Method for Verifying Accuracy of Secondary Cooling Solidification Model

Abstract

The present invention relates to the technical field of cooling models, and in particular to a method for verifying the accuracy of a secondary cooling solidification model. The method includes the steps of: (S1) establishing an online secondary cooling solidification model by Primetals; (S2) obtaining a slab through a continuous casting production process, and calculating the central solid fraction fs of the slab entering a tension leveler; (S3) using a tension leveler to perform soft reduction, and performing single-roll or multi-roll reduction for the region when the central solid fraction fs is 10-50%; and (S4) sampling the slab, pickling it, inspecting the crack initiation position at low magnification in the longitudinal direction, and comparing the measured value X based on the actual crack initiation position with the thickness D of the slab simulated by the secondary cooling solidification model. The accuracy of the secondary cooling solidification model can be verified by the crack generation method by the reduction process, and the accuracy of the secondary cooling solidification model can be verified based on the crack initiation position at low magnification in the longitudinal direction.

Description

Technical Field

[0001] The present invention relates to the technical field of cooling models, and particularly to a method for verifying the accuracy of a secondary cooling solidification model.

Background Art

[0002] For high-carbon steel, the means to improve its central segregation and central porosity basically use low superheat or soft reduction technology. For soft reduction technology, since the solidification behavior of the slab simulated using the secondary cooling solidification model is important, the verification of the accuracy of the secondary cooling solidification model is the first step to improve the central segregation and porosity of the slab by soft reduction. Generally, after establishing a continuous casting solidification model, the temperature field of the continuous casting slab is predicted, and verification and debugging are carried out on the calculation results of the solidification model using the nail piercing experiment or the lead precipitation method. However, due to safety problems with nail piercing, the said verification method cannot be implemented. It is difficult to implement the precipitation method for small square billets, and there is an easy risk of steel leakage during the implementation process. Moreover, since the solidification rate of small square billets is fast, the withdrawal speed is fast, and there is a relative movement speed between the slab and the lead during lead precipitation, it is necessary to verify the lead-containing position in the slab.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for verifying the accuracy of a secondary cooling solidification model in order to overcome the problems in the prior art that due to safety problems with nail piercing, the said verification method cannot be implemented, it is difficult to implement the precipitation method for small square billets, and there is an easy risk of steel leakage during the implementation process.

Means for Solving the Problems

[0004] As a technical means used in the present invention to solve its technical problems, the method for verifying the accuracy of a secondary cooling solidification model includes step S1 of establishing an online secondary cooling solidification model by Primetals, Obtaining a slab by a continuous casting production process, determining the specific water volume, drawing speed, and the temperature of the slab under process conditions by an on-line secondary cooling solidification model, and calculating the central solid fraction fs of the slab entering the tension leveler in step S2;

Number

[0005] Furthermore, in step S2, the crystallization device in the continuous casting production process has a water flow rate of 120 - 140 m 3 / h, a water temperature difference of 7.5 - 9.5 °C, a copper tube length of 900 mm, the nozzles of the foot roll use a total of 24 nozzles arranged in 3 rows and 2 columns, with a length of 0.45 m, and the secondary cooling section includes the first section of secondary cooling, the second section of secondary cooling, and the third section of secondary cooling. The length of the first section of secondary cooling is 1.9 m, the length of the second section of secondary cooling is 2.4 m, and the length of the third section of secondary cooling is 2.5 m.

[0006] Furthermore, in the step S2, for secondary cooling, the medium cooling and weak cooling modes are used, the specific water ratio is controlled to be 0.7 L / kg to 0.55 L / kg, the foot roll of the crystallization device uses complete water cooling, the first section of secondary cooling, the second section of secondary cooling, and the third section of secondary cooling use aerosol cooling, and the distribution ratio of the water volume in each section of secondary cooling is: 23% for the foot roll, 45% for the first section of secondary cooling, 22% for the second section of secondary cooling, and 10% for the third section of secondary cooling, and the withdrawal speed is 2.4 to 2.5 m / min.

[0007] Furthermore, in the step S3, for the tension leveler, the distance from the meniscus in the rolling reduction section is 14200 mm to 17900 mm, and the rolling reduction speed is 0.1 to 0.2 mm / sec.

[0008] Furthermore, in the step S3, when the carbon content in the slab > 0.45%, multi-roll rolling reduction is used. When 0 ≤ fs < 0.10, the rolling reduction amount is 0 mm. When 0.10 ≤ fs ≤ 0.50, the total rolling reduction amount is 4 to 12 mm. When the carbon content in the slab ≤ 0.45%, when the central solidification rate fs is 0.15 to 0.20, single-roll rolling reduction is performed on the region. When 0 ≤ fs < 0.10, the rolling reduction amount is 0 mm. When 0.10 ≤ fs ≤ 0.20, the total rolling reduction amount is 10 mm.

[0009] Furthermore, in the step S4, for sampling pickling, specifically, the selected slab is processed into a longitudinal section center sample along the direction of pulling out the slab, the sample is cut out, the cross-section of the selected slab is polished with a milling machine, the center sample is put into a 1:1 hydrochloric acid solution, and the etching surface is completely immersed in the acid. The pickling tank is heated to 70 to 80 °C and held for 20 minutes within this temperature range. Then the sample is taken out, and immediately after taking out, it is washed with clear water and alcohol and dried with a dryer. The cracks of the center sample are analyzed and measured to obtain X.

Advantages of the Invention

[0010] The beneficial effects of the present invention are as follows. The method for verifying the accuracy of the secondary cooling solidification model according to the present invention can verify the accuracy of the secondary cooling solidification model by the cracking mode in the rolling reduction process, provide a method for determining specific rolling reduction process implementation parameters including the selection of the rolling reduction position and the rolling reduction amount, ensure that the slab generates cracks in the longitudinal low magnification, and can verify the accuracy of the secondary cooling solidification model based on the crack initiation position.

Brief Description of the Drawings

[0011] Hereinafter, the present invention will be further described with reference to the drawings and embodiments.

[0012]

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Modes for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in more detail with reference to the drawings. These drawings are all simplified schematic diagrams and only illustrate the basic configuration of the present invention, so they only show the configurations related to the present invention.

[0014] The method for verifying the accuracy of the secondary cooling solidification model is Step S1 of establishing an online secondary cooling solidification model by Primetals, Obtaining a slab by a continuous casting production process, determining the specific water volume, drawing speed, and the temperature of the slab under process conditions by an on-line secondary cooling solidification model, and calculating the central solid phase fraction fs of the slab entering the tension leveler in step S2; [Number] (In the formula, T is the temperature, T L is the liquidus temperature of the steel, and T S is the solidus temperature of the steel.) Performing soft reduction using a tension leveler and performing rolling reduction of a single roll or multiple rolls on the region when the central solid phase fraction fs is 10 - 50% in step S3; After sampling the slab, pickling it to inspect the crack initiation position at a low magnification in the longitudinal direction, comparing X obtained by measurement based on the actually measured crack initiation position with the thickness D of the slab simulated using the secondary cooling solidification model, and if |X - D| ≤ 5 mm, the simulation of the secondary cooling solidification model is accurate in step S4, including.

[0015] In step S2, the crystallization device in the continuous casting production process has a water flow rate of 120 - 140 m 3 / h, a water temperature difference of 7.5 - 9.5 °C, a copper tube length of 900 mm, the nozzles of the foot roll use a total of 24 nozzles arranged in 3 rows and 2 columns, with a length of 0.45 m, the secondary cooling section includes the first section of secondary cooling, the second section of secondary cooling, and the third section of secondary cooling, the length of the first section of secondary cooling is 1.9 m, the length of the second section of secondary cooling is 2.4 m, and the length of the third section of secondary cooling is 2.5 m.

[0016] In the step S2, for secondary cooling, medium cooling and weak cooling modes are used, the specific water ratio is controlled to be 0.7 L / kg to 0.55 L / kg. For the foot rolls of the crystallization device, full water cooling is used. For the first section, the second section and the third section of secondary cooling, aerosol cooling is used. The distribution ratio of the water volume of each section of secondary cooling is as follows: 23% for the foot rolls, 45% for the first section of secondary cooling, 22% for the second section of secondary cooling, and 10% for the third section of secondary cooling. The withdrawal speed is 2.4 to 2.5 m / min.

[0017] In the step S3, for the tension leveler, the distance of the rolling reduction section from the meniscus is 14200 mm to 17900 mm, and the rolling reduction speed is 0.1 to 0.2 mm / sec.

[0018] In the step S3, when the carbon content in the slab > 0.45%, multi-roll rolling reduction is used. When 0 ≦ fs < 0.10, the rolling reduction amount is 0 mm. When 0.10 ≦ fs ≦ 0.50, the total rolling reduction amount is 4 to 12 mm. When the carbon content in the slab ≦ 0.45%, when the central solid fraction fs is 0.15 to 0.20, single-roll rolling reduction is performed on the region. When 0 ≦ fs < 0.10, the rolling reduction amount is 0 mm. When 0.10 ≦ fs ≦ 0.20, the total rolling reduction amount is 10 mm.

[0019] In the step S4, for sampling pickling, specifically, the selected slab is processed into a longitudinal section center sample along the direction of pulling out the slab, the sample is cut, the cross-section of the selected slab is polished by a milling machine, the center sample is put into a 1:1 hydrochloric acid solution, and the etching surface is completely immersed in the acid. The pickling tank is heated to 70 to 80 °C and held for 20 minutes within this temperature range. Then the sample is taken out, and immediately after taking out, it is washed with clear water and alcohol and dried with a dryer. The cracks of the center sample are analyzed and measured to obtain X.

[0020] (Example 1) Regarding measurement and analysis, a 300-mm slab is cut out online, and the selected slab is processed into a longitudinal-section center sample of 200 mm × 150 mm × 160 mm along the direction in which the slab is withdrawn. A schematic diagram of the sampled sample is shown in Fig. 1. The surface of the selected slab is polished with a milling machine, and crack analysis is performed by the acid immersion method. The center sample is placed in a 1:1 hydrochloric acid solution, and the etching surface is completely immersed in the acid. The acid pickling tank is heated to 70 - 80°C and held within this temperature range for 20 minutes. Then, the sample is taken out, and immediately after taking out, it is washed with clear water and alcohol and dried with a dryer. The cracks of the center sample are analyzed, and the distance X from the crack of the center sample to the inner arc or outer arc surface is measured. As shown in Fig. 2, the measured X and the thickness D of the slab used for the nth tension leveler (1 ≤ n ≤ 7) simulated using the secondary cooling solidification model are compared and analyzed. When |X - D| ≤ 5 mm, it is determined that the simulation of the secondary cooling solidification model is accurate.

[0021] (Example 2) Hereinafter, the present invention will be described in more detail with reference to specific examples.

[0022] Regarding an exemplary application of 70 steel, the C content is 0.65 - 0.75%, the Si content is 0.17 - 0.37%, the Mn content is 0.50 - 0.85%, the tundish superheat is 1490 - 1506°C, the withdrawal speed is 2.4 m / min, the specific water volume of secondary cooling is 0.75 L / kg, the water flow rate of the crystallization device is 140 m 3 / h. In the process of performing soft reduction, the reduction speed is 0.2 mm / sec, the total reduction amount is 12 mm, the maximum reduction amount per roll is 4 mm, and the relationship between the reduction amount of the soft reduction rack and the solid fraction of the slab is shown in the following table.

[0023] Relationship between reduction amount of 70 steel and solid fraction of slab [Table 1]

[0024] A longitudinal low-magnification photograph of the slab is shown in Fig. 4. The starting position of the occurrence of continuous intermediate cracks is at a distance of 46 - 48 mm from the surface of the slab. Compression cracks occurred at the first tension leveler. The solidification thickness of the slab simulated at the position of 14.2 m of the No. 1 roll using the secondary cooling solidification model is 47.6 mm, which is consistent with the occurrence of cracks in the longitudinal low-magnification photograph.

[0025] (Example 3) Regarding an exemplary application of cold-rolled steel SWRCH35K, the C content is 0.32 - 0.38%, the Si content is 0.10 - 0.35%, the Mn content is 0.60 - 0.90%, the Al content is 0.020 - 0.040%, the tundish superheat is 1517 - 1537 °C, the drawing speed is 2.5 m / min, the specific water volume of secondary cooling is 0.70 L / kg. In the process of performing soft reduction, the reduction rate is 0.10 mm / sec, the total reduction amount is 10 mm, and the maximum reduction amount per roll is 10 mm. The relationship between the reduction amount of the soft reduction rack and the solid fraction of the slab is shown in the following table.

[0026] Relationship between the reduction amount of SWRCH35K and the solid fraction of the slab

Table 2

[0027] A longitudinal low-magnification photograph of the slab is shown in Fig. 6. The starting position of the occurrence of continuous intermediate cracks is at a distance of 55 - 57 mm from the surface of the slab. Compression cracks occurred at the second tension leveler. The solidification thickness of the slab simulated at the position of 14.8 m of the No. 2 roll using the secondary cooling solidification model is 55.6 mm, which is consistent with the occurrence of cracks in the longitudinal low-magnification photograph.

[0028] A person skilled in the art, taking the above ideal embodiments of the present invention as inspiration, can make various changes and modifications through the above description without departing from the scope of the technical idea of the present invention. The technical scope of the present invention is not limited to the content described in the specification, but should be determined based on the scope of the claims.

Claims

1. Online, the step S1 of establishing a secondary cooling solidification model; Obtaining a slab through a continuous casting production process, determining the specific water volume, drawing speed, and the temperature of the slab under process conditions using the secondary cooling solidification model, and calculating the central solid fraction fs of the slab entering the roller leveler according to the following formula in step S2; 【Equation 1】 (In the formula, T is the temperature, T Ｌ is the liquidus temperature of the steel, and T Ｓ is the solidus temperature of the steel.) Performing soft reduction using a roller leveler, and performing single-roll or multi-roll reduction on the region when the calculated central solid fraction fs is 10 - 50% in step S3; After sampling the slab, pickling it to inspect the crack initiation position, comparing X obtained by measurement based on the inspected crack initiation position with the thickness D of the slab simulated using the secondary cooling solidification model, and if |X - D| ≤ 5 mm, the simulation of the secondary cooling solidification model is accurate in step S4, including; The said X is the distance from the crack to the inner arc or the outer arc, In the said step S3, When the carbon content in the slab > 0.45%, multi-roll reduction is used, when 0 ≤ fs < 0.10, the reduction amount is 0 mm, and when 0.10 ≤ fs ≤ 0.50, the total reduction amount is 4 - 12 mm, When the carbon content in the slab ≤ 0.45%, single-roll reduction is performed on the region when the central solid fraction fs is 0.15 - 0.20, when 0 ≤ fs < 0.10, the reduction amount is 0 mm, and when 0.10 ≤ fs ≤ 0.20, the total reduction amount is 10 mm, A method for verifying the accuracy of a secondary cooling solidification model, characterized by this.

2. In the said step S2, the crystallization device in the continuous casting production process has a water flow rate of 120 - 140 m ３It is / h, the water temperature difference is 7.5 to 9.5 °C, the length of the copper tube of the crystallization device is 900 mm, the nozzles of the foot roll use 24 nozzles arranged in 3 rows and 2 columns, and its length is 0.45 m. The secondary cooling section includes the first section of secondary cooling, the second section of secondary cooling, and the third section of secondary cooling. The length of the first section of secondary cooling is 1.9 m, the length of the second section of secondary cooling is 2.4 m, and the length of the third section of secondary cooling is 2.5 m. The method for verifying the accuracy of the secondary cooling solidification model according to claim 1, characterized in that.

3. In step S2, the secondary cooling uses an intermediate cooling mode and a weak cooling mode weaker than the intermediate cooling mode. The specific water volume is controlled to be 0.7 L / kg to 0.55 L / kg. The foot roll of the crystallization device uses complete water cooling. The first section of secondary cooling, the second section of secondary cooling, and the third section of secondary cooling use aerosol cooling. The distribution ratio of the water volume of each section of secondary cooling is 23% for the foot roll, 45% for the first section of secondary cooling, 22% for the second section of secondary cooling, and 10% for the third section of secondary cooling. The drawing speed is 2.4 to 2.5 m / min. The method for verifying the accuracy of the secondary cooling solidification model according to claim 1, characterized in that.

4. In step S3, for the roller leveler, the distance of the rolling reduction section from the meniscus is 14200 mm to 17900 mm, and the rolling reduction speed is 0.1 to 0.2 mm / sec. The method for verifying the accuracy of the secondary cooling solidification model according to claim 1, characterized in that.

5. In step S4, specifically, as for sampling pickling, the selected slab is processed into a sample along the direction in which the longitudinal section of the slab is drawn out, the sample is cut out, the cross-section of the selected slab is polished with a milling machine, the central sample is put into a hydrochloric acid solution of 1:1, and the etching surface is completely immersed in the acid. The pickling tank is heated to 70 to 80 °C and held for 20 minutes within the temperature range. Then, the sample is taken out. After taking out, it is immediately washed with clean water and alcohol and dried with a dryer. The cracks of the central sample are analyzed and measured to obtain X. A method for verifying the accuracy of the secondary cooling solidification model according to claim 1, characterized by the above.

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