Method for improving section structure and performance uniformity of track transition welding material

Abstract

The invention discloses a method for improving the section structure and performance uniformity of a rail transition welding material, and belongs to the technical field of welding material machining. The method comprises the following steps: casting molten steel of a transition welding material into an electrode ingot, and carrying out electroslag remelting, homogenization treatment and pre-forging to obtain a blank; the blank is subjected to gradient heating, a specific temperature field with the core temperature lower than the surface layer temperature is formed on the cross section of the blank, the temperature difference ranges from 30 DEG C to 50 DEG C, and the surface layer temperature ranges from 1000 DEG C to 1050 DEG C; and the blank subjected to gradient heating is rapidly transferred into a preheated extrusion container and passes through an extrusion die at the medium extrusion speed of 120-150 mm / s, and the rail transition welding material short rail is obtained. By controlling the two key thermodynamic and dynamic parameters of the blank section temperature gradient and the extrusion speed, the problem that the structure performance of the section of the hot extrusion part is not uniform is directly solved, the extrusion speed is limited at a medium speed, local overheating and hot cracks caused by deformation heat accumulation are prevented, and it is guaranteed that the extrusion process is conducted stably.

Description

Technical Field

[0001] This invention relates to the field of welding material processing technology, and in particular to a method for improving the cross-sectional microstructure and property uniformity of rail transition welding materials. Background Technology

[0002] Rail transition welding materials, used to connect high-manganese steel frogs to high-carbon steel rails, have a microstructure and properties whose uniformity and stability directly affect the welding quality and safe service life of the weld joint. To improve the yield of transition welding materials, hot extrusion is commonly used to prepare short rail welding materials with specific rail shapes. During hot extrusion, the large cross-sectional size of the original billet, the complex shape of the formed profile, and the influence of friction during deformation lead to differences in metal flow and recrystallization behavior across the cross-section. This inhomogeneity in the cross-sectional microstructure directly results in uneven distribution of mechanical properties (such as hardness, strength, and toughness), reducing the overall performance stability and reliability of the material.

[0003] While existing technologies refine grain size through composition optimization and rapid cooling, they do not systematically address the issue of cross-sectional inhomogeneity introduced by the hot working process itself. Chinese invention patent CN115261725A, entitled "An Intermediate Transition Material for Welding High-Manganese Steel Flippers and High-Carbon Steel Rails and Its Preparation Method," proposes a one-step extrusion molding method for preparing short rails for welding, and a four-stage heating method for heating the extruded steel ingot before hot extrusion. Chinese invention patent CN118875570A, entitled "A Rail Transition Welding Material Resistant to Stress Corrosion Damage, Its Preparation Method, and Its Application in Rail Welding," proposes reducing the extrusion deformation temperature of the welding material through composition optimization and combining it with rapid water cooling after extrusion to obtain a fine cross-sectional microstructure. However, none of the above patent methods address how to control the uniformity of the cross-sectional microstructure of the transition welding material short rails, which is crucial for improving the performance stability of the welding material and the weld joint.

[0004] Therefore, developing a method that can actively regulate the thermal deformation process and fundamentally improve the cross-sectional microstructure and property uniformity of track transition welding materials has significant industrial application value. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for improving the uniformity of cross-sectional microstructure and properties of rail transition welding materials. By controlling two key thermodynamic and kinetic parameters—the temperature gradient of the billet cross-section and the extrusion speed—the problem of uneven microstructure and properties of hot-extruded parts can be directly solved.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for improving the cross-sectional microstructure and performance uniformity of rail transition welding materials, comprising the following steps: casting molten steel of the transition welding material into an electrode ingot, performing electroslag remelting, homogenization treatment, and pre-forging to obtain a billet; subjecting the billet to gradient heating to form a specific temperature field on its cross-section where the core temperature is lower than the surface temperature, with a temperature difference between 30 and 50°C and a surface temperature of 1000 to 1050°C; maintaining the temperature difference between the core and the surface, rapidly transferring the gradient-heated billet to a preheated extrusion cylinder, and passing it through a hot extrusion die at a medium extrusion speed of 120 to 150 mm / s to obtain a short rail of rail transition welding material.

[0007] Furthermore, the chemical composition (wt.%) of the molten steel used in the transition welding material is C 0.06-0.09, Si 0.12-0.20, Mn 4.7-5.2, Ni 10.6-11.2, Cr 16.8-17.1, Mo 1.9-2.2, with the balance being Fe.

[0008] Furthermore, the pre-forging ratio is not less than 5, and the forging process includes upsetting and drawing operations, so that the grain size of the forging billet is not less than grade 4, and the difference in austenite grain size at different positions on the cross-section of the billet does not exceed grade 1.5.

[0009] Furthermore, the gradient heating is achieved through the coordinated control of medium-frequency induction heating and the heat preservation and temperature equalization process.

[0010] Furthermore, the hot extrusion die has a bottom entry angle of 90~95°, a waist entry angle of 110~115°, and a head entry angle of 95~100°.

[0011] Furthermore, the preheating temperature of the extrusion cylinder is 250℃~400℃.

[0012] Furthermore, the electroslag remelting is carried out in an electroslag remelting furnace, and after the smelting is completed, the steel ingot is cooled to 900~950℃ before being water-cooled.

[0013] Furthermore, after extrusion molding, the short rail is left to stand in the air for 2-5 minutes, and then cooled by water or strong wind.

[0014] The present invention also discloses a short rail made of transition welding material prepared by the method described above for improving the cross-sectional microstructure and property uniformity of the rail transition welding material.

[0015] Compared with the prior art, the present invention has at least the following advantages and technical effects: This invention fundamentally solves the technical challenge of uneven microstructure and properties in hot-extruded parts by synergistically controlling two key thermodynamic-kinetic parameters: the temperature gradient of the billet cross-section and the extrusion speed. This effectively reduces grain size differences at different locations across the product's cross-section, significantly improving the overall quality and service reliability of the track transition welding material. Simultaneously, considering the high strength and poor thermal conductivity of the transition welding material at high temperatures, the extrusion speed is scientifically limited to a moderate range, effectively avoiding localized overheating and hot cracking caused by heat accumulation during deformation, ensuring a stable and controllable extrusion process.

[0016] This invention optimizes the design of the entry angle at different positions of the hot extrusion die, further adjusting the metal flowability and reducing the difference in deformation across different parts of the cross-section, resulting in more coordinated and uniform material deformation. This method requires no major equipment additions; it can be implemented simply by optimizing and adjusting the heating regime, extrusion speed, and die structure of the existing hot extrusion production line. The modification cost is low, the cycle is short, and it has good engineering application value and promising prospects for industrialization. Detailed Implementation

[0017] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0018] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0019] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0020] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0021] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0022] This invention provides a method for improving the cross-sectional microstructure and property uniformity of rail transition welding materials, comprising the following steps: casting molten steel of the transition welding material into an electrode ingot, performing electroslag remelting, homogenization treatment, and pre-forging to obtain a billet; subjecting the billet to gradient heating to form a specific temperature field on its cross-section where the core temperature is lower than the surface temperature, with a temperature difference between 30 and 50°C and a surface temperature of 1000 to 1050°C; maintaining the temperature difference between the core and the surface, rapidly transferring the gradient-heated billet to a preheated extrusion cylinder, and passing it through a hot extrusion die at a medium extrusion speed of 120 to 150 mm / s to obtain a short rail of rail transition welding material.

[0023] In some preferred embodiments of the present invention, the chemical composition (wt.%) of the molten steel used for transition welding is C 0.06-0.09, Si 0.12-0.20, Mn 4.7-5.2, Ni 10.6-11.2, Cr 16.8-17.1, Mo 1.9-2.2, with the balance being Fe.

[0024] In some preferred embodiments of the present invention, the pre-forging ratio is not less than 5, and the forging process includes upsetting and drawing operations, so that the grain size of the forging billet is not less than grade 4, and the difference in austenite grain size at different positions on the cross-section of the billet does not exceed grade 1.5.

[0025] In some preferred embodiments of the present invention, the gradient heating is achieved through the coordinated control of medium-frequency induction heating and the heat preservation and temperature equalization process.

[0026] In some preferred embodiments of the present invention, the hot extrusion die has a bottom entry angle of 90~95°, a waist entry angle of 110~115°, and a head entry angle of 95~100°.

[0027] In some preferred embodiments of the present invention, the preheating temperature of the extrusion cylinder is 250°C to 400°C.

[0028] In some preferred embodiments of the present invention, the electroslag remelting is carried out in an electroslag remelting furnace, and after the smelting is completed, the steel ingot is cooled to 900~950°C before being removed and water-cooled.

[0029] In some preferred embodiments of the present invention, after extrusion molding, the short rail is left to stand in the air for 2 to 5 minutes, and then cooled by water or strong wind.

[0030] This invention also discloses a method for preparing short rails of transition welding material by improving the cross-sectional microstructure and property uniformity of the rail transition welding material.

[0031] Example 1 A method for improving the cross-sectional microstructure and property uniformity of rail transition welding materials includes the following steps: The molten steel of transition welding material with chemical composition (wt.%) of C 0.07, Si 0.12, Mn 5.2, Ni 10.6, Cr 17.1, Mo 1.9, and balance Fe was tapped and cast into electrode ingots. The electrode ingots were remelted in an electroslag remelting furnace. After the melting was completed, the steel ingots were mold-cooled to 930°C and then water-cooled.

[0032] The steel ingot was homogenized at 1210℃ for 10 hours, then pre-forged with a forging ratio of 5.5. The forging process included upsetting and drawing operations to ensure that the grain size of the forged billet reached level 4. Finally, it was processed into a billet with a diameter of 363mm.

[0033] The billet is subjected to gradient heating. Through the coordinated control of medium-frequency induction heating and heat preservation and temperature equalization process, a specific temperature field is formed on its cross-section where the core temperature is higher than the surface temperature. The surface temperature Ts is controlled at 1030℃, the core temperature Tc is controlled at 990℃, and the temperature difference between the core and the surface is ΔT=40℃.

[0034] The gradient-heated billet is rapidly transferred to an extrusion cylinder preheated to 350°C, maintaining the temperature difference between the core and the surface. It is then extruded at a speed of 135 mm / s through a hot extrusion die with a special structural design, where the rail bottom entry angle is 92°, the rail web entry angle is 112°, and the rail head entry angle is 97°, to obtain a short rail of rail transition welding material.

[0035] After extrusion molding, the resulting short rails are left to stand in the air for 3 minutes, and then water-cooled.

[0036] The mechanical properties and grain size of the short rails obtained from the track transition welding material were measured, and the results are shown in Table 1.

[0037] Table 1. Mechanical properties and austenite grain size of the short track material in Example 1. Example 2 A method for improving the cross-sectional microstructure and property uniformity of rail transition welding materials includes the following steps: The transition welding material molten steel with a chemical composition (wt.%) of C 0.06, Si 0.16, Mn 4.9, Ni 11.1, Cr 16.8, Mo 2.2, and balance Fe was selected, and the subsequent electroslag remelting method was the same as in Example 1.

[0038] The steel ingot was homogenized at 1190℃ for 11 hours, then pre-forged with a forging ratio of 5.5. The forging process included upsetting and drawing operations to ensure that the grain size of the forged billet reached grade 4.5. Finally, it was processed into a billet with a diameter of 363mm.

[0039] The billet is subjected to gradient heating, with the surface temperature Ts controlled at 1040℃ and the core temperature Tc at 1005℃, and the temperature difference ΔT = 35℃.

[0040] The billet is transferred to an extrusion cylinder preheated to 400°C, maintaining the temperature difference between the core and the surface. It is then extruded through a hot extrusion die at an extrusion speed of 120 mm / s, with the rail bottom entry angle at 95°, the rail web entry angle at 115°, and the rail head entry angle at 100°, to obtain a short rail of rail transition welding material.

[0041] After extrusion molding, the short rails are left to stand in the air for 5 minutes, followed by strong air cooling.

[0042] The mechanical properties and grain size of the short rails obtained from the track transition welding material were measured, and the results are shown in Table 2: Table 2. Mechanical properties and austenite grain size of the short track of the track transition material in Example 2. Comparative Example 1 A method for preparing a short rail of track transition welding material includes the following steps: The transition welding material molten steel with a chemical composition (wt.%) of C 0.08, Si 0.20, Mn 4.7, Ni 11.2, Cr 16.8, Mo 2.2, and the balance being Fe was selected, and the subsequent electroslag remelting method was the same as in Example 1.

[0043] The steel ingot was homogenized at 1190℃ for 11 hours, then pre-forged with a forging ratio of 5.5. The forging process included upsetting and drawing operations to ensure that the grain size of the forged billet reached grade 4.5. Finally, it was processed into a billet with a diameter of 363mm.

[0044] The billet is subjected to gradient heating. Through the coordinated control of medium-frequency induction heating and heat preservation and temperature equalization process, a specific temperature field is formed on its cross-section where the core temperature is higher than the surface temperature. The surface temperature Ts is controlled at 1000℃, the core temperature Tc is controlled at 960℃, and the temperature difference ΔT = 40℃.

[0045] The gradient-heated billet is rapidly transferred to an extrusion cylinder preheated to 350°C, maintaining the temperature difference between the core and the surface. It is then extruded at a speed of 210 mm / s through a hot extrusion die with a special structural design, where the rail bottom entry angle is 92°, the rail web entry angle is 112°, and the rail head entry angle is 97°, to obtain a short rail of rail transition welding material.

[0046] After extrusion molding, the resulting short rails are left to stand in the air for 3 minutes, and then water-cooled.

[0047] The mechanical properties and grain size of the short rails obtained from the track transition welding material were measured, and the results are shown in Table 3: Table 3. Mechanical properties and austenite grain size at different positions of the short track in the track transition material of Comparative Example 1 Comparative Example 2 A method for preparing a short rail of track transition welding material includes the following steps: The transition welding material molten steel with a chemical composition (wt.%) of C 0.09, Si 0.16, Mn 4.9, Ni 11.2, Cr 16.8, Mo 2.2, and the balance being Fe was selected, and the subsequent electroslag remelting method was the same as in Example 1.

[0048] The steel ingot was homogenized at 1190℃ for 11 hours, then pre-forged with a forging ratio of 5.5. The forging process included upsetting and drawing operations to ensure that the grain size of the forged billet reached grade 4.5. Finally, it was processed into a billet with a diameter of 363mm.

[0049] The billet is heated uniformly throughout at a temperature of 1020℃.

[0050] The gradient-heated billet is rapidly transferred to an extrusion cylinder preheated to 350°C and extruded at a speed of 150 mm / s through a hot extrusion die with a special structural design, wherein the rail bottom entry angle is 92°, the rail web entry angle is 112°, and the rail head entry angle is 97°, to obtain a short rail of rail transition welding material.

[0051] After extrusion molding, the resulting short rails are left to stand in the air for 3 minutes, and then water-cooled.

[0052] The mechanical properties and grain size of the short rails obtained from the track transition welding material were measured, and the results are shown in Table 4: Table 4. Mechanical properties and austenite grain size of the short track material at different locations. Comparative Example 3 A method for preparing a short rail of track transition welding material includes the following steps: The transition welding material molten steel with a chemical composition (wt.%) of C 0.08, Si 0.20, Mn 4.7, Ni 11.2, Cr 16.8, Mo 2.2, and the balance being Fe was selected, and the subsequent electroslag remelting method was the same as in Example 1. The steel ingot was homogenized at 1190℃ for 11 hours, then pre-forged with a forging ratio of 5.5. The forging process included upsetting and drawing operations to ensure that the grain size of the forged billet reached grade 4.5. Finally, it was processed into a billet with a diameter of 363mm.

[0053] The billet is subjected to gradient heating. Through the coordinated control of medium-frequency induction heating and heat preservation and temperature equalization process, a specific temperature field is formed on its cross-section where the core temperature is higher than the surface temperature. The surface temperature Ts is controlled at 1010℃, the core temperature Tc is controlled at 980℃, and the temperature difference ΔT = 30℃.

[0054] The gradient-heated billet is rapidly transferred to an extrusion cylinder preheated to 350°C, maintaining the temperature difference between the core and the surface. It is then extruded at a speed of 140 mm / s through an extrusion die with an entry angle of 95° to obtain a short rail of track transition welding material.

[0055] After extrusion molding, the resulting short rails are left to stand in the air for 5 minutes, and then water-cooled.

[0056] Visual inspection revealed that the short rails made of transition welding material had undergone severe bending and torsional deformation along their length, rendering them unusable.

[0057] A comparison of the data from Example 1 and Comparative Example 1 shows that: excessively high hot extrusion speed will lead to excessive differences in grain size, with a grain size difference of 2 between the top of the rail head and the center of the rail bottom, resulting in uneven mechanical properties and toughness of the short rail of the transition welding material throughout the track. A comparison of the data from Example 1 and Comparative Example 2 shows that: by changing the process parameters of gradient heating, the grain size levels and impact energy of the short rails in the track transition welding material are too different in different parts, and the mechanical properties and toughness of the entire short rail are not uniform. A comparison of the data from Example 1 and Comparative Example 3 shows that if the structure of the extrusion die cannot properly define the rail bottom entry angle, rail waist entry angle, and rail head entry angle, it is impossible to obtain a short rail of normal size and stable rail transition welding material.

[0058] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for improving the uniformity of cross-sectional microstructure and properties of rail transition welding materials, characterized in that, The process includes the following steps: casting molten steel for transition welding into electrode ingots, followed by electroslag remelting, homogenization treatment, and pre-forging to obtain a billet; subjecting the billet to gradient heating to create a specific temperature field on its cross-section where the core temperature is lower than the surface temperature, with a temperature difference between 30 and 50°C and a surface temperature of 1000 to 1050°C; maintaining the temperature difference between the core and the surface, transferring the gradient-heated billet to a preheated hot extrusion cylinder and extruding it through a hot extrusion die at an extrusion speed of 120 to 150 mm / s to obtain a short rail for the track transition welding material.

2. The method for improving the cross-sectional microstructure and property uniformity of the rail transition welding material according to claim 1, characterized in that, According to the mass fraction, the chemical composition of the molten steel for the transition welding material is C 0.06-0.09wt.%, Si 0.12-0.20wt.%, Mn 4.7-5.2wt.%, Ni 10.6-11.2wt.%, Cr 16.8-17.1wt.%, Mo 1.9-2.2wt.%, with the balance being Fe.

3. The method for improving the cross-sectional microstructure and property uniformity of the rail transition welding material according to claim 1, characterized in that, The forging ratio of the pre-forging is not less than 5. The pre-forging process includes upsetting and drawing operations, so that the grain size of the forging billet is not less than grade 4, and the difference in austenite grain size at different positions on the cross-section of the billet does not exceed grade 1.

5.

4. The method for improving the cross-sectional microstructure and property uniformity of the rail transition welding material according to claim 1, characterized in that, The gradient heating is achieved through the coordinated control of medium-frequency induction heating and the heat preservation and temperature equalization process.

5. The method for improving the cross-sectional microstructure and property uniformity of the rail transition welding material according to claim 1, characterized in that, The hot extrusion die has a bottom entry angle of 90~95°, a waist entry angle of 110~115°, and a head entry angle of 95~100°.

6. The method for improving the cross-sectional microstructure and property uniformity of the rail transition welding material according to claim 1, characterized in that, The preheating temperature of the extrusion cylinder is 250~400℃.

7. The method for improving the cross-sectional microstructure and property uniformity of rail transition welding material according to claim 1, characterized in that, After the electroslag remelting is completed, the steel ingot is cooled to 900~950℃ before being removed and water-cooled.

8. The method for improving the cross-sectional microstructure and property uniformity of track transition welding material according to claim 1, characterized in that, After passing through a hot extrusion die, the short rail of the track transition welding material is left to stand in the air for 2-5 minutes, and then cooled by water or strong wind.

9. A short rail made of transition welding material prepared by the method for improving the cross-sectional microstructure and property uniformity of the transition welding material according to any one of claims 1-8.

Images