42CrMoA steel continuous casting billet for high-quality crankshaft and preparation method of 42CrMoA steel continuous casting billet

Abstract

The invention relates to a 42CrMoA steel continuous casting billet for a high-quality crankshaft and a preparation method of the 42CrMoA steel continuous casting billet, and belongs to the technical field of crankshaft steel preparation. In order to solve the problems that an existing continuous casting billet for the crankshaft is uneven in component and poor in density, the invention provides a preparation method of a 42CrMoA steel continuous casting billet for the high-quality crankshaft, in the continuous casting process, the pouring superheat degree is 20-25 DEG C, the pulling speed is 0.65 m / min, the water volume of a crystallizer is 2350 L / min, the M-EMS is 150 A / 2 Hz, the F-EMS is 100 A / 8 Hz, the parameter of tail end soft reduction is 3 / 4 / 3, and the total reduction is 10 mm. The surface of the prepared continuous casting billet is free of cracks, the transverse macroscopic center porosity is smaller than or equal to 1 level, the shrinkage cavity is smaller than or equal to 0.5 level, the middle crack is smaller than or equal to 0.5 level, the overall segregation ranges from 0.904 to 1.071, and synergistic improvement of the component uniformity and density of the 42CrMoA steel continuous casting billet for the crankshaft is achieved.

Description

Technical Field

[0001] This invention belongs to the field of crankshaft steel preparation technology, and particularly relates to a high-quality 42CrMoA steel continuous casting billet for crankshafts and its preparation method. Background Technology

[0002] As one of the core components of an engine, the crankshaft plays a crucial role in converting the reciprocating motion of the piston into rotational motion, and its performance directly affects the engine's operating efficiency, durability, and reliability. Therefore, the selection and quality control of crankshaft steel are of paramount importance. 42CrMoA carbon structural steel, as a high-strength, high-toughness low-alloy steel, is widely used in crankshaft manufacturing in the automotive, shipbuilding, and heavy machinery industries due to its excellent mechanical properties, wear resistance, and fatigue resistance.

[0003] As the starting material for crankshaft manufacturing, the compositional uniformity and density of the continuously cast billet are key factors affecting crankshaft quality. The compositional uniformity of the continuously cast billet ensures that the crankshaft has consistent mechanical properties throughout its length and cross-section, while high density ensures that the crankshaft is less prone to defects such as cracks and deformation during processing and use.

[0004] However, during continuous casting, due to differences in molten steel flow, temperature gradient, and solubility of alloying elements, alloying elements are prone to segregation in the billet, resulting in uneven composition distribution of the crankshaft steel. Gases and non-metallic inclusions that are not completely removed during continuous casting will remain in the continuously cast billet, forming defects such as porosity and inclusions. This not only reduces density but may also become crack initiation points or stress concentration points, seriously affecting the service life of the crankshaft.

[0005] The uneven composition and poor density of continuously cast crankshaft billets not only affect the performance and reliability of crankshafts but also increase manufacturing costs and scrap rates, severely restricting the development of the crankshaft manufacturing industry. With the increasing demands on engine performance from the automotive, shipbuilding, and heavy machinery industries, higher requirements are being placed on the quality of crankshaft steel. Therefore, solving the problems of uneven composition and poor density in continuously cast billets has become crucial for improving crankshaft performance, reducing manufacturing costs, and promoting technological progress in the crankshaft manufacturing industry. Summary of the Invention

[0006] To address the problems of uneven composition and poor density in existing crankshaft continuous casting billets, this invention provides a high-quality 42CrMoA steel continuous casting billet for crankshafts and its preparation method.

[0007] The technical solution of this invention:

[0008] A high-quality crankshaft continuous casting billet of 42CrMoA steel has the following chemical composition: C: 0.39-0.45wt%, Si: 0.17-0.37wt%, Mn: 0.70-0.90wt%, P≤0.015wt%, S: 0.025-0.030wt%, Cr: 1.05-1.20wt%, Mo: 0.18-0.25wt%, Cu≤0.20wt%, As≤0.008wt%, Alt: 0.010-0.020wt%, O≤15ppm, H≤1.5ppm.

[0009] A method for preparing high-quality crankshaft 42CrMoA steel continuous casting billets involves sequentially processing molten iron in a converter or electric furnace, refining with LF, vacuum degassing with VD or RH, and continuous casting. In the continuous casting process, the casting superheat is 20-25℃, the casting speed is 0.65 m / min, the crystallizer water flow rate is 2350 L / min, the specific water content is 0.20 L / kg, and the distribution ratio is 36 / 39 / 25%. The crystallizer vibration parameters are: amplitude: 5.0, amplitude constant: 0, frequency: 150, frequency constant: -15, negative slip ratio: 0.1. The electromagnetic stirring parameters at the beginning are 150 A / 2 Hz, with continuous stirring; the electromagnetic stirring parameters at the end are 100 A / 8 Hz, with alternating stirring, and the alternation time is 10 seconds-3 seconds-10 seconds-3 seconds. The parameters for the final light reduction are 3 / 4 / 3, with a total reduction of 10 mm.

[0010] Furthermore, in the smelting process, the tapped steel is required to have a carbon content of not less than 0.10%, a phosphorus content of ≤0.010%, and a tapping temperature of 1610~1640℃.

[0011] Furthermore, during the steel tapping process of the smelting operation, aluminum ingots are added for precipitation and deoxidation when 30t of steel is tapped, based on the C content. When the carbon content of the tapped steel is 0.10~0.15%, 110kg of aluminum ingots are added per 100t of steel; when the carbon content is 0.16~0.23%, 90kg of aluminum ingots are added per 100t of steel; and when the carbon content is 0.24~0.35%, 70kg of aluminum ingots are added per 100t of steel, ensuring that the alt content at the tap is controlled at 0.020~0.035%.

[0012] Furthermore, during the steel tapping process of the smelting operation, 600 kg of lime per 100 t of steel and 400 kg of deoxidizing and desulfurizing refining slag per 100 t of steel are added when 50 t of steel is tapped; alloying operation is carried out to ensure that the composition of the molten steel leaving the station is C: 0.36~0.39%, Si: 0.18~0.24%, Mn: 0.67~0.73%, and Cr: 1.09~1.15%.

[0013] Furthermore, during the LF refining slag deoxidation process, 200 kg of carboxylic acid per 100 t of steel is added at the start of the first power supply. Aluminum granules of 30 kg per 100 t of steel, carbon powder of 20-30 kg per 100 t of steel, and silicon carbide of 20-30 kg are used for diffusion deoxidation. After mixing, the mixture is added in 2-3 batches. Half of the total amount is added in the first batch, and the remaining half is added within 15 minutes of power supply. The slag white sampling temperature is not lower than 1530℃.

[0014] Furthermore, in order to ensure the purity of the molten steel, the Al content in the LF refining process is adjusted based on the results of the first sampling. When Al ≤ 0.030% in the sample, aluminum wire is used to recover 100% of the Al content to adjust it to 0.035%. After sampling, the white slag operation is maintained. 20~30Kg / 100t steel of silicon carbide and 5~10kg / 100t steel of carbon powder are mixed and added in 2~3 batches for deoxidation, and the composition is adjusted to meet the internal control requirements.

[0015] Furthermore, the second power supply of the LF controls the heating rate according to the production rhythm and the continuous casting ladle time. 10~20kg of silicon carbide per 100t of steel is added in 1~2 batches to maintain white slag. Power is cut off when the temperature is suitable. The overall refining time is not less than 55min and the white slag holding time is not less than 25min. After all the components have entered the internal control, they can be transferred to the next process.

[0016] Furthermore, in the vacuum degassing process, a deep vacuum of ≤67Pa is used, the vacuum holding time is not less than 15min, and after breaking the vacuum, Si-Ca line is fed in at a rate of 60~80m / furnace, with calcium added at 8~12ppm to ensure that the finished product Ca is ≤12ppm; the soft blowing time is not less than 15min, and a ladle of heat-insulating agent and carbonized rice husk are added, with the slag surface slightly moving and the molten steel not exposed.

[0017] Furthermore, the tundish baking temperature during the continuous casting process must be maintained at no more than 300 degrees Celsius for 2.5 hours; the flame should reach 1 / 3 of the tundish wall within 1 hour of the start of the tundish baking, and 2 / 3 of the tundish wall within 1 to 2.5 hours of the start of the tundish baking; the flame should reach the bottom of the tundish with backfire, and the working layer at the bottom of the tundish should turn red before the main fire can be started; the main fire should be combined with air to bake until the specified tundish heat storage temperature is reached; the baking time for the tundish baking is 2.5 hours or more, the baking time for the medium fire is 1.5 hours or more, the baking time for the main fire is 1.5 hours or more, and the total baking time should not exceed 8 hours; the baking time for the stopper rod should not exceed 4 hours; the baking time for the immersion nozzle should not exceed 2 hours; and the temperature in the tundish casting zone should not be lower than 1050 degrees Celsius.

[0018] The beneficial effects of this invention are:

[0019] This invention addresses the problems of uneven composition and poor density in continuously cast billets for crankshafts. Starting from the source of continuous casting, it achieves a synergistic improvement in the uniformity of composition and density of 42CrMoA steel continuously cast billets for crankshafts through the meticulous design and optimization of key parameters such as continuous casting superheat, casting speed, cooling regime, electromagnetic stirring and light reduction.

[0020] This invention significantly improves the compositional uniformity of the 42CrMoA steel continuously cast billet for crankshafts, with overall segregation controlled within a narrow range of 0.952 to 1.071, achieving extreme compositional uniformity and laying a solid foundation for the stability of crankshaft performance. The continuous casting surface of the 42CrMoA steel for crankshafts is crack-free, with transverse low-magnification central porosity ≤1 grade, shrinkage cavities ≤0.5 grade, and intermediate cracks ≤0.5 grade, demonstrating significant optimization effects in density and microstructure.

[0021] The high-quality 42CrMoA steel continuously cast by this invention provides an ideal raw material for crankshaft manufacturing. It can not only significantly improve the comprehensive performance of crankshafts, such as strength, toughness, wear resistance and fatigue resistance, but also greatly reduce the scrap rate and reprocessing cost caused by unstable quality, thus achieving dual optimization of performance and cost. Attached Figure Description

[0022] Figure 1 These are photos verifying the surface quality of each stranded billet under full flow coverage in Example 1;

[0023] Figure 2 Photographs showing the external dimensions of the continuously cast billets in Example 1, Comparative Example 2, and Comparative Example 3;

[0024] Figure 3 These are low-magnification photographs of continuously cast billets from Example 1, Comparative Example 2, and Comparative Example 3.

[0025] Figure 4 These are photographs of the longitudinal low-magnification inspection of continuously cast billets in Example 1, Comparative Example 2, and Comparative Example 3;

[0026] Figure 5 This is a comparison chart of the changes in the segregation index of the five stranded billets obtained in Example 1.

[0027] Figure 6 A comparison chart showing the changes in the segregation index of the five stranded billets obtained in Comparative Example 2;

[0028] Figure 7 Low-magnification photographs of rolled products prepared from continuously cast billets of Example 1, Comparative Example 2, and Comparative Example 3;

[0029] Figure 8 The density test results for the central region of the rolled product prepared from the continuously cast billet in Example 1;

[0030] Figure 9The density test results of the central region of the rolled product prepared from the continuously cast billet of Comparative Example 2 are shown.

[0031] Figure 10 The density test results of the central region of the rolled product prepared from the three continuously cast billets for comparative example;

[0032] Figure 11 This is a graph showing the results of measuring the central porosity area of ​​a transverse low-magnification sample of a continuously cast billet in Example 1.

[0033] Figure 12 This is a diagram showing the results of measuring the central porosity area of ​​a low-magnification transverse sample of a continuously cast billet, as shown in Comparative Example 1. Detailed Implementation

[0034] The technical solution of the present invention will be further described below with reference to embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention. In the following embodiments, the process equipment or apparatus not specifically specified are all conventional equipment or apparatus in the art. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available; unless otherwise specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0035] Example 1

[0036] A high-quality crankshaft continuous casting billet of 42CrMoA steel has the following chemical composition: C: 0.43wt%, Si: 0.25wt%, Mn: 0.73wt%, P≤0.015wt%, S: 0.026wt%, Cr: 1.13wt%, Mo: 0.18wt%, Cu≤0.20wt%, As≤0.008wt%, Alt: 0.020wt%, O≤15ppm, H≤1.5ppm.

[0037] A method for preparing a high-quality crankshaft 42CrMoA steel continuous casting billet involves sequentially passing molten iron of a specified formula through converter or electric furnace smelting, LF refining, VD or RH vacuum degassing, and continuous casting processes.

[0038] During the smelting process, the tapped steel must have a carbon content of no less than 0.10%, a phosphorus content of ≤0.010%, and a tapping temperature of 1640℃.

[0039] When 30t of steel is tapped, aluminum ingots are added for precipitation and deoxidation according to the carbon content. When the carbon content of the tapped steel is 0.10~0.15%, 110kg of aluminum ingots are added per 100t of steel; when the carbon content of the tapped steel is 0.16~0.23%, 90kg of aluminum ingots are added per 100t of steel; and when the carbon content of the tapped steel is 0.24~0.35%, 70kg of aluminum ingots are added per 100t of steel, to ensure that the alt content is controlled at 0.020~0.035% when leaving the station.

[0040] When 50t of steel is produced, 600kg of lime per 100t of steel and 400kg of deoxidizing and desulfurizing refining slag per 100t of steel are added. At the same time, alloying is carried out with residual Mn: 0.08%, Cr: 0.10%, and alloy carbon increase: 0.21% to ensure that the composition of the molten steel leaving the station is C: 0.36~0.39%, Si: 0.18~0.24%, Mn: 0.67~0.73%, and Cr: 1.09~1.15%.

[0041] During the LF refining slag deoxidation process, 200 kg of carboxylic acid per 100 t of steel is added at the start of the first power supply. Aluminum granules, carbon powder, and silicon carbide are mixed and added in 2-3 batches. Half of the total amount is added in the first batch, and the remaining half is added within 15 minutes of power supply. The temperature of the slag white sample is not lower than 1530℃.

[0042] To ensure the purity of the molten steel, LF refining adjusts the Al content based on the results of the first sampling. When Al in the sample is ≤0.030%, aluminum wire is used to recover 100% of the Al to adjust it to 0.035%. After sampling, white slag operation is maintained. 30 kg of silicon carbide per 100 t of steel and 10 kg of carbon powder per 100 t of steel are mixed and added in 2-3 batches for deoxidation. The composition is adjusted to meet the internal control requirements.

[0043] The second power supply to LF controls the heating rate according to the production rhythm and the continuous casting time. 20kg of silicon carbide per 100t of steel is added in 1 to 2 batches to maintain white slag. Power is cut off when the temperature is suitable. The overall refining time is not less than 55 minutes and the white slag holding time is 30 minutes. After all the components are in the internal control, they can be transferred to the next process.

[0044] In the vacuum degassing process, a deep vacuum of ≤67Pa is used, the vacuum holding time is 20min, and after breaking the vacuum, Si-Ca line is fed in at 70m / furnace, with 10ppm of calcium added to ensure that the finished product Ca is ≤12ppm; the soft blowing time is 20min, and the ladle insulation agent and carbonized rice husk are added, with the slag surface slightly moving and the molten steel not exposed.

[0045] The tundish preheating temperature during continuous casting must be maintained at no more than 300 degrees Celsius for 2.5 hours. For the first hour of preheating, the flame should reach 1 / 3 of the tundish wall; for 1-2.5 hours, the flame should reach 2 / 3 of the tundish wall. For medium preheating, the flame should reach the bottom of the tundish with a backfire, and the working layer at the bottom of the tundish should be red-hot before high-temperature preheating. High-temperature preheating with air should be continued until the specified tundish heat storage temperature is reached. Preheating time should be 2.5 hours or more for preheating, 1.5 hours or more for medium preheating, and 1.5 hours or more for high-temperature preheating, with a total preheating time not exceeding 8 hours. Stopper rod preheating time should not exceed 4 hours. Submerged entry nozzle preheating time should not exceed 2 hours. The tundish casting zone temperature should not be lower than 1050 degrees Celsius.

[0046] The continuous casting process uses a 250×280mm continuous casting machine with five machines and five flow stages, with a maximum of 10 heats cast consecutively. The steel reserve in each ladle is ≥2.5t. This is to prevent slag from entering the ladle during casting and affecting the purity of the molten steel.

[0047] The casting superheat is 25℃, the casting speed is 0.65m / min, the crystallizer water flow rate is 2350L / min, the specific water volume is 0.20L / kg, and the distribution ratio is 36 / 39 / 25%. The crystallizer vibration parameters are: amplitude: 5.0, amplitude constant: 0, frequency: 150, frequency constant: -15, negative slip rate: 0.1. The electromagnetic stirring parameters at the beginning are 150A / 2Hz, and the stirring method is continuous stirring. The electromagnetic stirring parameters at the end are 100A / 8Hz, and the stirring method is alternating stirring with an alternation time of 10 seconds-3 seconds-10 seconds-3 seconds. The parameters for the end light pressing are 3 / 4 / 3, and the total pressing amount is 10mm.

[0048] Example 2

[0049] A high-quality crankshaft continuous casting billet of 42CrMoA steel has the following chemical composition: C: 0.40wt%, Si: 0.30wt%, Mn: 0.82wt%, P≤0.015wt%, S: 0.025wt%, Cr: 1.15wt%, Mo: 0.21wt%, Cu≤0.20wt%, As≤0.008wt%, Alt: 0.015wt%, O≤15ppm, H≤1.5ppm.

[0050] A method for preparing a high-quality crankshaft 42CrMoA steel continuous casting billet involves sequentially passing molten iron in a converter or electric furnace, refining it using an LF furnace, vacuum degassing it using a VD or RH furnace, and then continuously casting it.

[0051] During the smelting process, the tapped steel must have a carbon content of no less than 0.10%, a phosphorus content of ≤0.010%, and a tapping temperature of 1620℃.

[0052] When 30t of steel is tapped, aluminum ingots are added for precipitation and deoxidation according to the carbon content. When the carbon content of the tapped steel is 0.10~0.15%, 110kg of aluminum ingots are added per 100t of steel; when the carbon content of the tapped steel is 0.16~0.23%, 90kg of aluminum ingots are added per 100t of steel; and when the carbon content of the tapped steel is 0.24~0.35%, 70kg of aluminum ingots are added per 100t of steel, to ensure that the alt content is controlled at 0.020~0.035% when leaving the station.

[0053] When 50t of steel is produced, 600kg of lime per 100t of steel and 400kg of deoxidizing and desulfurizing refining slag per 100t of steel are added. At the same time, alloying is carried out with residual Mn: 0.08%, Cr: 0.10%, and alloy carbon increase: 0.21% to ensure that the composition of the molten steel leaving the station is C: 0.36~0.39%, Si: 0.18~0.24%, Mn: 0.67~0.73%, and Cr: 1.09~1.15%.

[0054] During the LF refining slag formation and deoxidation process, 200 kg of carboxylic acid per 100 t of steel is added at the beginning of the first power supply. Aluminum granules (30 kg / 100 t of steel), carbon powder (20 kg / 100 t of steel), and silicon carbide (20 kg) are used for diffusion deoxidation. After mixing, they are added in 2-3 batches. Half of the total amount is added in the first batch, and the remaining half is added within 15 minutes of power supply. The temperature of the slag white sample is not lower than 1530℃.

[0055] To ensure the purity of the molten steel, LF refining adjusts the Al content based on the results of the first sampling. When Al in the sample is ≤0.030%, aluminum wire is used to recover 100% of the Al to adjust it to 0.035%. After sampling, white slag operation is maintained. 20 kg of silicon carbide per 100 t of steel and 5 kg of carbon powder per 100 t of steel are mixed and added in 2 to 3 batches for deoxidation. The composition is adjusted to meet the internal control requirements.

[0056] The second power supply to LF controls the heating rate according to the production rhythm and the continuous casting time. Silicon carbide 10kg / 100t steel is added in 1-2 batches to maintain white slag. Power is cut off when the temperature is suitable. The overall refining time is not less than 55min and the white slag holding time is 30min. After all the components are in the internal control, they can be transferred to the next process.

[0057] In the vacuum degassing process, a deep vacuum of ≤67Pa is used, the vacuum holding time is 25min, and after breaking the vacuum, Si-Ca line is fed in at 80m / furnace, with 10ppm of calcium added to ensure that the finished product Ca is ≤12ppm; the soft blowing time is 25min, and the ladle insulation agent and carbonized rice husk are added, with the slag surface slightly moving and the molten steel not exposed.

[0058] The tundish preheating temperature during continuous casting must be maintained at no more than 300 degrees Celsius for 2.5 hours. For the first hour of preheating, the flame should reach 1 / 3 of the tundish wall; for 1-2.5 hours, the flame should reach 2 / 3 of the tundish wall. For medium preheating, the flame should reach the bottom of the tundish with a backfire, and the working layer at the bottom of the tundish should be red-hot before high-temperature preheating. High-temperature preheating with air should be continued until the specified tundish heat storage temperature is reached. Preheating time should be 2.5 hours or more for preheating, 1.5 hours or more for medium preheating, and 1.5 hours or more for high-temperature preheating, with a total preheating time not exceeding 8 hours. Stopper rod preheating time should not exceed 4 hours. Submerged entry nozzle preheating time should not exceed 2 hours. The tundish casting zone temperature should not be lower than 1050 degrees Celsius.

[0059] In the continuous casting process, the casting superheat is 25℃, the casting speed is 0.65m / min, the crystallizer water flow rate is 2350L / min, the specific water flow rate is 0.20L / kg, and the distribution ratio is 36 / 39 / 25%. The crystallizer vibration parameters are: amplitude: 5.0, amplitude constant: 0, frequency: 150, frequency constant: -15, and negative slip ratio: 0.1. The electromagnetic stirring parameters at the beginning of the process are 150A / 2Hz, and the stirring method is continuous stirring. The electromagnetic stirring parameters at the end are 100A / 8Hz, and the stirring method is alternating stirring with an alternation time of 10 seconds-3 seconds-10 seconds-3 seconds. The parameters for the final light reduction are 3 / 4 / 3, and the total reduction is 10mm.

[0060] Comparative Example 1

[0061] The only difference between this comparative example and Example 1 is that in the continuous casting process of this comparative example, the casting superheat is 35°C, the casting speed is 0.65 m / min, the crystallizer water flow rate is 2350 L / min, the specific water flow rate is 0.20 L / kg, and the distribution ratio is 36 / 39 / 25%; the crystallizer vibration parameters are: amplitude: 5.0, amplitude constant: 0, vibration frequency: 150, vibration frequency constant: -15, negative slip ratio: 0.1; the electromagnetic stirring parameters at the beginning of the electromagnetic stirring are 150 A / 2 Hz, and the stirring method is continuous stirring; the electromagnetic stirring parameters at the end are 100 A / 8 Hz, and the stirring method is alternating stirring, with an alternation time of 10 seconds-3 seconds-10 seconds-3 seconds; the parameters for the final light reduction are 3 / 4 / 3, and the total reduction is 10 mm.

[0062] Comparative Example 2

[0063] The only difference between this comparative example and Example 1 is that in the continuous casting process of this comparative example, the casting superheat is 25°C, the casting speed is 0.65 m / min, the crystallizer water flow rate is 2350 L / min, the specific water flow rate is 0.20 L / kg, and the distribution ratio is 36 / 39 / 25%; the crystallizer vibration parameters are: amplitude: 5.0, amplitude constant: 0, vibration frequency: 150, vibration frequency constant: -15, negative slip rate: 0.1; the electromagnetic stirring parameters at the beginning of the electromagnetic stirring are 150 A / 2 Hz, and the stirring method is continuous stirring; the electromagnetic stirring parameters at the end are 100 A / 8 Hz, and the stirring method is alternating stirring, with an alternation time of 10 seconds-3 seconds-10 seconds-3 seconds, and no light reduction treatment is performed.

[0064] Comparative Example 3

[0065] The only difference between this comparative example and Example 1 is that in the continuous casting process of this comparative example, the casting superheat is 30°C, the casting speed is 0.70 m / min, the crystallizer water flow rate is 2350 L / min, the specific water flow rate is 0.20 L / kg, and the distribution ratio is 36 / 39 / 25%; the crystallizer vibration parameters are: amplitude: 5.0, amplitude constant: 0, vibration frequency: 150, vibration frequency constant: -15, negative slip rate: 0.1; the electromagnetic stirring parameters at the beginning of the electromagnetic stirring are 150 A / 2 Hz, and the stirring method is continuous stirring; the electromagnetic stirring parameters at the end are 100 A / 8 Hz, and the stirring method is alternating stirring, with an alternation time of 10 seconds-3 seconds-10 seconds-3 seconds; the parameters for the final light reduction are 3 / 4 / 3, and the total reduction is 10 mm.

[0066] I. Quality verification of the continuously cast billets prepared in Example 1 and Comparative Examples 1-3:

[0067] (I) Verification of the surface quality of the cast billet:

[0068] A 350mm long section of the continuously cast billet obtained from the five-strand continuous casting machine in Example 1 was subjected to surface hot pickling after full-strand coverage. Figure 1 Verification photos of the surface quality of the full flow coverage of each strand of cast billet; such as Figure 1 As shown, the surfaces of each slab cast in the continuous casting are normal, without cracks or defects, and without slag pits, slag grooves, scratches or other defects. The vibration marks are clear and without overlap.

[0069] (ii) Verification of external dimensions and quality:

[0070] The external dimensions of the continuously cast billets obtained in Example 1, Comparative Example 2, and Comparative Example 3 were measured, and the results are as follows: Figure 2As shown, the continuous casting billet prepared in Example 1 has no visible defects such as square delamination or indentation, with a maximum cross-sectional dimensional deviation of 2 mm and a difference of 1-2 mm between the set reduction amount and the actual reduction amount on the vertical plane; the continuous casting billet prepared in Comparative Example 2 has no visible defects such as square delamination or indentation, with a maximum cross-sectional dimensional deviation of 4 mm and a maximum vertical dimensional deviation of 1 mm; the maximum indentation on the cross-section of Comparative Example 3 is 5 mm, the maximum vertical indentation is 250 mm, and the square delamination is 2 mm.

[0071] (iii) Low-magnification quality verification:

[0072] Low-magnification tests were conducted on the full flow coverage of the continuously cast billets obtained in Example 1, Comparative Example 2, and Comparative Example 3. The results are as follows: Figure 3 As shown, the low-magnification sample of the continuously cast billet in Example 1 was rated as Grade 1 for central porosity and Grade 0.5 for the presence of a pressing crack, according to metallurgical standards. No other defects were found. The low-magnification microstructure was normal, with clearly visible equiaxed and columnar crystals. Obvious porosity points were visible in the central equiaxed region. The measured porosity area was approximately <20 mm from the center, with an area of ​​<400 mm². 2 .

[0073] The low-magnification sample of the continuously cast billet in Comparative Example 2 was rated as Grade 1 (central porosity) according to metallurgical standards. No other defects were observed. The microstructure showed obvious coarse grains and mixed crystals. Obvious porosity points were visible in the central equiaxed region. The measured porosity area was approximately 20-40 mm from the center, with an area of ​​400 mm². 2 ~800mm 2 .

[0074] The low-magnification sample of the comparative example 3 continuously cast billet was rated as Grade 1 (central porosity) according to metallurgical standards, with an internal corner crack defect of Grade 0.5 in the S3 flow. The low-magnification microstructure was normal, showing obvious equiaxed and columnar crystals. Obvious porosity points were visible in the central equiaxed region. The measured porosity area was 20-40 mm, with a total porosity area of ​​400 mm². 2 ~1600mm 2 .

[0075] (iv) Vertical quality verification:

[0076] The continuously cast billets obtained in Example 1, Comparative Example 2, and Comparative Example 3 were cut laterally, and the results are as follows: Figure 4 As shown, the continuous casting billet prepared in Example 1 showed no obvious V-segregation in the longitudinal direction, no discontinuous or continuous shrinkage defects at the center position, but had slight pressing crack defects. The continuous casting billet prepared in Comparative Example 2 showed discontinuous shrinkage defects at the center position of the longitudinal sample; the continuous casting billet prepared in Comparative Example 3 showed obvious V-segregation, and obvious shrinkage defects were visible in the center region of part of the flow.

[0077] (v) Segregation quality verification:

[0078] To verify the segregation of the continuously cast billets obtained in Examples 1, 2, and 3, sampling was performed at 2cm / point intervals (in meters). Drilling was conducted at low magnification in the transverse direction, and the results were examined using an infrared carbon-sulfur analyzer. The segregation test results for the continuously cast billets of Example 1 are shown in Table 1 and... Figure 5 As shown.

[0079] Table 1

[0080]

[0081] From Table 1 and Figure 5 The highest segregation index was 1.095, and the lowest was 0.904. The segregation of the samples was evaluated according to the segregation index evaluation standard of 0.950–1.050, with positive segregation exceeding the standard in 3.17%–7.94% and negative segregation exceeding the standard in 7.94%–11.11%.

[0082] The segregation test results of the continuously cast billet in Comparative Example 2 are shown in Table 2 and Figure 6 As shown.

[0083] Table 2

[0084]

[0085] From Table 2 and Figure 6 The highest segregation index was 1.071, and the lowest was 0.902. The sample segregation was evaluated according to the segregation index evaluation standard of 0.950–1.050, with positive segregation exceeding the standard in 1.59%–3.17% and negative segregation exceeding the standard in 22.22%–36.98%. The compositional homogeneity of the samples was generally poor, with negative segregation being the predominant cause.

[0086] 2. The continuously cast billets prepared in Example 1, Comparative Example 2 and Comparative Example 3 were used for rolling φ100 round rolled products, and the quality of the rolled products was verified.

[0087] (a) Results of low-magnification inspection of rolled materials:

[0088] The low-magnification inspection results of the rolled products prepared from continuously cast billets in Examples 1, 2, and 3 are as follows: Figure 7 As shown, according to the rolling mill standard rating, the rolling mill of the continuously cast billet in Example 1 was rated as Grade 1 for central porosity and Grade 1 for general porosity; no obvious black core defects were observed. The rolling mill of the continuously cast billet in Comparative Example 2 was rated as Grade 1 for central porosity and Grade 1 for general porosity; black cores were present, and the microstructure of some samples was uneven. The rolling mill of the continuously cast billet in Comparative Example 3 was rated as Grade 1 for central porosity and Grade 1 for general porosity; no obvious black core defects were observed. The rolling mills of Example 1 and Comparative Example 3 were slightly more uniform in macroscopic observation than the rolling mill of Comparative Example 2.

[0089] (II) In-situ analysis:

[0090] Low-magnification samples of rolled products prepared from continuously cast billets of Example 1, Comparative Example 2 and Comparative Example 3 were randomly selected for in-situ analysis. Spots were made sequentially along the outer arc of the sample towards the center area, and the scanning area was 58×54mm.

[0091] In Example 1, the uniformity of C in the rolled product prepared from the continuously cast billet was 50.66%, the uniformity of S was 52.93%, the uniformity of Mn was 47.84%, the uniformity of Cr was 64.10%, and the uniformity of Mo was 64.10%.

[0092] like Figure 8 The density test results of the central region show that the central density of the rolled product prepared from the continuous casting billet in Example 1 is 94.88%, and the statistical porosity is 0.0436. The average particle size of inclusions was calculated to be 1.613 μm, the largest inclusions were 7-10 μm, accounting for 0.03%, and most inclusions were ≤3 μm, accounting for 95.64%.

[0093] The uniformity of C in the rolled product prepared by continuous casting in Comparative Example 2 was 11%, showing a clear annular variation trend; the uniformity of S was 30.89%; the uniformity of Mn was 32.17%; the uniformity of Cr was 37.19%; and the uniformity of Mo was 28.69%.

[0094] like Figure 9 The density test results of the central region show that the central density of the rolled product prepared from the continuously cast slab of Comparative Example 2 is 92.84%, and the statistical porosity is 0.0865. The average particle size of inclusions was calculated to be 1.645 μm, and the largest inclusion particles were 7–10 μm, accounting for 0.04%. Most inclusions were ≤3 μm, accounting for 94.43%.

[0095] The rolled products prepared from the continuously cast slabs of Comparative Example 3 had the following uniformities: C 97.28%, S 70.98%, Mn 82.20%, Cr 98.34%, and Mo 99.33%.

[0096] like Figure 10 The density test results of the central region show that the central density of the rolled product prepared from the continuously cast slab of Comparative Example 3 is 95.84%, and the statistical porosity is 0.0377. The average particle size of inclusions was calculated to be 1.623 μm, and the largest inclusion particles were 7–10 μm, accounting for 0.09%. Most inclusions were ≤3 μm, accounting for 95.37%.

[0097] III. The results of transverse low-magnification inspection and measurement of the central porosity area of ​​the continuously cast billets prepared in Example 1 and Comparative Example 1 are as follows: Figure 11 and Figure 12As shown, in Comparative Example 1, with a superheat of 35°C, the actual transverse low-magnification measurement revealed that the porous area in the central region was 49mm × 30mm = 1470mm². 2 Example 1: A transverse low-magnification actual measurement at a superheat of 25°C showed that the porous area of ​​the central region was 14mm × 10mm = 140mm². 2 The comparison shows that superheat is the main factor affecting the central loose area; the higher the superheat control, the larger the central loose area.

[0098] A comparison of the quality verification results of continuously cast billets and rolled products shows that the dimensional defects of continuously cast billets increase significantly with increasing casting speed. The maximum dimensional defect reaches 5mm when the casting speed is 0.70m / min. There is a significant difference in the density of continuously cast billets at low magnification; when the billet is subjected to reduction, the size of the porous area is significantly reduced. The porous area is largest when the casting speed is 0.70m / min. Although the reduction technique in Example 1 caused slight reduction cracks in the continuously cast billets at low magnification, these slight reduction cracks will not cause incompatibility during rolling. Reduction of the continuously cast billet has a significant effect on improving its density. Looking at the overall segregation inspection results of the continuously cast billets, the results of the billets with reduction are significantly better than those without. Therefore, light reduction has a significant effect on improving the segregation of the billets.

Claims

1. A high-quality 42CrMoA steel continuous casting billet for crankshafts, characterized in that, The chemical composition includes: C: 0.39-0.45 wt%, Si: 0.17-0.37 wt%, Mn: 0.70-0.90 wt%, P≤0.015 wt%, S: 0.025-0.030 wt%, Cr: 1.05-1.20 wt%, Mo: 0.18-0.25 wt%, Cu≤0.20 wt%, As≤0.008 wt%, Alt: 0.010-0.020 wt%, O≤15 ppm, H≤1.5 ppm.

2. A method for preparing a high-quality crankshaft 42CrMoA steel continuous casting billet as described in claim 1, characterized in that, The molten iron of the formula is prepared by sequentially passing it through a converter or electric furnace smelting, LF refining, VD or RH vacuum degassing, and continuous casting. In the continuous casting process, the casting superheat is 20~25℃, the casting speed is 0.65m / min, the crystallizer water flow rate is 2350L / min, the specific water volume is 0.20L / kg, and the distribution ratio is 36 / 39 / 25%. The crystallizer vibration parameters are: amplitude: 5.0, amplitude constant: 0, vibration frequency: 150, vibration frequency constant: -15, negative slip rate: 0.

1. The electromagnetic stirring parameters at the beginning are 150A / 2Hz, and the stirring method is continuous stirring. The electromagnetic stirring parameters at the end are 100A / 8Hz, and the stirring method is alternating stirring with an alternation time of 10 seconds-3 seconds-10 seconds-3 seconds. The parameters for the final light reduction are 3 / 4 / 3, and the total reduction is 10mm.

3. The method for preparing high-quality crankshaft 42CrMoA steel continuous casting billets according to claim 2, characterized in that, In the smelting process, the tapped steel is required to have a carbon content of not less than 0.10%, a phosphorus content of ≤0.010%, and a tapping temperature of 1610~1640℃.

4. The method for preparing high-quality crankshaft 42CrMoA steel continuous casting billets according to claim 2 or 3, characterized in that, During the steel tapping process of the smelting operation, aluminum ingots are added for precipitation and deoxidation when 30t of steel is tapped, based on the carbon content. When the carbon content of the tapped steel is 0.10~0.15%, 110kg of aluminum ingots are added per 100t of steel; when the carbon content is 0.16~0.23%, 90kg of aluminum ingots are added per 100t of steel; and when the carbon content is 0.24~0.35%, 70kg of aluminum ingots are added per 100t of steel, ensuring that the alt content at the tap is controlled at 0.020~0.035%.

5. The method for preparing high-quality crankshaft 42CrMoA steel continuous casting billets according to claim 4, characterized in that, During the steel tapping process of the smelting operation, 600 kg of lime per 100 t of steel and 400 kg of deoxidizing and desulfurizing refining slag per 100 t of steel are added when 50 t of steel is tapped; alloying operation is carried out to ensure that the composition of the molten steel leaving the station is C: 0.36~0.39%, Si: 0.18~0.24%, Mn: 0.67~0.73%, and Cr: 1.09~1.15%.

6. The method for preparing high-quality crankshaft 42CrMoA steel continuous casting billets according to claim 5, characterized in that, During the LF refining slag deoxidation process, 200 kg of carboxylic acid lime per 100 t of steel is added at the beginning of the first power supply. Aluminum granules of 30 kg per 100 t of steel, carbon powder of 20-30 kg per 100 t of steel, and silicon carbide of 20-30 kg are used for diffusion deoxidation. After mixing, the mixture is added in 2-3 batches. Half of the total amount is added in the first batch, and the remaining half is added within 15 minutes of power supply. The temperature of the slag white sample is not lower than 1530℃.

7. The method for preparing high-quality crankshaft 42CrMoA steel continuous casting billets according to claim 6, characterized in that, To ensure the purity of the molten steel, the Al content in the LF refining process was adjusted based on the results of the first sampling. When Al ≤ 0.030% in the sample, aluminum wire was used to recover 100% of the Al content to adjust it to 0.035%. After sampling, the white slag operation was maintained. 20-30 kg / 100t of silicon carbide and 5-10 kg / 100t of carbon powder were mixed and added in 2-3 batches for deoxidation, and the composition was adjusted to meet the internal control requirements.

8. The method for preparing high-quality crankshaft 42CrMoA steel continuous casting billets according to claim 7, characterized in that, The second power supply of the LF is controlled according to the production rhythm and the continuous casting ladle time. Silicon carbide 10~20kg / 100t steel is added in 1~2 batches to maintain white slag. Power is cut off when the temperature is suitable. The overall refining time is not less than 55min and the white slag holding time is not less than 25min. After all the components are in the internal control, they can be transferred to the next process.

9. The method for preparing high-quality crankshaft 42CrMoA steel continuous casting billets according to claim 8, characterized in that, In the vacuum degassing process, a deep vacuum of ≤67Pa is used, the vacuum holding time is not less than 15min, and after breaking the vacuum, Si-Ca line is fed in at 60~80m / furnace, with calcium added at 8~12ppm to ensure that the finished product Ca is ≤12ppm; the soft blowing time is not less than 15min, and ladle insulation agent and carbonized rice husk are added, with the slag surface slightly moving and the molten steel not exposed.

10. The method for preparing high-quality crankshaft 42CrMoA steel continuous casting billets according to claim 9, characterized in that, The tundish baking temperature during the continuous casting process must be maintained at no more than 300 degrees Celsius for 2.5 hours. For the first hour of the initial baking, the flame should reach 1 / 3 of the tundish wall; for the first 1-2.5 hours, the flame should reach 2 / 3 of the tundish wall. For the medium baking, the flame should reach the bottom of the tundish with a backfire, and the working layer at the bottom of the tundish should turn red before the main baking can begin. The main baking should be combined with air to reach the specified tundish heat storage temperature. The baking time for the initial baking should be 2.5 hours or more, the medium baking time 1.5 hours or more, and the main baking time 1.5 hours or more, with a total baking time not exceeding 8 hours. The stopper rod baking time should not exceed 4 hours; the immersion nozzle baking time should not exceed 2 hours; and the tundish casting zone temperature should not be lower than 1050 degrees Celsius.

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