Welding method for improving joint strength

Abstract

The invention discloses a welding method for improving joint strength. The welding method comprises the following steps that flash welding upsetting is conducted on a steel rail section and a transition material section; normalizing heat treatment is carried out; the transition material section and the frog steel are subjected to flash welding upsetting; and the fastening state is kept, and deformation treatment is conducted by applying reverse tension. According to the method, reverse tension is applied immediately after joint flash welding is finished to increase the micro-area deformation degree, recrystallization is promoted in the slow cooling process by fully utilizing welding waste heat, the machining strengthening effect of a welding seam and a heat affected zone can be further improved in the process, grains are refined, the joint strength is improved, meanwhile, the joint stress distribution state can be improved, and the welding quality is improved. And deformation is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to a welding method for improving joint strength. Background Art

[0002] In order to achieve long-term stable operation, high-speed rail transportation technology has put forward higher requirements on the quality of seamless connection between rails and switch. At present, my country's seamless rails are mainly welded by flash welding. The quality of welding joints such as mechanical properties and residual stress of flash welded joints is crucial to the safety of rail driving. Since high-carbon rails and high-manganese steel switch are heterogeneous materials, their chemical composition, organizational structure, physical properties and weldability are quite different, and welding defects, poor welding quality and mechanical properties are prone to occur during flash welding. In recent years, intermediate transition materials have been mainly used at home and abroad to achieve high-quality connection between high-carbon rails and high-manganese steel switch. For example, Chinese patent CN115261725A discloses a solution using single-phase austenitic stainless steel as a transition material, and Chinese patent CN117754098A discloses a flash welding method using single-phase austenitic extruded stainless steel as a transition material.

[0003] The strength and hardness of welded joints are crucial to the service life of rail weldments, while the grain size of intermediate transition materials is easy to grow after two welds, which damages the mechanical properties of welded joints. Therefore, how to strengthen welded joints to improve service performance is crucial to the development of high-speed rail transportation technology. Summary of the invention

[0004] The present invention aims at the above technical problems and provides a welding method for improving joint strength. Based on the existing flash welding process of rail segments and frog steels, the method further improves the mechanical properties of the welded joints of heterogeneous rail steel materials through short-time small deformation processing strengthening.

[0005] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides a welding method for improving joint strength, comprising the following steps:

[0007] (1) Flash welding and upsetting the rail section and the transition material section;

[0008] (2) performing normalizing heat treatment on the weld joint of the weldment obtained in step (1);

[0009] (3) performing flash welding upsetting on the transition material section at the weld joint of the welded part that has been subjected to normalizing heat treatment in step (2) and the frog steel;

[0010] (4) While maintaining the fastened state of the flash welding upset in step (3), the welded part in step (3) is deformed by applying a reverse tensile force.

[0011] In the technical solution of the present invention, the materials of the rail segment and frog steel are not particularly limited, and are all materials commonly used for rail segments and frog steel in the field, and their strength is higher than that of the transition material segment;

[0012] Preferably, the material of the rail section is high-carbon pearlite or bainite steel; the frog steel is high-manganese austenite steel; and the material of the transition material section is austenite stainless steel;

[0013] In the technical solution of the present invention, the chemical composition of the austenitic stainless steel is not particularly limited. In some specific embodiments, it includes, by mass percentage: C: 0.05-0.15%, Mn: 3.0-5.0%, Cr: 17.0-18.5%, Ni: 10.5-12.5%, Mo: 1.5-2.0%, and the remainder is iron and unavoidable impurities.

[0014] As a preferred embodiment, in step (1) and / or step (3), the charged upsetting time of the flash welding upsetting is 0.5 to 2 seconds; the upsetting amount is 3 to 15 mm; and the upsetting holding time is 2 to 8 seconds.

[0015] As a preferred embodiment, in step (2), the temperature of the normalizing heat treatment is 870-930° C.; the time of the normalizing heat treatment is 1-3 minutes;

[0016] In some specific embodiments, the normalizing heat treatment further includes a cooling process and a post-process of cutting off the remaining transition material section, and the cooling process is air cooling.

[0017] As a preferred embodiment, in step (4), during the process of applying the reverse tension, the initial temperature of the weldment is 850-1050° C., preferably 900-950° C.;

[0018] Preferably, the strength of the applied reverse tensile force is 5 to 45 MPa, more preferably 8 to 30 MPa;

[0019] Preferably, the time for applying the reverse pulling force is 2 to 10 seconds, more preferably 4 to 6 seconds;

[0020] Preferably, the deformation amount of the deformation treatment is 0.4% to 8%, more preferably 0.5% to 5%;

[0021] In some specific embodiments, the applying of the reverse pulling force further includes an air cooling treatment.

[0022] In some specific embodiments, the welding end surfaces of the rail segment, the transition material segment and the frog steel are pre-treated to be ground flat and smooth.

[0023] In the technical solution of the present invention, the welding method is applicable to mobile flash welding and fixed flash welding.

[0024] The above technical solution has the following advantages or beneficial effects:

[0025] In the prior art, the weak area of ​​the welded joint formed by the rail section-transition material section-frog steel is usually the transition material section. The austenitic stainless steel of the transition material section used in the present invention is a single-phase structure, and the precipitation tendency of carbides at high temperatures is small. Reverse deformation processing (applying reverse tension) after welding can increase the deformation degree of the micro-region, promote recrystallization during the slow cooling process of welding residual heat, further refine the grains of the welded joint and improve the processing strengthening effect, which can significantly improve the tensile strength, yield strength and hardness of the joint, and can also improve the drastic change of hardness on both sides of the weld, balance the distribution of welding residual stress, and reduce deformation. The welding method provided by the present invention makes full use of the residual heat of the workpiece after flash welding for process operation, does not require additional equipment investment, has a simple process flow, is applicable to existing rail sections and frog steels, and has a wide range of process applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a cross-sectional metallographic photograph of the heat-affected zone of the transition material section after welding in Example 1 of the present invention.

[0027] Figure 2 This is a cross-sectional metallographic photograph of the heat-affected zone of the transition material section after welding in the comparative example of the present invention. DETAILED DESCRIPTION

[0028] The following embodiments are only some embodiments of the present invention, rather than all embodiments. Therefore, the detailed description in the embodiments of the present invention provided below is not intended to limit the scope of the present invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the protection scope of the present invention.

[0029] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0030] The present invention provides a welding method for improving joint strength, comprising the following steps:

[0031] (1) Grind the welding end surface of the material to be welded flat and smooth;

[0032] (2) flash welding the rail section and the transition material section;

[0033] (3) performing normalizing heat treatment and air cooling on the welded joint of step (2); and cutting off the excess material of the transition material section;

[0034] (4) performing flash welding upsetting on the transition material section at the weld joint of the welded part that has been subjected to normalizing heat treatment in step (3) and the frog steel;

[0035] (5) Keeping both sides of the weld of the flash welding upsetting in step (4) in a tight state, deforming the weld by applying reverse tension; and air cooling.

[0036] In the above welding method, the material of the rail section is preferably high carbon pearlite or bainite steel; the material of the frog steel is preferably high manganese austenite steel; the transition material section is preferably austenite stainless steel with a small tendency of carbide precipitation; the flash welding method is mobile flash welding or fixed flash welding.

[0037] In the above welding method, in step (2) and / or step (4), the charged upsetting time of the flash welding upsetting is 0.5 seconds to 2 seconds; the upsetting amount is 3 mm to 15 mm, and the upsetting holding time is 2 seconds to 8 seconds.

[0038] In the above welding method, in step (3), the temperature of the normalizing heat treatment is 870°C to 930°C, and the time of the normalizing heat treatment is 1 to 3 minutes.

[0039] As a key strengthening process, the present invention applies reverse tension immediately after the flash welding upsetting of the transition material segment and the frog steel is completed for deformation treatment. This treatment can make full use of the residual heat of the workpiece, and the initial drawing temperature is 850°C to 1050°C. In some specific embodiments, the initial drawing temperature can be listed as 850°C, 900°C, 950°C, 1000°C, 1050°C or any variable therebetween. As a preferred embodiment, the initial drawing temperature is 900°C to 950°C. If the initial drawing temperature is too low, it is easy to cause cold deformation strengthening effect or form processing defects in the joint. If the temperature is too high, the local area is prone to liquefaction to form defects, or the recrystallization effect is poor, and the purpose of strengthening cannot be achieved.

[0040] In addition, the application of reverse tension and its holding time and deformation are also important and necessary control factors. The strength of the reverse tension is 5MPa~45MPa, the holding time is 2 seconds~10 seconds, and the deformation is 0.4%~8%. In some specific embodiments, the strength of the reverse tension can be listed as 5MPa, 10MPa, 15MPa, 20MPa, 25MPa, 30MPa, 35MPa, 40MPa, 45MPa or any variable therebetween; the holding time of the reverse tension can be listed as 2 seconds, 3 seconds, 4 seconds, 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, 10 seconds or any variable therebetween; the deformation can be listed as 0.4%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or any variable therebetween. As a preferred embodiment, the strength of the reverse tension is 8MPa~30MPa, the holding time is 4 seconds~6 seconds, and the preferred deformation is 0.5%~5%. If the reverse tension, holding time and deformation are too low, the deformation strengthening effect is poor; if the reverse tension, holding time and deformation are too high, processing defects are likely to form in local areas, and the purpose of strengthening cannot be achieved.

[0041] Embodiment 1:

[0042] The chemical composition of the rail segment material used in this embodiment includes, by mass percentage:

[0043] C: 0.70%, Mn: 0.75%, Si: 0.56%, V: 0.04%, and the balance is iron and inevitable impurities.

[0044] The chemical composition of the frog steel used in this embodiment includes the following in terms of mass percentage:

[0045] C: 0.60%, Mn: 18.42%, Cr: 6.85%, N: 0.18%, and the balance is iron and inevitable impurities.

[0046] The chemical composition of the austenitic stainless steel transition material used in this embodiment includes the following in terms of mass percentage:

[0047] C: 0.13%, Mn: 4.15%, Cr: 17.08%, Ni: 10.90%, Mo: 1.85%, and the balance is iron and inevitable impurities.

[0048] In this embodiment, welding the above material segments specifically includes the following steps:

[0049] (1) Grind the end faces of the above-mentioned materials to be welded until they are flat and smooth;

[0050] (2) Fixed flash welding is used to perform upsetting on the rail segment and the transition material. The specific process parameters are as follows: the live upsetting time is 1 second, the upsetting amount is 10 mm, and the holding time of the upsetting is 4 seconds;

[0051] (3) The welded joint is subjected to normalizing heat treatment and air cooling before the excess transition material is removed; the normalizing heat treatment temperature is 900°C and the time is 2 minutes;

[0052] (4) flash welding is used to perform upsetting of the transition material section and frog steel at the weld joint of the welded part that has been subjected to normalizing heat treatment in step (3) by fixed flash welding, and the specific process parameters are as follows: the charged upsetting time is 1 second; the upsetting amount is 10 mm, and the upsetting holding time is 4 seconds;

[0053] (5) Keeping the electrodes on both sides of the weld in step (4) in a tight state, apply reverse tension to the joint: the initial drawing temperature is 880°C, the tensile strength is 10 MPa, the tensile holding time is 5 seconds, and the deformation is 0.8%.

[0054] In this embodiment, no cracks or other defects are found on the cross section of the transition material segment ( Figure 1 ), the tensile strength of the joint is 636MPa, the yield strength is 336MPa, and the elongation after fracture is 25%.

[0055] Embodiment 2:

[0056] The chemical composition of the rail segment material used in this embodiment includes, by mass percentage:

[0057] C: 0.70%, Mn: 0.75%, Si: 0.56%, V: 0.04%, and the balance is iron and inevitable impurities.

[0058] The chemical composition of the frog steel used in this embodiment includes the following in terms of mass percentage:

[0059] C: 0.60%, Mn: 18.42%, Cr: 6.85%, N: 0.18%, and the balance is iron and inevitable impurities.

[0060] The chemical composition of the single-phase austenitic stainless steel transition material used in this embodiment includes the following in terms of mass percentage:

[0061] C: 0.13%, Mn: 4.15%, Cr: 17.08%, Ni: 10.90%, Mo: 1.85%, and the balance is iron and inevitable impurities.

[0062] In this embodiment, welding the above material segments specifically includes the following steps:

[0063] (1) Grind the end faces of the above-mentioned materials to be welded until they are flat and smooth;

[0064] (2) Fixed flash welding is used to perform upsetting on the rail segment and the transition material. The specific process parameters are as follows: the live upsetting time is 1 second; the upsetting amount is 10 mm, and the upsetting holding time is 4 seconds;

[0065] (3) The welded joint is subjected to normalizing heat treatment and air cooling before the excess transition material is removed; the normalizing heat treatment temperature is 900°C and the time is 2 minutes;

[0066] (4) flash welding is used to perform upsetting of the transition material section and frog steel at the weld joint of the welded part that has been subjected to normalizing heat treatment in step (3) by fixed flash welding, and the specific process parameters are as follows: the charged upsetting time is 1 second; the upsetting amount is 10 mm, and the upsetting holding time is 4 seconds;

[0067] (5) Keeping the electrodes on both sides of the weld in step (4) in a tight state, apply reverse tension to the joint: the initial drawing temperature is 980°C, the tensile strength is 30 MPa, the tensile holding time is 2 seconds, and the deformation is 1.2%.

[0068] In this embodiment, no cracks or other defects were found on the cross section of the transition material segment, the tensile strength of the joint was 642 MPa, the yield strength was 340 MPa, and the elongation after fracture was 28%.

[0069] Embodiment 3:

[0070] The chemical composition of the rail segment material used in this embodiment includes, by mass percentage:

[0071] C: 0.70%, Mn: 0.75%, Si: 0.56%, V: 0.04%, and the balance is iron and inevitable impurities.

[0072] The chemical composition of the frog steel used in this embodiment includes the following in terms of mass percentage:

[0073] C: 0.60%, Mn: 18.42%, Cr: 6.85%, N: 0.18%, and the balance is iron and inevitable impurities.

[0074] The chemical composition of the single-phase austenitic stainless steel transition material used in this embodiment includes the following in terms of mass percentage:

[0075] C: 0.13%, Mn: 4.15%, Cr: 17.08%, Ni: 10.90%, Mo: 1.85%, and the balance is iron and inevitable impurities.

[0076] In this embodiment, welding the above material segments specifically includes the following steps:

[0077] (1) Grind the end faces of the above-mentioned materials to be welded until they are flat and smooth;

[0078] (2) Fixed flash welding is used to perform upsetting on the rail segment and the transition material. The specific process parameters are as follows: the live upsetting time is 1 second; the upsetting amount is 10 mm, and the upsetting holding time is 4 seconds;

[0079] (3) The welded joint is subjected to normalizing heat treatment and air cooling before the excess transition material is removed; the normalizing heat treatment temperature is 900°C and the time is 2 minutes;

[0080] (4) flash welding is used to perform upsetting of the transition material section and frog steel at the weld joint of the welded part that has been subjected to normalizing heat treatment in step (3) by fixed flash welding, and the specific process parameters are as follows: the charged upsetting time is 1 second; the upsetting amount is 10 mm, and the upsetting holding time is 4 seconds;

[0081] (5) Keeping the electrodes on both sides of the weld in step (4) in a tight state, apply reverse tension to the joint: the initial drawing temperature is 1050°C, the tensile strength is 45 MPa, the tensile holding time is 8 seconds, and the deformation is 6.0%.

[0082] In this embodiment, no cracks or other defects were found on the cross section of the transition material segment, the tensile strength of the joint was 640 MPa, the yield strength was 331 MPa, and the elongation after fracture was 20%.

[0083] Embodiment 4:

[0084] The chemical composition of the rail segment material used in this embodiment includes, by mass percentage:

[0085] C: 0.70%, Mn: 0.75%, Si: 0.56%, V: 0.04%, and the balance is iron and inevitable impurities.

[0086] The chemical composition of the frog steel used in this embodiment includes the following in terms of mass percentage:

[0087] C: 0.60%, Mn: 18.42%, Cr: 6.85%, N: 0.18%, and the balance is iron and inevitable impurities.

[0088] The chemical composition of the single-phase austenitic stainless steel transition material used in this embodiment includes the following in terms of mass percentage:

[0089] C: 0.15%, Mn: 3.0%, Cr: 18.05%, Ni: 11.42%, Mo: 1.74%, and the balance is iron and inevitable impurities.

[0090] In this embodiment, welding the above material segments specifically includes the following steps:

[0091] (1) Grind the end faces of the above-mentioned materials to be welded until they are flat and smooth;

[0092] (2) Fixed flash welding is used to perform upsetting on the rail segment and the transition material. The specific process parameters are as follows: the live upsetting time is 1 second, the upsetting amount is 10 mm, and the holding time of the upsetting is 4 seconds;

[0093] (3) The welded joint is subjected to normalizing heat treatment and air cooling before the excess transition material is removed; the normalizing heat treatment temperature is 900°C and the time is 2 minutes;

[0094] (4) flash welding is used to perform upsetting of the transition material section and frog steel at the weld joint of the welded part that has been subjected to normalizing heat treatment in step (3) by fixed flash welding, and the specific process parameters are as follows: the charged upsetting time is 1 second; the upsetting amount is 10 mm, and the upsetting holding time is 4 seconds;

[0095] (5) Keeping the electrodes on both sides of the weld in step (4) in a tight state, apply reverse tension to the joint: the initial drawing temperature is 880°C, the tensile strength is 10 MPa, the tensile holding time is 5 seconds, and the deformation is 0.8%.

[0096] In this embodiment, no cracks or other defects were found on the cross section of the transition material segment, the tensile strength of the joint was 625 MPa, the yield strength was 316 MPa, and the elongation after fracture was 28%.

[0097] Comparative Example:

[0098] The chemical composition of the rail segment material used in this comparative example includes the following in terms of mass percentage:

[0099] C: 0.70%, Mn: 0.75%, Si: 0.56%, V: 0.04%, and the balance is iron and inevitable impurities.

[0100] The chemical composition of the frog steel used in this comparative example includes the following in terms of mass percentage:

[0101] C: 0.60%, Mn: 18.42%, Cr: 6.85%, N: 0.18%, and the balance is iron and inevitable impurities.

[0102] The chemical composition of the single-phase austenitic stainless steel transition material used in this comparative example includes the following in terms of mass percentage:

[0103] C: 0.13%, Mn: 4.15%, Cr: 17.08%, Ni: 10.90%, Mo: 1.85%, and the balance is iron and inevitable impurities.

[0104] This comparative example welds the above material segments, specifically comprising the following steps:

[0105] (1) Grind the end faces of the above-mentioned materials to be welded until they are flat and smooth;

[0106] (2) Fixed flash welding is used to perform upsetting on the rail segment and the transition material. The specific process parameters are as follows: the live upsetting time is 1 second, the upsetting amount is 10 mm, and the holding time of the upsetting is 4 seconds;

[0107] (3) The welded joint is subjected to normalizing heat treatment and air cooling before the excess transition material is removed; the normalizing heat treatment temperature is 900°C and the time is 2 minutes;

[0108] (4) Flash welding is used to perform upsetting on the transition material section and frog steel at the weld joint of the welded part that has undergone normalizing heat treatment in step (3). The specific process parameters are as follows: the charged upsetting time is 1 second; the upsetting amount is 10 mm, and the upsetting holding time is 4 seconds.

[0109] In this comparative example, no reverse tension was applied to the weld joint after the flash welding upsetting, and no cracks or other defects were found on the cross section of the transition material section (see Figure 2 ), but the tensile strength of the joint is 589MPa, the yield strength is 268MPa, and the elongation after fracture is 32%.

[0110] It can be seen from the above embodiments and comparative examples that the joints of the rail section-transition material section-frog steel obtained by the welding method of the present invention do not produce cracks, the grains in the heat-affected zone of the transition material section are significantly refined, and the joints have higher tensile strength and yield strength after applying reverse tension.

[0111] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A welding method for improving joint strength, characterized in that: The following steps are involved: (1) Flash welding and upsetting the rail section and the transition material section; (2) performing normalizing heat treatment on the weld joint of the weldment obtained in step (1); (3) performing flash welding upsetting on the transition material section at the weld joint of the welded part that has been subjected to normalizing heat treatment in step (2) and the frog steel; (4) While maintaining the fastened state of the flash welding upset in step (3), the welded part in step (3) is deformed by applying a reverse tensile force.

2. The welding method according to claim 1, characterized in that: The material of the rail section is high-carbon pearlite or bainite steel; the frog steel is high-manganese austenite steel; and the material of the transition material section is austenite stainless steel.

3. The welding method according to claim 2, characterized in that: The chemical composition of the austenitic stainless steel includes, by mass percentage, C: 0.05-0.15%, Mn: 3.0-5.0%, Cr: 17.0-18.5%, Ni: 10.5-12.5%, Mo: 1.5-2.0%, and the remainder is iron and inevitable impurities.

4. The welding method according to claim 1, characterized in that: In step (1) and / or step (3), the charged upsetting time of the flash welding upsetting is 0.5 to 2 seconds; the upsetting amount is 3 to 15 mm; and the upsetting holding time is 2 to 8 seconds.

5. The welding method according to claim 1, characterized in that: In step (2), the temperature of the normalizing heat treatment is 870-930° C.; and the time of the normalizing heat treatment is 1-3 minutes.

6. The welding method according to claim 1, characterized in that: In step (4), during the process of applying the reverse tension, the initial temperature of the weldment is 850-1050°C, preferably 900-950°C.

7. The welding method according to claim 1, characterized in that: In step (4), the strength of the applied reverse tensile force is 5 to 45 MPa, and more preferably 8 to 30 MPa.

8. The welding method according to claim 1, characterized in that: In step (4), the time for applying the reverse pulling force is 2 to 10 seconds, more preferably 4 to 6 seconds.

9. The welding method according to claim 1, characterized in that: In step (4), the deformation amount of the deformation treatment is 0.4% to 8%, and more preferably 0.5% to 5%.

10. The welding method according to claim 1, characterized in that: In step (4), the step of applying the reverse pulling force also includes air cooling treatment.

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