Processing method of large-size axle steel billet for high-speed train with speed of 400 km / h and above

Abstract

The application discloses a processing method of large-specification axle steel billets for high-speed trains with a speed of 400 km / h and above, which comprises the steps of continuous casting billet preparation, continuous casting billet heating, continuous casting billet forging and post-forging heat treatment, adopts a four-section heating process of continuous casting billets, a two-up-and-two-down forging process of continuous casting billets and a post-forging heat treatment process of waste heat normalizing and annealing, solves the problems of the uniformity of the structure, the compactness, the banded structure and the transverse and longitudinal impact toughness of the large-specification axle steel billets for high-speed trains with a speed of 400 km / h and above, and the banded structure of the produced large-specification axle steel billets is less than or equal to 1 level, the low-magnification structure center porosity is less than or equal to 1 level, and the transverse and longitudinal impact values ratio is greater than or equal to 0.9, which fully meets the application requirements of the axle of the high-speed trains with a speed of 400 km / h and above.

Description

Technical Field

[0001] This invention belongs to the field of forging and heat treatment technology, and more specifically relates to a processing method for large-size axle steel billets for high-speed trains with speeds of 400 km / h and above. Background Technology

[0002] Axles are crucial running gear components for the safe operation of high-speed trains. As high-speed train speeds increase, the dynamic loads on axles also increase, making them more susceptible to fatigue failure. The research and development of axles for high-speed trains operating at speeds of 400 km / h and above in my country has been put on the agenda. Compared to axle steel billets for high-speed trains operating at speeds of 250 km / h and 350 km / h, the steel billets for large-size axles operating at speeds of 400 km / h and above are larger. To ensure the safety of high-speed trains operating at speeds of 400 km / h and above, the requirements for the uniformity and density of the microstructure of large-size axle steel billets are more stringent. Specifically, the requirements include a porosity and segregation of ≤1 grade, a banded microstructure of ≤1 grade, and a transverse-to-longitudinal impact value ratio of ≥0.9. The internal quality of axle steel billets has very strict requirements for the forging process. Axle steel billets produced using existing traditional forging and heat treatment processes generally have serious porosity and compositional segregation. Moreover, they have low transverse and longitudinal impact toughness and strength, and the banded structure is only grade 2-3. They cannot meet the above-mentioned requirements for density, banded structure and transverse and longitudinal impact toughness of large-size axle steel billets for high-speed trains with speeds of 400 km / h and above. Summary of the Invention

[0003] To address some or all of the technical problems existing in the prior art, the present invention provides a method for processing large-size axle steel billets for high-speed trains with speeds of 400 km / h and above, comprising the following steps:

[0004] (I) Preparation of continuously cast billets

[0005] The process involves electric furnace smelting, LF furnace refining, VD degassing, and continuous casting to obtain a Φ690mm cross-section continuous casting round billet. The chemical composition of the continuous casting billet is controlled by mass percentage as follows: C: 0.24~0.32%, Si: 0.20~0.40%, Mn: 0.60~0.90%, P≤0.010%, S≤0.010%, Cr: 0.90~1.20%, Mo: 0.20~0.30%, Ni: 0.50~1.50%, V≤0.06%, Al: 0.010~0.040%, Cu≤0.20%, with the remainder being Fe and unavoidable impurities.

[0006] (ii) Heating of continuously cast billets

[0007] The continuous casting billet is heated by a four-stage heating process: (1) First stage heating: after the continuous casting billet is put into the furnace, it is kept at 500℃ for 2 hours; (2) Second stage heating: the billet is heated to 850±10℃ at a heating rate of ≤100℃ / h and kept at 2 hours; (3) Third stage heating: the billet is heated to 1150±10℃ at a heating rate of ≤120℃ / h and kept at 3 hours; (4) Fourth stage heating: the billet is heated to 1270±10℃ at a heating rate of ≤100℃ / h and kept at 4~5 hours before being taken out of the furnace.

[0008] (III) Forging of continuously cast billets

[0009] Forging a continuously cast round billet with a cross-section of Φ690mm into an axle steel billet with a cross-section of 300mm×300mm includes:

[0010] (1) First forging: The billet is upset in the first fire. A wide plate is used to upset the continuous casting billet to 1 / 2 of the original continuous casting billet height. Then the billet is drawn in the first fire to round the billet to the original continuous casting billet height. The forging temperature during the first forging process is controlled at 1200~850℃.

[0011] (2) Second forging: The billet is heated to 1240±30℃ in the furnace and held for 2 hours. Then, the billet is upset to 1 / 2 of the original continuous casting billet height. Then, the billet is drawn to a square shape to a 300mm×300mm axle steel billet. The forging temperature during the second forging process is controlled at 1200~900℃.

[0012] (iv) Post-forging heat treatment

[0013] (1) Residual heat normalizing: The axle steel billet is normalized using the residual heat of forging. After each axle steel billet is forged, it is placed on a cooling platform and cooled to below 200°C by a fan.

[0014] (2) Annealing: After the axle steel billet is cooled by blowing, it is put into the annealing furnace to perform stress relief annealing treatment. It is heated to 670±10℃ at a heating rate of 100℃ / h, held for 6~8 hours, and then furnace cooled to below 200℃ before being taken out of the furnace.

[0015] Furthermore, in the above-mentioned processing method for large-specification axle steel billets for high-speed trains with speeds of 400 km / h and above, in the continuous casting billet heating step, a chamber heating furnace is used to heat the continuous casting billet. The chamber heating furnace is 3.5m long and uses natural gas for heating.

[0016] Furthermore, in the above-mentioned processing method for large-size axle steel billets for high-speed trains with speeds of 400 km / h and above, in the continuous casting billet forging step, the number of passes in which the single-sided reduction amount is ≥80 mm during the second drawing process is controlled to be no less than two passes.

[0017] Furthermore, in the above-mentioned processing method for large-specification axle steel billets for high-speed trains with speeds of 400 km / h and above, the forging equipment used in the continuous casting billet forging step is a 5000-ton fast forging press.

[0018] The processing method for large-size axle steel billets for high-speed trains with speeds of 400 km / h and above, as described in this invention, has the following advantages and beneficial effects: By adopting a four-stage heating process for continuously cast billets, a two-upsetting and two-drawing forging process for continuously cast billets, and a post-forging heat treatment process of residual heat normalizing + annealing, this invention solves the problems of uniformity of microstructure, density, banded microstructure, and transverse and longitudinal impact toughness of large-size axle steel billets for high-speed trains with speeds of 400 km / h and above. The produced large-size axle steel billets have a banded microstructure ≤ Grade 1, a low-magnification microstructure center porosity ≤ Grade 1, and a transverse and longitudinal impact value ratio ≥ 0.9, fully meeting the application requirements of high-speed trains with speeds of 400 km / h and above. This is of great significance for promoting the development of my country's high-speed trains towards higher speeds and promoting the implementation of my country's leading strategy for high-end railway equipment technology. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0020] Figure 1 This is a diagram showing the heating process curve of the continuous casting billet in the processing method of large-size axle steel billets for high-speed trains with speeds of 400 km / h and above, according to the present invention.

[0021] Figure 2 This is a schematic diagram of the continuous casting billet forging process in the processing method of large-size axle steel billets for high-speed trains with speeds of 400 km / h and above according to the present invention.

[0022] Figure 3 This is a graph showing the annealing process curve of the steel billet in the processing method of large-size axle steel billets for high-speed trains with speeds of 400 km / h and above, according to the present invention.

[0023] Figure 4 A strip structure diagram of an axle steel billet manufactured using the processing method of the present invention for large-size axle steel billets for high-speed trains with speeds of 400 km / h and above.

[0024] Figure 5 A low-magnification microstructure image of an axle steel billet manufactured using the processing method of the present invention for large-size axle steel billets for high-speed trains with speeds of 400 km / h and above.

[0025] Figure 6 A strip microstructure diagram of the axle steel billet manufactured using Embodiment 1 of the present invention;

[0026] Figure 7 A low-magnification microstructure diagram of the axle steel billet manufactured using Embodiment 1 of the present invention;

[0027] Figure 8 A strip microstructure diagram of the axle steel billet manufactured using Embodiment 2 of the present invention;

[0028] Figure 9 This is a low-magnification microstructure diagram of the axle steel billet manufactured using Embodiment 2 of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0030] The basic process route of the processing method for large-size axle steel billets for high-speed trains with speeds of 400 km / h and above according to the present invention is as follows: continuous casting billet preparation → continuous casting billet heating → continuous casting billet forging → post-forging heat treatment. Specifically, the processing method for large-size axle steel billets for high-speed trains with speeds of 400 km / h and above according to the present invention includes the following steps:

[0031] (I) Preparation of continuously cast billets

[0032] A continuously cast round billet with a cross-section of Φ690mm was prepared by electric furnace smelting → LF furnace refining → VD degassing treatment → continuous casting. The chemical composition of the continuously cast billet was controlled by mass percentage as follows: C: 0.24~0.32%, Si: 0.20~0.40%, Mn: 0.60~0.90%, P≤0.010%, S≤0.010%, Cr: 0.90~1.20%, Mo: 0.20~0.30%, Ni: 0.50~1.50%, V≤0.06%, Al: 0.010~0.040%, Cu≤0.20%, with the remainder being Fe and unavoidable impurities.

[0033] (ii) Heating of continuously cast billets

[0034] A chamber furnace is used to heat the continuously cast billets. To ensure uniform heating temperature of the billets, such as... Figure 1As shown, the continuous casting billet heating process adopts a four-stage heating process: (1) First stage heating: after the continuous casting billet enters the furnace, it is first kept at 500℃ for 2 hours; (2) Second stage heating: the billet is heated to 850±10℃ at a heating rate of ≤100℃ / h and kept at 2 hours; (3) Third stage heating: the billet is heated to 1150±10℃ at a heating rate of ≤120℃ / h and kept at 3 hours; (4) Fourth stage heating: the billet is heated to 1270±10℃ at a heating rate of ≤100℃ / h and kept at 4~5 hours before being taken out of the furnace.

[0035] (III) Forging of continuously cast billets

[0036] A continuously cast round billet with a cross-section of Φ690mm is forged into an axle steel billet with a cross-section of 300mm×300mm, such as... Figure 2 As shown, the forging steps of continuously cast billets include:

[0037] (1) First forging: The billet is upset in the first fire. A wide plate is used to upset the continuous casting billet to 1 / 2 of the original continuous casting billet height. Then the billet is drawn in the first fire to round the billet to the original continuous casting billet height. The forging temperature during the first forging process is controlled at 1200~850℃.

[0038] (2) Second forging: The billet is heated to 1240±30℃ and held for 2 hours. Then, the billet is upset to 1 / 2 of the original continuous casting billet height. Then, the billet is drawn to a square shape to a 300mm×300mm axle billet. During the second drawing process, the single-sided reduction of ≥80mm should be ≥2 times. The forging temperature during the second forging process is controlled at 1200~900℃.

[0039] (iv) Post-forging heat treatment

[0040] To improve the banded microstructure and eliminate thermal stress in the axle steel billet, post-forging heat treatment is performed on the axle steel billet. The post-forging heat treatment includes:

[0041] (1) Residual heat normalizing: The axle steel billet is normalized using the residual heat of forging. After each axle steel billet is forged, it is placed on a cooling platform and cooled to below 200°C by a fan.

[0042] (2) Annealing: The axle steel billet, after being cooled by blowing air, is placed into an annealing furnace to perform stress-relieving annealing treatment, such as... Figure 3 As shown, the furnace is heated to 670±10℃ at a heating rate of 100℃ / h, held for 6~8 hours, and then cooled in the furnace to below 200℃ before being removed from the furnace.

[0043] In one specific implementation, the chamber heating furnace used in the continuous casting billet heating step is 3.5m long and uses natural gas for heating.

[0044] In one specific implementation, the forging equipment used in the continuous casting billet forging step is a 5000-ton high-speed forging press.

[0045] The strip microstructure diagram and low-magnification microstructure diagram of the axle steel billet manufactured using the processing method of the present invention for large-size axle steel billets for high-speed trains with speeds of 400 km / h and above are respectively shown in the figure. Figure 4 and Figure 5 Testing revealed that the large-size axle steel billets manufactured using this invention exhibit a banded structure ≤ Grade 1, a low-magnification central porosity ≤ Grade 1, and a transverse-to-longitudinal impact value ratio ≥ 0.9, fully meeting the application requirements for high-speed rail axles with speeds of 400 km / h and above.

[0046] The following detailed description of the processing method of large-size axle steel billets for high-speed trains with speeds of 400 km / h and above is provided in conjunction with the embodiments of the present invention. The implementation methods in the following embodiments without specific conditions are carried out according to conventional methods and conditions, and the present invention does not make specific limitations in this regard.

[0047] Example 1

[0048] The specific implementation of the processing method for large-specification axle steel billets for high-speed trains with speeds of 400 km / h and above in Embodiment 1 of the present invention is as follows:

[0049] (I) Preparation of continuously cast billets

[0050] A continuously cast round billet with a cross section of Φ690mm was prepared by electric furnace smelting → LF furnace refining → VD degassing treatment → continuous casting. The chemical composition of the continuously cast billet by mass percentage is as follows: C: 0.27%, Si: 0.25%, Mn: 0.70%, P: 0.007%, S: 0.001%, Cr: 1.00%, Mo: 0.26%, Ni: 1.13%, V: 0.04%, Al: 0.021%, with the remainder being Fe and unavoidable impurities.

[0051] (ii) Heating of continuously cast billets

[0052] Four Φ690mm×1500mm continuous casting billets were loaded into a chamber heating furnace for four-stage heating. After the billets were loaded into the furnace, they were first held at 500℃ for 2 hours, then heated to 850℃ at a heating rate of 100℃ / h and held for 2 hours. Next, they were heated to 1150℃ at a heating rate of 120℃ / h and held for 3 hours. Finally, they were heated to 1270℃ at a heating rate of 100℃ / h and held for 4 hours before being taken out of the furnace for forging.

[0053] (III) Forging of continuously cast billets

[0054] (1) First forging: The billet is upset in the first fire, and a wide plate is upset to a height of 750mm. After upset, the billet is drawn in the first fire and directly drawn to a round shape of 1500mm. The forging temperature in the first fire forging process is 1200~850℃.

[0055] (2) Second forging: The billet is heated to 1270℃ and held for 2 hours. Then, it is upset to a height of 750mm. Then, the billet is drawn to a square shape to a 300mm×300mm axle billet. During the second drawing, the single-sided reduction of the third and fourth passes is 80mm. The forging temperature during the second forging process is controlled at 1200~900℃.

[0056] (iv) Post-forging heat treatment

[0057] (1) Residual heat normalizing: The final forging temperatures of the four axle steel billets are 910℃, 915℃, 900℃ and 910℃ respectively. After each axle steel billet is forged, the axle steel billet is placed on a cooling platform and cooled to below 200℃ by a fan.

[0058] (2) Annealing: After the axle steel billet is cooled by blowing, it is put into the annealing furnace to perform stress relief annealing treatment. It is heated to 670°C at a heating rate of 100°C / h, held for 7 hours, and then furnace cooled to below 200°C before being taken out of the furnace.

[0059] The banded microstructure diagram and low-magnification microstructure diagram of the axle steel billet processed and manufactured using Embodiment 1 of the present invention are respectively shown in the figure. Figure 6 and Figure 7 Upon testing, the axle steel billet manufactured using Example 1 of the present invention has a banded structure of grade 0.5, a low-magnification structure with central porosity of grade 1, and as shown in Table 1 below, a transverse-to-longitudinal impact value ratio of 0.95.

[0060] Table 1. Ratio of transverse and longitudinal impact values ​​of axle steel billets in Example 1

[0061]

[0062] Example 2

[0063] The specific implementation of the processing method for large-specification axle steel billets for high-speed trains with speeds of 400 km / h and above in Embodiment 2 of the present invention is as follows:

[0064] (I) Preparation of continuously cast billets

[0065] A continuously cast round billet with a cross section of Φ690mm was prepared by electric furnace smelting → LF furnace refining → VD degassing treatment → continuous casting. The chemical composition of the continuously cast billet by mass percentage is as follows: C: 0.28%, Si: 0.26%, Mn: 0.71%, P: 0.007%, S: 0.001%, Cr: 1.01%, Mo: 0.26%, Ni: 1.14%, V: 0.05%, Al: 0.022%, with the remainder being Fe and unavoidable impurities.

[0066] (ii) Heating of continuously cast billets

[0067] Six Φ690mm×1520mm continuous casting billets were loaded into a chamber heating furnace for four-stage heating. After the billets were loaded into the furnace, they were first held at 500℃ for 2 hours, then heated to 850℃ at a heating rate of 100℃ / h and held for 2 hours, then heated to 1150℃ at a heating rate of 120℃ / h and held for 3 hours, and then heated to 1270℃ at a heating rate of 100℃ / h and held for 5 hours before being taken out of the furnace for forging.

[0068] (III) Forging of continuously cast billets

[0069] (1) First forging: The billet is upset in the first fire, using a wide plate to upset to a height of 760mm. After upset, the billet is drawn in the first fire and directly drawn to a round shape of 1520mm. The forging temperature in the first fire forging process is 1200~850℃.

[0070] (2) Second forging: The billet is heated to 1270℃ and held for 2 hours. Then, it is upset to a height of 760mm. Then, the billet is drawn to a square shape to a 300mm×300mm axle billet. During the second drawing, the single-sided reduction of the third and fourth passes is 80mm. The forging temperature during the second forging process is controlled at 1200~900℃.

[0071] (iv) Post-forging heat treatment

[0072] (1) Residual heat normalizing: The final forging temperatures of the six axle steel billets are 905℃, 910℃, 915℃, 905℃, 900℃ and 910℃ respectively. After each axle steel billet is forged, the axle steel billet is placed on a cooling platform and cooled to below 200℃ by a fan.

[0073] (2) Annealing: After the axle steel billet is cooled by blowing, it is put into the annealing furnace to perform stress relief annealing treatment. It is heated to 680°C at a heating rate of 100°C / h, held for 8 hours, and then furnace cooled to below 200°C before being taken out of the furnace.

[0074] The strip microstructure diagram and low-magnification microstructure diagram of the axle steel billet processed and manufactured using Embodiment 2 of the present invention are respectively shown in the figure. Figure 8 and Figure 9 Upon testing, the axle steel billet manufactured using Example 2 of the present invention has a banded structure of grade 0.5, a low-magnification central porosity of grade 0.5, and as shown in Table 2 below, the ratio of transverse to longitudinal impact values ​​is 0.92.

[0075] Table 2. Ratio of transverse and longitudinal impact values ​​of axle steel billets in Example 2

[0076]

[0077] In summary, the processing method for large-size axle steel billets for high-speed trains with speeds of 400 km / h and above, as presented in this invention, solves the problems of uniformity, density, banded structure, and transverse and longitudinal impact toughness of large-size axle steel billets for high-speed trains with speeds of 400 km / h and above by adopting a four-stage heating process for continuously cast billets, a two-upsetting and two-drawing forging process for continuously cast billets, and a post-forging heat treatment process of residual heat normalizing + annealing. The produced large-size axle steel billets have a banded structure ≤ grade 1, a low-magnification structure center porosity ≤ grade 1, and a transverse and longitudinal impact value ratio ≥ 0.9, fully meeting the application requirements of high-speed trains with speeds of 400 km / h and above. This method is of great significance for promoting the development of high-speed trains in my country to higher speeds and for promoting the implementation of my country's leading strategy in high-end railway equipment technology.

[0078] It should be noted that, in this document, relational terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for processing large-size axle steel billets for high-speed trains with speeds of 400 km / h and above, characterized in that, Includes the following steps: (I) Preparation of continuously cast billets The process involves electric furnace smelting, LF furnace refining, VD degassing, and continuous casting to obtain a Φ690mm cross-section continuous casting round billet. The chemical composition of the continuous casting billet is controlled by mass percentage as follows: C: 0.24~0.32%, Si: 0.20~0.40%, Mn: 0.60~0.90%, P≤0.010%, S≤0.010%, Cr: 0.90~1.20%, Mo: 0.20~0.30%, Ni: 0.50~1.50%, V≤0.06%, Al: 0.010~0.040%, Cu≤0.20%, with the remainder being Fe and unavoidable impurities. (ii) Heating of continuously cast billets The continuous casting billet is heated by a four-stage heating process: (1) First stage heating: after the continuous casting billet is put into the furnace, it is kept at 500℃ for 2 hours; (2) Second stage heating: the billet is heated to 850±10℃ at a heating rate of ≤100℃ / h and kept at 2 hours; (3) Third stage heating: the billet is heated to 1150±10℃ at a heating rate of ≤120℃ / h and kept at 3 hours; (4) Fourth stage heating: the billet is heated to 1270±10℃ at a heating rate of ≤100℃ / h and kept at 4~5 hours before being taken out of the furnace. (III) Forging of continuously cast billets Forging a continuously cast round billet with a cross-section of Φ690mm into an axle steel billet with a cross-section of 300mm×300mm includes: (1) First forging: The billet is upset in the first fire. A wide plate is used to upset the continuous casting billet to 1 / 2 of the original continuous casting billet height. Then the billet is drawn in the first fire to round the billet to the original continuous casting billet height. The forging temperature during the first forging process is controlled at 1200~850℃. (2) Second forging: The billet is heated to 1240±30℃ in the furnace and held for 2 hours. Then, the billet is upset to 1 / 2 of the original continuous casting billet height. Then, the billet is drawn to a square shape to a 300mm×300mm axle steel billet. The forging temperature during the second forging process is controlled at 1200~900℃. (iv) Post-forging heat treatment (1) Residual heat normalizing: The axle steel billet is normalized using the residual heat of forging. After each axle steel billet is forged, it is placed on a cooling platform and cooled to below 200°C by a fan. (2) Annealing: After the axle steel billet is cooled by blowing, it is put into the annealing furnace to perform stress relief annealing treatment. It is heated to 670±10℃ at a heating rate of 100℃ / h, held for 6~8 hours, and then furnace cooled to below 200℃ before being taken out of the furnace.

2. The processing method for large-size axle steel billets for high-speed trains with speeds of 400 km / h and above according to claim 1, characterized in that, In the continuous casting billet heating step, a chamber heating furnace is used to heat the continuous casting billet. The chamber heating furnace is 3.5m long and uses natural gas for heating.

3. The processing method for large-size axle steel billets for high-speed trains with speeds of 400 km / h and above, as described in claim 1, is characterized in that... In the continuous casting billet forging process, the number of passes with a single-sided reduction of ≥80mm during the second drawing process should be controlled to be no less than two passes.

4. The processing method for large-size axle steel billets for high-speed trains with speeds of 400 km / h and above, as described in claim 1, is characterized in that... In the continuous casting billet forging process, the forging equipment used is a 5000-ton high-speed forging press.

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