A method for forging and pressing a 60-50kg / m U75V special-shaped rail tail end

Abstract

The application discloses a 60-50kg / m U75V special-shaped rail heel end forging and pressing forming method, and a production process is as follows: track feeding, heel end forging and pressing heating position marking, heel end position entering a heating furnace, first time medium frequency induction heating, stopping heating, heel end heating position entering an oil press, first time forging and pressing, i.e., initial forging, heel end position entering the heating furnace, second time medium frequency induction heating, stopping heating, heel end heating position entering the oil press, second time forging and pressing, i.e., finish forging, and air cooling. The method can guarantee the surface quality and size precision of the 60kg / m forged 50kg / m special-shaped rail, shorten the special-shaped rail production process, improve work efficiency, and reduce energy consumption and labor cost under the premise of guaranteeing the strength and hardness of the special-shaped rail heel end forging and pressing section.

Description

Technical Field

[0001] This invention relates to a method for forging and forming the heel end of a 60-50kg / m U75V special-shaped steel rail. Background Technology

[0002] Domestic heavy-haul lines, mixed passenger and freight lines, high-speed lines, intercity lines, and urban subways all use symmetrical rails with a cross-section of 50kg / m, 60kg / m, or 75kg / m within the standard range. Due to differences in transportation conditions, service environments, and train axle loads between existing lines and newly built lines, and considering the economic efficiency of rail laying, different rail types are used on different lines. Connecting lines with different rail types has become a challenging and crucial aspect. While flash welding, aluminothermic welding, and gas pressure welding are commonly used for rails with the same cross-section, they cannot meet the requirements for welding connections between rails with different cross-sections. Therefore, forged special-shaped rails are needed to connect lines with different cross-section rails. The forged special-shaped rail connection method has advantages such as safety and reliability, good mechanical properties, excellent structure, high utilization rate, and high cost-effectiveness, ensuring the safe and stable operation of trains passing through lines with different cross-section rails.

[0003] Because the rail heel end undergoes multiple high-temperature thermal cycles and deformations, its microstructure and mechanical properties change compared to the rail base material. To ensure that the microstructure and properties of the special-shaped rail after actual heel end forging meet the standard requirements, solve the wear and crushing of the heel end during train operation, extend the service life of the rail, and increase the smoothness of train passage, it is necessary to design a reasonable rail heel end forging process and heat treatment process to ensure that its microstructure and properties meet the standard and technical requirements. Summary of the Invention

[0004] The purpose of this invention is to provide a method for forging the heel end of 60-50kg / m U75V special-shaped steel rails. This method combines the basic characteristics of steel rail materials, theoretical calculations, and practical applications. This method can ensure the surface quality and dimensional accuracy of 60kg / m forged into 50kg / m special-shaped steel rails. While ensuring the strength and hardness of the forged section at the heel end of the special-shaped steel rail, it shortens the production process of special-shaped steel rails, improves work efficiency, and reduces energy consumption and labor costs.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a method for forging the heel end of a 60-50kg / m U75V special-shaped steel rail. The production process is as follows: rail mounting → marking the heating area for heel end forging → heel end entering the heating furnace → first medium-frequency induction heating → stopping heating → the heated heel end entering the hydraulic press → first forging (preliminary forging) → heel end entering the heating furnace → second medium-frequency induction heating → stopping heating → the heated heel end entering the hydraulic press → second forging (finish forging) → air cooling; specifically:

[0007] 1) CCT and TTT curves were measured on U75V rail base material to formulate the forging process of 60-50kg / m U75V special-shaped rails;

[0008] 2) The cross-sectional area of ​​a 50kg / m rail is smaller than that of a 60kg / m rail. The flow direction of the rail metal material is along the length of the rail. The entire process of forming the rail heel end is elongation. The requirements for forming the rail heel end are to keep the rail head width basically unchanged, reduce the web height, narrow the rail bottom width, and thin the rail web and rail bottom.

[0009] 3) 60kg / m rails are forged into 50kg / m rails. The forging ratio of the rail head is 1.15, the forging ratio of the rail web is 1.25, the forging ratio of the rail base is 1.17, and the overall forging ratio is 1.18. The cross-sectional forging ratio of each part is greater than 1, and there is a lot of material surplus in each part.

[0010] 4) Based on the rail head section with the smallest compression elongation, the calculation is 450 + 150 - 68 = 532 mm;

[0011] 5) Therefore, the blanking length during forging is determined to be at least 532mm. Considering the friction factors between the die and the blank and the influence of the die structure, the actual pressing elongation will not reach the theoretical calculation result. At the same time, since some metal will be squeezed out of the die in the form of flash during the pressing process, the blanking length is finally set to 700-750mm.

[0012] 5) Before the first forging, the die needs to be preheated appropriately to improve the impact toughness of the die and reduce the temperature stress caused by repeated heating and cooling. When preheating the die, the temperature of the rail should be controlled at 800℃ and the preheating time should be controlled at about 20 minutes. The preheating of the die should be as uniform and thorough as possible to avoid local high temperature.

[0013] 6) During the forging process, the iron oxide scale inside the mold must be cleaned with an iron brush or compressed air gun before forging. If the iron oxide scale on the mold surface is not cleaned properly, it will seep into the forming section during forming, affecting the surface quality of the forging.

[0014] 7) The forging process for 60-50kg / m U75V steel rails involves two heating stages and two forging stages.

[0015] The initial forging heating temperature is 900-1000℃. After the initial forging heating is completed, the rail end is returned from the medium frequency induction heating furnace to the hydraulic press head die for initial forging. The precision forging heating temperature is 1000-1100℃. After the precision forging heating is completed, the rail end is returned from the medium frequency induction heating furnace to the hydraulic press head die for precision forging. After precision forging, the special-shaped part of the rail is air-cooled to room temperature. The heating temperature of both heating processes should not exceed 1150℃.

[0016] 8) After the special-shaped parts of the rail are precision forged and air-cooled to room temperature, measure the length of the forming section and transition section, the width of the rail base, the width of the rail head, and the thickness of the rail web.

[0017] Furthermore, the final cutting length was set at 720mm.

[0018] Furthermore, the initial forging heating temperature is 900℃ or 1000℃.

[0019] Furthermore, the precision forging heating temperature is 1100℃.

[0020] Furthermore, the length and limit deviation of the forming section of the 60-50kg / m U75V special-shaped rail should meet the following requirements: 450mm±30mm, and the length and limit deviation of the transition section should meet the following requirements: 150mm±30mm.

[0021] Furthermore, the intersecting surfaces of the transition section of the irregular-shaped rail should be smoothly and evenly transitioned; the forming section of the irregular-shaped rail should not have cracks, overheating, folding, or forging defects; the depth of surface defects such as local pits caused by forging should not exceed 0.5mm.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0023] This invention effectively improves the plasticity of forged rails, reduces deformation resistance, and saves energy while increasing production efficiency, while ensuring that the performance indicators, surface quality, and dimensions of the forged parts of the special-shaped rails meet the standard requirements. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings.

[0025] Figure 1 TTT curve of U75V rail base material;

[0026] Figure 2 The CCT curve of the U75V rail base material. Detailed Implementation

[0027] The manufacturing process for 60-50kg / m U75V special-shaped steel rails by heel end forging is as follows: upper rail → marking the heel end forging heating area → heel end enters the heating furnace → first medium frequency induction heating → stop heating → heel end heating area enters the hydraulic press → first forging (preliminary forging) → heel end enters the heating furnace → second medium frequency induction heating → stop heating → heel end heating area enters the hydraulic press → second forging (precision forging) → air cooling.

[0028] 1) CCT and TTT curves were measured on U75V rail base material to formulate the forging process of 60-50kg / m U75V special-shaped rails.

[0029] Depend on Figure 1 and Figure 2 The TTT and CCT curves of the U75V steel rail show that the nose temperature of the U75V steel rail is 525℃. At this temperature, the transformation time from supercooled austenite to pearlite is the shortest, with an incubation period of only 3 seconds and a pearlite transformation time of approximately 17 seconds. Based on microstructure analysis, the optimal temperature control range is 525-550℃. During the transformation from supercooled austenite to pearlite in the U75V steel rail, the critical cooling rate for the appearance of martensite in the microstructure is 7℃ / s. When the cooling rate exceeds 7℃ / s, rapid cooling is required above the temperature (525℃) that prevents the formation of bainite, taking into account the TTT curve. Simultaneously, the time required for pearlite transformation must be considered to ensure complete transformation of the supercooled austenite; otherwise, martensite will form below the Ms point due to the retained austenite.

[0030] 2) The cross-sectional area of ​​a 50kg / m rail is smaller than that of a 60kg / m rail. The flow direction of the rail metal material is along the length of the rail. The entire process of forming the rail heel end is elongation. The requirements for forming the rail heel end are to keep the rail head width basically unchanged, reduce the web height, narrow the rail bottom width, and thin the rail web and rail bottom.

[0031] 3) 60kg / m rails are forged into 50kg / m rails. The forging ratio for the rail head is 1.15, for the rail web is 1.25, for the rail base is 1.17, and the overall forging ratio is 1.18. The forging ratio of each section is greater than 1, and there is a significant material surplus in each section.

[0032] 4) Based on the rail head section with the minimum compression elongation, 450 + 150 - 68 = 532 mm. Therefore, the minimum blanking length during forging is determined to be 532 mm. Considering the friction between the die and the blank, as well as the influence of the die structure, the actual compression elongation may not reach the theoretical calculation result. In addition, since some metal will be extruded outside the die as flash during the pressing process, the final blanking length is set at approximately 720 mm.

[0033] 5) Before the first forging, the mold needs to be preheated appropriately to improve the impact toughness of the mold and reduce the temperature stress caused by repeated heating and cooling. When preheating the mold, the temperature of the rail should be controlled at about 800℃ and the preheating time should be controlled at about 20 minutes. The mold preheating should be as uniform and thorough as possible to avoid local high temperature.

[0034] 6) During the forging process, the iron oxide scale inside the mold must be cleaned with an iron brush or compressed air gun before forging. Iron oxide scale from the mold surface that is not cleaned properly will seep into the forming section during forming, affecting the surface quality of the forging.

[0035] 7) The forging process of 60-50kg / m U75V steel rail heel end is divided into two heating and two forging processes.

[0036] The initial forging heating temperature is 900-1000℃. After initial forging, the rail heel end is returned from the medium-frequency induction heating furnace to the hydraulic press head die for further initial forging. The finish forging heating temperature is 1000-1100℃. After finish forging, the rail heel end is returned from the medium-frequency induction heating furnace to the hydraulic press head die for further finish forging. After finish forging, the irregularly shaped part of the rail is air-cooled to room temperature. The heating temperature for both processes must not exceed 1150℃. The rails produced within the forging heating temperature range of this invention exhibit good forgeability and suitable metallographic structure. While ensuring that the surface quality and dimensions of the forged parts of the irregularly shaped rail meet standard requirements, it effectively improves the plasticity of the forged rails, reduces deformation resistance, saves energy, and increases production efficiency.

[0037] 8) After the special-shaped sections of the rail are precision forged and air-cooled to room temperature, measure the length of the forming section, the transition section, the rail base width, the rail head width, and the rail web thickness. For 60-50kg / m U75V special-shaped rails, the length of the forming section (LF) and its limit deviation should meet the following requirements: 450mm±30mm; the length of the transition section (LT) and its limit deviation should meet the following requirements: 150mm±30mm.

[0038] 9) The intersecting surfaces of the irregularly shaped rail transition section should have a smooth and rounded transition. The formed section of the irregularly shaped rail should be free from forging defects such as cracks, overheating, and folds. The depth of surface defects such as local pits caused by forging should not exceed 0.5 mm.

[0039] Example:

[0040] A method for forging and forming the heel end of a 60-50kg / m U75V special-shaped steel rail includes:

[0041] 1) Before the first forging, the mold needs to be preheated appropriately to improve the impact toughness of the mold and reduce the temperature stress caused by repeated heating and cooling. When preheating the mold, the temperature of the rail should be controlled at about 800℃ and the preheating time should be controlled at about 20 minutes. The mold preheating should be as uniform and thorough as possible to avoid local high temperature.

[0042] 2) During the forging process, the iron oxide scale inside the mold must be cleaned with an iron brush or compressed air gun before forging. Iron oxide scale from the mold surface that is not cleaned properly will seep into the forming section during forming, affecting the surface quality of the forging.

[0043] 3) Send the end of the rail 700mm-750mm into the medium frequency induction heating furnace. The rail should move slowly when it enters the equipment to avoid hitting the equipment.

[0044] 4) First heating: The end of the rail is heated to 900-1000℃ for the first time, and should not exceed 1150℃. After heating, the rail end is returned from the medium frequency induction heating furnace to the hydraulic press head die for initial forging.

[0045] 5) Second heating: The rail forging section is heated again to 1000-1100℃, not exceeding 1150℃. After heating, the rail heel end is returned from the medium frequency induction heating furnace to the hydraulic press head die for precision forging.

[0046] 6) After forming, measure the length of the forming section, transition section, rail base width, rail head width, and rail web thickness. For 60-50kg / m U75V hot-rolled special-shaped rails, the forming section length (LF) and its limit deviation should meet: 450mm±30mm, and the transition section length (LT) and its limit deviation should meet: 150mm±30mm. The intersecting surfaces of the transition section of the special-shaped rail should have a smooth and rounded transition. The forming section of the special-shaped rail should be free from forging defects such as cracks, overheating, and folds. The depth of surface defects such as localized pits caused by forging should not exceed 0.5mm.

[0047] Process comparison during implementation:

[0048] During implementation, the forging number of times, forging heating temperature, and cooling method of the forging area of ​​60-50kg / m U75V special-shaped steel rails were compared and analyzed. Based on production experience, the invention sets the initial forging temperature to 900℃, 1000℃, and 1100℃, and the fine forging temperature to 1000℃ and 1100℃, and compares and analyzes the forging effect and production efficiency.

[0049] Table 1. Heating process for forging the heel end of 60-50kg / mU75V special-shaped steel rails

[0050] Example 1 2 1100 1100 air cooling 500 Long production cycle Example 2 2 1100 1000 air cooling 500 The product size qualification rate was low; all three samples tested failed to meet the requirements. Example 3 2 1000 1100 air cooling 500 Quality meets requirements Example 4 2 900 1100 air cooling 500 Save 2 minutes in producing each rail

[0051] As shown in Table 1, in Example 1, both the initial forging temperature and the finishing forging temperature were 1100℃, resulting in a longer production cycle for the special-shaped rails. In Example 2, the finishing forging temperature was reduced to 1000℃, but the dimensional qualification rate of the produced special-shaped rails was low. In Example 3, the initial forging temperature was reduced to 1000℃, and the performance indicators and quality of the special-shaped rails met the requirements. In Example 4, the initial forging temperature was further reduced to 900℃, and the performance indicators and quality of the special-shaped rails met the requirements, while the forging time for each special-shaped rail was reduced by about 2 minutes. Furthermore, the forming section and transition section of the special-shaped rails had a smooth transition, and no forging defects such as cracks, overheating, or folds were found.

[0052] The irregularly shaped steel rail of this invention possesses good forgeability and a suitable metallographic structure. While ensuring that the performance indicators, surface quality, and dimensions of the forged parts of the irregularly shaped steel rail meet standard requirements, it effectively improves the plasticity of the forged steel rail, reduces deformation resistance, saves energy, and increases production efficiency.

[0053] 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 forging and forming the heel end of a 60-50kg / m U75V special-shaped steel rail, characterized in that: The production process is as follows: upper rail → marking the heel end forging heating area → heel end enters the heating furnace → first medium-frequency induction heating → stop heating → heel end heated area enters the hydraulic press → first forging (preliminary forging) → heel end enters the heating furnace → second medium-frequency induction heating → stop heating → heel end heated area enters the hydraulic press → second forging (finish forging) → air cooling; specifically: 1) CCT and TTT curves were measured on U75V rail base material to formulate the forging process of 60-50kg / m U75V special-shaped rails; 2) The cross-sectional area of ​​a 50kg / m rail is smaller than that of a 60kg / m rail. The flow direction of the rail metal material is along the length of the rail. The entire process of forming the rail heel end is elongation. The requirements for forming the rail heel end are to keep the rail head width basically unchanged, reduce the web height, narrow the rail bottom width, and thin the rail web and rail bottom. 3) 60kg / m rails are forged into 50kg / m rails. The forging ratio of the rail head is 1.15, the forging ratio of the rail web is 1.25, the forging ratio of the rail base is 1.17, and the overall forging ratio is 1.

18. The cross-sectional forging ratio of each part is greater than 1, and there is a lot of material surplus in each part. 4) Based on the rail head section with the smallest compression elongation, the calculation is 450 + 150 - 68 = 532 mm; 5) Therefore, the blanking length during forging is determined to be at least 532mm. Considering the friction factors between the die and the blank and the influence of the die structure, the actual pressing elongation will not reach the theoretical calculation result. At the same time, since some metal will be squeezed out of the die in the form of flash during the pressing process, the blanking length is finally set to 700-750mm. 6) Before the first forging, the die needs to be preheated appropriately to improve the impact toughness of the die and reduce the temperature stress caused by repeated heating and cooling. When preheating the die, the temperature of the rail should be controlled at 800℃ and the preheating time should be controlled at about 20 minutes. The preheating of the die should be as uniform and thorough as possible to avoid local high temperature. 7) During the forging process, the iron oxide scale inside the mold must be cleaned with an iron brush or compressed air gun before forging. If the iron oxide scale on the mold surface is not cleaned properly, it will seep into the forming section during forming, affecting the surface quality of the forging. 8) The forging process for 60-50kg / m U75V steel rails involves two heating stages and two forging stages. The initial forging heating temperature is 900-1000℃. After the initial forging heating is completed, the rail end is returned from the medium frequency induction heating furnace to the hydraulic press head die for initial forging. The precision forging heating temperature is 1000-1100℃. After the precision forging heating is completed, the rail end is returned from the medium frequency induction heating furnace to the hydraulic press head die for precision forging. After precision forging, the special-shaped part of the rail is air-cooled to room temperature. The heating temperature of both heating processes should not exceed 1150℃. 9) After the special-shaped parts of the rail are precision forged and air-cooled to room temperature, measure the length of the forming section and transition section, the width of the rail base, the width of the rail head, and the thickness of the rail web.

2. The forging and forming method for the heel end of a 60-50kg / m U75V special-shaped steel rail according to claim 1, characterized in that: The final cutting length was set at 720mm.

3. The forging and forming method for the heel end of a 60-50kg / m U75V special-shaped steel rail according to claim 1, characterized in that: The initial forging heating temperature is 900℃ or 1000℃.

4. The forging and forming method for the heel end of a 60-50kg / m U75V special-shaped steel rail according to claim 1, characterized in that: The precision forging heating temperature is 1100℃.

5. The forging and forming method for the heel end of a 60-50kg / m U75V special-shaped steel rail according to claim 1, characterized in that: The forming section length and limit deviation of the 60-50kg / m U75V special-shaped rail should meet the following requirements: 450mm±30mm, and the transition section length and limit deviation should meet the following requirements: 150mm±30mm.

6. The forging and forming method for the heel end of a 60-50kg / m U75V special-shaped steel rail according to claim 1, characterized in that: The intersecting surfaces of the irregular-shaped rail transition section should be smooth and rounded; the forming section of the irregular-shaped rail should not have cracks, overheating, folding, or forging defects; the depth of surface defects such as local pits caused by forging should not exceed 0.5mm.

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