Continuous Casting Billet Solidification End Point Intensive Cooling Control Method

Abstract

The present invention relates to a method for controlling intensive cooling at the solidification end of continuous casting billets, belonging to the technical field of continuous casting billet quality control. Based on the mechanism of intensive cooling at the solidification end, the optimal intensive cooling area at the solidification end is determined according to the central cooling rate of the billet and the central solid fraction of the billet. By establishing a quantitative relationship model and control requirements among the surface cooling rate of the billet, the surface temperature of the billet in the straightening area, the surface temperature rise rate of the billet, and the intensive cooling water volume at the solidification end, the optimal intensive cooling water volume range at the solidification end is clarified. Using this method to control intensive cooling at the solidification end can play the role of improving the internal quality of the billet by intensive cooling at the solidification end and solve the problem of billet cracks caused by intensive cooling. This method is applicable to slab, bloom, and round billet continuous casting machines to improve the internal quality of billets.

Description

Technical Field

[0001] The present invention belongs to the technical field of continuous casting billet quality control, and relates to a method for controlling intensive cooling at the solidification end of a continuous casting billet. Background Art

[0002] Internal quality defects such as central segregation, porosity, and shrinkage cavity of continuous casting billets have an important impact on the microstructure and properties of rolled materials. Mechanical soft reduction, electromagnetic stirring, permanent magnetic stirring, intensive cooling at the solidification end, etc. are the main technical means to improve the internal quality of continuous casting billets. Among them, intensive cooling at the solidification end can quickly reduce the surface temperature of the casting billet by spraying water for intensive cooling at the solidification end of the billet, compensate for the solidification shrinkage in the central region through the thermal shrinkage of the billet surface, and then inhibit the flow of molten steel rich in solute elements, so as to achieve the purpose of improving the internal quality of the casting billet.

[0003] At present, the application of intensive cooling at the solidification end is relatively less. The main reason is that its action position is close to the straightening area and it is implemented by spraying water for intensive cooling, which is likely to cause the generation of surface cracks and internal cracks of the warming-back type. However, compared with technologies such as mechanical soft reduction, electromagnetic stirring, and permanent magnetic stirring, intensive cooling at the solidification end has many advantages such as simple equipment, low investment, and easy maintenance. If the generation of billet cracks can be avoided by reasonably controlling and using intensive cooling at the solidification end, this technology can be a better choice for improving the internal quality of continuous casting billets. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for controlling intensive cooling at the solidification end of a continuous casting billet, which can achieve the purpose of improving the internal quality of the continuous casting billet on the basis of avoiding crack generation by controlling the position and water volume of intensive cooling at the solidification end.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A method for controlling intensive cooling at the solidification end of a continuous casting billet, comprising the following steps:

[0007] S1: Establish a solidification heat transfer model according to the initial continuous casting process parameters, and use this model to calculate the central cooling rate, central solid fraction, surface cooling rate, surface temperature, and surface warming-back rate of the casting billet;

[0008] S2: Determine the starting position of intensive cooling at the solidification end according to the central cooling rate of the casting billet, and determine the ending position of intensive cooling at the solidification end according to the central solid fraction of the casting billet;

[0009] S3: Establish a quantitative relationship model between the surface cooling rate of the casting billet in the intensive cooling area at the solidification end and the water volume of intensive cooling at the solidification end, and determine the range Q1 of the water volume of intensive cooling at the solidification end under the first factor according to this model;

[0010] S4: Establish a quantitative relationship model between the surface temperature of the slab in the straightening zone and the intensive cooling water volume at the solidification end. Determine the range of the intensive cooling water volume Q2 at the solidification end under the second factor according to this model;

[0011] S5: Establish a quantitative relationship model between the surface reheating rate of the slab and the intensive cooling water volume at the solidification end. Determine the range of the intensive cooling water volume Q3 at the solidification end under the third factor according to this model;

[0012] S6: Determine the reasonable range of the intensive cooling water volume Q4 at the solidification end, where Q4 = Q1 ∩ Q2 ∩ Q3.

[0013] Optionally, the quantitative relationship models between the surface cooling rate of the slab in the intensive cooling area at the solidification end, the surface temperature of the slab in the straightening zone, the surface reheating rate of the slab, and the intensive cooling water volume at the solidification end are determined by regression fitting, and the specific expressions are as follows:

[0014] V c = A1Q 2 + B1Q + C1

[0015] T c = A2Q 2 + B2Q + C2

[0016] R c = A3Q 2 + B3Q + C3

[0017] Among them, V c represents the surface cooling rate of the slab in the intensive cooling area at the solidification end, °C / s; T c represents the surface temperature of the slab in the straightening zone, °C; R c represents the surface reheating rate of the slab, °C / m; Q represents the intensive cooling water volume at the solidification end, m 3 / h; A1, B1, C1, A2, B2, C2, A3, B3, C3 are constant coefficients.

[0018] Optionally, the range of the intensive cooling water volume Q1 at the solidification end under the first factor, the range of the intensive cooling water volume Q2 at the solidification end under the second factor, and the range of the intensive cooling water volume Q3 at the solidification end under the third factor are obtained by back-calculation through the quantitative relationship model and the control requirements of the surface cooling rate of the slab in the intensive cooling area at the solidification end, the surface reheating rate of the slab, and the surface temperature of the slab in the straightening zone.

[0019] Optionally, the maximum value within the range of Q4 is taken for the intensive cooling water volume at the solidification end, so as to fully exert the improvement effect of the intensive cooling at the solidification end on the internal quality of the slab.

[0020] Optionally, at the starting position of the intensive cooling at the solidification end, the central cooling rate of the slab is 0.2 - 0.6 °C / s. After this position, the central temperature of the slab begins to decrease rapidly, and the intensive cooling at the solidification end can fully play its role.

[0021] Optionally, at the end position of the intensive cooling at the solidification end, the solid fraction at the center of the continuous casting billet is 0.85 - 0.90. After this position, the molten steel inside the billet is lower than the viscous temperature of the steel, and the molten steel cannot flow between the dendrites. Continuing the intensive cooling at the solidification end has limited effect on improving the internal quality of the billet, but instead will reduce the surface temperature of the billet in the straightening zone and increase the probability of surface cracks.

[0022] Optionally, control the surface cooling rate of the continuous casting billet in the intensive cooling area at the solidification end to be more than 2 times the cooling rate at the center of the billet, so as to ensure the improvement effect of the intensive cooling at the solidification end on the internal quality of the billet.

[0023] Optionally, control the surface temperature recovery rate of the continuous casting billet after the intensive cooling at the solidification end to be less than 100 °C / m, so as to avoid the generation of internal cracks of the type of temperature recovery in the continuous casting billet.

[0024] Optionally, control the surface temperature of the continuous casting billet in the straightening zone to be higher than the upper limit of the third brittle temperature zone of the steel, so as to avoid the generation of surface cracks in the continuous casting billet.

[0025] Optionally, the third brittle temperature zone of the steel is measured by high-temperature thermal simulation experiments.

[0026] The beneficial effects of the present invention are as follows:

[0027] For the intensive cooling at the solidification end carried out according to the above method, the mechanism of the intensive cooling at the solidification end and the causes of crack generation are fully considered. Compared with the prior art, the optimal action area of the intensive cooling at the solidification end is determined, and by controlling the surface cooling rate of the billet, the surface temperature of the billet in the straightening zone, and the surface temperature recovery rate of the billet, the optimal water volume range of the intensive cooling at the solidification end is determined, so as to effectively solve the problem of billet cracks caused by intensive cooling on the basis of ensuring the improvement effect of the intensive cooling at the solidification end on the internal quality of the billet.

[0028] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent description, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in preferred detail below in conjunction with the drawings, where:

[0030] Figure 1 The flowchart of the control method for intensive cooling at the solidification end of the continuous casting billet according to the embodiment of the present invention is shown;

[0031] Figure 2 The change of the cooling rate at the center of the billet in the embodiment is shown;

[0032] Figure 3Shown is the change in the central solid fraction of the continuous casting slab in the embodiment. Detailed implementation manners

[0033] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the diagrams provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0034] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and should not be construed as a limitation to the present invention; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0035] In the drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, it is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and should not be construed as a limitation to the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0036] Please refer to Figures 1 to 3 , and the following uses a specific implementation case to further illustrate a method for controlling intensive cooling at the solidification end of continuous casting billets proposed in this application for a bloom continuous caster of a certain steel plant.

[0037] The arc radius of the continuous caster is 10 m, the cross-sectional size of the produced continuous casting slab is 160 mm × 160 mm, the steel grade is LX82B steel, the casting temperature is 1493 °C, the casting speed is 1.6 m / min, the cooling water volume in the mold is 122 m 3 / h, and the specific secondary cooling water volume is 0.80 L / kg. A solidification heat transfer model is established to analyze the central cooling rate of the continuous casting slab, the central solid fraction of the continuous casting slab, the surface cooling rate, the surface temperature, and the surface reheat rate of the continuous casting slab.

[0038] Figure 2The figure shows the change in the central cooling rate of the continuous casting billet during the continuous casting process. As can be seen from the figure, in the central area of the billet, at a position about 8.0 m from the meniscus, due to the release of the latent heat of solidification, the cooling rate begins to increase. Taking the position where the central cooling rate of the billet is 0.5 °C / s as the starting position of intensive cooling at the end of solidification, this position is 8.83 m from the meniscus. Figure 3 The figure shows the change in the central solid fraction of the continuous casting billet during the continuous casting process. Taking the position where the central solid fraction of the billet is 0.9 as the ending position of intensive cooling at the end of solidification, this position is 10.44 m from the meniscus. Considering the above factors comprehensively, the intensive cooling position at the end of solidification is determined to be 8.83 - 10.44 m from the meniscus.

[0039] On the basis of clarifying the intensive cooling at the end of solidification, a quantitative relationship model between the intensive cooling water volume at the end of solidification and the surface cooling rate of the billet, the surface temperature of the billet in the straightening zone, and the surface reheat rate of the billet is established. The specific results are as follows:

[0040] V c =-0.067Q 2 +1.255Q + 0.562R 2 =0.9991

[0041] T c =-1.483Q 2 -14.647Q + 839.6R 2 =0.9979

[0042] R c =0.566Q 2 +22.569Q + 42.08R 2 =0.9938

[0043] Among them, V c represents the surface cooling rate of the billet in the intensive cooling area at the end of solidification, °C / s; T c represents the surface temperature of the billet in the straightening zone, °C; R c represents the surface reheat rate of the billet, °C / m; Q represents the intensive cooling water volume at the end of solidification, m 3 / h.

[0044] Analyzing the average central cooling rate of the billet in the intensive cooling area at the end of solidification, the result is 1.03 °C / s. To ensure the improvement effect of the intensive cooling at the end of solidification on the internal quality of the billet, control the surface cooling rate of the billet in the intensive cooling area at the end of solidification to be greater than 2 times the central cooling rate of the billet, that is, it is required that the surface cooling rate of the billet in the intensive cooling area at the end of solidification is greater than 2.06 °C / s. According to the quantitative relationship model between the intensive cooling water volume at the end of solidification and the surface cooling rate of the billet, the intensive cooling water volume at the end of solidification is calculated inversely, and the range of the intensive cooling water volume Q1 under the first factor is determined to be (1.25, +∞) m 3 / h.

[0045] To avoid the generation of internal cracks in the continuous casting billet, the surface reheat rate of the billet after intensive cooling at the solidification end is controlled to be less than 100 °C / m. According to the quantitative relationship model between the intensive cooling water volume at the solidification end and the surface reheat rate of the billet, the intensive cooling water volume at the solidification end is calculated inversely, and the range of the intensive cooling water volume Q2 at the solidification end under the second factor is determined to be [0, 2.41) m 3 / h.

[0046] The third brittle temperature range of LX82B steel is measured through thermal simulation experiments, and its range is < 750 °C. To avoid the generation of surface cracks in the continuous casting billet, the surface temperature of the billet in the straightening zone is controlled to be higher than the upper limit of the third brittle temperature range of the steel, that is, the surface temperature of the billet in the straightening zone is controlled to be higher than 750 °C. According to the quantitative relationship model between the intensive cooling water volume at the solidification end and the surface temperature of the billet in the straightening zone of the billet, the intensive cooling water volume at the solidification end is calculated inversely, and the range of the intensive cooling water volume Q3 at the solidification end under the third factor is determined to be [0, 4.27) m 3 / h.

[0047] According to the range of the intensive cooling water volume Q1 at the solidification end under the first factor, the range of the intensive cooling water volume Q2 at the solidification end under the second factor, and the range of the intensive cooling water volume Q3 at the solidification end under the third factor, the reasonable range Q4 of the intensive cooling water volume at the solidification end is determined, and Q4 = Q1 ∩ Q2 ∩ Q3, and its control range is (1.25, 2.41) m 3 / h. To give full play to the improvement effect of intensive cooling at the solidification end on the internal quality of the billet, the intensive cooling water volume at the solidification end is taken as the maximum value within the range of Q4, that is, 2.41 m 3 / h.

[0048] By adopting a method for controlling intensive cooling at the solidification end of a continuous casting billet proposed in this application, the position of intensive cooling at the solidification end is finally determined to be in the range of 8.83 - 10.44 m from the meniscus, and the intensive cooling water volume at the solidification end is 2.40 m 3 / h. Industrial tests are carried out according to these parameters. The average carbon segregation index at the center of the billet is reduced from 1.15 to 1.04, and no cracks are found on the billet. To sum up, by adopting the method proposed in this application, the problem of billet cracks caused by intensive cooling can be solved on the basis of ensuring the improvement effect of intensive cooling at the solidification end on the internal quality of the billet.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for controlling intensive cooling at the solidification end of a continuous casting billet, characterized in that, It includes the following steps: S1: Establish a solidification heat transfer model based on the initial continuous casting process parameters, and use this model to calculate the center cooling rate, center solid fraction, surface cooling rate, surface temperature, and surface reheat rate of the billet; S2: Determine the starting position of intensive cooling at the solidification end according to the center cooling rate of the billet, and determine the ending position of intensive cooling at the solidification end according to the center solid fraction of the billet; S3: Establish a quantitative relationship model between the surface cooling rate of the billet in the intensive cooling area at the solidification end and the amount of intensive cooling water at the solidification end, and determine the range Q1 of the amount of intensive cooling water at the solidification end under the first factor according to this model; S4: Establish a quantitative relationship model between the surface temperature of the billet in the straightening area and the amount of intensive cooling water at the solidification end, and determine the range Q2 of the amount of intensive cooling water at the solidification end under the second factor according to this model; S5: Establish a quantitative relationship model between the surface reheat rate of the billet and the amount of intensive cooling water at the solidification end, and determine the range Q3 of the amount of intensive cooling water at the solidification end under the third factor according to this model; S6: Determine the reasonable range Q4 of the amount of intensive cooling water at the solidification end, Q4 = Q1 ∩ Q2 ∩ Q3; Among them, the quantitative relationship model between the surface cooling rate of the billet in the intensive cooling area at the solidification end, the surface temperature of the billet in the straightening area, the surface reheat rate of the billet, and the amount of intensive cooling water at the solidification end is determined by regression fitting, and the specific expression is: V c = -0.067Q 2 +1.255Q + 0.562 T c = -1.483Q 2 -14.647Q + 839.6 R c = 0.566Q 2 + 22.569Q + 42.08 Among them, V c represents the surface cooling rate of the slab in the solidification intensive cooling area, °C / s; T c represents the surface temperature of the slab in the straightening area, °C; R c represents the surface reheat rate of the slab, °C / m; Q represents the amount of intensive cooling water at the end of solidification, m 3 / h.

2. The continuous casting billet solidification end strong cooling control method according to claim 1, characterized in that, The maximum value within the range of Q4 is taken as the amount of intensive cooling water at the solidification end.

3. The continuous casting billet solidification end strong cooling control method according to claim 1, characterized in that At the starting position of intensive cooling at the solidification end, the center cooling rate of the billet is 0.2 - 0.6 °C / s.

4. The continuous casting billet solidification end strong cooling control method according to claim 1, characterized in that, At the ending position of intensive cooling at the solidification end, the center solid fraction of the billet is 0.85 - 0.

90.

5. The continuous casting billet solidification end strong cooling control method according to claim 1, characterized in that Control the surface cooling rate of the billet in the intensive cooling area at the solidification end to be greater than twice the center cooling rate of the billet.

6. The continuous casting billet solidification end strong cooling control method according to claim 1, characterized in that Control the surface reheat rate of the billet after intensive cooling at the solidification end to be less than 100 °C / m.

7. The continuous casting billet solidification end strong cooling control method according to claim 1, characterized in that Control the surface temperature of the billet in the straightening area to be greater than the upper limit of the third brittle temperature zone of the steel.

8. The continuous casting billet solidification end strong cooling control method according to claim 7, characterized in that, The third brittle temperature zone of the steel is measured by high-temperature thermal simulation experiments.

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