Production method and application of rare earth hot-rolled round steel for coupler yoke

Abstract

The invention discloses a production method and application of rare earth hot-rolled round steel for a coupler yoke, and the rare earth hot-rolled round steel comprises the following chemical components in percentage by mass: 0.24%-0.28% of C, 0.20%-0.40% of Si, 0.90%-1.10% of Mn, less than or equal to 0.025% of P, less than or equal to 0.025% of S, 0.20%-0.30% of Cr, 0.10%-0.20% of Mo, 0.15%-0.30% of Ni, 0.030%-0.040% of Re and the balance of Fe and inevitable impurities, and the total mass fraction is 100%. The low-cost and high-performance steel for the coupler yoke is produced through converter smelting, LF refining, VD vacuum degassing, continuous casting and casting blank heating furnace heating methods, for the hot-rolled round steel for the coupler yoke with specific components, the more accurate production method is determined, the manufactured hot-rolled round steel for the coupler yoke is more durable, the overall service life is prolonged, and use safety is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of structural steel, and particularly relates to a production method and application of rare earth hot-rolled round steel for a hook tail frame. Background Art

[0002] As an important part of the railway transport vehicle coupler buffer device, the hook tail frame realizes the longitudinal force transmission between vehicles during vehicle traction, coupling and buffering. Because the hook tail frame bears huge longitudinal impact loads, the performance and quality of the hook tail frame have an important impact on train operation safety. In 2000, China required that the hook tail frame could only use E-grade steel materials to replace the traditional ordinary carbon cast steel and became the dominant material for railway freight car hook tail frames in China. In 2008, Pangang successfully developed 25MnCrNiMoA forged hook tail frame steel for railway vehicles, and the technology reached the domestic advanced level. The physical properties of the 25MnCrNiMA hook tail frame steel prepared by design are Rel: 692 - 1040 MPa, Rm: 850 - 1080 MPa, A: 14 - 19%, 2: 45 - 68%, Akv2: 40 - 80 J.

[0003] With the implementation of the heavy haul and speed increase strategies in the field of railway freight transportation, the production technology of railway freight trains and vehicle performance have been continuously improved. The load per freight car has been successively increased from 60 tons to 70 tons and 80 tons, the running speed has been increased from 80 km / h to 100 - 120 km / h, and the train formation has been increased from 10,000 tons to 20,000 tons. At the same time, the requirements for the performance (mechanical properties and low-temperature toughness) of the hook tail frame, which is the largest longitudinal force-bearing part, are also getting higher and higher to better meet the development needs of heavy-haul locomotives.

[0004] Therefore, in view of the above factors, in order to meet the needs of high-speed trains, a production method and application of rare earth hot-rolled round steel for a hook tail frame are developed. By adopting a production method different from the prior art for the hot-rolled round steel for a hook tail frame with specific components, the service life and use safety can be further improved. Summary of the Invention

[0005] The present invention aims to make up for the deficiencies of the prior art, and provides a production method and application of rare earth hot-rolled round steel for a hook tail frame, so that it has good comprehensive mechanical properties and low-temperature impact toughness, and thus significantly improves the overall service life and safety of the steel for a hook tail frame.

[0006] The object of the present invention is to provide a production method of rare earth hot-rolled round steel 25MnCrNiMoA-RE for coupler yokes, and the mass percentage content of its chemical components includes: C 0.24% - 0.28%, Si 0.20% - 0.40%, Mn 0.90% - 1.10%, P≤0.025%, S≤0.025%, Cr 0.20% - 0.30%, Mo 0.10% - 0.20%, Ni 0.15% - 0.30%, Re 0.030% - 0.040%, and the rest are Fe and inevitable impurities, and the total mass fraction is 100%.

[0007] Further, in the 25MnCrNiMoA, the contents of P and S are low, P≤0.020%, and S<0.003%.

[0008] The production method of rare earth hot-rolled round steel 25MnCrNiMoA-RE for coupler yokes, and the mass percentage content of its chemical components includes: C 0.24%, Si 0.27%, Mn 1.05%, P 0.0024%, S 0.0087%, Cr 0.27%, Mo 0.12%, Ni 0.25%, RE 0.036%, and the rest are Fe and inevitable impurities, and the total mass fraction is 100%.

[0009] The production method of rare earth hot-rolled round steel 25MnCrNiMoA-RE for coupler yokes, and the mass percentage content of its chemical components includes: C 0.28%, Si 0.35%, Mn 1.02%, P 0.0086%, S 0.0065%, Cr 0.24%, Mo 0.13%, Ni 0.28%, RE 0.039%, and the rest are Fe and inevitable impurities, and the total mass fraction is 100%.

[0010] The production method of rare earth hot-rolled round steel 25MnCrNiMoA-RE for coupler yokes specifically includes the following steps;

[0011] Converter smelting: Adopt top and bottom combined blown converter for smelting, all use pre-desulfurized hot metal, the carbon content of the converter tapping steel shall not be greater than 0.15%, the carbon content of the converter end molten steel is controlled between 0.08% - 0.15%, use SiMn, MnFe and CrFe for deoxidation alloying, and use Al for final deoxidation;

[0012] The slag in the converter contains about 18% of FeO, and according to the conventional tapping method, the slag volume is 5 - 10 kg / t;

[0013] Deoxidize with aluminum according to the conventional process, and adopt "slag-free tapping" to reduce the slag volume to less than 5 kg / t. During tapping, add a certain amount of lime to dilute FeO, control the addition sequence of alloys, add Si and Mn alloys with oxides that are easy to remove first, and finally add a small amount of Al;

[0014] RH vacuum treatment: First, carry out RH vacuum treatment and then LF treatment. Utilize the vacuum condition to remove as much oxygen as possible from the molten steel, so that the oxygen in the molten steel is as low as possible before final deoxidization with aluminum. In this way, the Al2O3 inclusions generated by deoxidization with aluminum in the molten steel will be less, which is very beneficial to improving the purity of the molten steel. At the same time, due to the reduction of aluminum deoxidization, the process treatment cost is reduced;

[0015] LF refining: In LF refining, the slag-making amount of the refining furnace should meet the requirements of refining effect, the alkalinity is maintained between 2.0 - 2.5, the white slag holding time is not less than 5 min before tapping, the molten steel composition is qualified, the slag is white, the deoxidization is good, and the temperature meets the temperature required for continuous casting. When the composition meets the standard, the molten steel can be tapped;

[0016] VD vacuum degassing: The vacuum degree ≤ 0.10 Kpa, the deep vacuum time ≥ 13 min. After breaking the vacuum, feed 150 m of calcium-silicon wire, and the soft blowing time is greater than 10 min. The molten steel shall not be exposed during soft blowing;

[0017] Continuous casting: In order to obtain high-quality continuous casting billets, it is required to cast at a low overheat casting speed, and constant casting speed control electromagnetic stirring is adopted during continuous casting;

[0018] Casting billet: During the heating of the casting billet in the heating furnace, control the total heating time to 3.5 h, the rolling starting temperature is 1100 - 1200 °C, the temperature difference of the same steel billet is not more than 50 °C, and subsequent round steel rolling can be carried out. The heat treatment system is quenching at 950 °C for 90 min and tempering at 600 °C for 120 min.

[0019] Furthermore, in LF refining, 0.3 kg of Ca-Si wire is fed per ton of steel, the speed is 80 - 120 m / min, and after wire feeding, soft blowing with argon is not less than 5 min, and then the argon is turned off and the ladle is lifted.

[0020] Furthermore, LF refining adopts three-furnace refining, and different temperatures are controlled for the three furnaces. The first furnace is between 1590 - 1610 °C, the second furnace is between 1580 - 1600 °C; the third furnace and subsequent furnaces are between 1570 - 1590 °C.

[0021] Furthermore, during continuous casting, the average overheat ΔT of the molten steel is controlled between 32 - 48 °C.

[0022] Furthermore, the continuous casting process includes the following steps;

[0023] Temperature of molten steel in the ladle: 1515 - 1535 °C;

[0024] Tundish liquid level: operating liquid level is 700 - 800 mm, remaining liquid level for casting is 200 - 250 mm;

[0025] Casting speed: for a rectangular billet of 320 mm × 415 mm, starting casting speed is 0.6 m / min, reaching normal casting speed of 1.6 - 2.5 m / min within 3 min, and slow cooling in a slow cooling pit for 48 h.

[0026] Application of a production method of rare earth hot - rolled round steel 25MnCrNiMoA - RE for coupler yokes. The production method of rare earth hot - rolled round steel 25MnCrNiMoA - RE for coupler yokes is applied to the smelting and rolling of connectors between railway vehicles to improve their mechanical properties, internal and external quality.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] For the hot - rolled round steel for coupler yokes with specific components, the present invention determines a more precise production method. The hot - rolled round steel for coupler yokes produced in this way is more durable, providing overall service life and use safety.

[0029] The method of producing rare earth hot - rolled round steel 25MnCrNiMoA - RE by converter → LF → continuous casting in the present invention is feasible, and the mechanical properties, microstructure and macro - inspection of the steel meet the standard requirements.

[0030] The method of producing rare earth hot - rolled round steel 25MnCrNiMoA - RE by converter → LF → continuous casting in the present invention has low cost and high efficiency, and has good economic and social benefits. Specific embodiments

[0031] In order to enable those skilled in the art of this technology to better understand the technical solutions in the embodiments of the present invention, and to make the above - mentioned objects, features and advantages of the present invention more obvious and understandable, the following further describes the specific embodiments of the present invention.

[0032] The endpoints and any values disclosed in the ranges in this article are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article.

[0033] A production method of rare earth hot-rolled round steel 25MnCrNiMoA-RE for coupler yokes, characterized in that; the mass percentage content of its chemical composition includes: C 0.24% - 0.28%, Si 0.20% - 0.40%, Mn 0.90% - 1.10%, P ≤ 0.025%, S ≤ 0.025%, Cr 0.20% - 0.30%, Mo 0.10% - 0.20%, Ni 0.15% - 0.30%, Re 0.030% - 0.040%, and the rest is Fe and inevitable impurities, and the total mass fraction is 100%. Specific Example 1:

[0034] A production method of rare earth hot-rolled round steel 25MnCrNiMoA-RE for coupler yokes, the mass percentage content of its chemical composition includes: C 0.24%, Si 0.27%, Mn 1.05%, P 0.0024%, S 0.0087%, Cr 0.27%, Mo 0.12%, Ni 0.25%, RE 0.036%, and the rest is Fe and inevitable impurities, and the total mass fraction is 100%.

[0035] In the 25MnCrNiMoA, the contents of P and S are low, P ≤ 0.020%, S < 0.003%.

[0036] Specifically, it includes the following steps;

[0037] Converter smelting: Adopt top-bottom combined blowing converter for smelting, all use pre-desulfurized hot metal, the carbon content in the converter tapping shall not be greater than 0.15%, the carbon content of the converter end molten steel is controlled between 0.08% - 0.15%, use SiMn, MnFe and CrFe for deoxidation alloying, and use Al for final deoxidation;

[0038] The slag in the converter contains about 18% of FeO. According to the conventional tapping method, the slag volume is 5 - 10 kg / t;

[0039] And deoxidize with aluminum according to the conventional process, adopt "slag-free tapping" to reduce the slag volume to less than 5 kg / t. When tapping, add a certain amount of lime to dilute FeO, control the addition order of the alloy, add the Si and Mn alloys with oxides that are easy to remove first, and finally add a small amount of Al;

[0040] RH vacuum treatment: First, go through RH vacuum treatment and then through LF treatment. Use the vacuum condition to remove as much oxygen as possible from the molten steel, so that the oxygen in the molten steel before final deoxidation with aluminum is as low as possible. In this way, the Al2O3 inclusions generated by deoxidation with aluminum in the molten steel will be less, which is very beneficial to improving the purity of the molten steel. At the same time, due to the reduction of aluminum deoxidation, the process treatment cost is reduced;

[0041] LF Refining: During LF refining, the slag-making amount in the refining furnace should meet the requirements of refining effect, the alkalinity should be maintained between 2.1, the white slag holding time should be not less than 5 minutes before tapping. The molten steel should have qualified composition, white slag, good deoxidation, and the temperature should meet the requirements of continuous casting. When the composition meets the standard, the molten steel can be tapped.

[0042] VD Vacuum Degassing: The vacuum degree ≤ 0.060 Kpa, the deep vacuum time is 18 minutes. After breaking the vacuum, 150 m of calcium-silicon wire is fed, the soft blowing time is more than 10 minutes, and the molten steel should not be exposed during soft blowing.

[0043] Continuous Casting: In order to obtain high-quality continuous casting billets, it is required to pour at a low overheat casting speed, and constant casting speed control and electromagnetic stirring are adopted during continuous casting.

[0044] Casting Billet: During the heating of the casting billet in the heating furnace, the total heating time is controlled at 3.5 h, the rolling start temperature is 1100 °C, the temperature difference of the same steel billet is not more than 50 °C, and then the subsequent round steel rolling can be carried out. The heat treatment system is quenching at 950 °C for 90 minutes and tempering at 600 °C for 120 minutes.

[0045] During LF refining, 0.3 kg of Ca-Si wire is fed per ton of steel at a speed of 80 m / min. After wire feeding, soft blowing with argon is carried out for not less than 5 minutes, and then the argon is turned off and the ladle is lifted.

[0046] LF refining adopts three-furnace refining, and different temperatures are controlled for the three furnaces. The first furnace is between 1610 °C, the second furnace is between 1580 °C; the third furnace and subsequent furnaces are between 1570 °C.

[0047] During continuous casting, the average overheat ΔT of the molten steel is controlled at 32 °C.

[0048] The continuous casting process includes the following steps;

[0049] Liquid steel temperature in the ladle: 1535 °C;

[0050] Tundish liquid level: The working liquid level is 700 mm, and the remaining liquid level after pouring is 200 mm;

[0051] Casting speed: For a rectangular billet of 320 mm × 415 mm, the starting casting speed is 0.6 m / min, and it reaches the normal casting speed of 2.5 m / min within 3 minutes, and then it enters the slow cooling pit for slow cooling for 48 h.

[0052] The mechanical property indexes of each example of the hook tail frame made of rare earth hot-rolled round steel are shown in the following table;

[0053] Specific Example Two:

[0055] Production method of rare earth hot-rolled round steel 25MnCrNiMoA-RE for coupler yokes, the mass percentage content of its chemical composition includes: C 0.28%, Si 0.35%, Mn 1.02%, P 0.0086%, S 0.0065%, Cr 0.24%, Mo 0.13%, Ni 0.28%, RE 0.039%, and the rest are Fe and inevitable impurities, and the total mass fraction is 100%.

[0056] Production method of rare earth hot-rolled round steel 25MnCrNiMoA-RE for coupler yokes specifically includes the following steps;

[0057] Converter smelting: Adopt top-bottom combined blown converter for smelting, all use pre-desulfurized hot metal, the carbon content in the converter tapping shall not be greater than 0.15%, the carbon content of the converter end molten steel is controlled at 0.15%, use SiMn, MnFe and CrFe for deoxidation alloying, and use Al for final deoxidation;

[0058] The slag in the converter contains about 18% of FeO. According to the conventional tapping method, the slag volume is 5-10 kg / t;

[0059] And deoxidize with aluminum according to the conventional process, adopt "slag-free tapping" to reduce the slag volume to less than 5 kg / t. When tapping, add a certain amount of lime to dilute FeO, control the addition order of alloys, add Si and Mn alloys with oxides that are easy to remove first, and finally add a small amount of Al;

[0060] RH vacuum treatment: First, carry out RH vacuum treatment and then LF treatment. Use the vacuum condition to remove as much oxygen in the molten steel as possible, so that the oxygen in the molten steel is as low as possible before final deoxidation with aluminum. In this way, the Al2O3 inclusions generated by deoxidation with aluminum in the molten steel will be less, which is very beneficial to improving the purity of the molten steel. At the same time, due to the reduction of aluminum deoxidation, the process treatment cost is reduced;

[0061] LF refining: In LF refining, the slag-making amount in the refining furnace should meet the requirements of refining effect, the alkalinity is maintained at 2.2, the white slag holding time is not less than 5 min before tapping, the molten steel composition is qualified, the slag is white, the deoxidation is good, and the temperature meets the temperature required for continuous casting. The molten steel can be tapped when the composition meets the standard;

[0062] VD vacuum degassing: The vacuum degree is 0.070 Kpa, the deep vacuum time is 23 min. After breaking the vacuum, feed 150 m of silicon-calcium wire, and the soft blowing time is greater than 10 min. The molten steel shall not be exposed during soft blowing;

[0063] Continuous casting: In order to obtain high-quality continuous casting billets, it is required to pour at a low overheat casting speed, and adopt constant casting speed control and electromagnetic stirring during continuous casting;

[0064] Billet: During the heating process in the billet heating furnace, control the total heating time to 3.5 h, the starting rolling temperature to 1200 °C, and the temperature difference of the same billet to no more than 50 °C. Then, subsequent round steel rolling can be carried out. The heat treatment system is quenching at 950 °C for 90 min and tempering at 600 °C for 120 min.

[0065] During LF refining, 0.3 kg of Ca-Si wire is fed per ton of steel at a speed of 100 m / min. After wire feeding, soft blowing of argon is carried out for no less than 5 min, and then the argon is turned off and the ladle is lifted.

[0066] LF refining adopts three-furnace refining, and different temperatures are controlled for the three furnaces. The first furnace is between 1600 °C, the second furnace is between 1580 °C; the third furnace and subsequent furnaces are between 1570 °C.

[0067] During continuous casting, the average superheat ΔT of the molten steel is controlled at 48 °C.

[0068] The continuous casting process includes the following steps;

[0069] Liquid steel temperature in the ladle: 1530 °C;

[0070] Tundish liquid level: working liquid level 750 mm, remaining liquid level 220 mm;

[0071] Drawing speed: For a rectangular billet of 320 mm × 415 mm, the starting drawing speed is 0.6 m / min, and it reaches the normal drawing speed of 2.2 m / min within 3 min, and then enters the slow cooling pit for slow cooling for 48 h.

[0072] The mechanical property indexes of each example of the rare earth hot-rolled round steel for the hook tail frame are shown in the following table;

[0073] Specific Example 4:

[0075] An application of the production method of rare earth hot-rolled round steel 25MnCrNiMoA-RE for the hook tail frame. The production method of rare earth hot-rolled round steel 25MnCrNiMoA-RE for the hook tail frame is applied to the connection parts between train vehicles during smelting and rolling, so as to improve its mechanical properties, internal and external quality.

[0076] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention.

[0077] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only includes an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A production method of rare earth hot-rolled round steel 25MnCrNiMoA-RE for coupler yokes, characterized in that ； The mass percentage content of its chemical components includes: C 0.24% - 0.28%, Si 0.20% - 0.40%, Mn 0.90% - 1.10%, P ≤ 0.025%, S ≤ 0.025%, Cr 0.20% - 0.30%, Mo 0.10% - 0.20%, Ni 0.15% - 0.30%, Re 0.030% - 0.040%, and the rest is Fe and inevitable impurities, and the total mass fraction is 100%.

2. The production method of the rare earth hot-rolled round steel for the coupler yoke according to claim 1, characterized in that; In the 25MnCrNiMoA, the contents of P and S are low, P ≤ 0.020%, and S < 0.003%.

3. The production method of the rare earth hot-rolled round steel 25MnCrNiMoA-RE for the coupler yoke according to claim 2, characterized in that; The mass percentage content of its chemical components includes: C 0.24%, Si 0.27%, Mn 1.05%, P 0.0024%, S 0.0087%, Cr 0.27%, Mo 0.12%, Ni 0.25%, RE 0.036%, and the rest is Fe and inevitable impurities, and the total mass fraction is 100%.

4. The production method of the rare earth hot-rolled round steel 25MnCrNiMoA-RE for the coupler yoke according to claim 2, characterized in that; The mass percentage content of its chemical components includes: C 0.28%, Si 0.35%, Mn 1.02%, P 0.0086%, S 0.0065%, Cr 0.24%, Mo 0.13%, Ni 0.28%, RE 0.039%, and the rest is Fe and inevitable impurities, and the total mass fraction is 100%.

5. The production method of the rare earth hot-rolled round steel 25MnCrNiMoA-RE for the coupler yoke according to any one of claims 1-4, characterized in that; Specifically, it includes the following steps; Converter smelting: Adopt top-bottom combined blowing converter for smelting, all use pre-desulfurized hot metal. The carbon content of the converter tapping steel shall not be greater than 0.15%. The carbon content of the converter end molten steel is controlled between 0.08% - 0.15%. Use SiMn, MnFe, and CrFe for deoxidation alloying, and use Al for final deoxidation; The slag in the converter contains about 18% of FeO. According to the conventional tapping method, the slag volume is 5 - 10 kg / t; And deoxidize with aluminum according to the conventional process, adopt "slag-free tapping" to reduce the slag volume to less than 5 kg / t. When tapping, add a certain amount of lime to dilute FeO, control the order of adding alloys, add Si and Mn alloys with oxides that are easy to remove first, and finally add a small amount of Al; RH vacuum treatment: First, go through RH vacuum treatment and then through LF treatment. Utilize the vacuum condition to remove as much oxygen as possible from the molten steel, so that the oxygen in the molten steel is as low as possible before final deoxidation with aluminum. In this way, the Al2O3 inclusions generated by deoxidation with aluminum in the molten steel will be less, which is very beneficial to improving the purity of the molten steel. At the same time, due to the reduction of aluminum deoxidation, the process treatment cost is reduced; LF refining: In LF refining, the slag-making amount of the refining furnace should meet the requirements of refining effect, the alkalinity is maintained between 2.0 - 2.5, the white slag holding time is not less than 5 min before tapping. When the molten steel composition is qualified, the slag is white, the deoxidation is good, and the temperature meets the temperature required for continuous casting, and the composition meets the standard, then it can be tapped; VD vacuum degassing: The vacuum degree ≤ 0.10 Kpa, the deep vacuum time ≥ 13 min. After breaking the vacuum, feed 150 m of silicon-calcium wire, and the soft blowing time is greater than 10 min. The molten steel shall not be exposed during soft blowing; Continuous casting: To obtain high-quality continuous casting billets, it is required to pour at a low overheat temperature and a constant casting speed, and electromagnetic stirring is adopted with constant casting speed control during continuous casting; Billet: During the heating of the billet in the heating furnace, the total heating time is controlled at 3.5 h, the rolling start temperature is 1100 - 1200 °C, the temperature difference of the same steel billet is not more than 50 °C, and subsequent round steel rolling can be carried out. The heat treatment system is quenching at 950 °C for 90 min and tempering at 600 °C for 120 min.

6. The production method of the rare earth hot-rolled round steel 25MnCrNiMoA-RE for the tail hook box according to claim 5, characterized in that ; During LF refining, 0.3 kg of Ca-Si wire is fed per ton of steel at a speed of 80 - 120 m / min. After wire feeding, soft blowing of argon is carried out for not less than 5 min, and then the argon is turned off and the ladle is lifted.

7. The production method of the rare earth hot-rolled round steel 25MnCrNiMoA-RE for the coupler yoke according to claim 6, characterized in that; LF refining adopts three-hearth refining, and different temperatures are controlled for the three hearths. The first hearth is between 1590 - 1610 °C, the second hearth is between 1580 - 1600 °C; the third hearth and subsequent hearths are between 1570 - 1590 °C.

8. The production method of the rare earth hot-rolled round steel 25MnCrNiMoA-RE for the coupler yoke according to claim 7, characterized in that; During the continuous casting process, the average overheat temperature ΔT of the molten steel is controlled between 32 - 48 °C.

9. The production method of the rare earth hot-rolled round steel 25MnCrNiMoA-RE for the tail hook frame according to claim 5, characterized in that; The continuous casting process includes the following steps; Liquid steel temperature in the ladle: 1515 - 1535 °C; Tundish liquid level: The working liquid level is 700 - 800 mm, and the remaining liquid level after casting is 200 - 250 mm; Casting speed: For a rectangular billet of 320 mm × 415 mm, the starting casting speed is 0.6 m / min, and it reaches the normal casting speed of 1.6 - 2.5 m / min within 3 min, and then enters the slow cooling pit for slow cooling for 48 h.

10. An application of the production method of rare earth hot-rolled round steel 25MnCrNiMoA-RE for coupler yokes according to any one of claims 1-9, characterized in that; The production method of the hook tail frame made of rare earth hot-rolled round steel 25MnCrNiMoA-RE according to any one of claims 1 - 9 is applied to the smelting and rolling of the connectors between railway vehicles to improve their mechanical properties, internal and external quality.

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