Welding method for reducing gray spot area of joint of bainite steel rail and pearlite steel rail

Abstract

The invention provides a welding method for reducing the gray spot area of a joint of a bainite steel rail and a pearlite steel rail, and relates to the technical field of steel rail welding. The welding method comprises the step of welding a bainite steel rail and a pearlite steel rail, wherein the welding comprises the stages of flash flattening, preheating, burning, upsetting and pressure maintaining in sequence; the burning stage comprises a slow burning stage and a rapid burning stage; wherein the secondary voltage of the slow burning stage ranges from 5.05 V to 5.35 V, and the flash speed of the slow burning stage ranges from 0.2 mm / s to 0.4 mm / s; the secondary voltage of the rapid burning stage is 5.35-5.65 V, and the flash speed of the rapid burning stage is 2.1-2.3 mm / s; wherein the pressure of the upsetting stage ranges from 470 kN to 490 kN, and the displacement limit of the upsetting stage ranges from 32 mm to 35 mm. The welding method can effectively reduce the gray spot area of the welding joint of the two steel rails.

Description

Technical Field

[0001] The invention relates to the technical field of welding of dissimilar steel rails, and in particular to a welding method for reducing the gray spot area of ​​a joint of a bainite steel rail and a pearlite steel rail. Background Art

[0002] The frog is a device that allows the train wheels to switch from one track to another. According to the structural type, it can be divided into two types: movable heart rail frog and fixed frog. The fixed frog can be divided into high manganese steel frog and alloy steel composite frog. With the development of the railway industry, the requirements for the performance of railway frogs are constantly improving. With the application and development of seamless technology, alloy steel frogs have become the development trend of fixed frogs in railways of various countries.

[0003] At present, there are two types of welded reinforced wing rail combined frogs in China, and the main difference lies in the wing rail structure. The first type of wing rail is welded by the pearlite rails at both ends and the standard section steel billet processed by the middle bainite forged steel billet to form a reinforced wing rail, and there are two welds in the middle of the wing rail; the second type of wing rail is welded by the pearlite rail of the front section (the frog toe end direction is called the front section) and the bainite rail of the rear section to form a reinforced wing rail, and there is a weld in the middle of the wing rail. The front section of the above two types of wing rails uses pearlite rails of the same material as the line, which can meet the seamless requirements of fixed frogs; in addition, the weak area of ​​the frog near the throat uses bainite billets / rails with excellent wear resistance, which can increase the service life of the frog. In the past decade, it has been widely used in conventional railways and heavy-duty railways. However, during the service of the rails, affected by the welding quality and the complexity of the actual operating conditions of the line, the rail fractures of the line mostly occur at the welded joints, so the welded joints become the weak link of the seamless line. The quality of rail welding is directly related to the service life of the railway line and even driving safety.

[0004] Gray spots are an area defect that exists inside the flash weld of rails. They are usually local smooth areas in the weld fracture. The color is different from the metal in the weld fracture and is commonly seen in rail bottom welds. Most gray spots are accompanied by silicon-manganese inclusions. This is mainly because the Si and Mn elements in the base metal matrix are oxidized during the welding process, forming Si and Mn oxide enrichment areas. That is, the silicon and manganese elements come from the base metal, but the inclusions are formed during the welding process.

[0005] Practice has found that if there are large areas and a large number of excessive gray spot defects inside the joint, its mechanical properties will drop significantly, especially when it appears at the bottom corner edge of the rail. The probability of breaking it with a 1t hammer is almost 100%. During post-weld inspection, since the thickness of the gray spots is usually very thin, the sound wave energy will be fully projected when ultrasonic testing is used, and no reflection will be formed, resulting in the difficulty of detecting the joints through ultrasonic testing after the rail welding is completed, which poses a great safety hazard to the joints. Therefore, during the type inspection stage when formulating the welding process, the welding process personnel must control the area and number of gray spots by reasonably matching the welding process parameters. The domestic industry standard TB / T1632.2 "Rail Welding Part 2: Flash Welding" has strict restrictions on gray spots, that is, gray spots are allowed to exist, but the area of ​​a single gray spot is ≤10mm 2 , total gray spot area ≤ 20mm 2 .

[0006] CN115488483A discloses a method for improving the bonding strength of rail flash butt welding joints. The method uses a mobile flash welding machine to implement the welding process, which includes pre-flash, accelerated burning, top forging and forging; after the welding process is completed, the joint is placed in the air to naturally cool to room temperature; and it is claimed that the rail weld welded by this method has no welding defects such as gray spots, unwelded and over-burned. However, the invention is only aimed at the welding of pearlite rails and hypereutectoid rails, and the burning stage adopts the method of setting the rising current gradient, that is, the current value of the accelerated burning stage is divided into three stages of setting values, current setting value 1 is 180-250A, current setting value 2 is 200-270A, and current setting value 3 is 220-300A. Therefore, this method cannot be used for the welding of bainite rails and pearlite rails.

[0007] Therefore, how to find a welding method that can effectively control the number of gray spot defects formed in the welded joints of bainite rails and pearlite rails to improve the service performance of welded wing rail reinforced combined frogs and ensure operational safety has become one of the problems that need to be urgently solved in this field.

[0008] In view of this, the present invention is proposed. Summary of the invention

[0009] The object of the present invention is to provide a welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail. The welding method is for bainite rails and pearlite rails and can effectively reduce the gray spot area of ​​the welded joints of the two rails.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0011] In a first aspect, the present invention provides a welding method for reducing the gray spot area of ​​a joint of a bainite rail and a pearlite rail, the welding method comprising:

[0012] A flash welder is used to weld the ends of the bainite rail and the pearlite rail to be welded, wherein the welding includes a flash flattening stage, a preheating stage, a sintering stage, an upsetting stage and a pressure holding stage which are performed in sequence;

[0013] The burning stage includes a slow burning stage and a fast burning stage; the secondary voltage of the slow burning stage is 5.05-5.35V, and the flash speed of the slow burning stage is 0.2-0.4mm / s; the secondary voltage of the fast burning stage is 5.35-5.65V, and the flash speed of the fast burning stage is 2.1-2.3mm / s;

[0014] The pressure in the upsetting stage is 470-490 kN, and the displacement limit in the upsetting stage is 32-35 mm.

[0015] Preferably, the bainite rail consists of the following components in terms of mass percentage:

[0016] C 0.16~0.30%, Si 1.20~1.80%, Mn 1.50~2.30%, Cr 0.40~1.00%, Mo0.15~0.60%, and the balance is Fe.

[0017] Preferably, the pearlite rail consists of the following components in terms of mass percentage:

[0018] C 0.71~0.80%, Si 0.50~0.80%, Mn 0.75~1.05%, V 0.04~0.12%, and the balance is Fe.

[0019] Preferably, the average current of the burning stage is 13-18 kA, and the duration of the burning stage is 19-21 s.

[0020] Preferably, the slow burning stage lasts for 14 to 16 seconds, and the fast burning stage lasts for 4 to 6 seconds.

[0021] Preferably, the temperature after the rapid sintering stage is 1300-1350°C.

[0022] Preferably, the total duration of the welding is 120-125 seconds, and the total rail consumption of the welding is 31-33 mm.

[0023] Preferably, the average current in the flash-flat stage is 12-15 kA, and the rail consumption in the flash-flat stage is 4.0-4.5 mm;

[0024] Preferably, the average current in the preheating stage is 52-62 kA, the time of the preheating stage is 53-54 s, and the temperature in the preheating stage is 1300-1350°C.

[0025] Preferably, the pressure in the upsetting stage is 470-490 kN, the time in the upsetting stage is 1-3 s, and the displacement limit in the upsetting stage is 32-35 mm.

[0026] Preferably, the pressure holding stage includes a first pressure holding stage and a second pressure holding stage;

[0027] The holding pressure in the first holding stage is 470-490 kN, and the duration of the first holding stage is 4-6 s; the holding pressure in the second holding stage is 210-230 kN, and the duration of the second holding stage is 8-10 s.

[0028] Preferably, the welding method further comprises pre-treating the end to be welded before welding:

[0029] The contact parts between the ends of the bainite rail and the pearlite rail to be welded and the welding machine electrodes are respectively ground and polished, and then preheated.

[0030] Preferably, the grinding and polishing area is within 200-250 mm of the contact position between the end to be welded and the welding machine electrode.

[0031] Preferably, the temperature of the preheating treatment is 100-150° C., and the time of the preheating treatment is 0.5-2.0 h.

[0032] Preferably, the welding method further comprises a cooling stage after welding:

[0033] The slow cooling device is used to cool the welding section of the bainite rail and the pearlite rail.

[0034] Preferably, the cooling stage includes a first cooling stage and a second cooling stage:

[0035] The first cooling stage is to reduce the temperature of the center line of the rail top tread of the welded joint from the temperature at the end of welding to 330-360°C at a cooling rate of 0.8-1.0°C / s;

[0036] The second cooling stage is to cool the welding joint of the bainite rail and the pearlite rail from the temperature at the end of the first cooling stage to room temperature at a cooling rate of 0.01-0.03°C / s.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The welding method of the present invention is aimed at bainite rails and pearlite rails, and can effectively reduce the gray spot area of ​​the welded joints of the two rails, avoid the problem of a significant decrease in mechanical properties due to the presence of gray spots, and achieve a good match between the welding performance and mechanical properties of the rails, thereby improving the comprehensive performance and service life of the rails and ensuring the safety of railway operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 This is a cross-sectional view of the joint between a bainite rail and a pearlite rail provided in Example 1.

[0041] Figure 2 This is a cross-sectional view of the joint between a bainite rail and a pearlite rail provided in Example 2.

[0042] Figure 3 A cross-sectional view of a joint between a bainite rail and a pearlite rail provided for Comparative Example 1.

[0043] Figure 4 A cross-sectional view of a joint between a bainite rail and a pearlite rail provided for Comparative Example 2. DETAILED DESCRIPTION

[0044] Unless otherwise defined herein, scientific and technical terms used in conjunction with the present invention shall have the meanings commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear, however, in the case of any potential ambiguity, the definitions provided herein take precedence over any dictionary or external definitions. In this application, unless otherwise stated, the use of "or" means "and / or". In addition, the use of the term "including" and other forms is non-limiting.

[0045] It should be noted that specific details are described in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in a variety of other ways different from those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0046] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] In a first aspect, the present invention provides a welding method for reducing the gray spot area of ​​a joint of a bainite rail and a pearlite rail, the welding method comprising:

[0048] A flash welder is used to weld the to-be-welded ends of a bainite rail and a pearlite rail. The welding comprises a flash flattening stage, a preheating stage, a sintering stage, an upsetting stage and a pressure holding stage which are performed in sequence.

[0049] The burning stage includes a slow burning stage and a fast burning stage; the secondary voltage of the slow burning stage is 5.05-5.35V, and the flash speed of the slow burning stage is 0.2-0.4mm / s; the secondary voltage of the fast burning stage is 5.35-5.65V, and the flash speed of the fast burning stage is 2.1-2.3mm / s;

[0050] The pressure in the upsetting stage is 470-490 kN, and the displacement limit in the upsetting stage is 32-35 mm.

[0051] It should be noted that the burning stage is mainly to form a protective atmosphere in the welding area to prevent oxidation through flash explosions at different speeds. At this stage, the welding end surface melts to a liquid state, and the molten high-temperature metal has a strong oxygen dissolving capacity and is easily oxidized. If the burning speed is accelerated too slowly, gray spots will appear. This stage is the key stage for the occurrence and resolution of gray spots and their reduction.

[0052] Based on this, the present invention divides the burning stage into a slow burning stage and a fast burning stage, and in particular limits the voltage and flash speed of the two burning stages as shown above, so as to specifically reduce the welding difficulty between the bainite rail and the pearlite rail, so that there is no flash interruption in the flash process, and the flash is stable and intense during accelerated burning, and there is a good protective atmosphere. Therefore, a higher heat matching is selected in the accelerated burning stage of rail welding, and a larger flash speed is assisted to make the gray spot formation lose the environmental conditions, which can significantly reduce the gray spot area of ​​the welded joint, and even enable the welded joint to no longer produce gray spots, thereby avoiding the problem of a significant decrease in mechanical properties due to the presence of gray spots.

[0053] In an optional embodiment, the secondary voltage of the slow burning stage is 5.05-5.35V, for example, it can be 5.05V, 5.06V, 5.08V, 5.10V, 5.12V, 5.14V, 5.16V, 5.18V, 5.20V, 5.22V, 5.24V, 5.26V, 5.28V, 5.30V, 5.32V, 5.34V, 5.35V, etc.

[0054] In an optional embodiment, the flash speed in the slow burning stage is 0.2-0.4 mm / s, for example, it can be 0.2 mm / s, 0.22 mm / s, 0.24 mm / s, 0.26 mm / s, 0.28 mm / s, 0.30 mm / s, 0.32 mm / s, 0.34 mm / s, 0.36 mm / s, 0.38 mm / s, 0.4 mm / s, etc.

[0055] In an optional embodiment, the secondary voltage of the rapid burning stage is 5.35-5.65V, for example, it can be 5.35V, 5.36V, 5.38V, 5.40V, 5.42V, 5.44V, 5.46V, 5.48V, 5.50V, 5.52V, 5.54V, 5.56V, 5.58V, 5.60V, 5.62V, 5.64V, 5.65V, etc.

[0056] In an optional embodiment, the flash speed in the rapid burning stage is 2.1-2.3 mm / s, for example, it can be 2.1 mm / s, 2.12 mm / s, 2.14 mm / s, 2.16 mm / s, 2.18 mm / s, 2.2 mm / s, 2.22 mm / s, 2.24 mm / s, 2.26 mm / s, 2.28 mm / s, or 2.3 mm / s.

[0057] In an optional embodiment, the pressure in the upsetting stage is 470-490 kN, for example, it can be 470 kN, 472 kN, 474 kN, 476 kN, 478 kN, 480 kN, 482 kN, 484 kN, 486 kN, 488 kN, 490 kN, etc., and the displacement limit in the upsetting stage is 32-35 mm, for example, it can be 32 mm, 32.5 mm, 33 mm, 33.5 mm, 34 mm, 34.5 mm, 35 mm, etc.

[0058] In the present invention, the upsetting stage mainly applies a longitudinal load to the end of the rail to be welded, so that the high-temperature molten metal and oxide at the end are quickly squeezed out of the weld, and the end faces of the rail to be welded are welded. During upsetting, the molten metal is squeezed together with the oxide, and flows along the edge direction perpendicular to the workpiece. The oxide that is not completely squeezed out and remains in the weld forms gray spots on the fracture. This stage is another key link in controlling gray spots. Whether the oxide is easily squeezed out during upsetting is mainly determined by the extrusion amount and its fluidity, and the fluidity depends on the temperature and composition of the oxide. When the welding temperature is high, the oxide has good fluidity and is easily squeezed out. Based on this, the present invention can effectively reduce the size and number of gray spots formed by the coordination of the above-mentioned displacement limit and upsetting force.

[0059] In an optional embodiment, the bainite rail is composed of the following components in terms of mass percentage:

[0060] C 0.16~0.30%, Si 1.20~1.80%, Mn 1.50~2.30%, Cr 0.40~1.00%, Mo0.15~0.60%, and the balance is Fe.

[0061] Taking the total mass percentage of the components in the bainite rail as 100%, the C content is 0.16-0.30%, for example, 0.16%, 0.18%, 0.20%, 0.22%, 0.24%, 0.26%, 0.28%, 0.30%, etc.

[0062] Taking the total mass percentage of the components in the bainite rail as 100%, the Si content is 1.20-1.80%, for example, 1.20%, 1.25%, 1.30%, 1.35%, 1.40%, 1.45%, 1.50%, 1.55%, 1.60%, 1.65%, 1.70%, 1.75%, 1.80%, etc.

[0063] Taking the total mass percentage of the components in the bainite rail as 100%, the Mn content is 1.50-2.30%, for example, 1.50%, 1.55%, 1.60%, 1.65%, 1.70%, 1.75%, 1.80%, 1.85%, 1.90%, 1.95%, 2.00%, 2.05%, 2.10%, 2.15%, 2.20%, 2.25%, 2.30%, etc.

[0064] Taking the total mass percentage of each component in the bainite rail as 100%, the Cr content is 0.40-1.00%, for example, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1.00%, etc.

[0065] Taking the total mass percentage of each component in the bainite rail as 100%, the Mo content is 0.15-0.60%, for example, it can be 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, etc.

[0066] In an optional embodiment, the pearlite rail is composed of the following components in terms of mass percentage:

[0067] C 0.71~0.80%, Si 0.50~0.80%, Mn 0.75~1.05%, V 0.04~0.12%, and the balance is Fe.

[0068] Taking the total mass percentage of the components in the pearlite rail as 100%, the C content is 0.71-0.80%, for example, 0.71%, 0.72%, 0.73%, 0.74%, 0.75%, 0.76%, 0.77%, 0.78%, 0.79%, 0.80%, etc.

[0069] Taking the total mass percentage of each component in the pearlite rail as 100%, the Si content is 0.50-0.80%, for example, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, etc.

[0070] Taking the total mass percentage of each component in the pearlite rail as 100%, the Mn content is 0.75-1.05%, for example, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1.00%, 1.05%, etc.

[0071] Taking the total mass percentage of the components in the pearlite rail as 100%, the V content is 0.04-0.12%, for example, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, etc.

[0072] In an optional embodiment, the average current of the burning stage is 13-18 kA, for example, it can be 13 kA, 14 kA, 15 kA, 16 kA, 17 kA, 18 kA, etc.; the duration of the burning stage is 19-21 s, for example, it can be 19 s, 19.5 s, 20 s, 20.5 s, 21 s, etc.

[0073] In an optional embodiment, the time of the slow burning stage is 14 to 16 s, for example, it can be 14s, 14.5s, 15s, 15.5s, 16s, etc.; the time of the fast burning stage is 4 to 6 s, for example, it can be 4s, 4.5s, 5s, 5.5s, 6s, etc.

[0074] In an optional embodiment, the temperature after the rapid sintering stage is 1300-1350°C, for example, it can be 1300°C, 1310°C, 1320°C, 1330°C, 1340°C, 1350°C, etc.

[0075] In an optional embodiment, the total welding time is 120 to 125 s, for example, it can be 120s, 120.5s, 121s, 121.5s, 122s, 122.5s, 123s, 123.5s, 124s, 124.5s, 125s, etc.; the total consumption of the welding rail is 31 to 33 mm, for example, it can be 31 mm, 31.5 mm, 32 mm, 32.5 mm, 33 mm, etc.

[0076] In an optional embodiment, the average current in the flash-leveling stage is 12-15kA, for example, it can be 12kA, 12.5kA, 13kA, 13.5kA, 14kA, 14.5kA, 15kA, etc.; the rail consumption in the flash-leveling stage is 4.0-4.5mm, for example, it can be 4.0mm, 4.1mm, 4.2mm, 4.3mm, 4.4mm, 4.5mm, etc.

[0077] In the present invention, in the flashing stage, a certain current is loaded on the weldment, and the solid metal is transformed into molten metal by lintel blasting, so as to solve the problem of the end face slope of the rail to be welded, and at the same time provide heat conditions for the subsequent uniform short circuit of the entire section.

[0078] In an optional embodiment, the average current in the preheating stage is 52-62kA, for example, it can be 52kA, 53kA, 54kA, 55kA, 56kA, 57kA, 58kA, 59kA, 60kA, 61kA, 62kA, etc.; the time of the preheating stage is 53-54s, for example, it can be 53s, 53.2s, 53.4s, 53.6s, 53.8s, 54s, etc.; the temperature in the preheating stage is 1300-1350°C, for example, it can be 1300°C, 1310°C, 1320°C, 1330°C, 1340°C, 1350°C, etc.

[0079] In the present invention, the preheating stage of the welding process is to heat the rail to be welded by short-circuiting the two ends of the rail to be welded multiple times to generate resistance heat, so that a sufficient heating zone and an appropriate temperature gradient are formed in the longitudinal direction, and the cross-sectional temperature is uniform. The reasonable combination of preheating time and preheating current in this stage is the main factor affecting the heat of the joint.

[0080] In an optional embodiment, the duration of the upset forging stage is 1 to 3 seconds, for example, 1 second, 1.5 seconds, 2 seconds, 2.5 seconds, 3 seconds, etc.

[0081] In an optional embodiment, the pressure holding stage includes a first pressure holding stage and a second pressure holding stage; wherein the pressure holding pressure in the first pressure holding stage is 470-490 kN, for example, 472 kN, 474 kN, 476 kN, 478 kN, 480 kN, 482 kN, 484 kN, 486 kN, 488 kN, 490 kN, etc., and the time of the first pressure holding stage is 4-6 s, for example, 4 s, 4.5 s, etc. the holding pressure of the second holding stage is 210-230 kN, for example, it can be 210 kN, 212 kN, 214 kN, 216 kN, 218 kN, 220 kN, 222 kN, 224 kN, 226 kN, 228 kN, 230 kN, etc., and the time of the second holding stage is 8-10 s, for example, it can be 8 s, 8.5 s, 9 s, 9.5 s, 10 s, etc.

[0082] In the present invention, the longitudinal load is continuously applied to the welded rail through the above-mentioned specific pressure-maintaining procedure, so as to further improve the joint bonding strength and ensure that the joint has sufficient plastic deformation area.

[0083] In an optional embodiment, the welding method further includes pre-treating the end to be welded before welding:

[0084] The contact parts between the ends of the bainite rail and the pearlite rail to be welded and the welding machine electrodes are respectively ground and polished, and then preheated.

[0085] In the present invention, the contact portion between the end to be welded of the bainite rail and the pearlite rail and the welding machine electrode is polished to expose the metallic luster; and then a preheating treatment is performed to fully remove the moisture on the surface and inside of the end to be welded and to increase the temperature, so as to reduce the temperature gradient and internal stress in the welding area and reduce the risk of post-weld cracks.

[0086] In an optional embodiment, the polished area is within 200-250 mm of the contact point between the end to be welded and the welding machine electrode, for example, it can be 200 mm, 205 mm, 210 mm, 215 mm, 220 mm, 225 mm, 230 mm, 235 mm, 240 mm, 245 mm, 250 mm, etc.

[0087] In an optional embodiment, the heating box can adopt an ordinary heating tube heating furnace to heat and dry the ends of the bainite rail and the pearlite rail to be welded within a range of at least 200 mm (for example, 200 mm, 205 mm, 210 mm, 215 mm, 220 mm, 225 mm, 230 mm, 240 mm, 250 mm, etc.).

[0088] In an optional embodiment, the temperature of the preheat treatment is 100-150°C, for example, it can be 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, etc., and the time of the preheat treatment is 0.5-2.0h, for example, it can be 0.5h, 0.6h, 0.8h, 1.0h, 1.2h, 1.4h, 1.6h, 1.8h, 2.0h, etc.

[0089] It should be noted that when the air humidity is low, below 60% RH, the preheating time can generally be selected as 0.5 to 1.5 hours; when the air humidity is high, especially exceeding 60% RH, the rail drying time needs to be extended to 1.5 to 2 hours.

[0090] In the present invention, the welding problem of bainite rails and pearlite rails is specifically solved, and the two belong to the alloy steel and high carbon steel series respectively, and the carbon equivalent is large. During the cooling process of the weld metal, the temperature changes too quickly, resulting in large internal stress in the weld area. When these internal stresses exceed the crack resistance of the material, cracks will form. In order to avoid this situation, preheating before welding is increased to reduce the temperature gradient and internal stress in the welding area, thereby reducing the possibility of crack formation. Preheating can effectively reduce the cooling rate of the welding area and reduce the generation of internal stress.

[0091] In an optional embodiment, the welding method further comprises a cooling stage after welding:

[0092] The slow cooling device is used to cool the welding section of the bainite rail and the pearlite rail:

[0093] Wherein, the first cooling stage is: at a cooling rate of 0.8-1.0°C / s (for example, it can be 0.8°C / s, 0.82°C / s, 0.84°C / s, 0.86°C / s, 0.88°C / s, 0.9°C / s, 0.92°C / s, 0.94°C / s, 0.96°C / s, 0.98°C / s, 1.0°C / s, etc.), so that the temperature of the center line of the top tread of the welded joint rail is reduced from the temperature at the end of welding to 330-360°C (for example, it can be 330°C, 335°C, 340°C, 345°C, 350°C, 355°C, 360°C, etc.).

[0094] The second cooling stage is to reduce the temperature of the welded joint of the bainite rail and the pearlite rail from the end temperature of the first cooling stage to room temperature at a cooling rate of 0.01 to 0.03°C / s (for example, 0.01°C / s, 0.012°C / s, 0.014°C / s, 0.016°C / s, 0.018°C / s, 0.02°C / s, 0.022°C / s, 0.024°C / s, 0.026°C / s, 0.028°C / s, 0.03°C / s, etc.).

[0095] In the present invention, the above-mentioned specific cooling program is adopted to effectively avoid the generation of hard and brittle martensitic structure, eliminate the residual stress generated during the welding process, and further reduce the risk of cracks in the joint.

[0096] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or directly purchased from the market.

[0097] Example 1

[0098] This embodiment provides a welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail.

[0099] The bainite rail is composed of the following components by mass percentage: C 0.23%, Si 1.50%, Mn 1.90%, Cr 0.70%, Mo 0.40%, and the balance is Fe;

[0100] The pearlite rail is composed of the following components in terms of mass percentage: C 0.76%, Si 0.65%, Mn 0.90%, V 0.08%, and the balance is Fe.

[0101] The welding method comprises the following steps:

[0102] S1. Pretreatment before welding:

[0103] The bainite rail and pearlite rail to be welded are ground and polished within 220mm of the contact part between the welding machine electrode and the end to be welded to reveal the metallic luster; then a common heating tube heating furnace is used to heat and dry the bainite rail and pearlite rail to be welded within 220mm for 45 minutes at 120℃.

[0104] S2. Welding:

[0105] A fixed flash welder is used to weld the ends of the bainite rail and the pearlite rail to be welded; wherein the total welding time is 123 seconds, and the total rail consumption of the welding is 32 mm;

[0106] S2-1, flashing stage: rail consumption is 4.25mm, average current is 13.5kA.

[0107] S2-2, preheating stage: average current 57kA, duration 53.5s, temperature 1325℃.

[0108] S2-3, burning stage: the average current is 15.5kA; the burning stage includes a slow burning stage and a fast burning stage carried out in sequence;

[0109] The secondary voltage of the slow burning stage is 5.20V, the flash speed of the slow burning stage is 0.3mm / s, and the time of the slow burning stage is 15s.

[0110] The secondary voltage of the rapid burning stage is 5.50 V, the flash speed of the rapid burning stage is 2.2 mm / s, the time of the rapid burning stage is 5 s, and the temperature after the rapid burning stage ends is 1325° C.

[0111] S2-4, upsetting stage: the upsetting pressure is 480 kN, the upsetting time is 2.3 s, and the displacement limit is 32 mm.

[0112] S2-5, pressure holding stage: the pressure holding stage includes a first pressure holding stage and a second pressure holding stage;

[0113] The holding pressure of the first holding stage is 480 kN, and the time of the first holding stage is 5 s; the holding pressure of the second holding stage is 220 kN, and the time of the second holding stage is 9 s.

[0114] S3, cooling stage:

[0115] The temperature of the center line of the rail top tread of the welded joint is reduced from the temperature at the end of welding to 360°C at a cooling rate of 0.9°C / s; then the welded joint of the bainite rail and the pearlite rail is slowly cooled in a slow cooling box for 3.5 hours to room temperature.

[0116] Example 2

[0117] This embodiment provides a welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail.

[0118] The bainite rail is composed of the following components by mass percentage: C 0.23%, Si 1.50%, Mn 1.90%, Cr 0.70%, Mo 0.40%, and the balance is Fe;

[0119] The pearlite rail is composed of the following components in terms of mass percentage: C 0.76%, Si 0.65%, Mn 0.90%, V 0.08%, and the balance is Fe.

[0120] The welding method comprises the following steps:

[0121] S1. Pretreatment before welding:

[0122] The bainite rail and pearlite rail to be welded are ground and polished within 220mm of the contact area between the welding machine electrode and the end to be welded to reveal their metallic luster; then a common heating tube heating furnace is used to heat and dry the bainite rail and pearlite rail to be welded within 220mm at 120℃ for 1h.

[0123] S2. Welding:

[0124] A fixed flash welder is used to weld the ends of the bainite rail and the pearlite rail to be welded; wherein the total welding time is 123 seconds, and the total rail consumption of the welding is 32 mm;

[0125] S2-1, flashing stage: rail consumption is 4.25mm, average current is 13.5kA.

[0126] S2-2, preheating stage: average current 57kA, duration 53.5s, temperature 1325℃.

[0127] S2-3, burning stage: the average current is 15.5kA; the burning stage includes a slow burning stage and a fast burning stage carried out in sequence;

[0128] The secondary voltage of the slow burning stage is 5.20V, the flash speed of the slow burning stage is 0.3mm / s, and the time of the slow burning stage is 15s.

[0129] The secondary voltage of the rapid burning stage is 5.65 V, the flash speed of the rapid burning stage is 2.3 mm / s, the time of the slow burning stage is 5 s, and the temperature after the rapid burning stage is 1340° C.

[0130] S2-4, upsetting stage: the upsetting pressure is 485 kN, the upsetting time is 2.1 s, and the displacement limit is 33 mm.

[0131] S2-5, pressure holding stage: the pressure holding stage includes a first pressure holding stage and a second pressure holding stage;

[0132] The holding pressure in the first holding stage is 485 kN, and the time in the first holding stage is 5 s; the holding pressure in the second holding stage is 220 kN, and the time in the second holding stage is 9 s.

[0133] S3, cooling stage:

[0134] At a cooling rate of 1.0°C / s, the temperature of the center line of the rail top tread of the welded joint is reduced from the temperature at the end of welding to 340°C; then the welded joint of the bainite rail and the pearlite rail is slowly cooled in a slow cooling box for 3 hours to room temperature.

[0135] Example 3

[0136] This embodiment provides a welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail.

[0137] The bainite rail is composed of the following components by mass percentage: C 0.16%, Si 1.20%, Mn 1.50%, Cr 0.40%, Mo 0.15%, and the balance is Fe;

[0138] The pearlite rail is composed of the following components in terms of mass percentage: C 0.80%, Si 0.80%, Mn 1.05%, V 0.12%, and the balance is Fe.

[0139] The welding method comprises the following steps:

[0140] S1. Pretreatment before welding:

[0141] The bainite rail and pearlite rail to be welded are ground and polished within 200mm of the contact part with the welding machine electrode to make both of them show metallic luster; then a common heating tube heating furnace is used to heat and dry the bainite rail and pearlite rail to be welded within 200mm at 100℃ for 1.0h.

[0142] S2. Welding:

[0143] A fixed flash welder is used to weld the to-be-welded ends of a bainite rail and a pearlite rail, wherein the total welding time is 124 seconds and the total rail consumption during welding is 31 mm;

[0144] S2-1, flashing stage: rail consumption is 4.0mm, average current is 12kA.

[0145] S2-2, preheating stage: average current 52kA, duration 54s, temperature 1300℃.

[0146] S2-3, burning stage: the average current is 13kA; the burning stage includes a slow burning stage and a fast burning stage carried out in sequence;

[0147] The secondary voltage of the slow burning stage is 5.05V, the flash speed of the slow burning stage is 0.2mm / s, and the time of the slow burning stage is 14s.

[0148] The secondary voltage of the rapid burning stage is 5.35 V, the flash speed of the rapid burning stage is 2.1 mm / s, the time of the slow burning stage is 4 s, and the temperature after the rapid burning stage is 1300° C.

[0149] S2-4, upsetting stage: the upsetting pressure is 470 kN, the upsetting time is 3.0 s, and the displacement limit is 33 mm.

[0150] S2-5, pressure holding stage: the pressure holding stage includes a first pressure holding stage and a second pressure holding stage;

[0151] The holding pressure in the first holding stage is 470 kN, and the time in the first holding stage is 6 s; the holding pressure in the second holding stage is 210 kN, and the time in the second holding stage is 10 s.

[0152] S3, cooling stage:

[0153] At a cooling rate of 1.0℃ / s, the temperature of the center line of the rail top tread of the welded joint is reduced from the temperature at the end of welding to 340℃; then the welded joint of the bainite rail and the pearlite rail is slowly cooled in a slow cooling box for 4 hours to room temperature.

[0154] Example 4

[0155] This embodiment provides a welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail.

[0156] The bainite rail is composed of the following components by mass percentage: C 0.30%, Si 1.80%, Mn 2.30%, Cr 1.00%, Mo 0.60%, and the balance is Fe;

[0157] The pearlite rail is composed of the following components in terms of mass percentage: C 0.71%, Si 0.50%, Mn 0.75%, V 0.04%, and the balance is Fe.

[0158] The welding method comprises the following steps:

[0159] S1. Pretreatment before welding:

[0160] The bainite rail and pearlite rail to be welded are ground and polished within 250mm of the contact part between the welding machine electrode and the end to be welded to reveal the metallic luster; then a common heating tube heating furnace is used to heat and dry the bainite rail and pearlite rail to be welded within 250mm at 150℃ for 0.5h.

[0161] S2. Welding:

[0162] A fixed flash welder is used to weld the ends of the bainite rail and the pearlite rail to be welded, wherein the total welding time is 121 seconds and the total rail consumption of the welding is 33 mm;

[0163] S2-1, flashing stage: rail consumption is 4.5mm, average current is 15kA.

[0164] S2-2, preheating stage: average current 62kA, duration 53s, temperature 1350℃.

[0165] S2-3, burning stage: the average current is 18kA; the burning stage includes a slow burning stage and a fast burning stage carried out in sequence;

[0166] The secondary voltage of the slow burning stage is 5.35V, the flash speed of the slow burning stage is 0.4mm / s, and the time of the slow burning stage is 16s.

[0167] The secondary voltage of the rapid burning stage is 5.65 V, the flash speed of the rapid burning stage is 2.3 mm / s, the time of the slow burning stage is 6 s, and the temperature after the rapid burning stage is 1350° C.

[0168] S2-4, upsetting stage: the upsetting pressure is 490 kN, the upsetting time is 1.0 s, and the displacement limit is 35 mm.

[0169] S2-5, pressure holding stage: the pressure holding stage includes a first pressure holding stage and a second pressure holding stage;

[0170] The holding pressure of the first holding stage is 490 kN, and the time of the first holding stage is 4 s; the holding pressure of the second holding stage is 230 kN, and the time of the second holding stage is 8 s.

[0171] S3, cooling stage:

[0172] At a cooling rate of 1.0°C / s, the temperature of the center line of the rail top tread of the welded joint is reduced from the temperature at the end of welding to 330°C; then the welded joint of the bainite rail and the pearlite rail is slowly cooled in a slow cooling box for 4.5 hours to room temperature.

[0173] Comparative Example 1

[0174] This comparative example provides a welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail. The difference between the welding method and Example 1 is that: the secondary voltage in the rapid burning stage is 3.77V, and the flash speed in the rapid burning stage is 1.5mm / s; the upsetting pressure is 530kN, the upsetting time is 1.5s, and the displacement limit is 32mm; the other steps are completely consistent with Example 1.

[0175] Comparative Example 2

[0176] This comparative example provides a welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail. The welding method is different from that in Example 1 only in that the upset pressure is 420 kN, the upset time is 2.2 s, and the displacement limit is 33 mm; the other steps are completely consistent with those in Example 1.

[0177] Comparative Example 3

[0178] This comparative example provides a welding method for a bainite rail and a pearlite rail, which is different from Example 1 only in that only grinding and polishing are performed in S1, and no preheating treatment is performed; the other steps are completely consistent with Example 1.

[0179] Comparative Example 4

[0180] This comparative example provides a welding method for a bainite rail and a pearlite rail, which is different from Example 1 only in that only a slow sintering stage is performed in S2-3, and no rapid sintering step is performed subsequently; the other steps are completely consistent with Example 1.

[0181] Comparative Example 5

[0182] This comparative example provides a welding method for a bainite rail and a pearlite rail, which is different from Example 1 only in that in S2-3, there is no longer a slow sintering stage, but only a fast sintering stage; the other steps are completely consistent with Example 1.

[0183] Comparative Example 6

[0184] This comparative example provides a welding method for a bainite rail and a pearlite rail, which is different from Example 1 only in that only the first pressure holding stage is performed in S2-5; the other steps are completely consistent with Example 1.

[0185] Comparative Example 7

[0186] This comparative example provides a welding method for a bainite rail and a pearlite rail, which is different from Example 1 only in that only the second pressure holding stage is performed in S2-5; the other steps are completely consistent with Example 1.

[0187] Comparative Example 8

[0188] This comparative example provides a welding method for a bainite rail and a pearlite rail, which is different from Example 1 only in that the welded joint of the bainite rail and the pearlite rail is directly cooled to room temperature at a cooling rate of 0.9°C / s in S3; the other steps are completely consistent with Example 1.

[0189] Test Case

[0190] Test samples: heterogeneous rails obtained by the welding methods of Examples 1 to 4 and heterogeneous rails obtained by the welding methods of Comparative Examples 1 to 8.

[0191] Test method: 5 joints are welded for each set of processes; the test standard refers to TB / T 1632.2 "Rail welding Part 2: Flash welding".

[0192] The test results are shown in Table 1 below:

[0193] Table 1

[0194]

[0195]

[0196] As shown in Table 1, the welding method of the present invention can effectively reduce the gray spot area of ​​the welded joints of bainite rails and pearlite rails, avoid the problem of a significant decrease in mechanical properties due to the presence of gray spots, and achieve a good match between the welding performance and mechanical properties of the rails.

[0197] Among them, Example 1 is the best welding solution for reducing the gray spot area of ​​the joints of bainite rails and pearlite rails. The five welded joints were tested and found that the drop hammer results were all qualified, and no gray spots appeared on the fracture, that is, the gray spot area of ​​the fracture was 0mm. 2 ;like Figure 1 As shown, it is more intuitively observed that there are no gray spots at the welding joints of the two rails of No. 1.

[0198] The five welded joints in Example 2 were tested and found to be qualified by the drop hammer test. No gray spots appeared on the fracture surfaces of the four welded joints, and a small gray spot appeared on the joint with serial number 4. Figure 2 As shown in the figure, a small gray spot with an area of ​​5.0 mm appeared at the welded joint of the two rails No. 4. 2 .

[0199] Compared with the comparative example 1 and the embodiment, the most important difference is that the secondary voltage in the burn-in stage is reduced, the rapid burn-in speed is reduced, and the upset force is increased. Among the five joints completed with this parameter, four joints are broken, and the gray spots on the fracture of four joints exceed the standard. This is mainly because after the secondary voltage and the flash speed are reduced in the burn-in stage, the welding current is not intensive, which will lead to less intense burn-in in the welding acceleration stage, and fail to form a good protective atmosphere for the end metal. The end is easily oxidized to form gray spots; although the excessive upset force can easily squeeze the oxide out of the weld, resulting in the gray spot area on the fracture not completely exceeding the standard, the plastic zone is over-extruded, the grain is bent, and the impact performance of the joint is reduced. In particular, if Figure 3 As shown in the figure, gray spots appear on the edge of the rail angle of the welding joint with serial number 3, and the area of ​​the gray spots reaches 7.5mm 2 .

[0200] The main difference between Comparative Example 2 and Example 1 is that the upset force is reduced. Four of the five joints completed with this parameter broke, and the gray spots on the fractures of four joints exceeded the standard. This is mainly because the silicon-manganese oxides formed in the flashing stage are not easily squeezed out and eventually remain to form large areas of gray spots, even appearing at the edge of the rail angle, resulting in insufficient plastic deformation of the entire joint. In particular, if the upset force is too small, the silicon-manganese oxides formed in the flashing stage are not easily squeezed out and eventually remain to form large areas of gray spots, even appearing at the edge of the rail angle, resulting in insufficient plastic deformation of the entire joint. Figure 4 As shown in the figure, multiple dense gray spots appear on the edge of the rail angle of the welding head with serial number 5, and the total area of ​​the gray spots reaches 12mm 2 .

[0201] Compared with Comparative Example 3 and the embodiment, the main difference is that the end to be welded is not preheated, and the temperature of the weld metal changes too quickly during the cooling process, resulting in large internal stress in the weld area of ​​the joint. Although the gray spots on the joint are not completely exceeded, when the stress exceeds the crack resistance of the material, it will cause cracks in the joint and the drop hammer performance will fail to meet the standards.

[0202] Compared with the embodiment, the main difference between comparative examples 4 to 5 is that only one sintering stage is performed, and the joint does not form a continuous flash explosion, resulting in an oxidized atmosphere in the cross section of the welding area and an increase in gray spots.

[0203] Compared with the embodiment, the main difference between comparative examples 6 to 7 is that only one pressure holding stage is performed, and the gray spots meet the requirements, but the joint bonding strength is not effectively improved, the plastic deformation zone is insufficient, and the drop hammer performance is reduced.

[0204] Compared with the embodiment, comparative example 8 did not perform slow cooling after welding, and a large amount of martensite structure was generated inside the joint. The strength and hardness of the structure were relatively high, but its toughness was poor, which easily caused brittle fracture. The gray spot area inside the joint was qualified, but the drop weight performance of the joint was unqualified under the combined effect of internal stress and organizational stress.

[0205] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail, characterized in that: The welding method comprises: A flash welder is used to weld the ends of the bainite rail and the pearlite rail to be welded, wherein the welding includes a flash flattening stage, a preheating stage, a sintering stage, an upsetting stage and a pressure holding stage which are performed in sequence; The burning stage includes a slow burning stage and a fast burning stage; the secondary voltage of the slow burning stage is 5.05-5.35V, and the flash speed of the slow burning stage is 0.2-0.4mm / s; the secondary voltage of the fast burning stage is 5.35-5.65V, and the flash speed of the fast burning stage is 2.1-2.3mm / s; The pressure in the upsetting stage is 470-490 kN, and the displacement limit in the upsetting stage is 32-35 mm.

2. The welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail according to claim 1, characterized in that: The bainite rail is composed of the following components by mass percentage: C 0.16~0.30%, Si 1.20~1.80%, Mn 1.50~2.30%, Cr 0.40~1.00%, Mo0.15~0.60%, and the balance is Fe.

3. The welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail according to claim 1, characterized in that: The pearlite rail is composed of the following components by mass percentage: C 0.71~0.80%, Si 0.50~0.80%, Mn 0.75~1.05%, V 0.04~0.12%, and the balance is Fe.

4. The welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail according to claim 1, characterized in that: The average current of the burning stage is 13-18 kA, and the duration of the burning stage is 19-21 s; Preferably, the slow burning stage lasts for 14 to 16 seconds, and the fast burning stage lasts for 4 to 6 seconds; Preferably, the temperature after the rapid sintering stage is 1300-1350°C.

5. The welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail according to claim 1, characterized in that: The total duration of the welding is 120 to 125 seconds, and the total rail consumption of the welding is 31 to 33 mm; Preferably, the average current in the flash-flat stage is 12-15 kA, and the rail consumption in the flash-flat stage is 4.0-4.5 mm; Preferably, the average current in the preheating stage is 52-62 kA, the time of the preheating stage is 53-54 s, and the temperature in the preheating stage is 1300-1350°C.

6. The welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail according to claim 1, characterized in that: The duration of the upsetting stage is 1 to 3 seconds; Preferably, the pressure holding stage includes a first pressure holding stage and a second pressure holding stage; The holding pressure in the first holding stage is 470-490 kN, and the duration of the first holding stage is 4-6 s; the holding pressure in the second holding stage is 210-230 kN, and the duration of the second holding stage is 8-10 s.

7. The welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail according to claim 1, characterized in that: The welding method also includes pre-treatment of the end to be welded before welding: The contact parts between the ends of the bainite rail and the pearlite rail to be welded and the welding machine electrodes are respectively ground and polished, and then preheated.

8. The welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail according to claim 7, characterized in that: The polished area is within 200-250 mm of the contact area between the end to be welded and the welding machine electrode; Preferably, the temperature of the preheating treatment is 100-150° C., and the time of the preheating treatment is 0.5-2.0 h.

9. The welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail according to claim 1, characterized in that: The welding method also includes a cooling phase after welding: The slow cooling device is used to cool the welding section of the bainite rail and the pearlite rail.

10. The welding method for reducing the gray spot area of ​​the joint of a bainite rail and a pearlite rail according to claim 9, characterized in that: The cooling stage includes a first cooling stage and a second cooling stage: The first cooling stage is to reduce the temperature of the center line of the rail top tread of the welded joint from the temperature at the end of welding to 330-360°C at a cooling rate of 0.8-1.0°C / s; The second cooling stage is to cool the welding joint of the bainite rail and the pearlite rail from the temperature at the end of the first cooling stage to room temperature at a cooling rate of 0.01-0.03°C / s.

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