A welding method to improve joint strength

Abstract

This invention discloses a welding method for improving joint strength, comprising the following steps: flash welding and upsetting of a rail section and a transition material section; normalizing heat treatment; flash welding and upsetting of the transition material section and a frog steel; maintaining a tight state, and applying a reverse tensile force for deformation treatment. This invention applies a reverse tensile force immediately after the flash welding of the joint to increase the micro-area deformation, fully utilizing the residual welding heat to promote recrystallization during slow cooling. This process can further increase the work-strengthening effect of the weld and heat-affected zone, refine the grains, improve joint strength, and simultaneously improve the stress distribution of the joint, reducing deformation.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more particularly to a welding method for improving joint strength. Background Technology

[0002] To ensure stable long-term operation, high-speed rail technology places higher demands on the quality of seamless connections between rails and frogs. Currently, my country primarily uses flash welding for seamless rails. The mechanical properties and residual stress of the welded joints are crucial to the safety of rail transport. Because high-carbon steel rails and high-manganese steel frogs are dissimilar materials with significant differences in chemical composition, microstructure, physical properties, and weldability, flash welding can easily lead to welding defects, poor weld quality, and poor mechanical properties. In recent years, both domestically and internationally, intermediate transition materials have been primarily used to achieve high-quality connections between high-carbon steel rails and high-manganese steel frogs. For example, Chinese patent CN115261725A discloses a scheme 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 welded rail components. However, the intermediate transition material is prone to grain growth after two welding processes, which can damage the mechanical properties of the welded joint. Therefore, strengthening welded joints to improve service performance is essential for the development of high-speed rail transportation technology. Summary of the Invention

[0004] This invention addresses the above-mentioned technical problems by providing a welding method to improve joint strength. Based on existing flash welding processes for rail sections and frog steel, this method further enhances the mechanical properties of welded joints made of dissimilar rail steel materials through short-time, small-deformation processing.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

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

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

[0008] (2) The weld joint of the welded part obtained in step (1) is subjected to normalizing heat treatment;

[0009] (3) The transition material section at the weld joint of the welded part that has undergone normalizing heat treatment in step (2) is flash welded and up-forged with the turnout steel.

[0010] (4) Keep the flash welding upsetting in step (3) in a tight state, and deform the welded part in step (3) by applying a reverse tensile force.

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

[0012] Preferably, the rail section is made of high-carbon pearlitic or bainitic steel; the frog steel is made of high-manganese austenitic steel; and the transition material section is made of austenitic stainless steel.

[0013] In the technical solution of this 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%, with the balance being iron and unavoidable impurities.

[0014] In a preferred embodiment, in step (1) and / or step (3), the electric 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] In a preferred embodiment, in step (2), the normalizing heat treatment temperature is 870–930°C; and the normalizing heat treatment time is 1–3 minutes.

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

[0017] In a preferred embodiment, during step (4), the initial temperature of the welded part is 850-1050°C, preferably 900-950°C, during the application of the reverse tensile force.

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

[0019] Preferably, the time for applying the reverse tension 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 implementations, the application of the reverse tensile force is further accompanied by air cooling.

[0022] In some specific implementations, the welded end faces of the rail section, transition material section, and frog steel are pre-treated by grinding to make them smooth.

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

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

[0025] In existing technologies, the weakest area of ​​the welded joint formed by the rail section, transition material section, and frog steel is usually the transition material section. The austenitic stainless steel transition material used in this invention has a single-phase structure and a low tendency for carbide precipitation at high temperatures. Reverse deformation processing (applying reverse tensile force) after welding increases the deformation degree of the micro-region. During the slow cooling process of the welding residual heat, recrystallization is promoted, further refining the grain size of the welded joint and improving the work-strengthening effect. This significantly improves the tensile strength, yield strength, and hardness of the joint, and also mitigates the drastic hardness changes on both sides of the weld, balancing the distribution of residual welding stress and reducing deformation. The welding method provided by this invention fully utilizes the residual heat of the workpiece after flash welding for process operation, requiring no additional equipment investment, with a simple process flow, and is applicable to existing rail sections and frog steel, exhibiting broad process applicability. Attached Figure Description

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

[0027] Figure 2 This is a metallographic photograph of the cross-section of the heat-affected zone of the transition material section after welding in the comparative example of this invention. Detailed Implementation

[0028] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0029] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

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

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

[0032] (2) Flash welding and upsetting of the rail section and the transition material section;

[0033] (3) Perform normalizing heat treatment and air cooling on the welded joint from step (2); remove excess material from the transition material section;

[0034] (4) The transition material section at the weld joint of the welded part that has undergone normalizing heat treatment in step (3) is flash welded and up-forged with the turnout steel.

[0035] (5) Keep the weld seam on both sides of the flash welding upsetting in step (4) in a tight state, and deform it by applying reverse tensile force; air cooling.

[0036] In the above welding methods, the preferred material for the rail section is high-carbon pearlitic or bainitic steel; the preferred material for the frog steel is high-manganese austenitic steel; the preferred material for the transition section is austenitic stainless steel with a low tendency for carbide precipitation; and the flash welding method is either moving flash welding or fixed flash welding.

[0037] In the above welding method, in step (2) and / or step (4), the electric upsetting time of 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 normalizing heat treatment temperature is 870℃~930℃ and the normalizing heat treatment time is 1~3 minutes.

[0039] As a key strengthening process, this invention applies a reverse tensile force immediately after the flash welding and upsetting of the transition material section and the turnout steel for deformation treatment. This treatment can fully utilize the residual heat of the workpiece, with an initial drawing temperature of 850℃~1050℃. In some specific embodiments, the initial drawing temperature can be listed as 850℃, 900℃, 950℃, 1000℃, 1050℃, or any variable between them. As a preferred embodiment, the initial drawing temperature is 900℃~950℃. 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, local areas are prone to liquefaction forming defects, or the recrystallization effect is poor, failing to achieve the purpose of strengthening.

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

[0041] Example 1:

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

[0043] C: 0.70%, Mn: 0.75%, Si: 0.56%, V: 0.04%, balance being iron and unavoidable impurities.

[0044] The chemical composition of the forklift steel used in this embodiment, expressed as a percentage by mass, includes:

[0045] C: 0.60%, Mn: 18.42%, Cr: 6.85%, N: 0.18%, balance being iron and unavoidable impurities.

[0046] The chemical composition of the austenitic stainless steel transition material used in this embodiment, expressed as a percentage by mass, includes:

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

[0048] This embodiment involves welding the aforementioned material segments, specifically including 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 upset the rail section and the transition material. The specific process parameters are as follows: the upsetting time is 1 second, the upsetting amount is 10mm, and the upsetting holding time is 4 seconds.

[0051] (3) After welding, the welded joint is subjected to normalizing heat treatment, air cooling and then the excess transition material is removed; the normalizing heat treatment temperature is 900℃ and the time is 2 minutes;

[0052] (4) Using fixed flash welding, the transition material section at the weld joint of the welded part after normalizing heat treatment in step (3) is flash welded and upsetting is performed with the turnout steel. The specific process parameters are as follows: the upsetting time is 1 second; the upsetting amount is 10mm; and the upsetting holding time is 4 seconds.

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

[0054] In this embodiment, no cracks or other defects were observed on the cross-section of the transition material section. Figure 1 The joint has a tensile strength of 636 MPa, a yield strength of 336 MPa, and an elongation after fracture of 25%.

[0055] Example 2:

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

[0057] C: 0.70%, Mn: 0.75%, Si: 0.56%, V: 0.04%, balance being iron and unavoidable impurities.

[0058] The chemical composition of the forklift steel used in this embodiment, expressed as a percentage by mass, includes:

[0059] C: 0.60%, Mn: 18.42%, Cr: 6.85%, N: 0.18%, balance being iron and unavoidable impurities.

[0060] The chemical composition of the single-phase austenitic stainless steel transition material used in this embodiment, expressed as a percentage by mass, includes:

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

[0062] This embodiment involves welding the aforementioned material segments, specifically including 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 upset the rail section and the transition material. The specific process parameters are as follows: the upsetting time is 1 second; the upsetting amount is 10 mm; and the upsetting holding time is 4 seconds.

[0065] (3) After welding, the welded joint is subjected to normalizing heat treatment, air cooling and then the excess transition material is removed; the normalizing heat treatment temperature is 900℃ and the time is 2 minutes;

[0066] (4) Using fixed flash welding, the transition material section at the weld joint of the welded part after normalizing heat treatment in step (3) is flash welded and upsetting is performed with the turnout steel. The specific process parameters are as follows: the upsetting time is 1 second; the upsetting amount is 10mm; and the upsetting holding time is 4 seconds.

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

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

[0069] Example 3:

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

[0071] C: 0.70%, Mn: 0.75%, Si: 0.56%, V: 0.04%, balance being iron and unavoidable impurities.

[0072] The chemical composition of the forklift steel used in this embodiment, expressed as a percentage by mass, includes:

[0073] C: 0.60%, Mn: 18.42%, Cr: 6.85%, N: 0.18%, balance being iron and unavoidable impurities.

[0074] The chemical composition of the single-phase austenitic stainless steel transition material used in this embodiment, expressed as a percentage by mass, includes:

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

[0076] This embodiment involves welding the aforementioned material segments, specifically including 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 upset the rail section and the transition material. The specific process parameters are as follows: the upsetting time is 1 second; the upsetting amount is 10 mm; and the upsetting holding time is 4 seconds.

[0079] (3) After welding, the welded joint is subjected to normalizing heat treatment, air cooling and then the excess transition material is removed; the normalizing heat treatment temperature is 900℃ and the time is 2 minutes;

[0080] (4) Using fixed flash welding, the transition material section at the weld joint of the welded part after normalizing heat treatment in step (3) is flash welded and upsetting is performed with the turnout steel. The specific process parameters are as follows: the upsetting time is 1 second; the upsetting amount is 10mm; and the upsetting holding time is 4 seconds.

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

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

[0083] Example 4:

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

[0085] C: 0.70%, Mn: 0.75%, Si: 0.56%, V: 0.04%, balance being iron and unavoidable impurities.

[0086] The chemical composition of the forklift steel used in this embodiment, expressed as a percentage by mass, includes:

[0087] C: 0.60%, Mn: 18.42%, Cr: 6.85%, N: 0.18%, balance being iron and unavoidable impurities.

[0088] The chemical composition of the single-phase austenitic stainless steel transition material used in this embodiment, expressed as a percentage by mass, includes:

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

[0090] This embodiment involves welding the aforementioned material segments, specifically including 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 upset the rail section and the transition material. The specific process parameters are as follows: the upsetting time is 1 second, the upsetting amount is 10mm, and the upsetting holding time is 4 seconds.

[0093] (3) After welding, the welded joint is subjected to normalizing heat treatment, air cooling and then the excess transition material is removed; the normalizing heat treatment temperature is 900℃ and the time is 2 minutes;

[0094] (4) Using fixed flash welding, the transition material section at the weld joint of the welded part after normalizing heat treatment in step (3) is flash welded and upsetting is performed with the turnout steel. The specific process parameters are as follows: the upsetting time is 1 second; the upsetting amount is 10mm; and the upsetting holding time is 4 seconds.

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

[0096] In this embodiment, no cracks or other defects were observed on the cross section of the transition material section. 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 section material used in this comparative example, expressed as a percentage by mass, includes:

[0099] C: 0.70%, Mn: 0.75%, Si: 0.56%, V: 0.04%, balance being iron and unavoidable impurities.

[0100] The chemical composition of the turnout steel used in this comparative example, expressed as a percentage by mass, includes:

[0101] C: 0.60%, Mn: 18.42%, Cr: 6.85%, N: 0.18%, balance being iron and unavoidable impurities.

[0102] The chemical composition of the single-phase austenitic stainless steel transition material used in this comparative example, expressed as a percentage by mass, includes:

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

[0104] This comparative example demonstrates the welding of the aforementioned material segments, specifically including 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 upset the rail section and the transition material. The specific process parameters are as follows: the upsetting time is 1 second, the upsetting amount is 10mm, and the upsetting holding time is 4 seconds.

[0107] (3) After welding, the welded joint is subjected to normalizing heat treatment, air cooling and then the excess transition material is removed; the normalizing heat treatment temperature is 900℃ and the time is 2 minutes;

[0108] (4) Using fixed flash welding, the transition material section at the weld joint of the welded part after normalizing heat treatment in step (3) is flash welded and upsetting is performed with the turnout steel. The specific process parameters are as follows: the upsetting time is 1 second; the upsetting amount is 10mm; and the upsetting holding time is 4 seconds.

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

[0110] As can be seen from the above embodiments and comparative examples, the joints of rail section-transition material section-flip steel obtained by the welding method of the present invention do not produce cracks, the grains of 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 tensile force.

[0111] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A welding method for improving joint strength, characterized in that, Includes the following steps: (1) Flash welding and upsetting of the rail section and the transition material section; (2) The weld joint of the welded part obtained in step (1) is subjected to normalizing heat treatment; (3) The transition material section at the weld joint of the welded part that has undergone normalizing heat treatment in step (2) is flash welded and up-forged with the turnout steel; (4) Keep the flash welding upsetting in step (3) in a tight state, and deform the welded part in step (3) by applying a reverse tensile force; The rail section is made of high-carbon pearlitic or bainitic steel; the frog steel is made of high-manganese austenitic steel; and the transition material section is made of austenitic stainless steel. In step (4), during the application of reverse tensile force, the initial temperature of the welded part is 850~1050℃; the strength of the applied reverse tensile force is 5~45 MPa; the time for applying the reverse tensile force is 2~10 seconds; and the deformation amount of the deformation treatment is 0.4%~8%.

2. The welding method according to claim 1, characterized in that, The chemical composition of the austenitic stainless steel, by mass percentage, includes: 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%, with the balance being iron and unavoidable impurities.

3. The welding method according to claim 1, characterized in that, In step (1) and / or step (3), the electric 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.

4. The welding method according to claim 1, characterized in that, In step (2), the normalizing heat treatment temperature is 870~930℃; the normalizing heat treatment time is 1~3 minutes.

5. The welding method according to claim 1, characterized in that, In step (4), the initial temperature of the welded part is 900~950℃ during the process of applying the reverse tensile force.

6. The welding method according to claim 1, characterized in that, In step (4), the strength of the applied reverse tensile force is 8~30 MPa.

7. The welding method according to claim 1, characterized in that, In step (4), the time for applying the reverse tension is 4 to 6 seconds.

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

9. The welding method according to claim 1, characterized in that, In step (4), the application of reverse tension also includes air cooling.

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