Design method of light press-down amount of large section billet solidification end

Abstract

The application discloses a design method of a light press-down amount of a large-section casting blank solidification end, which comprises the following steps: T1, determining influencing factors of a press-down amount Hi of any rack, including a section and solidification two-phase zone interval length coefficient a of the casting blank, a carbon content influencing coefficient b of the steel grade, a center solid phase rate Si of the casting blank at any rack and a press-down efficiency or a reduction rate Mi of a two-phase zone area when the solidification end is implemented; T2, calculating the press-down amount Hi of any rack according to a formula Hi=ab(Si / Mi) n The design method of the light press-down amount of the large-section casting blank solidification end comprehensively considers influences of the carbon content of the steel grade, the section thickness of the casting blank, the center solid phase rate of the press-down position of the casting blank and the press-down efficiency and other key factors, establishes a function relation formula of the press-down amount of any rack, and can quickly and effectively give the press-down interval of the casting blank solidification end, the number of light press-down racks and the press-down amount of each rack.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal solidification and continuous casting, and particularly relates to a design method of a light press-down amount at a solidification end of a large-section billet. BACKGROUND

[0002] With the development of metallurgical technology in the world, modern continuous casting technology is constantly progressing, and castable steel types are constantly expanding. Some high-carbon and high-alloy steel types have been produced in the continuous casting process of large steel enterprises. In particular, the development of large-section billet continuous casting technology has increased the compression ratio of steel and improved the product quality of steel. However, the increase in the section of the billet has brought about the deterioration of the core quality of the billet. In recent years, the thickness of the large bloom and large rectangular billet produced by the continuous casting machine has reached more than 350-500 mm, and the light press-down technology at the solidification end has become a necessary equipment for the special steel large bloom continuous casting machine and is widely used.

[0003] However, the application of the light press-down technology at the solidification end has brought about two key problems. One is that the shrinkage cavity in the core of the billet cannot be completely healed, and the other is the generation of press-down cracks. Therefore, in addition to optimizing the quality of molten steel and the secondary cooling technology, the main technical measures taken by metallurgical workers are to optimize the press-down amount, press-down position, and shape of the press-down roller at the solidification end, so as to effectively improve the center solidification segregation and shrinkage cavity of the billet while eliminating stress concentration and crack generation.

[0004] The patent document with the publication number CN101648263A provides a light press-down scheme at the solidification end of a high-quality cord steel at different solid phase rate positions. In the technical scheme disclosed in the patent document, there are two problems. First, only a single steel press-down scheme is given, without considering the press-down technology at the solidification end of bearing steel, cord steel, spring steel, and high-quality structural steel with different carbon contents, so the application range is limited. Second, the influence of the section of the billet is not considered, so it lacks systematicness. SUMMARY

[0005] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application provides a design method of a light press-down amount at the solidification end of a large-section billet, which aims to improve the application range.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: the design method of the light press-down amount at the solidification end of the large-section billet, comprising the steps of:

[0007] T1, determining the influencing factors of the press-down amount Hi of any stand, including the section of the billet and the length coefficient a of the two-phase zone interval of solidification, the carbon content influencing coefficient b of the steel type, the center solid phase rate Si of the billet at any stand, and the press-down efficiency or the reduction rate Mi of the two-phase zone area when the solidification end press-down is implemented;

[0008] T2, according to the formula Hi = ab(Si / Mi) n , calculate any frame pressure Hi.

[0009] In the step T2, the value range of the index n is 0.2-0.5.

[0010] The value range of the cross section and solidification two-phase zone interval length coefficient a of the casting blank is 3-4.5.

[0011] The value range of the carbon content influence coefficient b of the steel grade is 0.4-1.1.

[0012] The value range of the center solid phase rate Si of the casting blank at any frame is 40%-100%.

[0013] The value range of the reduction rate Mi of the reduction efficiency or two-phase zone area when the solidification end reduction is implemented is 5%-60%.

[0014] The application also provides another design method of the large cross section casting blank solidification end light reduction amount, characterized by comprising the steps of:

[0015] F1, determine the influencing factors of any frame pressure Hi, including the casting blank cross section and steel grade influence coefficient c, the center solid phase rate Si of the casting blank at any frame and the reduction efficiency or two-phase zone area reduction rate Mi when the solidification end reduction is implemented;

[0016] F2, according to the formula Hi = c(Si / Mi) n , calculate any frame pressure Hi.

[0017] In the step F2, the value range of the index n is 0.2-0.5.

[0018] The value range of the casting blank cross section and steel grade influence coefficient c is 1.2-4.95.

[0019] The value range of the center solid phase rate Si of the casting blank at any frame is 40%-100%.

[0020] The value range of the reduction rate Mi of the reduction efficiency or two-phase zone area when the solidification end reduction is implemented is 5%-60%.

[0021] The design method of the light press-down amount of the solidification end of the large-section casting blank comprehensively considers the influences of the carbon content of the steel grade, the section thickness of the casting blank, the solid phase rate of the casting blank center at the press-down position and the press-down efficiency and other key factors, establishes a function relationship of the press-down amount of any rack, can quickly and effectively give the press-down interval of the solidification end of the casting blank, the number of light press-down racks and the press-down amount of each rack, can directly obtain the solidification end press-down parameters of different steel grades and different section casting blanks, and is applied to industrial production, effectively improves the segregation and shrinkage of the casting blank, and improves the application range. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application are further described below through the description of the embodiments, which aims to help the skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present application, and to help the implementation thereof.

[0023] Example One

[0024] The present embodiment provides a design method of the light press-down amount of the solidification end of the large-section casting blank, which comprises the following steps:

[0025] T1, determining the influencing factors of the press-down amount Hi of any rack, including the section and solidification two-phase zone interval length coefficient a of the casting blank, the carbon content influencing coefficient b of the steel grade, the center solid phase rate Si of the casting blank at any rack and the press-down efficiency or the reduction rate Mi of the two-phase zone area when the solidification end press-down is implemented;

[0026] T2, calculating the press-down amount Hi of any rack according to the formula Hi = ab(Si / Mi). n

[0027] In the method, the press-down amount Hi of any rack is mainly influenced by the following four factors: one is the section and solidification two-phase zone interval length coefficient a of the casting blank; two is the carbon content influencing coefficient b of the produced steel grade; three is the center solid phase rate Si of the casting blank at any rack; four is the press-down efficiency or the reduction rate Mi of the two-phase zone area when the solidification end press-down is implemented under the condition of the center solid phase rate of the casting blank at any rack to compensate for the solidification shrinkage.

[0028] In the above step T2, the value range of the index n is 0.2-0.5, and the value of the index n can be given by the statistical results of different types of production casting machines.

[0029] ​The reduction amount Hi of any stand represents the reduction amounts of H1, H2, H3, etc., i.e., the reduction amounts of the first, second, third, etc. stands. The central solids content Si of the billet at any stand represents the central solids content of the billet at the first, second, third, etc. stands. The reduction efficiency or the reduction rate of the two-phase region area Mi at the end of solidification at any stand represents the reduction efficiency or the reduction rate of the two-phase region area at the first, second, third, etc. stands.

[0030] The design method for the light reduction at the end of solidification of large cross-section billets in this embodiment is applicable to billet thicknesses of 200mm-450mm. Furthermore, as the cross-section of the billet and the casting speed increase, the length coefficient 'a' between the cross-section of the billet and the solidification two-phase region continuously increases. The value range of the length coefficient 'a' between the cross-section of the billet and the solidification two-phase region is 3-4.5.

[0031] The design method for the solidification end reduction of large-section cast billets in this embodiment is applicable to the production of steel grades with a carbon content range of 0.4%-1.1%. The carbon content influence coefficient b of the steel grade ranges from 0.4 to 1.1, meaning that the value of b is approximately equal to 100 times the carbon content of the steel grade being produced. The value of b increases with increasing carbon content. The carbon content influence coefficient of the steel grade can also be the carbon equivalent influence coefficient; although there is a difference in their values, they are approximately the same. Therefore, the higher the carbon content of the steel grade, the larger the value of the carbon content influence coefficient b, and the larger the corresponding solidification end reduction. As the carbon content decreases, the solidification end reduction at any stand and the total reduction both decrease accordingly.

[0032] The central solids fraction Si of the billet at any stand ranges from 40% to 100%. As the carbon content increases, the length of this 40%-100% central solids fraction interval increases, determining the length of the solidification end reduction interval. Generally, the spacing between the solidification end reduction stands in a large billet continuous casting machine is approximately 900-1100 mm, which determines the number of reduction stands required. That is, as the carbon content increases, the required number of solidification end reduction stands increases. Conversely, as the carbon content decreases, the required number of solidification end reduction stands decreases accordingly.

[0033] Other major factors affecting the length of the 40%-100% solids content range at the center of the billet include the casting speed of the continuous casting machine and the billet cross-section. As the casting speed of the continuous casting machine increases and the billet cross-section increases, the length of the 40%-100% solids content range at the center of the billet also increases, and the number of solidification end-reduction stands required also increases.

[0034] Computer simulation studies show that, within the range of 40%-100% central solids content of the billet, under the condition of central solids content Si of the billet at any stand, the value of the reduction efficiency or the reduction rate Mi of the two-phase region area during solidification end-reduction ranges from 5% to 60%, and as the central solids content Si of the billet increases, the value of Mi decreases.

[0035] If the above-mentioned design method for light reduction at the end of solidification is used, and reduction cracks appear inside the billet, it indicates that the reduction amount is too large. Based on the stress and strain calculation results, the reduction amount should be corrected with the standard that the deformation rate at the solidification front caused by the reduction of each stand is less than 0.1%-0.3% to prevent the generation of reduction cracks caused by excessive reduction at the solidification front.

[0036] The design method for the light reduction at the end of solidification of large-section billets in this embodiment is based on computer simulation of heat transfer during continuous casting. First, the distribution of the solid fraction at the center of the billet along its length is obtained. Then, a range of 40% to 100% solid fraction at the center of the billet is selected as the light reduction interval. A reasonable number of light reduction stands is determined, and then the reduction is applied according to the functional relationship Hi = ab(Si / Mi) given in this design method. n This allows for the determination of the reduction amount for each stand. This method can directly obtain the solidification end reduction parameters for slabs of different steel grades and cross-sections, and can be applied to industrial production, effectively improving slab segregation and shrinkage cavities. It has a series of advantages such as simplicity, reliability, and practicality.

[0037] Example 2

[0038] This embodiment provides a design method for the light reduction at the end of solidification of a large-section cast billet, including the following steps:

[0039] F1. Determine the influencing factors of the reduction amount Hi of any stand, including the influence coefficients of billet cross section and steel grade c, the central solid fraction Si of the billet at any stand, and the reduction efficiency or the reduction rate Mi of the two-phase region area when implementing the final reduction of solidification.

[0040] F2. According to the formula Hi=c(Si / Mi) n Calculate the reduction Hi of any frame.

[0041] In step F2 above, the value of the exponent n ranges from 0.2 to 0.5, and the value of the exponent n can be given by statistical results of different types of casting machines used in production.

[0042] The difference between this embodiment and Embodiment 1 is that the length coefficient a between the cross-section of the billet and the solidification two-phase region and the carbon content influence coefficient b of the steel grade in Embodiment 1 are combined into the cross-section of the billet and the influence coefficient c of the steel grade. The rest of the content is the same as that in Embodiment 1.

[0043] In this embodiment, the formula for the reduction amount of any rack is transformed into Hi = c(Si / Mi). n The value of c ranges from 1.2 to 4.95.

[0044] The design method for the light reduction at the end of solidification of large cross-section cast billets in this embodiment should be used in conjunction with electromagnetic stirring technology, and ensure that the area of ​​the central equiaxed crystals of the cast billet accounts for 10%-50% of the cross-sectional area of ​​the cast billet.

[0045] Example 3

[0046] Taking the production of 250mm high-carbon bearing steel as an example, computer simulation was used to calculate that under three-dimensional solidification heat transfer conditions at a drawing speed of 1.2m / min, the length of the core solids content of the billet between 50% and 100% is approximately 5400mm. Based on a design with a spacing of approximately 1000mm between each pressing roll, it is expected that six pressing rolls can be used. At this point, the core solids content of the billet under each stand, S1, S2, S3, S4, S5, and S6, are 51%, 62%, 70%, 83%, 92%, and 100%, respectively.

[0047] Secondly, based on the analysis of the compression stress technology model, or based on the existing analysis of compression deformation at the solidification end of the billet, the compression efficiency or the reduction rate of the two-phase region area when compression is carried out at the solidification end to compensate for solidification shrinkage under the condition of the solid fraction of the billet center at any stand is 45%, 38%, 30%, 22%, 15%, and 8%, respectively.

[0048] Then, according to the functional relationship Hi = ab(Si / Mi) n In the formula:

[0049] Exponent n: takes the value 1 / 3;

[0050] The carbon content influence coefficient b of steel grade: for bearing steel, the value is 0.99;

[0051] The length coefficient a between the cross section of the billet and the solidification two-phase region is 3.0 for a 250×250 square billet.

[0052] Therefore, the compression under each frame can be calculated as follows: H1 = 3.1mm, H2 = 3.6mm, H3 = 4.4mm, H4 = 4.7mm, H5 = 5.5mm, H6 = 6.7mm.

[0053] Based on the principle that the deformation rate at the solidification front caused by the pressing down of each frame should be less than 0.1%-0.3%, the pressing amount is corrected, and the pressing amount of roller #6 is reduced to 6.0mm to prevent the formation of pressing cracks caused by excessive pressing down at the solidification front.

[0054] The adjusted pressing amounts for frames 1-6 are as follows: H1 = 3.1mm, H2 = 3.6mm, H3 = 4.4mm, H4 = 4.7mm, H5 = 5.5mm, and H6 = 6.0mm.

[0055] At a drawing speed of 1.2 m / min, the total reduction of a 250×250 mm square billet is 27.3 mm.

[0056] The above process can effectively improve the degree of V-type segregation during solidification and reduce carbon segregation in the center of the billet.

[0057] Example 4

[0058] Taking the production of 350mm thick spring steel as an example, computer simulation was used to calculate that under three-dimensional solidification heat transfer conditions at a drawing speed of 0.45m / min, the length of the core solids content of the billet between 45% and 100% is approximately 4300mm. Based on a design with a spacing of approximately 1000mm between each pressing roll, it is expected that five pressing rolls can be used for pressing. At this point, the core solids content of the billet under each stand, S1, S2, S3, S4, and S5, are 46%, 59%, 79%, 92%, and 100%, respectively.

[0059] Secondly, based on the analysis of the compression stress technology model, or based on the existing analysis of the compression deformation at the solidification end of the billet, the compression efficiency or the reduction rate of the two-phase region area when compression is carried out at the solidification end to compensate for solidification shrinkage under the condition of the solid fraction of the billet center at any stand is 39%, 28%, 20%, 15%, and 8%, respectively.

[0060] Then, according to the functional relationship Hi = ab(Si / Mi) n In the formula:

[0061] Exponent n: takes the value 1 / 3;

[0062] The carbon content influence coefficient b of steel grade: for spring steel, the value is 0.60;

[0063] The length coefficient a between the cross section of the billet and the solidification two-phase region is 3.8 for a 380×450 square billet.

[0064] Therefore, the compression under each frame can be calculated as follows: H1 = 2.4 mm, H2 = 3.0 mm, H3 = 3.6 mm, H4 = 4.2 mm, H5 = 5.3 mm.

[0065] The reduction was reviewed based on the baseline principle that the solidification front deformation rate caused by each press down should be less than 0.1%-0.3%. The results showed that each reduction met the above requirements.

[0066] Therefore, it is determined that at a drawing speed of 0.45 m / min, the total reduction of the 380×450 mm square billet is 18.5 mm.

[0067] The above process can effectively improve the degree of V-type segregation during solidification and reduce carbon segregation in the center of the billet.

[0068] The present invention has been described above by way of example. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention; or the direct application of the inventive concept and technical solution to other situations without modification, are all within the protection scope of the present invention.

Claims

1. A method for designing the amount of light reduction at the end of solidification of large-section cast billets, characterized in that, Including the following steps: T1. Determine the influencing factors of the reduction amount Hi of any stand, including the cross section of the billet and the length coefficient between the solidification two-phase region a, the carbon content influence coefficient of the steel grade b, the central solid fraction Si of the billet at any stand, and the reduction efficiency or the reduction rate Mi of the two-phase region area when implementing the final reduction of solidification. T2. According to the formula Hi=ab(Si / Mi) n Calculate the reduction Hi of any frame; The value range of the carbon content influence coefficient b for the steel grade is 0.4-1.1; The value of the central solid fraction Si of the billet at any stand ranges from 40% to 100%. In step T2, the value of the exponent n ranges from 0.2 to 0.

5.

2. The design method for the light reduction at the end of solidification of large-section cast billets according to claim 1, characterized in that, The value range of the length coefficient 'a' between the cross section of the billet and the solidification two-phase region is 3-4.

5.

3. The design method for the light reduction at the end of solidification of large-section cast billets according to claim 1, characterized in that, The value of the reduction efficiency or the reduction rate Mi of the two-phase region area during the solidification end reduction is in the range of 5%-60%.

4. A method for designing the amount of light reduction at the end of solidification of large-section cast billets, characterized in that, Including the following steps: F1. Determine the influencing factors of the reduction amount Hi of any stand, including the influence coefficients of billet cross section and steel grade c, the central solid fraction Si of the billet at any stand, and the reduction efficiency or the reduction rate Mi of the two-phase region area when implementing the final reduction of solidification. F2. According to the formula Hi=c(Si / Mi) n Calculate the reduction Hi of any frame; The value range of the influence coefficient c between the billet cross-section and steel grade is 1.2-4.95; The value of the central solid fraction Si of the billet at any stand ranges from 40% to 100%. In step F2, the value of the exponent n ranges from 0.2 to 0.

5.

5. The design method for the light reduction at the end of solidification of large-section cast billets according to claim 4, characterized in that, The value of the reduction efficiency or the reduction rate Mi of the two-phase region area during the solidification end reduction is in the range of 5%-60%.