A welding method for controlling the hardness of a joint of a bainite rail and a pearlite rail

Abstract

The application provides a welding method for controlling the joint hardness of bainite steel rails and pearlite steel rails, and relates to the technical field of rail welding. The welding method comprises the following steps: performing induction heating normalizing treatment on the welded joint of the bainite steel rail and the pearlite steel rail at 900-920 DEG C; air cooling one side of the pearlite steel rail after normalizing until the temperature of the one side of the pearlite steel rail decreases to 450-550 DEG C; performing speed-reducing cooling on the one side of the pearlite steel rail after the first stage of cooling; the temperature decreasing mode of the speed-reducing cooling comprises the following steps: firstly, decreasing the temperature to 350-450 DEG C at a first temperature decreasing rate; secondly, decreasing the temperature to 100-150 DEG C at a second temperature decreasing rate; and finally, decreasing the temperature to 15-35 DEG C at a third temperature decreasing rate; and performing heating tempering treatment on the welded joint after the second stage of cooling at 400-450 DEG C. The application can significantly improve the joint hardness, and the hardness of the two sides of the dissimilar steel rails is well matched.

Description

Technical Field

[0001] This invention relates to the field of dissimilar rail welding technology, and in particular to a welding method for controlling the joint hardness of bainitic and pearlitic rails. Background Technology

[0002] Currently, there are two types of welded reinforced wing rail combination frogs in China, mainly differing in the wing rail structure. The first type consists of pearlitic steel rails at both ends welded to a standard-section rail made from a bainitic forged steel billet in the middle, forming a reinforced wing rail with two weld seams in the middle. The second type consists of a pearlitic steel rail at the front section (referred to as the front section in the direction of the frog toe) welded to a bainitic steel rail at the rear section, forming a reinforced wing rail with one weld seam in the middle. Both types use pearlitic steel rails of the same material as the track in the front section, meeting the seamless requirements of fixed frogs. Furthermore, the weak areas near the throat of the frog use bainitic steel billets / rails with excellent wear resistance, improving the frog's service life. In the past decade or so, these frogs have been widely used in conventional and heavy-haul railways. However, during rail service, due to the influence of welding quality and the complexity of actual operating conditions, rail fractures often occur at welded joints, making these joints a weak point in seamless tracks. The quality of rail welding is directly related to the service life of railway lines and even traffic safety.

[0003] Bainitic rails are superior to pearlitic rails in terms of strength, hardness, and toughness. During the service of rail welded joints, the service life of dissimilar material welded joints depends on the weakest part of the joint.

[0004] Referring to my country's railway industry standard TB / T1632.2 "Rail Welding Part 2: Flash Welding", the quality requirements for welded joints between rails of different steel grades shall be implemented according to the requirements for rails with lower strength grades.

[0005] The hardness of the pearlite side of the joint should meet the following requirement: H J珠光体 ≥0.9H P珠光体 H J1珠光体 ≥0.8H P珠光体 ("H" J珠光体 "H" indicates the average hardness value of the joint on the pearlite side. P珠光体 "H" indicates the average hardness of the parent material on the pearlite side. J1珠光体 "This represents the average soft spot value on one side of the pearlite."

[0006] The hardness of the bainitic side joint should meet the following requirement: H J贝氏体 ≥0.9H P珠光体 H J1贝氏体 ≥0.8H P珠光体 ("H" J贝氏体 "H" indicates the average hardness value of the joint on the bainitic side.J1贝氏体 "This represents the average soft spot value on one side of the bainite body."

[0007] In addition, the range of soft spots below 90% of the average hardness of the base material, i.e., the width of the soft area, should not exceed 20 mm.

[0008] CN112359179A discloses a post-weld heat treatment method applicable to welded joints formed by a moving flash welding machine for bainitic and eutectoid pearlitic rails. Although this method heat-treats the welded joints of dissimilar rails, the average hardness of the bainitic rail side of the joint only reaches 87% of the base material, and the soft zone width reaches 45mm. This does not meet the requirements of the domestic rail flash welding standard TB / T 1632.2 "Rail Welding Part 2: Flash Welding" regarding hardness (heat-affected zone hardness ≥ 0.90 base material hardness, and heat-affected zone width W ≤ 20mm, soft spot hardness ≥ 0.8 base material hardness).

[0009] CN118996098A discloses a heat treatment apparatus and method for dissimilar rail welded joints. This heat treatment method utilizes the residual heat of welding to perform different cooling rates. However, the welded joint is not normalized or re-austenitized after welding, inevitably leading to problems such as uneven grain size and high structural stress within the joint.

[0010] Therefore, after the welding of bainitic and pearlitic rails, how to ensure that the hardness of the weld on the pearlitic side matches that of the base material well, while preventing the formation of large blocks of hard and brittle acicular martensite on the bainitic rail side, has become a prerequisite for the increasingly widespread application and safe service of welded reinforced wing rail combination frogs.

[0011] In view of this, the present invention is hereby proposed. Summary of the Invention

[0012] The purpose of this invention is to provide a welding method for controlling the joint hardness of bainitic and pearlitic rails. The welding method described in this invention can significantly improve the joint hardness and match it well with the hardness of dissimilar rails on both sides, thus ensuring the safety of railway operation.

[0013] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0014] This invention provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails, the welding method comprising:

[0015] Normalizing: The welded joints of bainitic and pearlitic steel rails are subjected to induction heating normalizing treatment at 900-920℃.

[0016] The first stage of cooling involves air cooling one side of the normalized pearlitic steel rail until the temperature of that side drops to 450–550°C.

[0017] The second stage of cooling involves slowing down one side of the pearlitic steel rail after the first stage of cooling. The slowing down cooling method includes: first cooling to 350-450°C at a first cooling rate, then cooling to 100-150°C at a second cooling rate, and finally cooling to 15-35°C at a third cooling rate. The first cooling rate is greater than the second cooling rate, and the third cooling rate is greater than or equal to the second cooling rate.

[0018] Tempering: The welded joint that has cooled in the second stage is heated and tempered at 400-450℃.

[0019] Furthermore, the hardness of the bainitic rail is 400–420 HBW.

[0020] Furthermore, the hardness of the pearlitic steel rail is 340–390 HBW.

[0021] Furthermore, during the normalizing process, the welded joint specifically refers to the area within a range of 30 to 50 mm on both sides of the fusion line.

[0022] Furthermore, the induction heating normalizing treatment time is 95–105 seconds.

[0023] Furthermore, during the first stage of cooling, the pearlitic rail side specifically refers to the area of ​​more than 80mm on one side of the pearlitic rail along the fusion line.

[0024] Furthermore, during the second stage of cooling, the pearlitic rail side specifically refers to the area of ​​more than 80mm on one side of the pearlitic rail along the fusion line.

[0025] Furthermore, during the tempering process, the welded joint specifically refers to an area of ​​more than 80mm on both sides of the fusion line.

[0026] Furthermore, during the first stage of cooling, the cooling rate on one side of the pearlitic steel rail is 3.5–6.0 °C / s.

[0027] Furthermore, during the first stage of cooling, the air pressure of the air cooling system is 0.10 to 0.15 MPa.

[0028] Furthermore, during the first stage of cooling, one side of the normalized bainitic rail is air-cooled.

[0029] Furthermore, during the first stage of cooling, the cooling rate on one side of the bainitic rail is 2.5–4.5 °C / s.

[0030] Furthermore, when the temperature on one side of the pearlitic rail drops to 450–550°C, the temperature on the other side of the bainitic rail drops to 550–650°C.

[0031] Furthermore, the first cooling rate is 0.1 to 1.0 °C / s, preferably 0.4 to 0.6 °C / s.

[0032] Further, the second cooling rate is 0.005 to 0.05 °C / s, preferably 0.01 to 0.03 °C / s.

[0033] Furthermore, the third cooling rate is 0.01 to 0.1 °C / s, preferably 0.08 to 0.1 °C / s.

[0034] Furthermore, the holding time for the heating and tempering treatment is 5 to 6 hours.

[0035] Furthermore, after the heating and tempering treatment, the temperature is naturally cooled to 15–35°C.

[0036] Furthermore, the natural cooling time is 3 to 5 hours.

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

[0038] The welding method for controlling the joint hardness of bainitic and pearlitic rails described in this invention employs a sequential process of normalizing, two-stage cooling, and tempering. Different cooling processes are used for different parts and stages of the welded joint to achieve optimal hardness matching between the bainitic and pearlitic rails after flash welding. This welding method significantly improves the joint hardness and ensures good matching with the hardness of the rails on both sides, guaranteeing railway operation safety. Attached Figure Description

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 This is a front view of the first stage of cooling in the welding method.

[0041] Figure 2 This is a side view of the first stage of cooling in the welding method.

[0042] Among them, 1 is a bainitic rail, 2 is a pearlitic rail, 21 is the top surface of the pearlitic rail, 22 is the side of the rail head of the pearlitic rail, 3 is the fusion line of the welded joint, and 4 is the air jet device.

[0043] Figure 3 This is a front view of the slow cooling device in the second stage of cooling in the welding method.

[0044] Figure 4 This is a top view of the slow cooling device in the second stage of the welding method.

[0045] Figure 5 This is a side sectional view of the slow cooling device in the second stage of the welding method.

[0046] Among them, 5 is the handle, 6 is the locking switch, 7 is the hinge, 8 is the rail groove, and 9 is the insulation cotton.

[0047] Figure 6 The distribution curve of hardness of the rail welded joint provided in Example 1. Detailed Implementation

[0048] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0049] It should be noted that specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many ways other than those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0050] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] This invention provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails, the welding method comprising:

[0052] Normalizing: The welded joints of bainitic and pearlitic steel rails are subjected to induction heating normalizing treatment at 900-920℃.

[0053] The first stage of cooling involves air cooling one side of the normalized pearlitic steel rail until the temperature of that side drops to 450–550°C.

[0054] The second stage of cooling involves slowing down one side of the pearlitic steel rail after the first stage of cooling. The slowing down cooling method includes: first cooling to 350-450°C at a first cooling rate, then cooling to 100-150°C at a second cooling rate, and finally cooling to 15-35°C at a third cooling rate. The first cooling rate is greater than the second cooling rate, and the third cooling rate is greater than or equal to the second cooling rate.

[0055] Tempering: The welded joint that has cooled in the second stage is heated and tempered at 400-450℃.

[0056] It should be noted that the rail provided by the present invention is a rail formed by flash welding of bainitic steel rail and pearlitic steel rail. Due to the characteristics of flash welding of rail, such as high heating temperature, fast heating speed, short high temperature dwell time and uneven temperature distribution, problems such as coarse structure and significant decrease in plasticity and toughness occur at the weld joint. In addition, the rail generates internal stress after welding, and the weld joint is very prone to fracture under impact load.

[0057] Based on this, the present invention adopts the technical route of normalizing, two-stage cooling and tempering in sequence using the welding method described above. Different cooling processes are used for different parts and stages of the welded joint to achieve the best matching of hardness of the joint after flash welding of bainitic and pearlitic rails, so as to achieve the purpose of controlling the hardness of the rail welded joint.

[0058] First, this invention applies induction heating normalizing to the welded joint of the rail after welding. The principle of normalizing is to reheat the joint to a temperature exceeding AC3, causing the microstructure to completely transform into austenite, resulting in fine austenite grains. Then, it is cooled at an appropriate rate to eliminate welding stress, improve the microstructure, thereby enhancing the mechanical properties of the welded joint and extending its service life. Specifically, this invention employs induction heating normalizing. Eddy currents are generated inside the rail by an applied current. The combined effect of these eddy currents and the skin effect heats the rail, providing a heating method from the inside out. This method offers rapid heating, a small heat-affected zone, and stable quality.

[0059] Secondly, in this invention, after the austenitization of the joint is completed, only the pearlite side is rapidly cooled, while the bainitic steel side of the welded joint is air-cooled. When the temperature of the top surface of the pearlite side of the joint drops to a temperature higher than M after the austenite has transformed into pearlite, the temperature remains constant. s高 Point (M) s高 The point, namely, the M value in bainitic and pearlitic steel rails. s M of the material with higher points After reaching a certain temperature, the entire welded joint is slowly cooled to 100–150°C, followed by air cooling to 15–35°C. This gradient cooling process not only increases the hardness of the pearlite side to ensure sufficient wear resistance, but also prevents the hardness of the bainitic steel side from becoming too high, which could lead to acicular martensite hard and brittle structures, while also saving production time.

[0060] Finally, the present invention performs a heat tempering treatment on the welded joint portion after the second stage of cooling at 400-450°C; the reason for this is to eliminate the internal stress of the welded joint.

[0061] As an optional implementation, the hardness of the bainitic rail is 400-420 HBW, for example, it can be 400 HBW, 402 HBW, 404 HBW, 406 HBW, 408 HBW, 410 HBW, 412 HBW, 414 HBW, 416 HBW, 418 HBW, 420 HBW, etc.

[0062] As an optional implementation, the hardness of the pearlitic steel rail is 340-390 HBW, for example, it can be 340 HBW, 345 HBW, 350 HBW, 355 HBW, 360 HBW, 365 HBW, 370 HBW, 375 HBW, 380 HBW, 385 HBW, 390 HBW, etc.

[0063] It is important to note that the bainitic rail base material targeted in this invention has a hardness of 400–420 HBW. This type of steel can form bainitic and martensitic structures under air cooling conditions. Pearlitic rail base materials, on the other hand, have a slightly different hardness, ranging from 340–390 HBW. Therefore, the difficulty in welding these two types of rails lies in how to increase the hardness of the heat-affected zone on the pearlitic side of the joint to achieve a good match with the base material. Simultaneously, the hardness of the bainitic side of the joint should not be too high, as hardness is closely related to internal structure. Excessive hardness on the bainitic rail side often leads to the formation of a large amount of hard, brittle acicular martensite, which is detrimental to the safe service life of the joint. In fact, bainitic rails can form bainitic and martensitic structures under air cooling conditions. If, after normalizing heating, the bainitic rail side undergoes the same rapid cooling process as the pearlitic side, a large amount of martensite will appear on the bainitic side. The processing method described in this invention can effectively solve the problems of low hardness in the heat-affected zone on one side of the pearlitic rail joint and abnormal microstructure on the other side of the bainitic rail joint.

[0064] As an optional implementation, the bainitic 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%, Mo 0.15-0.60%, with the balance being Fe.

[0065] As an optional embodiment, the pearlitic 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%, with the balance being Fe.

[0066] It should be noted that, due to the differences in the C content and various alloying element content in bainitic and pearlitic steel rails, the bainitic steel rail M in this invention... s The temperature range is 220–330℃, higher than that of pearlitic steel rail M. s The temperature range is 190–240℃.

[0067] As an optional implementation, the induction heating normalizing treatment is performed on the joint using a medium-frequency induction machine.

[0068] As an optional implementation, during the normalizing process, the welded joint is specifically an area within a range of 30 to 50 mm on both sides of the fusion line (for example, it can be 30 mm, 32 mm, 34 mm, 36 mm, 38 mm, 40 mm, 42 mm, 44 mm, 46 mm, 48 mm, 50 mm, etc.).

[0069] As an optional implementation, the temperature of the induction heating normalizing treatment is 900-920℃, for example, it can be 900℃, 902℃, 904℃, 906℃, 908℃, 910℃, 912℃, 914℃, 916℃, 918℃, 920℃, etc.

[0070] As an optional implementation, the induction heating normalizing treatment time is 95 to 105 seconds, for example, 95 seconds, 96 seconds, 97 seconds, 98 seconds, 99 seconds, 100 seconds, 101 seconds, 102 seconds, 103 seconds, 104 seconds, 105 seconds, etc.

[0071] As an optional implementation, after the normalizing is completed, the normalized rail is quickly transferred to the air-jetting mechanism; and the temperature of the joint rail head is controlled above 800°C (just after being transferred to the air-jetting mechanism, before air cooling).

[0072] It is important to note that Figure 1 This is a front view of the first stage of cooling in the welding method. Figure 2 This is a side view of the first stage of cooling in the welding method described. Figure 1 and Figure 2 As shown, during the first stage of cooling, the edge of the air jet device 4 is aligned with the weld of the pearlitic steel rail 2, and air cooling is performed only on the top surface 21 and the side surface 22 of the rail head of the pearlitic steel rail.

[0073] As an optional implementation, during the first stage of cooling, the pearlitic rail side specifically refers to the area of ​​more than 80mm on the side of the pearlitic rail of the fusion line, such as 80mm, 85mm, 90mm, 95mm, 100mm, 110mm, 120mm, 140mm, 150mm, 160mm, 180mm, 200mm, 300mm, 400mm, 500mm, 600mm, 800mm, etc. on the side of the pearlitic rail of the fusion line.

[0074] As an optional implementation, during the second stage of cooling, the pearlitic rail side specifically refers to the area of ​​more than 80mm on the side of the pearlitic rail of the fusion line, such as 80mm, 85mm, 90mm, 95mm, 100mm, 110mm, 120mm, 140mm, 150mm, 160mm, 180mm, 200mm, 300mm, 400mm, 500mm, 600mm, 800mm, etc. on the side of the pearlitic rail of the fusion line.

[0075] As an optional implementation, during the tempering process, the welded joint is specifically defined as an area of ​​more than 80mm on both sides of the fusion line, such as 80mm, 85mm, 90mm, 95mm, 100mm, 110mm, 120mm, 140mm, 150mm, 160mm, 180mm, 200mm, 300mm, 400mm, 500mm, 600mm, 800mm, etc. on both sides of the fusion line.

[0076] As an optional implementation, during the first stage of cooling, the cooling rate on one side of the pearlitic steel rail is 3.5 to 6.0℃ / s, for example, it can be 3.5℃ / s, 4.0℃ / s, 4.5℃ / s, 5.0℃ / s, 5.5℃ / s, 6.0℃ / s, etc.

[0077] As an optional implementation, during the first stage of cooling, the air pressure of the air cooler is 0.10 to 0.15 MPa, for example, 0.10 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, 0.15 MPa, etc.

[0078] As an optional implementation, during the first stage of cooling, the end point of the first cooling stage is to cool the temperature of one side of the pearlitic steel rail to 450-550°C by air cooling, for example, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, etc.

[0079] As an optional implementation, during the first stage of cooling, one side of the normalized bainitic rail is air-cooled.

[0080] As an optional implementation, during the first stage of cooling, the cooling rate of one side of the bainitic rail is 2.5 to 4.5℃ / s, for example, it can be 2.5℃ / s, 2.8℃ / s, 3℃ / s, 3.2℃ / s, 3.5℃ / s, 3.8℃ / s, 4℃ / s, 4.2℃ / s, 4.5℃ / s, etc.

[0081] As an optional implementation, when the temperature on one side of the pearlitic rail drops to 450-550°C, the temperature on the other side of the bainitic rail drops to 550-650°C.

[0082] As an optional implementation, a second stage of cooling is carried out starting from a temperature of 450-550°C on one side of the pearlitic steel rail, and the second stage of cooling adopts a decreasing cooling rate method.

[0083] As an optional implementation, the cooling method of the deceleration cooling includes:

[0084] First, cool down to 350-450℃ at the first cooling rate, for example, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, etc.

[0085] Then, cool down to 100-150℃ at a second cooling rate, for example, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, etc.

[0086] Finally, the temperature is lowered to 15-35℃ at a third cooling rate, for example, 15℃, 16℃, 18℃, 20℃, 22℃, 24℃, 25℃, 28℃, 30℃, 32℃, 35℃, etc.

[0087] As an optional implementation, the first cooling rate is 0.1 to 1.0℃ / s, for example, it can be 0.1℃ / s, 0.2℃ / s, 0.3℃ / s, 0.4℃ / s, 0.5℃ / s, 0.6℃ / s, 0.7℃ / s, 0.8℃ / s, 0.9℃ / s, 1.0℃ / s, etc.

[0088] In a preferred embodiment, the first cooling rate is 0.4 to 0.6 °C / s.

[0089] It is important to note that Figure 3 This is a front view of the slow cooling device in the second stage of cooling in the welding method. Figure 4 This is a top view of the slow cooling device in the second stage of the welding method. Figure 5 This is a side sectional view of the slow cooling device in the second stage of cooling in the welding method described above. Figures 3-5 As shown, the present invention provides a slow cooling device for controlling the second cooling rate. The self-made slow cooling device is wrapped around the rail welded joint so that it can be cooled to 100-150°C at the second cooling rate.

[0090] As an optional implementation, the second cooling rate is 0.005 to 0.05℃ / s, for example, it can be 0.005℃ / s, 0.006℃ / s, 0.008℃ / s, 0.01℃ / s, 0.015℃ / s, 0.02℃ / s, 0.025℃ / s, 0.03℃ / s, 0.035℃ / s, 0.04℃ / s, 0.045℃ / s, 0.05℃ / s, etc.

[0091] In a preferred embodiment, the second cooling rate is 0.01 to 0.03 °C / s.

[0092] As an optional implementation, the third cooling rate is 0.01 to 0.1℃ / s, for example, it can be 0.01℃ / s, 0.02℃ / s, 0.03℃ / s, 0.04℃ / s, 0.05℃ / s, 0.06℃ / s, 0.07℃ / s, 0.08℃ / s, 0.09℃ / s, 0.1℃ / s, etc.

[0093] In a preferred embodiment, the third cooling rate is 0.08–0.1 °C / s.

[0094] As an optional implementation, the heating and tempering treatment is carried out in a tempering furnace.

[0095] As an optional implementation, the temperature of the heating and tempering treatment is 400-450°C, for example, 400°C, 405°C, 410°C, 415°C, 420°C, 425°C, 430°C, 435°C, 440°C, 445°C, 450°C, etc.

[0096] As an optional implementation, the holding time for the heating and tempering treatment is 5 to 6 hours, for example, 5 hours, 5.1 hours, 5.2 hours, 5.3 hours, 5.4 hours, 5.5 hours, 5.6 hours, 5.7 hours, 5.8 hours, 5.9 hours, 6 hours, etc.

[0097] As an optional implementation, the heating and tempering treatment is followed by natural cooling to 15-35°C, for example, 15°C, 16°C, 18°C, 20°C, 22°C, 24°C, 25°C, 28°C, 30°C, 32°C, 35°C, etc.

[0098] As an optional implementation, the natural cooling time is 3 to 5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, etc.

[0099] As an optional implementation, the present invention provides a welding method for bainitic steel rails and pearlitic steel rails, the welding method specifically including the following steps:

[0100] S1. Preheating before welding:

[0101] Grind and polish the 200-250mm area between the bainitic and pearlitic rail ends to be welded and the welding machine electrode to expose the metallic luster; then preheat the 200-250mm area between the bainitic and pearlitic rail ends to be welded in a heating box at 100-150℃ for 0.5-2 hours.

[0102] S2, Welding:

[0103] A fixed flash welding machine is used to weld the ends of bainitic and pearlitic steel rails; the total welding time is 120-125 seconds, and the total rail consumption is 31-33 mm; the welding includes sequential flash leveling, preheating, melting, upsetting, and pressure holding stages; the melting stage includes a slow melting stage and a fast melting stage.

[0104] S2-1, Leveling stage: Rail consumption is 4.0-4.5mm, average current is 12-15kA.

[0105] S2-2, Preheating stage: Average current 52-62kA, duration 53-54s.

[0106] S2-3, Burning Stage: The average current is 13-18kA; the burning stage includes a slow burning stage and a fast burning stage performed sequentially.

[0107] The secondary voltage of the slow burning stage is 5.05 to 5.35V, the flash speed of the slow burning stage is 0.2 to 0.4 mm / s, and the duration of the slow burning stage is 14 to 16 s.

[0108] The secondary voltage of the rapid burning stage is 5.35–5.65V, the flash speed of the rapid burning stage is 2.1–2.3 mm / s, the duration of the slow burning stage is 4–6 s, and the temperature after the rapid burning stage is 1300–1350℃.

[0109] S2-4, Upsetting stage: Upsetting pressure is 470~490kN, upsetting time is 1~3s, and displacement limit is 32~35mm.

[0110] S2-5, Pressure Holding Stage: The pressure holding stage includes a first pressure holding stage and a second pressure holding stage;

[0111] The holding pressure in the first holding stage is 470–490 kN, and the holding time is 4–6 s; the holding pressure in the second holding stage is 210–230 kN, and the holding time is 8–10 s.

[0112] It is important to note that the purpose of the aforementioned S1 preheating before welding is to thoroughly remove surface and internal moisture from the weld end and increase the temperature to reduce the temperature gradient and internal stress in the welding area, thereby reducing the risk of post-weld cracking. This is because bainitic rails have a high alloy element content, while pearlitic rails belong to the eutectoid steel category, specifically bainitic and high-carbon steel series, respectively, with high carbon equivalents. During the cooling process of the weld metal, the rapid temperature change leads to significant internal stress in the weld area. When these internal stresses exceed the material's crack resistance, cracks will form. To avoid this, preheating before welding and post-weld heat treatment are added to reduce the temperature gradient and internal stress in the welding area, thus lowering the likelihood of crack formation. Preheating effectively reduces the cooling rate of the welding area and decreases the generation of internal stress, while post-weld heat treatment helps eliminate residual stress generated during welding, further reducing the risk of cracking and improving the joint's service performance.

[0113] It is important to note that S2 above divides the burning stage into a slow burning stage and a fast burning stage. In particular, as shown above, the voltage and flash speed of the two burning stages are limited to specifically reduce the welding difficulty between bainitic and pearlitic rails. This ensures that the flashing process is not interrupted, and the flash is stable and intense during accelerated burning with a good protective atmosphere. Therefore, by selecting a higher heat matching and assisting with a larger flash speed in the accelerated burning stage of rail welding, the environmental conditions for ash spot formation are eliminated, which can significantly reduce the ash spot area of ​​the weld joint, or even prevent the weld joint from producing ash spots at all. This avoids the problem of a significant decrease in mechanical properties caused by the presence of ash spots.

[0114] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0115] Preparation Example 1

[0116] This preparation example provides a welding method for bainitic steel rails and pearlitic steel rails. The composition and welding method of the bainitic steel rails and pearlitic steel rails are as follows:

[0117] The bainitic 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%, with the balance being Fe; the hardness of the bainitic rail is 410 HBW. The pearlitic rail is composed of the following components by mass percentage: C 0.76%, Si 0.65%, Mn 0.90%, V 0.08%, with the balance being Fe; the hardness of the pearlitic rail is 370 HBW.

[0118] The welding method includes the following steps:

[0119] S1. Pre-welding treatment:

[0120] The 225mm area between the bainitic and pearlitic steel rail ends to be welded and the welding machine electrode was ground and polished to expose the metallic luster; then, the 225mm area between the bainitic and pearlitic steel rail ends to be welded was heated and dried in a heating box at 125℃ for 1 hour.

[0121] S2, Welding:

[0122] The ends of bainitic and pearlitic steel rails to be welded were joined using a fixed flash welding machine; the total welding time was 123 seconds, and the total rail consumption was 32 mm.

[0123] S2-1, Leveling stage: Rail consumption is 4.25mm, average current is 13.5kA.

[0124] S2-2, Preheating stage: Average current 57kA, duration 53.5s.

[0125] S2-3, Burning stage: The average current is 15.5kA; the burning stage includes a slow burning stage and a fast burning stage performed sequentially.

[0126] 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 duration of the slow burning stage is 15s.

[0127] The secondary voltage of the rapid burning stage is 5.50V, the flash speed of the rapid burning stage is 2.2mm / s, the duration of the rapid burning stage is 5s, and the temperature after the rapid burning stage ends is 1325℃.

[0128] S2-4, Upsetting stage: Upsetting pressure is 480kN, upsetting time is 2.3s, and displacement limit is 32mm.

[0129] S2-5, Pressure Holding Stage: The pressure holding stage includes a first pressure holding stage and a second pressure holding stage, resulting in the welded rail;

[0130] The pressure during the first pressure holding stage is 480 kN, and the duration of the first pressure holding stage is 5 s; the pressure during the second pressure holding stage is 220 kN, and the duration of the second pressure holding stage is 9 s; the temperature of the welded rail after the pressure holding stage ends is 900–1100 °C.

[0131] Preparation Example 2

[0132] This preparation example provides a welding method for bainitic and pearlitic steel rails, differing from Preparation Example 1 only in that: the bainitic steel rail is composed of the following components by mass percentage: C 0.21%, Si 1.60%, Mn 1.90%, Cr 0.69%, Mo 0.41%, with the balance being Fe; the hardness of the bainitic steel rail is 400 HBW; the pearlitic steel rail is composed of the following components by mass percentage: C 0.74%, Si 0.65%, Mn 0.80%, V 0.06%, with the balance being Fe; the hardness of the pearlitic steel rail is 360 HBW. All other steps are completely identical to Preparation Example 1.

[0133] Preparation Example 3

[0134] This preparation example provides a welding method for bainitic and pearlitic steel rails, differing from Preparation Example 1 only in that: the bainitic steel rail is composed of the following components by mass percentage: C 0.24%, S 1.50%, Mn 2.00%, Cr 0.75%, Mo 0.43%, with the balance being Fe; the hardness of the bainitic steel rail is 420 HBW; the pearlitic steel rail is composed of the following components by mass percentage: C 0.79%, Si 0.70%, Mn 0.92%, V 0.06%, with the balance being Fe; the hardness of the pearlitic steel rail is 390 HBW. All other steps are completely identical to Preparation Example 1.

[0135] Example 1

[0136] This embodiment provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails, the welding method specifically including the following steps:

[0137] (1) Poisoning:

[0138] Centered on the fusion line of the welded joint provided in Preparation Example 1 above, induction heating normalizing treatment was performed on a 32mm area on both sides of it. The normalizing temperature was 900℃ and the time was 100s.

[0139] (2) First stage cooling;

[0140] The rails after normalizing in step (1) are quickly transferred to the air-jet cooling mechanism for the first stage of cooling. The first stage of cooling includes: air cooling of the pearlitic rail side of the normalized rail (the edge of the air-jet device is aligned with the weld of the pearlitic rail 2, and air cooling is only performed on the top surface and the side of the rail head of the pearlitic rail), the air pressure of the air cooling treatment is 0.12MPa, the cooling rate of the pearlitic rail side is 3.9℃ / s, and the time is 90s, until the temperature of the pearlitic rail side drops to 550℃; air cooling of the bainitic rail side of the normalized rail, the cooling rate of the bainitic rail side is 2.8℃ / s, and the time is 90s, when the temperature of the pearlitic rail side drops to 550℃ and the temperature of the bainitic rail side drops to 650℃, the first cooling stage ends.

[0141] (3) Second stage cooling:

[0142] After the first stage of cooling is completed, the pearlite side of the rail is subjected to decelerated cooling. The decelerated cooling method includes: first, air cooling is used to cool the joint to 350°C at a rate of 0.5°C / s; then, starting from the 350°C temperature on the pearlite side of the joint, a self-made slow cooling device is wrapped around the joint to cool it to 100°C at a rate of 0.02°C / s; and then, the temperature is reduced to 25°C at a rate of 0.08°C / s.

[0143] (4) Tempering:

[0144] The welded joint, after cooling in the second stage, was heated and tempered at 425℃ for 5.5 hours, and then allowed to cool naturally to 25℃ after 3.5 hours after being taken out of the furnace.

[0145] The hardness test results of the welded joint between bainitic and pearlitic steel rails are shown in [link to relevant documentation]. Figure 6 The hardness meets the standard requirements, and the soft zone width is only 10mm compared to the standard. No abnormal microstructure is observed on the pearlitic rail side of the fusion line. The bainitic side exhibits a good microstructure with no carbide precipitation, and the retained austenite shows the best stability, with both impact toughness and fracture toughness reaching high levels. It can be considered that when the joint is subjected to train wheel impact, it has a large reserve of wear resistance and fracture prevention performance, providing a reliable guarantee for the safe service of the welded frog.

[0146] Example 2

[0147] This embodiment provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails, the welding method specifically including the following steps:

[0148] (1) Poisoning:

[0149] Centered on the fusion line of the welded joint provided in Preparation Example 1, induction heating normalizing treatment was performed on a 35mm area on both sides of the joint. The normalizing temperature was 910°C and the time was 105s.

[0150] (2) First stage cooling;

[0151] The rails after normalizing in step (1) are quickly transferred to the air-jet cooling mechanism for the first stage of cooling. The first stage of cooling includes: air cooling of the pearlitic rail side of the normalized rail (the edge of the air-jet device is aligned with the weld of the pearlitic rail 2, and air cooling is only performed on the top surface and the side of the rail head of the pearlitic rail), the air pressure of the air cooling treatment is 0.14 MPa, the cooling rate of the pearlitic rail side is 4.1℃ / s, and the time is 100s, until the temperature of the pearlitic rail side drops to 500℃; air cooling of the bainitic rail side of the normalized rail, the cooling rate of the bainitic rail side is 3.1℃ / s, and the time is 100s, until the temperature of the pearlitic rail side drops to 500℃ and the temperature of the bainitic rail side drops to 600℃, the first cooling stage ends.

[0152] (3) Second stage cooling:

[0153] After the first stage of cooling is completed, the pearlite side of the rail is subjected to decelerated cooling. The decelerated cooling method includes: first, air cooling is used to cool the joint to 400°C at a rate of 0.4°C / s; then, starting from the 400°C temperature on the pearlite side of the joint, a self-made slow cooling device is wrapped around the joint to cool it to 100°C at a rate of 0.01°C / s; and then, the temperature is reduced to 25°C at a rate of 0.09°C / s.

[0154] (4) Tempering:

[0155] After the second stage of cooling, the welded joint was heated and tempered at 400℃ for 6 hours, and then allowed to cool naturally to 25℃ after 3 hours.

[0156] Example 3

[0157] This embodiment provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails, the welding method specifically including the following steps:

[0158] (1) Poisoning:

[0159] Centered on the fusion line of the welded joint provided in Preparation Example 1, induction heating normalizing treatment was performed on a 30mm radius on both sides of the joint. The normalizing temperature was 900℃ and the time was 102s.

[0160] (2) First stage cooling;

[0161] The rails after normalizing in step (1) are quickly transferred to the air-jet cooling mechanism for the first stage of cooling. The first stage of cooling includes: air cooling of the pearlitic rail side of the normalized rail (the edge of the air-jet device is aligned with the weld of the pearlitic rail 2, and air cooling is only performed on the top surface and the side of the rail head of the pearlitic rail), the air pressure of the air cooling treatment is 0.10 MPa, the cooling rate of the pearlitic rail side is 3.5℃ / s, and the time is 122s, until the temperature of the pearlitic rail side drops to 470℃; air cooling of the bainitic rail side of the normalized rail, the cooling rate of the bainitic rail side is 2.8℃ / s, and the time is 122s, when the temperature of the pearlitic rail side drops to 470℃ and the temperature of the bainitic rail side drops to 560℃, the first cooling stage ends.

[0162] (3) Second stage cooling:

[0163] After the first stage of cooling is completed, the pearlite side of the rail is subjected to decelerated cooling. The decelerated cooling method includes: first, air cooling is used to cool the joint to 400°C at a rate of 0.6°C / s; then, starting from the 400°C temperature on the pearlite side of the joint, a self-made slow cooling device is wrapped around the joint to cool it to 100°C at a rate of 0.03°C / s; and then, the temperature is reduced to 25°C at a rate of 0.09°C / s.

[0164] (4) Tempering:

[0165] After the second stage of cooling, the welded joint was heated and tempered at 450°C for 5 hours, and then allowed to cool naturally to 25°C after 4 hours.

[0166] Example 4

[0167] This embodiment provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Embodiment 1 is that the welded steel rail provided in Preparation Example 1 is replaced with the welded steel rail provided in Preparation Example 2. The other steps are completely the same as in Embodiment 1.

[0168] Example 5

[0169] This embodiment provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Embodiment 1 is that the welded steel rail provided in Preparation Example 1 is replaced with the welded steel rail provided in Preparation Example 3. The other steps are completely the same as in Embodiment 1.

[0170] Comparative Example 1

[0171] This comparative example provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Example 1 is that the normalizing step (1) and subsequent steps are not performed.

[0172] Results: The weld head was not normalized, resulting in a welded joint. The high heating temperature, short heating time, and rapid heating rate after flash welding of the rail components led to uneven temperature distribution within the joint, resulting in an uneven internal microstructure, coarse grains, and poor plasticity and toughness. Under long-term impact loads, the welded joint is highly susceptible to fracture.

[0173] Comparative Example 2

[0174] This comparative example provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Example 1 is that in step (1), the heating and normalizing treatment temperature is 850°C and the time is 75s. The other steps are completely consistent with Example 1.

[0175] Results: The short normalizing heating time of the joint exacerbated the uneven temperature distribution across the entire cross section. The rail edge near the fusion line, due to its thin structure, experienced more intense heat exchange with the surrounding environment. As a result, the final heating temperature did not reach the austenite temperature range, leading to the retention of coarse weld grains within the joint. This failed to improve the joint's toughness, and the internal stress could not be effectively released, affecting the overall performance of the joint.

[0176] Comparative Example 3

[0177] This comparative example provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Example 1 is that in step (1), the heating and normalizing treatment temperature is 950°C and the time is 120s. The other steps are completely consistent with Example 1.

[0178] Result: The high normalizing temperature of the joint resulted in coarse grains in the material, which reduced its ductility and toughness, affecting the overall service performance of the joint.

[0179] Comparative Example 4

[0180] This comparative example provides a welding method for controlling the joint hardness of bainitic and pearlitic rails. The difference from Example 1 is that in step (2), during the first stage of cooling, the pearlitic side of the rail after normalizing is also air-cooled at a cooling rate of 2.4℃ / s for 146s until the temperature at the weld seam at the center line of the top surface of the joint rail drops to 550℃, at which point the first cooling stage ends.

[0181] Result: After heating the welded joint to the austenitizing temperature, air cooling was used on both sides of the fusion line, resulting in an excessively wide heat-affected zone on the pearlite side. During long-term service, this type of joint will experience saddle-shaped wear, affecting track smoothness and passenger comfort.

[0182] Comparative Example 5

[0183] This comparative example provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Example 1 is that in step (2), the air pressure of the air cooling treatment is 0.20 MPa, and the cooling rate of the pearlitic steel rail side is 10℃ / s until the temperature of the pearlitic steel rail side drops to 550℃. The other steps are completely consistent with Example 1.

[0184] Result: After normalizing the welded joint, the cooling rate on the pearlite side was too high, which caused martensitic transformation to occur near the fusion line on the pearlite side, especially in the segregation area at the center of the cross section. Martensitic structure is a hard and brittle phase. After such joints are put into service, they are very prone to brittle fracture under the cyclic load of trains, which affects the safe operation of trains.

[0185] Comparative Example 6

[0186] This comparative example provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Example 1 is that in step (2), the air pressure of the air cooling treatment is 0.05MPa, the cooling rate of the pearlitic steel rail side is 2.0℃ / s, until the temperature of the pearlitic steel rail side drops to 650℃. The other steps are completely consistent with Example 1.

[0187] Result: After normalizing the welded joint, the cooling rate on the pearlite side was low and the cooling time was short, resulting in significant temperature rebound after the joint stopped cooling. This caused the heat-affected zone width to be about 40mm, which did not meet the standard requirements. After the joint was put into service, it was very easy to develop saddle-shaped wear, which affected the smoothness of the train.

[0188] Comparative Example 7

[0189] This comparative example provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Example 1 is that during the normalizing and cooling of the joint, simultaneous air blowing from both sides is used for rapid cooling, and slow cooling is not used; the joint is directly air-cooled to room temperature. The other steps are completely consistent with Example 1.

[0190] Result: The cooling rate on the bainitic side of the joint was too fast, and the bainitic M... s If the cooling rate is not reduced near the point, a large amount of acicular martensite + bainite will appear near the fusion line on the bainite side. This uneven structure will cause high residual stress in the rail. During service, repeated rolling by the wheels may cause nuclear damage or chipping at the joint, affecting the safe operation of the train.

[0191] Comparative Example 8

[0192] This comparative example provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Example 1 is that in step (3), the cooling method of the deceleration includes: first, air cooling is used to cool the joint to 300°C on the pearlitic side at a rate of 0.5°C / s; then, starting from 300°C on the pearlitic side of the joint, a self-made slow cooling device is wrapped around the joint to cool it to 100°C at a rate of 0.01°C / s; and then, the joint is cooled to 25°C at a rate of 0.11°C / s. The other steps are completely consistent with Example 1.

[0193] Result: The welded joint is in bainitic M... s The temperature was not reduced at 330℃, resulting in a large number of acicular martensite + bainite structures near the fusion line on the bainite side.

[0194] Comparative Example 9

[0195] This comparative example provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Example 1 is that in step (3), the cooling method of slow cooling includes: using a slow cooling method to directly cool down to 25°C at a constant cooling rate of 0.02°C / s. The other steps are completely consistent with Example 1.

[0196] Result: The joint hardness meets the requirements, but cooling takes about 7.5-9 hours, resulting in a long process cycle and seriously affecting production efficiency.

[0197] Comparative Example 10

[0198] This comparative example provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Example 1 is that step (4) of heating and tempering is not performed, while the other steps are completely consistent with Example 1.

[0199] Result: The hardness of the welded joint meets the requirements, but there is a large internal stress inside the joint, which is not conducive to the joint's service.

[0200] Comparative Example 11

[0201] This comparative example provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Example 1 is that in step (4), the temperature of the heating and tempering treatment is 350°C and the holding time is 7h. The other steps are completely consistent with Example 1.

[0202] Results: The tempering temperature of the welded joint was below 400℃, and the joint hardness met the requirements. However, the stability of the residual austenite on the bainite side inside the joint was reduced, and the impact toughness and elongation of the joint decreased to varying degrees, which was not conducive to the joint's service.

[0203] Comparative Example 12

[0204] This comparative example provides a welding method for controlling the joint hardness of bainitic and pearlitic steel rails. The difference from Example 1 is that in step (4), the temperature of the heating and tempering treatment is 500°C and the holding time is 4h. The other steps are completely consistent with Example 1.

[0205] Results: When the tempering temperature of the welded joint was increased to 500℃, the hardness of the pearlite side base material of the tempered part decreased by 20-30 HBW, and the hardness of the bainite side base material decreased by 50-60 HBW. In addition, there were obvious carbide precipitations on the bainitic ferrite laths, which reduced the wear resistance and impact toughness of the rail components within the tempering range and seriously affected the service performance of the joint after it was put into operation.

[0206] Test case

[0207] Test samples: rail welded joints treated with the welding methods provided in Examples 1-5, and rail welded joints treated with the welding methods provided in Comparative Examples 1-12.

[0208] Test method: The weld is located at the center of the sample length. After removing 1mm from the top surface of the weld joint, the Brinell hardness is tested within 100mm on both sides of the weld.

[0209] The specific test results are shown in Table 1 below. Figure 6 As shown:

[0210] Table 1

[0211]

[0212]

[0213] Among them, H J珠光体 H represents the average hardness value of the joint on the pearlite side; P珠光体 H represents the average hardness of the parent material on the pearlite side. J1珠光体 H represents the average soft spot value on the pearlite side; J贝氏体 H represents the average hardness value of the joint on the bainitic side; J1贝氏体This represents the average soft spot value on one side of the bainite.

[0214] As shown in Table 1, the welding method for controlling the joint hardness of bainitic and pearlitic rails according to the present invention employs a technical route of one normalizing, two-stage cooling, and one tempering. Furthermore, different cooling processes are used for different parts and stages of the welded joint to achieve optimal hardness matching between the bainitic and pearlitic rails after flash welding. The welding method of the present invention can significantly improve the joint hardness and achieve good matching with the hardness of the rails on both sides, ensuring railway operation safety.

[0215] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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 controlling the joint hardness of bainitic and pearlitic steel rails, characterized in that, The welding method includes: Normalizing: The welded joint of the bainitic and pearlitic steel rails is subjected to induction heating normalizing treatment at 900~920℃; the hardness of the bainitic steel rail is 400~420 HBW; the hardness of the pearlitic steel rail is 340~390 HBW; the induction heating normalizing treatment time is 95~105 s; The first stage of cooling involves air cooling one side of the normalized pearlitic steel rail until its temperature drops to 450-550°C. During this first stage, the cooling rate of the pearlitic steel rail side is 3.5-6.0°C / s, and the air pressure is 0.10-0.15 MPa. Simultaneously, the second stage of cooling involves air cooling one side of the normalized bainitic steel rail. During this first stage, the cooling rate of the bainitic steel rail side is 2.5-4.5°C / s. When the temperature of the pearlitic steel rail side drops to 450-550°C, the temperature of the bainitic steel rail side drops to 550-650°C. The second stage of cooling involves slowing down one side of the pearlitic steel rail after the first stage of cooling. The slowing down cooling method includes: first cooling to 350~450℃ at a first cooling rate, then cooling to 100~150℃ at a second cooling rate, and finally cooling to 15~35℃ at a third cooling rate. The first cooling rate is greater than the second cooling rate, and the third cooling rate is greater than or equal to the second cooling rate. Tempering: The welded joint that has cooled in the second stage is subjected to tempering treatment at 400~450℃; Wherein, the first cooling rate is 0.1~1.0℃ / s; the second cooling rate is 0.005~0.05℃ / s; and the third cooling rate is 0.01~0.1℃ / s.

2. The welding method for controlling the joint hardness of bainitic and pearlitic steel rails according to claim 1, characterized in that, During the normalizing process, the weld joint specifically refers to the area within a range of 30 to 50 mm on both sides of the fusion line.

3. The welding method for controlling the joint hardness of bainitic and pearlitic steel rails according to claim 1, characterized in that, During the first stage of cooling, the pearlitic rail side specifically refers to the area of ​​more than 80 mm on the pearlitic rail side of the fusion line. And / or, during the second stage of cooling, the pearlitic rail side specifically refers to the area of ​​more than 80 mm on the pearlitic rail side of the fusion line. And / or, during the tempering process, the weld joint specifically refers to an area of ​​more than 80 mm on each side of the fusion line.

4. The welding method for controlling the joint hardness of bainitic and pearlitic steel rails according to claim 1, characterized in that, The first cooling rate is 0.4~0.6℃ / s; the second cooling rate is 0.01~0.03℃ / s; and the third cooling rate is 0.08~0.1℃ / s.

5. The welding method for controlling the joint hardness of bainitic and pearlitic steel rails according to claim 1, characterized in that, The holding time for the heating and tempering treatment is 5-6 hours.

6. The welding method for controlling the joint hardness of bainitic and pearlitic steel rails according to claim 1, characterized in that, After the heating and tempering treatment, the temperature is naturally cooled to 15~35℃.

7. The welding method for controlling the joint hardness of bainitic and pearlitic steel rails according to claim 6, characterized in that, The natural cooling time is 3 to 5 hours.

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