and accelerated burning stage.

[0070]

[0071]

[0072] During the upsetting stage, the upsetting time is 1.0s and the upsetting amount is 14.8mm.

[0073] The main function of the forging stage is to continuously apply load to the rail joint during the metal crystallization process after the rail is upset, thereby increasing the joint's hardness. To achieve this, the rail consumption during the forging stage is 2.0 mm, the forging time is 2.0 s, the average speed is 1.0 mm / s, and the forging pressure is 70 T.

[0074] After flash welding, the residual heat generated during rail welding is used to spray air onto the rail head using a special air spraying device to accelerate its cooling. At the start of air spraying, the rail head temperature is 695℃, the spraying distance is 35mm, and the spraying pressure is 0.45MPa. When the temperature at the center of the rail head weld drops to 300℃, the air spraying is stopped, and the welded joint is left to cool naturally to room temperature in the air.

[0075] The rail flash welded joint described in this embodiment has a longitudinal hardness HJ / HP of 0.92, a softening zone width of ≤17mm on both sides of the joint, and a microstructure of pearlite + proeutectoid ferrite, exhibiting good service performance.

[0076] Comparative Example 1

[0077] In this comparative example, the measured mass fraction of carbon in the rail was 0.60%, the mass fraction of Si was 0.55%, the mass fraction of Mn was 0.67%, the mass fraction of Cr+Ni+Cu+V was 0.58%, and P and S ≤ 0.025%.

[0078] The rails were subjected to pre-flame, flash, accelerated melting, upsetting, and forging processes in sequence. The specific operating parameters for the pre-flame, flash, and accelerated melting stages were the same as in Example 1.

[0079] During the upsetting stage, the upsetting time is 1.0s and the upsetting amount is 14.8mm.

[0080] The main function of the forging stage is to continuously apply load to the rail joint during the metal solidification process after the rail is upset, thereby enhancing the joint quality. To achieve this objective, the rail consumption during the forging stage is 2.0 mm, the forging time is 2.0 s, the average speed is 1.0 mm / s, and the forging pressure is 72 T.

[0081] After flash welding is completed, do not spray air; allow the welded joint to cool naturally to room temperature in the air.

[0082] In this embodiment, the rail flash welded joint is naturally cooled after flash welding, and the longitudinal hardness HJ / HP reaches 0.82. The width of the softened zone on both sides of the joint is 25mm. The joint hardness is insufficient and the width of the softened zone exceeds the standard.

[0083] Comparative Example 2

[0084] In this comparative example, the measured mass fraction of carbon in the rail was 0.60%, the mass fraction of Si was 0.55%, the mass fraction of Mn was 0.67%, the mass fraction of Cr+Ni+Cu+V was 0.58%, and P and S ≤ 0.025%.

[0085] The rails were subjected to pre-flame, flash, accelerated melting, upsetting, and forging processes in sequence. The specific operating parameters for the pre-flame, flash, and accelerated melting stages were the same as in Example 1.

[0086] During the upsetting stage, the upsetting time was 1.0s and the upsetting amount was 13.8mm.

[0087] The main function of the forging stage is to continuously apply load to the rail joint during the metal solidification process after the rail is upset, thereby enhancing the joint quality. To achieve this purpose, the rail consumption during the forging stage is 2.5 mm, the forging time is 1.8 s, the average speed is 1.4 mm / s, and the forging pressure is 70 T.

[0088] After flash welding, the residual heat generated during rail welding is used to spray air onto the rail head using a special air spraying device to accelerate its cooling. At the start of air spraying, the rail head temperature is 630℃, the spraying distance is 40mm, and the spraying pressure is 0.2MPa. When the temperature at the center of the rail head weld drops to 300℃, the air spraying is stopped, and the welded joint is left to cool naturally to room temperature in the air.

[0089] In this embodiment, the rail head temperature was too low when the flash welding joint of the rail started to spray air, the longitudinal hardness HJ / HP reached 0.85, the width of the softened zone on the left and right sides of the joint was 23mm, the joint hardness was insufficient, and the width of the softened zone exceeded the standard.

[0090] Comparative Example 3

[0091] In this comparative example, the measured mass fraction of carbon in the actual chemical composition of the rail was 0.59%, the mass fraction of Si was 0.55%, the mass fraction of Mn was 0.7%, the mass fraction of Cr+Ni+Cu+V was 0.6%, and P and S ≤ 0.025%.

[0092] The rails were subjected to pre-flame, flash, accelerated melting, upsetting, and forging processes in sequence. The specific operating parameters for the pre-flame, flash, and accelerated melting stages were the same as in Example 1.

[0093] During the upsetting stage, the upsetting time is 1.0s and the upsetting amount is 12.2mm.

[0094] The main function of the forging stage is to continuously apply load to the rail joint during the metal solidification process after the rail is upset, thereby enhancing the joint quality. To achieve this purpose, the rail consumption during the forging stage is 3.2 mm, the forging time is 2 seconds, the average speed is 1.6 mm / s, and the forging pressure is 70 T.

[0095] After flash welding, the residual heat generated during rail welding is used to spray air onto the rail head using a special air spraying device to accelerate its cooling. At the start of air spraying, the rail head temperature is 680℃, the spraying distance is 60mm, and the spraying pressure is 0.25MPa. When the temperature at the center of the rail head weld drops to 300℃, the air spraying is stopped, and the welded joint is left to cool naturally to room temperature in the air.

[0096] In this embodiment, the air spray distance of the rail flash welding head is too large, the longitudinal hardness HJ / HP reaches 0.88, the width of the softened zone on the left and right sides of the joint is 21mm, the joint hardness is insufficient, and the width of the softened zone exceeds the standard.

[0097] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for improving the hardness of flash-welded joints of medium-carbon low-alloy steel rails, characterized in that, The medium-carbon low-alloy steel rail comprises the following components by mass fraction: C: 0.50%–0.70%, Si: 0.30%–0.60%, Mn: 0.50%–0.80%, Cr+Ni+Cu+V: 0.30%–1.0%, P, S ≤ 0.025%, with the balance being Fe and unavoidable impurities. The method includes the following steps: The rails were subjected to pre-flashing, flashing, accelerated melting, and upsetting processes in sequence. Perform forging; as well as The welded joint of the rail is cooled by air spray to obtain a flash welded joint of medium carbon low alloy steel rail that does not require post-weld normalizing. The initial air spray temperature is ≥650℃, the air spray distance is 20~50mm, and the air spray pressure is 0.30~0.50MPa. The flashing stage is divided into four sub-stages, with each subsequent sub-stage having lower voltage and current than the preceding sub-stage. Specifically, these sub-stages include: Flash sub-stage 1: Set time is 10s to 25s, voltage is 330V to 360V, set current 1 is 200A to 280A, current 2 is 350A to 500A, current 3 is 450A to 550A, pre-flash displacement is 6mm to 12mm, forward speed is 1.2mm / s to 1.7mm / s, and backward speed is 0.5mm / s to 1.2mm / s; Flash sub-stage 2: Set time is 10s to 25s, voltage is 300V to 340V, set current 1 is 220A to 250A, current 2 is 310A to 460A, current 3 is 400A to 530A, pre-flash displacement is 6mm to 10mm, forward speed is 1.5mm / s to 2.5mm / s, and backward speed is 0.5mm / s to 1.2mm / s; Flash sub-stage 3: Set time is 5s to 15s, voltage is 300V to 330V, set current 1 is 230A to 300A, current 2 is 300A to 450A, current 3 is 380A to 520A, pre-flash displacement is 3mm to 6mm, forward speed is 1.3mm / s to 2.3mm / s, and backward speed is 0.5mm / s to 1.5mm / s; Flash sub-stage 4: Set time is 5s to 15s, voltage is 320V to 360V, set current 1 is 150A to 300A, current 2 is 300A to 400A, current 3 is 350A to 500A, pre-flash displacement is 3mm to 5mm, forward speed is 0.6mm / s to 1.3mm / s, and backward speed is 0.3mm / s to 1.0mm / s; The accelerated burning stage is divided into two sub-stages, with the current and voltage gradually increasing, specifically including: Accelerated burning stage 1: set time is 3s to 8s, voltage is 350V to 380V, set current 1 is 150A to 300A, current 2 is 350A to 500A, current 3 is 450A to 550A, pre-flash displacement is 5mm to 10mm, forward speed is 0.6mm / s to 1.3mm / s, and backward speed is 0.3mm / s to 0.8mm / s; Accelerated burning stage 2: The set time is 1s to 5s, the voltage is 360V to 400V, the set current 1 is 200A to 300A, the set current 2 is 350A to 500A, the set current 3 is 450A to 550A, the pre-flash displacement is 5mm to 10mm, the forward speed is 0.6mm / s to 1.3mm / s, and the backward speed is 0.1mm / s to 0.4mm / s.

2. The method according to claim 1, characterized in that, The process of cooling the welded joint of the rail by blowing air includes: The rail head weld of the rail is cooled by air spraying, wherein the initial air spraying temperature is the temperature at the center of the rail head weld.

3. The method according to claim 2, characterized in that, The process of cooling the welded joint of the rail by blowing air includes: When the temperature at the center of the rail head weld drops to 300-350°C, stop the air cooling.

4. The method according to claim 1, characterized in that, The pre-flash phase includes: The setting time is 15s to 30s, the voltage is 370V to 400V, the setting current 1 is 180A to 220A, the current 2 is 270A to 400A, the current 3 is 350A to 450A, the pre-flash displacement is 3mm to 7mm, the forward speed is 1mm / s to 1.5mm / s, and the backward speed is 0.5mm / s to 1.2mm / s.

5. The method according to claim 1, characterized in that, The upsetting stage includes setting the electric upsetting time to 0.1s to 2.0s and the upsetting amount to 12mm to 15.0mm.

6. The method according to claim 1, characterized in that, The rail consumption during the forging stage is 2.0mm to 4.0mm, the forging time is 2.0s to 3.0s, the average speed is 1.0mm / s to 2.0mm / s, and the forging pressure is 50T to 80T.

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