Heat treatment process and application of hot-rolled round steel for coupler yoke

Abstract

The invention discloses a heat treatment process and application of hot-rolled round steel for a coupler yoke, and the heat treatment process comprises the following steps: putting a rough-machined rare-earth microalloyed 25MnCrNiMoA hot-rolled round steel blank sample for the coupler yoke into a heating furnace for solution treatment, then carrying out quenching and water cooling by using water, and stirring by using a pipeline type impeller during water cooling, a medium stirred by an impeller flows to a fire workpiece through a pipeline system, the flow speed of the medium can be changed by changing the rotating speed of a stirring motor through a pipeline type impeller stirrer, so that the cooling speed of the medium is changed, normalizing treatment is carried out after solution treatment, 25MnCrNiMoA is heated to 840-880 DEG C, heat preservation is carried out for 120 min, and then a sample is taken out and rapidly cooled in a water cooling or oil cooling mode. And the normalized 25MnCrNiMoA is subjected to tempering treatment, the tempering temperature range is 580 DEG C + / -20 DEG C, and the heat preservation time is 120 min, so that the required mechanical property and structure are obtained.

Description

Technical Field

[0001] The present invention relates to the field of industrial technologies, and particularly relates to a heat treatment process and application of hot-rolled round steel for a coupler yoke. Background Art

[0002] In recent years, the high-speed railways in China have developed rapidly. With the increase in the train speed and load, the quality requirements for the parts at the key positions of the train have also increased accordingly. The coupler buffer device is a device in railway vehicles that enables the connection, traction between vehicles and cushions the impact force during train operation. The coupler yoke is an important part of the coupler device. When the vehicle is towing, coupling and buffering, the coupler yoke will complete the longitudinal force transmission between vehicles and often bear huge impact loads during work. Due to its complex shape, the traditional coupler yokes are all produced by casting. However, casting workpieces often have defects such as pores, sand holes, shrinkage cavities, cold laps, etc., and the density of casting workpieces is lower than that of forging workpieces, and their strength and toughness cannot meet the requirements of high-speed railway trains. If the coupler yoke cracks during the train's travel, it will cause serious accidents and pose a great threat to railway transportation safety.

[0003] Therefore, in view of the above factors, in order to meet the needs of high-speed trains, a heat treatment process and application of hot-rolled round steel for a coupler yoke are developed. For the hot-rolled round steel for a coupler yoke with specific components, through the influence of different heat treatment parameters on the performance, a more accurate heat treatment system is determined, and the hot-rolled round steel for a coupler yoke produced is more durable, providing the overall service life and use safety. Summary of the Invention

[0004] The present invention aims to make up for the deficiencies of the prior art and provides a heat treatment process and application of hot-rolled round steel for a coupler yoke, so that it has good comprehensive mechanical properties and low-temperature impact toughness, thereby significantly improving the overall service life and safety of the steel for a coupler yoke.

[0005] The object of the present invention is to provide a heat treatment process of hot-rolled round steel for a coupler yoke. The chemical components of the hot-rolled round steel for a coupler yoke include 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%;

[0006] The mixed molten iron is desulfurized and slagged in the hot metal desulfurization and slagging station by injecting magnesium powder and lime powder. After desulfurization and slagging of the hot metal, [S]≤0.005%, and it is required that the temperature of the hot metal entering the converter is ≥1300°C;

[0007] Smelted in an 180t top and bottom combined blown converter, with the hot metal addition accounting for 90% and the scrap steel approximately 10%. Control the carbon content of the molten steel at the end of blowing to be not less than 0.10% and the phosphorus content not more than 0.015%. Use a slag stopper to block the slag during tapping to control the ladle slag volume. Add a composite deoxidizer for deoxidation during tapping and modify the top slag of the ladle;

[0008] At the LF station, complete operations such as adjusting the temperature and chemical composition of the molten steel, deoxidizing and desulfurizing, and removing inclusions. The LF slag-making refining should produce a reducing slag, and the holding time under the reducing slag should be not less than 15 minutes. The whole process involves bottom argon stirring of the ladle to ensure that inclusions float up sufficiently to ensure the purity of the molten steel. Add alloys to fine-tune the composition to meet the target composition. After the chemical composition and temperature of the molten steel are qualified, perform RH vacuum treatment;

[0009] Seal the tundish well to prevent secondary oxidation and gas absorption of the molten steel. To prevent the "white spot" defect in the steel, control the [H] in the tundish molten steel ≤ 3×10-6;

[0010] If the temperature of the tundish molten steel is too high, the central porosity of the continuous casting billet will be aggravated, and shrinkage cavities will appear in severe cases; if the temperature is too low, the fluidity of the molten steel is poor, which is not conducive to the melting of the mold powder and the removal of inclusions in the steel. Therefore, the superheat of the tundish molten steel is controlled within the range of 25±5°C;

[0011] The rectangular billet continuous casting machine is an arc continuous casting machine, four machines and four strands. Adopt submerged entry nozzle casting to avoid a large amount of nitrogen increase during the casting process. Control the starting casting tonnage, reasonably use the secondary cooling water system, control the casting speed at 0.5m / min, ensure the constancy of the casting speed, turn on the mold electromagnetic stirrer, the electromagnetic stirring current is 480A, turn on the electromagnetic stirring at the end of solidification, the electromagnetic stirring current is 450A, and put into the operation of light reduction of the continuous casting billet, with the reduction amount of 9mm;

[0012] Put the rough processed rare earth microalloyed 25MnCrNiMoA coupler yoke blank sample made of hot rolled round steel into the heating furnace for solution treatment. Heat up to 860°C - 890°C±10°C, hold for 50 minutes, and then quench with water. During water cooling, use a pipe type impeller stirrer. The medium of the impeller stirrer flows through the pipeline system to the workpiece. The pipe type impeller stirrer can change the flow rate of the medium by changing the rotation speed of the stirring motor, thereby changing its cooling rate;

[0013] After solution treatment, perform normalizing treatment. Heat 25MnCrNiMoA to 590°C±10°C or 840°C - 880°C, hold for 120 minutes, and then take out the sample and quickly cool it by water cooling or oil cooling;

[0014] The 25MnCrNiMoA after normalizing treatment is subjected to tempering treatment. The tempering temperature range is 150°C - 350°C or 580°C ± 20°C, and the holding time is 120 minutes to obtain the required mechanical properties and microstructure.

[0015] Furthermore, the steel for the 25MnCrNiMoA coupler yoke has low P and S contents, P ≤ 0.010%, S < 0.003%. Among them, the steel for the 25MnCrNiMoA coupler yoke also includes that the sum of W, V, and Ti ≤ 0.02%.

[0016] Furthermore, during quenching, the medium is clear water at 10 - 35°C, and the time interval between quenching and tempering treatments is less than 8 hours.

[0017] Furthermore, the rough - machined hot - rolled round steel blank sample of rare - earth micro - alloyed 25MnCrNiMoA for the coupler yoke is put into a heating furnace for solution treatment. It is heated to 860°C and held for 50 minutes, and then quenched with water (water - cooling). During water - cooling, a pipe - type impeller stirrer is used. The medium of the impeller stirrer flows through the pipe system to the workpiece. The pipe - type impeller stirrer can change the flow rate of the medium by changing the rotation speed of the stirring motor, thereby changing its cooling rate.

[0018] After solution treatment, normalizing treatment is carried out. The 25MnCrNiMoA is heated to 880°C, held for 120 minutes, and then the sample is taken out and rapidly cooled by water - cooling or oil - cooling.

[0019] The 25MnCrNiMoA after normalizing treatment is subjected to tempering treatment. The tempering temperature range is 350°C, and the holding time is 120 minutes to obtain the required mechanical properties and microstructure.

[0020] Furthermore, the rough - machined hot - rolled round steel blank sample of rare - earth micro - alloyed 25MnCrNiMoA for the coupler yoke is put into a heating furnace for solution treatment. It is heated to 890°C ± 10°C, held for 50 minutes, and then quenched with water (water - cooling). During water - cooling, a pipe - type impeller stirrer is used. The medium of the impeller stirrer flows through the pipe system to the workpiece. The pipe - type impeller stirrer can change the flow rate of the medium by changing the rotation speed of the stirring motor, thereby changing its cooling rate.

[0021] The 25MnCrNiMoA after the above - mentioned treatment is subjected to tempering treatment. The tempering temperature range is 580°C, and the holding time is 120 minutes to obtain the required mechanical properties and microstructure.

[0022] Further, the rough-rolled round steel blank sample of rare earth microalloyed 25MnCrNiMoA coupler yokes after processing is placed in a heating furnace, heated to 890 °C, held for 50 min, and then quenched with water; the quenched sample is placed in a heating furnace, heated to 590 °C, held for 90 min, and then the sample is taken out and water-cooled.

[0023] Further, the rough-rolled round steel blank sample of rare earth microalloyed 25MnCrNiMoA coupler yokes after processing is placed in a heating furnace, heated to 910 °C, held for 50 min, and then quenched with water; the quenched sample is placed in a heating furnace, heated to 600 °C, held for 90 min, and then the sample is taken out and water-cooled.

[0024] An application of a heat treatment process for hot-rolled round steel for coupler yokes, applying the heat treatment process of hot-rolled round steel for coupler yokes to the field of hot-rolled round steel manufacturing, particularly relating to the coupler buffer device of railway vehicles.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] For the hot-rolled round steel for coupler yokes with specific components, through the influence of different heat treatment parameters on the performance, the present invention determines a more precise heat treatment system. The produced hot-rolled round steel for coupler yokes is more durable, providing overall service life and use safety.

[0027] The present invention uses a pipe-type impeller stirring method. The medium stirred by the impeller flows towards the workpiece through a pipe system. By changing the rotation speed of the stirring motor through the pipe-type impeller stirrer, the flow rate of the medium can be changed, thereby changing its cooling rate, ensuring the uniformity of the material structure, and solving the problem of unstable performance caused by temperature fluctuations in the traditional process.

[0028] By narrowing the temperature control range and reducing the holding time, the present invention reduces energy consumption, improves production efficiency, and at the same time, on the premise of ensuring mechanical properties, enhances the economy and environmental protection of heat treatment. Specific Embodiments

[0029] 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 make the above-mentioned objects, features, and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention are further described below.

[0030] In the ranges disclosed herein, the endpoints and any values 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 herein.

[0031] A heat treatment process for hot-rolled round steel used for coupler yokes. The chemical composition of the hot-rolled round steel for coupler yokes 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%.

[0032] The hot metal mixture is desulfurized and slagged at the hot metal desulfurization and slag removal station by injecting magnesium powder and lime powder. After desulfurization and slag removal, [S] ≤ 0.005% in the hot metal, and the temperature of the hot metal entering the converter is required to be ≥ 1300°C.

[0033] Smelting is carried out in a 180t top-bottom combined blowing converter. The hot metal addition accounts for 90%, and the scrap accounts for about 10%. Control the carbon content of the molten steel at the end of blowing to be not less than 0.10% and the phosphorus content to be not more than 0.015%. During tapping, a slag stopper is used to stop the slag and control the slag amount in the ladle. During tapping, a composite deoxidizer is added for deoxidation, and the top slag of the ladle is modified.

[0034] At the LF station, operations such as adjusting the temperature and chemical composition of the molten steel, deoxidation, desulfurization, and removal of inclusions are completed. The LF slag-making refining should produce a reducing slag, and the holding time under the reducing slag should be not less than 15 minutes. The whole process is stirred by bottom blowing argon in the ladle to ensure that inclusions float up sufficiently to ensure the purity of the molten steel. Alloys are added to fine-tune the composition to meet the target composition. After the chemical composition and temperature of the molten steel are qualified, RH vacuum treatment is carried out.

[0035] The tundish is well sealed to prevent secondary oxidation and gas absorption of the molten steel. To prevent the "white spot" defect in the steel, control [H] ≤ 3×10-6 in the tundish molten steel.

[0036] If the temperature of the molten steel in the tundish is too high, the central porosity of the continuous casting billet will be aggravated, and shrinkage cavities will appear in severe cases; if the temperature is too low, the fluidity of the molten steel will be poor, which is not conducive to the melting of the mold powder and the removal of inclusions in the steel. The superheat of the molten steel in the tundish is controlled within the range of 25 ± 5°C.

[0037] The rectangular billet continuous caster is an arc continuous caster, four machines and four strands. Submerged entry nozzle casting is adopted to avoid a large amount of nitrogen pickup during casting. Control the starting casting tonnage, reasonably use the secondary cooling water system, control the casting speed at 0.5 m / min, ensure the casting speed is constant, turn on the mold electromagnetic stirrer, the electromagnetic stirring current is 480 A, turn on the electromagnetic stirrer at the end of solidification, the electromagnetic stirring current is 450 A, and carry out the soft reduction operation of the continuous casting billet, with the reduction amount being 9 mm.

[0038] Put the rough-rolled rare earth microalloyed 25MnCrNiMoA coupler yoke blank round steel sample into a heating furnace for solution treatment. Heat it up to 860°C - 890°C ± 10°C, hold for 50 minutes, and then quench it with water by water cooling. During water cooling, use a pipeline type impeller for stirring. The medium for impeller stirring flows through the pipeline system to the workpiece. By changing the rotation speed of the stirring motor through the pipeline type impeller stirrer, the flow rate of the medium can be changed, thereby changing its cooling rate;

[0039] After solution treatment, perform normalizing treatment. Heat 25MnCrNiMoA to 590°C ± 10°C or 840°C - 880°C, hold for 120 minutes, and then take out the sample and quickly cool it by water cooling or oil cooling;

[0040] Perform tempering treatment on the 25MnCrNiMoA after normalizing treatment. The tempering temperature range is 150°C - 350°C or 580°C ± 20°C, and the holding time is 120 minutes to obtain the required mechanical properties and microstructure.

[0041] In order to facilitate improving the purity of the steel and its subsequent durability in the use state, the steel for the 25MnCrNiMoA coupler yoke not only has low P and S contents, P ≤ 0.010%, S < 0.003%, and in addition, the sum of W, V, and Ti in the steel for the 25MnCrNiMoA coupler yoke is ≤ 0.02%.

[0042] In order to avoid the stress formed during quenching not being eliminated in time in the use state, the medium for quenching is clear water at 10 - 35°C, and the time interval between quenching and tempering treatment is less than 8 hours. Specific Example 1:

[0044] A heat treatment process for hot-rolled round steel for coupler yokes. The chemical composition of the hot-rolled round steel for coupler yokes 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%;

[0045] The mixed hot metal is desulfurized and slagged at the hot metal desulfurization and slag removal station by injecting magnesium powder and lime powder. After desulfurization and slag removal of the hot metal, [S] ≤ 0.005%, and the temperature of the hot metal entering the converter is required to be ≥ 1300°C;

[0046] Smelted in an 180t top and bottom combined blown converter, with the hot metal addition accounting for 90% and scrap steel about 10%. Control the carbon content of the molten steel at the end of blowing to be not less than 0.10% and the phosphorus content not more than 0.015%. Use a slag stopper to stop slag during tapping to control the ladle slag volume. Add a composite deoxidizer for deoxidation during tapping and modify the ladle top slag;

[0047] At the LF station, adjust the temperature and chemical composition of the molten steel, deoxidize and desulfurize, and remove inclusions. The LF slag-making refining should produce a reducing slag and maintain it for not less than 15 minutes under the reducing slag. Argon is blown from the bottom of the ladle throughout the process to ensure that inclusions float up sufficiently to ensure the purity of the molten steel. Add alloys to fine-tune the composition to meet the target composition. After the chemical composition and temperature of the molten steel are qualified, perform RH vacuum treatment;

[0048] Seal the tundish well to prevent secondary oxidation and gas absorption of the molten steel. To prevent the "white spot" defect in the steel, control the [H] in the tundish molten steel ≤ 3×10-6;

[0049] If the temperature of the tundish molten steel is too high, the central porosity of the continuous casting billet will increase, and shrinkage cavities will appear in severe cases; if the temperature is too low, the fluidity of the molten steel is poor, which is not conducive to the melting of the mold powder and the removal of inclusions in the steel. The superheat of the tundish molten steel is controlled within the range of 25±5℃;

[0050] The rectangular billet continuous caster is an arc continuous caster, four machines and four strands. Immersion protection casting is adopted to avoid a large amount of nitrogen increase during casting. Control the starting casting tonnage, reasonably use the secondary cooling water system, control the casting speed at 0.5m / min to ensure a constant casting speed. Turn on the mold electromagnetic stirrer with an electromagnetic stirring current of 480A, turn on the electromagnetic stirrer at the end of solidification with an electromagnetic stirring current of 450A, and carry out the light reduction operation of the continuous casting billet with a reduction amount of 9mm;

[0051] The hot-rolled round steel blank sample of the rare earth microalloyed 25MnCrNiMoA hook tail frame after rough machining is put into a heating furnace for solution treatment. Heat up to 860℃, hold for 50 minutes, and then quench with water. During water cooling, a pipeline type impeller stirrer is used. The medium of the impeller stirrer flows through the pipeline system to the workpiece. The pipeline type impeller stirrer can change the flow rate of the medium by changing the rotation speed of the stirring motor, thereby changing its cooling rate;

[0052] After solution treatment, perform normalizing treatment. Heat 25MnCrNiMoA to 880℃, hold for 120 minutes, and then quickly cool the sample by water cooling or oil cooling;

[0053] The 25MnCrNiMoA after normalizing treatment is subjected to tempering treatment. The tempering temperature range is 350℃, and the holding time is 120 minutes to obtain the required mechanical properties and microstructures.

[0054] In the above embodiments, according to different usage states and application environments, solution treatment, normalizing treatment, and tempering treatment are adopted to obtain the required mechanical properties and organizational structures. Specific Embodiment Two:

[0056] A heat treatment process for hot-rolled round steel used for coupler yokes. The chemical composition of the hot-rolled round steel for coupler yokes 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%.

[0057] In the hot metal desulfurization and slag skimming station, the hot metal is subjected to desulfurization and slag skimming treatment by injecting magnesium powder and lime powder. After desulfurization and slag skimming, [S] ≤ 0.005% in the hot metal, and the temperature of the hot metal entering the converter is required to be ≥ 1300°C.

[0058] Smelting is carried out using a 180t top-bottom combined blowing converter. The hot metal addition accounts for 90%, and scrap steel accounts for about 10%. Control the carbon content of the molten steel at the end of blowing to be not less than 0.10% and the phosphorus content to be not more than 0.015%. During tapping, a slag stopper is used to block the slag to control the slag amount in the ladle. During tapping, a composite deoxidizer is added for deoxidation, and the top slag of the ladle is subjected to modification treatment.

[0059] At the LF station, operations such as adjusting the temperature and chemical composition of the molten steel, deoxidation, desulfurization, and removal of inclusions are completed. The LF slag-making refining should produce a reducing slag, and the holding time under the reducing slag should be not less than 15 minutes. The whole process is carried out with bottom argon stirring in the ladle to ensure that inclusions float up sufficiently to ensure the purity of the molten steel. Alloys are added to fine-tune the composition to meet the target composition. After the chemical composition and temperature of the molten steel are qualified, RH vacuum treatment is carried out.

[0060] The tundish is well sealed to prevent secondary oxidation and gas absorption of the molten steel. To prevent the "white spot" defect in the steel, control [H] ≤ 3×10-6 in the tundish molten steel.

[0061] If the temperature of the molten steel in the tundish is too high, the central porosity of the continuous casting billet will be aggravated, and shrinkage cavities will appear in severe cases; if the temperature is too low, the fluidity of the molten steel will be poor, which is not conducive to the melting of the mold powder and the removal of inclusions in the steel. The superheat of the molten steel in the tundish is controlled within the range of 25 ± 5°C.

[0062] The rectangular billet continuous caster is an arc continuous caster, four machines and four strands. Submerged entry nozzle casting is adopted to avoid a large amount of nitrogen increase during casting. Control the starting casting tonnage, reasonably use the secondary cooling water system, control the casting speed at 0.5 m / min to ensure a constant casting speed, turn on the mold electromagnetic stirrer with an electromagnetic stirring current of 480 A, turn on the electromagnetic stirrer at the end of solidification with an electromagnetic stirring current of 450 A, and carry out the soft reduction operation of the continuous casting billet with a reduction amount of 9 mm.

[0063] The hot-rolled round steel blank sample of 25MnCrNiMoA coupler yokes with rare earth microalloying after rough machining is put into a heating furnace for solution treatment, heated to 890°C ± 10°C, held for 50 min, and then quenched with water by water cooling. During water cooling, a pipe-type impeller is used for stirring. The medium for impeller stirring flows through the pipe system to the workpiece. The flow rate of the medium can be changed by changing the rotational speed of the stirring motor through the pipe-type impeller stirrer, thereby changing its cooling rate.

[0064] The 25MnCrNiMoA after the above treatment is subjected to tempering treatment. The tempering temperature range is 580°C, and the holding time is 120 min to obtain the required mechanical properties and microstructure.

[0065] During heat treatment, the loading quantity of workpieces should be determined according to the placement position of workpieces in the furnace and actual production conditions, and adjusted by analyzing the heat treatment effect. In order not to affect the enterprise's production plan, the method of increasing the quenching heating temperature is adopted to make up for the shortage of short local holding time caused by the large loading density of workpieces, without changing the existing loading quantity.

[0066] The above quenching heating temperature is 890°C ± 10°C or 920 + 10°C, and the holding time is 120 min; the time from furnace discharging to water entry is no more than 40 seconds; the water temperature before quenching is controlled at 30°C, and the upper limit of the quenching water temperature cannot be higher than 40°C: the coupler yoke stays in water for about 3 minutes; the water outlet temperature of the workpiece depends on the cooling time and is controlled below 200°C. Tempering should be carried out immediately after quenching.

[0067] The above tempering heating temperature is 570°C ± 10°C, and the holding time is 120 min. After air cooling after furnace discharging, the formulated process specifications need to be further improved after optimizing the heat treatment process parameters and researching the quenching technology. Specific Embodiment Three:

[0069] A heat treatment process for hot-rolled round steel for coupler yokes. The chemical composition of the hot-rolled round steel for coupler yokes 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%.

[0070] The mixed hot metal is subjected to desulfurization and slag skimming treatment by injecting magnesium powder and lime powder in the hot metal desulfurization and slag skimming station. After desulfurization and slag skimming of the hot metal, [S] ≤ 0.005%, and it is required that the temperature of the hot metal entering the converter is ≥ 1300°C.

[0071] Smelted by an 180t top and bottom combined blown converter, with the hot metal addition accounting for 90% and scrap steel about 10%. Control the carbon content of the molten steel at the end of blowing to be not less than 0.10% and the phosphorus content not more than 0.015%. Use a slag stopper to stop slag during tapping to control the ladle slag volume. Add a composite deoxidizer for deoxidation during tapping and modify the top slag of the ladle;

[0072] At the LF station, complete operations such as adjusting the temperature and chemical composition of the molten steel, deoxidizing and desulfurizing, and removing inclusions. The LF slag-making refining should produce a reducing slag and maintain it for not less than 15 minutes under the reducing slag. The whole process is stirred by bottom blowing argon in the ladle to ensure that inclusions float up sufficiently to ensure the purity of the molten steel. Add alloys to fine-tune the composition to meet the target composition. After the chemical composition and temperature of the molten steel are qualified, perform RH vacuum treatment;

[0073] Seal the tundish well to prevent secondary oxidation and gas absorption of the molten steel. To prevent the "white spot" defect in the steel, control the [H] in the tundish molten steel ≤ 3×10-6;

[0074] If the temperature of the tundish molten steel is too high, the center porosity of the continuous casting billet will be aggravated, and shrinkage cavities will appear seriously. If the temperature is too low, the fluidity of the molten steel is poor, which is not conducive to the melting of the mold powder and the removal of inclusions in the steel. The superheat of the tundish molten steel is controlled within the range of 25±5℃;

[0075] The rectangular billet continuous caster is an arc continuous caster, four machines and four strands. Adopt submerged entry nozzle casting to avoid a large amount of nitrogen increase during casting. Control the starting casting tonnage, reasonably use the secondary cooling water system, control the casting speed at 0.5m / min to ensure a constant casting speed. Turn on the mold electromagnetic stirrer with an electromagnetic stirring current of 480A, turn on the electromagnetic stirrer at the end of solidification with an electromagnetic stirring current of 450A, and carry out the soft reduction operation of the continuous casting billet with a reduction amount of 9mm;

[0076] Put the hot-rolled round steel blank sample of the processed rare earth microalloyed 25MnCrNiMoA coupler yoke into a heating furnace, heat it up to 890℃, keep it warm for 50 minutes, and then quench it with water. Put the quenched sample into the heating furnace, heat it to 590℃, keep it warm for 90 minutes, and then take out the sample and perform water cooling.

[0077] The loading quantity of workpieces should be determined according to the placement position of the workpieces in the furnace and the actual production conditions, and adjusted by analyzing the heat treatment effect. In order not to affect the enterprise's production plan, make up for the shortage of short local holding time caused by the large loading density of workpieces by increasing the quenching heating temperature without changing the existing loading quantity.

[0078] The above-mentioned quenching heating temperature is 890 - 920°C, and the holding time is 50 - 120 min; the time from furnace discharging to water immersion is no more than 40 seconds, the water temperature before quenching is controlled at 30°C, the upper limit of the quenching water temperature cannot be higher than 40°C, and the hook tail frame stays in water for about 3 minutes; the workpiece water outlet temperature depends on the cooling time and is controlled below 200°C; tempering should be carried out immediately after quenching.

[0079] The above-mentioned tempering heating temperature is 590°C, and the holding time is 90 - 120 min. After air cooling after furnace discharging, the formulated process specifications need to be further improved after optimizing the heat treatment process parameters and researching the quenching technology. Specific Embodiment Four:

[0081] A heat treatment process for hot-rolled round steel used for hook tail frames. The chemical composition of the hot-rolled round steel used for hook tail frames 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%;

[0082] In the hot metal desulfurization and slag skimming station, the hot metal is subjected to desulfurization and slag skimming treatment by injecting magnesium powder and lime powder. After desulfurization and slag skimming of the hot metal, [S] ≤ 0.005%, and it is required that the temperature of the hot metal entering the converter is ≥ 1300°C;

[0083] Smelting is carried out using a 180t top-bottom combined blowing converter. The hot metal addition accounts for 90%, and the scrap steel accounts for about 10%. Control the carbon content of the molten steel at the end of blowing to be not less than 0.10% and the phosphorus content to be not more than 0.015%. During tapping, a slag stopper is used to block the slag to control the slag amount in the ladle. During tapping, a composite deoxidizer is added for deoxidation, and the top slag of the ladle is modified;

[0084] At the LF station, operations such as adjusting the temperature and chemical composition of the molten steel, deoxidation, desulfurization, and removal of inclusions are completed. The LF slag-making refining should produce a reducing slag, and the holding time under the reducing slag is not less than 15 min. The whole process is carried out with bottom argon stirring in the ladle to ensure that inclusions float up sufficiently to ensure the purity of the molten steel. Alloys are added to fine-tune the composition to meet the target composition. After the chemical composition and temperature of the molten steel are qualified, RH vacuum treatment is carried out;

[0085] The tundish is well sealed to prevent secondary oxidation and gas absorption of the molten steel. To prevent the "white spot" defect in the steel, control the [H] in the tundish molten steel ≤ 3×10-6;

[0086] If the tundish molten steel temperature is too high, the central porosity of the continuous casting billet will be aggravated, and shrinkage cavities will appear seriously; if the temperature is too low, the fluidity of the molten steel is poor, which is not conducive to the melting of the mold powder and the removal of inclusions in the steel. The superheat of the tundish molten steel is controlled within the range of 25 ± 5°C;

[0087] The rectangular billet continuous casting machine is an arc continuous casting machine with four strands and four machines. Immersion protection casting is adopted to avoid a large amount of nitrogen absorption during casting, control the starting pouring tonnage, reasonably use the secondary cooling water system, control the casting speed at 0.5 m / min, ensure the constancy of the casting speed, turn on the mold electromagnetic stirrer with an electromagnetic stirring current of 480 A, turn on the electromagnetic stirring at the end of solidification with an electromagnetic stirring current of 450 A, and put into the operation of slab soft reduction with a reduction amount of 9 mm;

[0088] The hot-rolled round steel blank sample of the rare earth microalloyed 25MnCrNiMoA coupler yoke after rough machining is put into a heating furnace, heated to 910 °C, held for 50 min, and then quenched with water; the quenched sample is put into the heating furnace, heated to 600 °C, held for 90 min, and then the sample is taken out and water-cooled.

[0089] The loading quantity of workpieces should be determined according to the placement position of workpieces in the furnace and actual production conditions, and adjusted by analyzing the heat treatment effect. In order not to affect the production plan of the enterprise, the method of increasing the quenching heating temperature is adopted to make up for the shortage of short local holding time caused by the large loading density of workpieces without changing the existing loading quantity.

[0090] The above-mentioned quenching heating temperature is 890 - 920 °C, and the holding time is 50 - 120 min; the time from furnace discharging to water entry is not more than 40 seconds, the water temperature before quenching is controlled at 30 °C, the upper limit of the quenching water temperature cannot be higher than 40 °C, and the coupler yoke stays in water for about 3 minutes; the water outlet temperature of the workpiece depends on the cooling time and is controlled below 200 °C; tempering should be carried out immediately after quenching.

[0091] The above-mentioned tempering heating temperature is 580 - 620 °C, and the holding time is 90 - 120 min. After air cooling after furnace discharging, the formulated process specifications need to be further improved after optimizing the heat treatment process parameters and researching the quenching technology. Specific Embodiment Five:

[0093] The application of a heat treatment process for hot-rolled round steel for coupler yokes is applied to the field of manufacturing hot-rolled round steel, especially related to the coupler buffer device of railway vehicles.

[0094] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-mentioned 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, it is intended to embrace all changes falling within the meaning and scope of the equivalent elements of the claims within the present invention.

[0095] 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 heat treatment process for hot-rolled round steel used for a coupler yoke, characterized in that; The chemical composition of the hot-rolled round steel for coupler yokes 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%; The hot metal mixture undergoes desulfurization and slag skimming treatment by injecting magnesium powder and lime powder at the hot metal desulfurization and slag skimming station. After desulfurization and slag skimming, [S] ≤ 0.005% in the hot metal, and the temperature of the hot metal entering the converter is required to be ≥ 1300°C; Smelting is carried out using a 180t top-bottom combined blowing converter. The hot metal addition accounts for 90%, and scrap steel accounts for about 10%. Control the carbon content in the molten steel at the end of blowing to be not less than 0.10% and the phosphorus content to be not more than 0.015%. Use a slag stopper to stop the slag during tapping to control the slag volume in the ladle. Add a composite deoxidizer for deoxidation during tapping and modify the top slag of the ladle; At the LF station, adjust the temperature and chemical composition of the molten steel, carry out deoxidation, desulfurization, and inclusion removal operations. The LF slag-making refining should produce a reducing slag, and the holding time under the reducing slag should be not less than 15 minutes. The whole process is carried out with bottom argon stirring in the ladle to ensure that inclusions float up sufficiently to ensure the purity of the molten steel. Add alloys to fine-tune the composition to meet the target composition. After the chemical composition and temperature of the molten steel are qualified, carry out RH vacuum treatment; Seal the tundish well to prevent secondary oxidation and gas absorption of the molten steel. To prevent the "white spot" defect in the steel, control [H] ≤ 3×10-6 in the tundish molten steel; If the temperature of the tundish molten steel is too high, the central porosity of the continuous casting billet will increase, and shrinkage cavities will appear seriously. If the temperature is too low, the fluidity of the molten steel is poor, which is not conducive to the melting of the mold powder and the removal of inclusions in the steel. The superheat of the tundish molten steel is controlled within the range of 25 ± 5°C; The rectangular billet continuous caster is an arc continuous caster, four machines and four strands. Adopt submerged entry nozzle casting to avoid a large amount of nitrogen increase during the casting process. Control the starting casting tonnage, reasonably use the secondary cooling water system, control the casting speed at 0.5m / min, ensure the casting speed is constant, turn on the mold electromagnetic stirrer, the electromagnetic stirring current is 480A, turn on the electromagnetic stirrer at the end of solidification, the electromagnetic stirring current is 450A, and carry out the soft reduction operation of the continuous casting billet, with a reduction amount of 9mm; Put the rough-machined hot-rolled round steel blank sample of rare earth microalloyed 25MnCrNiMoA for coupler yokes into a heating furnace for solution treatment. Heat it up to 860°C - 890°C ± 10°C, hold for 50 minutes, and then quench it with water. During water cooling, use a pipe-type impeller stirrer. The medium of the impeller stirrer flows through the pipe system to the workpiece. The flow rate of the medium can be changed by changing the rotation speed of the stirring motor through the pipe-type impeller stirrer, thereby changing its cooling rate; Carry out normalizing treatment after solution treatment. Heat 25MnCrNiMoA to 590°C ± 10°C or 840°C - 880°C, hold for 120 minutes, and then quickly cool the sample by water cooling or oil cooling; The 25MnCrNiMoA after normalizing treatment is subjected to tempering treatment. The tempering temperature range is 150°C - 350°C or 580°C ± 20°C, and the holding time is 120 min to obtain the required mechanical properties and microstructure.

2. The heat treatment process of the hot-rolled round steel for the coupler yoke according to claim 1, characterized in that; The steel for the 25MnCrNiMoA coupler yoke not only has low P and S contents, P ≤ 0.010%, S < 0.003%, and in addition, the sum of W, V, and Ti in the steel for the 25MnCrNiMoA coupler yoke is ≤ 0.02%.

3. The heat treatment process of the hot-rolled round steel for the coupler yoke according to claim 2, characterized in that; The medium during quenching is clear water at 10 - 35°C, and the time interval between quenching and tempering treatments is less than 8 h.

4. The heat treatment process of the hot-rolled round steel for the coupler yoke according to claim 3, characterized in that; The rough - machined hot - rolled round steel blank sample of rare - earth micro - alloyed 25MnCrNiMoA for the coupler yoke is put into a heating furnace for solution treatment. It is heated to 860°C, held for 50 min, and then quenched with water by water - cooling. During water - cooling, a pipe - type impeller is used for stirring. The medium for impeller stirring flows to the workpiece through the pipe system. The pipe - type impeller stirrer can change the flow rate of the medium by changing the rotation speed of the stirring motor, thereby changing its cooling rate. After solution treatment, normalizing treatment is carried out. The 25MnCrNiMoA is heated to 880°C, held for 120 min, and then the sample is taken out and rapidly cooled by water - cooling or oil - cooling. The 25MnCrNiMoA after normalizing treatment is subjected to tempering treatment. The tempering temperature is 350°C, and the holding time is 120 min to obtain the required mechanical properties and microstructure.

5. The heat treatment process of the hot-rolled round steel for the tail hook frame according to claim 3, characterized in that; The rough - machined hot - rolled round steel blank sample of rare - earth micro - alloyed 25MnCrNiMoA for the coupler yoke is put into a heating furnace for solution treatment. It is heated to 890°C ± 10°C, held for 50 min, and then quenched with water by water - cooling. During water - cooling, a pipe - type impeller is used for stirring. The medium for impeller stirring flows to the workpiece through the pipe system. The pipe - type impeller stirrer can change the flow rate of the medium by changing the rotation speed of the stirring motor, thereby changing its cooling rate. The 25MnCrNiMoA after the above - mentioned treatment is subjected to tempering treatment. The tempering temperature range is 580°C, and the holding time is 120 min to obtain the required mechanical properties and microstructure.

6. The heat treatment process of the hot-rolled round steel for the tail hook frame according to claim 3, characterized in that; The rough - machined hot - rolled round steel blank sample of rare - earth micro - alloyed 25MnCrNiMoA for the coupler yoke is put into a heating furnace, heated to 890°C, held for 50 min, and then quenched with water. The quenched sample is put into a heating furnace, heated to 590°C, held for 90 min, and then the sample is taken out and water - cooled.

7. The heat treatment process of the hot-rolled round steel for the tail hook frame according to claim 3, characterized in that; The rough - machined hot - rolled round steel blank sample of rare - earth micro - alloyed 25MnCrNiMoA for the coupler yoke is put into a heating furnace, heated to 910°C, held for 50 min, and then quenched with water. The quenched sample is put into a heating furnace, heated to 600°C, held for 90 min, and then the sample is taken out and water - cooled.

8. Application of a heat treatment process for the hot-rolled round steel used for the tail hook frame according to claim 1, characterized in that; The heat - treatment process of the hot - rolled round steel for the coupler yoke described in any one of claims 1 - 7 is applied to the field of hot - rolled round steel manufacturing, especially related to the coupler buffer device of railway vehicles.