A method for improving the metal yield of mixed casting billets

Abstract

This invention discloses a method for improving the metal yield of cast billets, relating to the technical field of continuous casting control methods. Specifically, it includes determining the range of width contraction coefficients for various steel grades, selecting the maximum and minimum values ​​among the width contraction coefficients, calculating the lower opening dimension of the crystallizer based on the minimum width contraction coefficient, calculating the insufficient width and length of the cast billet based on the maximum and minimum width contraction coefficients and the original length of the cast billet, and then determining the final width and final length of the cast billet according to the principle of width reduction and length adjustment. The final dimensions determined in this way not only solve the problem of high continuous casting consumption caused by the large variety of mixed steel grades in continuous casting and the lack of online fine-tuning width adjustment functions in the crystallizers of most steel plants, making it impossible to accurately control the width of the cold-cast billet, but also improve the metal yield of continuous casting and reduce steel production cost losses.

Description

Technical Field

[0001] This invention relates to the field of continuous casting control methods, and in particular to a method for improving the metal yield of mixed casting billets. Background Technology

[0002] Competition in the steel industry is becoming increasingly fierce, and profit margins for steel products are being squeezed sharply. To meet the challenges brought by the market, high efficiency, high profitability, and low cost have become important directions for enterprise development. Steel material consumption has always been the most critical indicator related to the profitability of steel enterprises and the reduction of their product costs. Reducing steel material consumption in continuous casting processes can be achieved by reducing continuous casting consumption and increasing metal yield.

[0003] During the casting process, factors such as the shape, structure, and production conditions of the cast steel parts hinder the solid-state linear shrinkage, thus affecting the dimensional deviations of the cast steel parts. This results in some dimensions being insufficient for machining, increasing the amount of welding work required for repairing the castings, and consequently increasing the scrap rate of the cast steel parts. Continuous casting is a process in which molten steel is poured, cooled, and cut using a continuous casting machine to directly obtain a billet of a predetermined size and shape. It is an intermediate link between steelmaking and rolling, and an important component of steelmaking production. Continuous casting billets are mainly classified into slabs, square billets, rectangular billets, and round billets in terms of shape, with different sizes for different types. The standard size of the slab is an important indicator of the quality of the continuous casting billet. During the continuous casting process, the temperature, composition, and casting speed of the billet affect the amount of shrinkage, while the precision of equipment such as the crystallizer, the fan-shaped section, and the flame cutter also affects the width, length, and thickness of the billet. The crystallizer is a crucial piece of equipment in continuous casting production. The width of the billet in the cold state is controlled by the difference between the bottom width of the crystallizer and the shrinkage coefficient. Different steels have different casting speeds, temperatures, and compositions, resulting in different shrinkage coefficients. The accuracy of the width dimension is a critical factor in determining the metal yield of continuous casting. On the one hand, if the billet is too wide, the continuous casting consumption is high, leading to increased waste from trimming and a lower metal yield. On the other hand, if the billet is too narrow, it results in insufficient dimensions, with insufficient trimming allowance for wide plates, which can easily cause problems with width.

[0004] Therefore, inventing a method that can effectively improve metal yield is of great significance to the steel industry. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention provides a method for improving the metal yield of mixed-cast slabs, which fully considers the different steel grades, cross-sections, and casting speed requirements to precisely control the slab width. This is specifically achieved through the following techniques.

[0006] The present invention provides a method for improving the metal yield of cast billets, comprising the following steps:

[0007] S1. Based on the original width of the billet and the casting speed, measure the actual shrinkage ratio of the width of various steel grades, and calculate and determine the width shrinkage coefficient of the cross-section of various steel grades.

[0008] S2. Based on the minimum width shrinkage coefficient in step S1 and the original width of the billet, calculate the lower opening size of the crystallizer, and then use the crystallizer width adjustment program to input the lower opening size of the crystallizer and the percentage taper of the crystallizer.

[0009] S3. Based on the maximum and minimum values ​​of the width shrinkage coefficient in step S1, and combined with the original length of the billet, calculate the insufficient width and the length of the billet. Then, based on the principle of width reduction and lengthening, determine the final width and final length of the billet.

[0010] Furthermore, the formula for calculating the lower opening size of the crystallizer is: W 下 =W×A1; The formula for calculating the insufficient width of the billet is: (A2-A1)×W; The formula for calculating the length extension of the billet is: L×W / [W-(A2-A1)W]-L. In the formula, W is the original width of the billet, A1 is the minimum value of the shrinkage coefficient, A2 is the maximum value of the shrinkage coefficient, and L is the original length of the billet to be cut.

[0011] Furthermore, the formula for calculating the final width of the billet, based on the above formula, is: W-(A2-A1)W, and the formula for calculating the final length is: L×W / [W-(A2-A1)W].

[0012] Furthermore, the range of the width reduction coefficient for the various steel grades mentioned above is 0.995-1.016. Different steel grades have different carbon contents and alloy element contents, resulting in significant differences in their linear shrinkage rates. The disclosed range of width reduction coefficients is based on measurements taken during the applicant's actual production process.

[0013] Furthermore, the verification method for the lower opening size of the crystallizer is as follows: calculate the theoretical upper opening size and theoretical taper of the crystallizer, measure the actual upper opening size and actual taper of the crystallizer. If the difference between the theoretical upper opening size and the actual upper opening size of the crystallizer does not exceed 1 mm, and the difference between the actual taper and the theoretical taper of the crystallizer does not exceed 0.2 mm, then the lower opening size of the crystallizer meets the production requirements.

[0014] Furthermore, the formula for calculating the theoretical size of the upper opening of the crystallizer mentioned above is: W 上= W 下 ×(1+T); The theoretical taper is a narrow-face millimeter taper, and the calculation formula for the narrow-face millimeter taper is: (W 上 -W 下 ) / 2; where W 下 denoted as the lower opening size of the crystallizer, and T as the percentage taper of the crystallizer.

[0015] Furthermore, the percentage taper of the crystallizer is (0.9-1.2)%.

[0016] The principle of determining the final width and length of the cast billet based on the principle of width reduction and length compensation in this invention is as follows: Generally, the width of the cast billet will fluctuate to some extent, especially for some steel grades with low high-temperature strength. Therefore, this invention takes the solidification shrinkage characteristics of the billet shell as its starting point, and provides the minimum width shrinkage coefficient required for the steel grade in each production run. For steel grades with insufficient width, the minimum width shrinkage coefficient among different mixed-cast steel grades is selected according to the length compensation principle. For steel grades with a large width shrinkage coefficient, the insufficient width and the length compensation of the cast billet are calculated. Based on the length compensation, the cast billet is lengthened in the length direction to meet the billet volume ratio requirements. Wide and thick plates are rolled according to the actual matching dimensions provided by continuous casting to reduce the amount of wide plate trimming. This reduces continuous casting consumption, reduces trimming losses during production, and achieves the goal of improving the slab metal yield.

[0017] Compared with existing technologies, the advantages of this invention are as follows: This invention calculates the insufficient width and length of the cast billet based on the maximum and minimum values ​​of the cross-sectional width contraction coefficient for steel grades with insufficient width, according to the principle of length compensation. Then, it calculates the final width and length of the cast billet based on these calculations. The billet is then lengthened in the longitudinal direction to meet the required volume ratio. The thick plates are rolled according to the final width to reduce the amount of trimming. On the one hand, this solves the problem of high continuous casting consumption caused by the lack of online micro-adjustment functionality in most steel mills' crystallizers due to the wide variety of mixed steel grades in continuous casting. On the other hand, it increases the continuous casting metal recovery rate by 0.5%. Based on a price difference of 1000 yuan between the cast billet and scrap steel, this translates to a cost reduction of 9 million yuan per year for a steel mill producing 1.8 million tons of slabs annually. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Experimental Example 1

[0020] This experimental example involves the planned production of 10 heats of Q235 and 10 heats of Q355B steel with a cross section of 250*2200mm. The typical casting speed for the steel is 1.05m / min, and the percentage taper T is selected as 1.05% according to the characteristics of the steel.

[0021] Based on the shrinkage characteristics of different steel grades, the width shrinkage coefficient of Q235 is 0.996, and that of Q355B is 1.006. Therefore, the minimum coefficient value selected is 0.996, i.e., A1 is 0.996. The calculated lower opening dimension W of the crystallizer is then obtained. 下 Given 2200 × 0.996 = 2191.2 mm, the upper opening size W of the crystallizer is... 上 The diameter is 2191.2 × (1 + 1.05%) = 2214.2 mm. Therefore, the taper of the narrow face of the crystallizer is (2214.2 - 2191.2) / 2 = 11.5 mm.

[0022] For the Q355B steel series, its width reduction coefficient is 1.006, i.e., A2 is 1.006. Therefore, the insufficient width is: 2200 × (1.006 - 0.996) = 22mm. After the billet cools, the actual width of the Q235 cold billet is 2200mm, which meets the dimensional width requirements. However, the actual width of the Q355B cold billet is 2180mm, which is too narrow. If the length is not extended, the volume will not meet the requirements, and rolling will result in short lengths, causing unplanned losses.

[0023] Experiment Example 2

[0024] This experimental example involves the planned production of 10 heats of Q235 and 10 heats of Q355B steel with a cross section of 250*2200mm. The typical casting speed for the steel is 1.05m / min, and the percentage taper T is selected as 1.05% according to the characteristics of the steel.

[0025] Based on the shrinkage characteristics of different steel grades, the width shrinkage coefficient of Q235 is 0.996 and that of Q355B is 1.006. Therefore, the minimum value A1 and the maximum value A2 selected in this experimental example are 0.996 and 1.006, respectively.

[0026] The lower opening size of the crystallizer, W_lower, is 2200 × 0.996 = 2213.2 mm. The upper opening size of the crystallizer, W_upper, is 2213.2 × (1 + 1.05%) = 2236.4 mm. The taper of the narrow face of the crystallizer is (2236.4 - 2213.2) / 2 = 11.6 mm.

[0027] After cooling, the actual width of the Q355B cold billet is 2200mm, which meets the dimensional width requirements. However, for the Q235 series, because its width shrinkage coefficient is 0.996, the width allowance is: 2200×(1.006-0.996)=22mm. After cooling, the actual width of the Q235 cold billet is 2222mm, which is too wide, resulting in high continuous casting consumption and low metal yield.

[0028] Experimental Example 3

[0029] Based on the problems of either being too narrow or too wide that occurred in Experiment Examples 1-2 above, this experiment adopts the principle of reducing width and compensating for length. According to the calculation method of insufficient billet width and billet length compensation provided by this invention, it is planned to produce 10 heats of Q235 and 10 heats of Q355B steel with a cross section of 250*2200mm, using a typical casting speed of 1.05m / min for the steel grade, and the percentage taper T is selected as 1.05% according to the characteristics of the steel grade.

[0030] Based on the shrinkage characteristics of different steel grades, the width shrinkage coefficient of Q235 is 0.996, and the width shrinkage coefficient of Q355B is 1.006. Therefore, the minimum coefficient selected in this experimental example is 0.996, that is, A1 is 0.996.

[0031] Therefore, the calculated lower opening size W of the crystallizer is 2200 × 0.996 = 2191.2 mm, and the upper opening size W of the crystallizer is... 上 The diameter is 2191.2 × (1 + 1.05%) = 2214.2 mm. Therefore, the taper of the narrow face of the crystallizer is (2214.2 - 2191.2) / 2 = 11.5 mm.

[0032] For the Q355B series, since its width shrinkage coefficient is 1.006, the insufficient width is: 2200 × (1.006 - 0.996) = 22mm. Therefore, the length adjustment is L × 2200 / (2200 - 22) - L. The standard length L of a single cast billet ranges from 2400mm to 4100mm. For example, if L is taken as 3000mm, the length adjustment is 3000 × 2200 / 2178 - 3000 = 30mm. Therefore, the dimensional information is matched according to 250*2178*3030. This is then sent to the heavy plate mill, which rolls the billet according to the matching information.

[0033] Because the standard length L of a single cast billet ranges from 2400mm to 4100mm, with most L around 3000mm, any length adjustments can be calculated based on a standard length of 3000mm. Therefore, the actual length of the cast billet corresponding to the Q355B steel grade in this casting, cut by adding 30mm to the original length, can meet the volume requirements.

[0034] Application Example 1: Evaluation of Metal Yield and Slab Width Dimensions in Experiment Example 1

[0035] This application example will use the method of Experimental Example 1 to plan the production of 10 heats of Q235 and 10 heats of Q355B steel with a cross section of 250*2200mm. The minimum width reduction coefficient is 0.996. The metal yield of this casting will be calculated. The calculation process and results are shown below:

[0036] If each heat of molten steel produces 150 tons, with a cut length of 500mm at the beginning and 700mm at the end, an 8mm kerf, and a 5-ton reserve in the ladle during the pouring stop, and all cuts are planned to be 3000mm, and the steel density is 7.83t / m³, then the weight per meter of a 250×2200 cross-section billet would be 0.25×2.2×7.83=4.3065 tons.

[0037] The calculation process of theoretical metal yield for this casting (only the theoretical values ​​of width and length are considered here, and the influence of other factors on metal yield is not considered):

[0038] Head cut + tail cut + remaining amount injected = (0.5 + 0.7) m × 4.3065 m / t + 5t = 10.16t;

[0039] Number of steel blocks per furnace = 150t ÷ 4.3065t / m ÷ 3m = 11, then the number of cuts per furnace is 11 - 1 = 10;

[0040] The loss from the kerf in a single furnace is 0.008m × 10 × 4.3065t = 0.08m × 4.3065t = 0.6264t;

[0041] Therefore, the dimensions of Q235 meet the requirements, and the theoretical qualified casting quantity of Q235 per furnace is 150t - 0.6264t = 149.37t; the dimensions of Q355B are too narrow, which translates to a single casting billet that is 30mm shorter in length. Therefore, the actual theoretical qualified casting quantity of Q355B per furnace is 149.37 + 11 × 0.03mm × 4.3056t = 150.79t.

[0042] The amount of molten steel to be poured in this batch is 150t / heat × 20 heats = 3000t;

[0043] The theoretical yield of qualified billets in this casting is: 149.37×10 + 150.79×10 - 10.16t = 3001.6t;

[0044] The metal yield of this casting is 2991.44 / 3000×100%=99.71%. Therefore, the metal yield of this casting is 99.71%. Although the metal yield is high due to the use of a smaller coefficient, the width of Q355B is too narrow and does not meet the size requirements. The volume ratio does not meet the requirements for wide and thick plates.

[0045] Application Example 2: Evaluation of Metal Yield and Slab Width Dimensions in Experiment Example 2

[0046] This application example will use the method of Experimental Example 2 to plan the production of 10 heats of Q235 and 10 heats of Q355B steel with a cross section of 250*2200mm. The maximum width reduction coefficient is 1.006. The metal yield of this casting will be calculated. The calculation process and results are shown below:

[0047] If each heat of molten steel produces 150 tons, with a cut length of 500mm at the beginning and 700mm at the end, an 8mm kerf, and a 5-ton reserve in the ladle during the pouring stop, and all cuts are planned to be 3000mm, and the steel density is 7.83t / m³, then the weight per meter of a 250×2200 cross-section billet would be 0.25×2.2×7.83=4.3065 tons.

[0048] Theoretical metal yield calculation for this casting (only the theoretical values ​​of width and length are considered here, and the influence of other factors on metal yield is not taken into account):

[0049] Head cut + tail cut + remaining amount injected = (0.5 + 0.7) m × 4.3065 m / t + 5t = 10.16t;

[0050] Number of steel blocks per furnace = 150t ÷ 4.3065t / m ÷ 3m = 11, then the number of cuts per furnace is 11 - 1 = 10;

[0051] The loss from the kerf in a single furnace is 0.008m × 10 × 4.3065t = 0.08m × 4.3065t = 0.6264t;

[0052] Therefore, the dimensions of Q355B meet the requirements, and the theoretical qualified casting quantity of Q355B per furnace is 150t - 0.6264t = 149.37t; the dimensions of Q235B are too wide, which translates to a single casting billet length of 30mm. Therefore, the actual theoretical qualified casting quantity of Q235 per furnace is 149.37 - 11 × 0.03mm × 4.3056t = 147.95t.

[0053] The amount of molten steel to be poured in this batch is 150t / heat × 20 heats = 3000t;

[0054] The theoretical yield of qualified billets in this casting is: 147.95×10 + 149.37×10 - 10.16t = 2963.04t;

[0055] The metal yield of this casting is 2963.04 / 3000×100%=98.76%. Therefore, the metal yield of this casting is 98.76%. This casting used a relatively large coefficient, and the Q235 billet was too wide, resulting in a low metal yield.

[0056] Application Example 3: Evaluation of Metal Yield and Slab Width Dimensions in Experiment Example 3

[0057] This application example will use the method of Experimental Example 3 to plan the production of 10 heats of Q235 and 10 heats of Q355B steel with a cross section of 250*2200mm. The minimum width reduction coefficient is 0.996. The length of each Q355B steel billet will be increased by 30mm, and the billet size will be matched to 250*2178*3030. The metal yield of this casting will be calculated. The calculation process and results are shown below:

[0058] If each heat of molten steel produces 150 tons, with a cut length of 500mm at the beginning and 700mm at the end, an 8mm kerf, and a 5-ton reserve in the ladle during the pouring stop, and all cuts are planned to be 3000mm, and the steel density is 7.83t / m³, then the weight per meter of a 250×2200 cross-section billet would be 0.25×2.2×7.83=4.3065 tons.

[0059] The calculation process of theoretical metal yield for this casting (only the theoretical values ​​of width and length are considered here, and the influence of other factors on metal yield is not considered):

[0060] Head cut + tail cut + remaining amount injected = (0.5 + 0.7) m × 4.3065 m / t + 5t = 10.16t;

[0061] Number of steel blocks per furnace = 150t ÷ 4.3065t / m ÷ 3m = 11, then the number of cuts per furnace is 11 - 1 = 10;

[0062] The loss from the kerf in a single furnace is 0.008m × 10 × 4.3065t = 0.08m × 4.3065t = 0.6264t;

[0063] Therefore, the dimensions of Q235 meet the requirements, and the theoretical qualified casting quantity of Q235 per furnace is 150t - 0.6264t = 149.37t; the dimensions of Q355B are slightly narrower, but their lengths have been increased by 30mm, so the volume ratio remains unchanged. Converted to a length where each casting billet is 30mm shorter, the theoretical qualified casting quantity of Q355B per furnace is 150t - 0.6264t = 149.37t.

[0064] The amount of molten steel to be poured in this batch is 150t / heat × 20 heats = 3000t;

[0065] The theoretical yield of qualified billets in this casting is: 149.37 × 20 - 10.16 t = 2977.24 t;

[0066] The metal yield of this casting is 2977.24 / 3000×100%=99.24%. Therefore, the metal yield of this casting is 99.24%. The use of a smaller coefficient in this casting not only effectively improved the metal yield but also met the requirements of the billet size for the thick plate.

[0067] In addition, the applicant also evaluated the metal yield and billet width of other steel grades. For example, the width shrinkage coefficient of Q355K steel grade is 0.995, and the width shrinkage coefficient of Q960(K2ZL) steel grade is 1.016. If there is mixed casting of these steel grades, the width reduction and lengthening process can also achieve a high metal yield and meet the dimensional requirements.

[0068] In summary, based on the principle of width reduction and length compensation, the calculated amount of insufficient billet width and billet length compensation can not only increase the metal yield from the original 98.76% to 99.24%, but also meet the dimensional requirements and save a lot of production costs.

[0069] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for improving the metal yield of mixed-cast billets, characterized in that, Includes the following steps: S1. Based on the original width of the billet and the casting speed, measure the actual shrinkage ratio of the width of various mixed steel grades, and calculate and determine the maximum and minimum values ​​of the width shrinkage coefficient of the cross section of various mixed steel grades. S2. Based on the minimum width shrinkage coefficient and the original width of the billet in step S1, calculate the lower opening size of the crystallizer. Then, use the crystallizer width adjustment program to input the lower opening size and the percentage taper of the crystallizer. The formula for calculating the lower opening size of the crystallizer is: W 下 =W×A1, where W is the original width of the billet and A1 is the minimum value of the shrinkage coefficient; S3. Based on the maximum and minimum values ​​of the width shrinkage coefficient in step S1, and combined with the original length of the billet, calculate the insufficient width and the length extension of the billet. Then, based on the principle of width reduction and length extension, determine the final width and final length of the mixed-cast billet. The formula for calculating the insufficient width of the billet is: (A2-A1)×W, where A2 is the maximum value of the shrinkage coefficient. The formula for calculating the length extension of the billet is: L×W / [W-(A2-A1)W]-L, where L is the original length of the cut billet. The formula for calculating the final width of the mixed-cast billet is: W-(A2-A1)W, and the formula for calculating the final length is: L×W / [W-(A2-A1)W].

2. The method for improving the metal yield of mixed-cast billets according to claim 1, characterized in that, In step S1, the range of the cross-sectional width contraction coefficient of the various mixed-cast steel grades is 0.995-1.016, and the mixed-cast steel grades are carbon steel or low alloy steel.

3. The method for improving the metal yield of mixed-cast billets according to claim 1, characterized in that, The verification method for the lower opening size of the crystallizer is as follows: calculate the theoretical upper opening size and theoretical taper of the crystallizer, and measure the actual upper opening size and actual taper of the crystallizer. If the difference between the theoretical upper opening size and the actual upper opening size of the crystallizer does not exceed 1 mm, and the difference between the actual taper and the theoretical taper of the crystallizer does not exceed 0.2 mm, then the lower opening size of the crystallizer meets the production requirements.

4. The method for improving the metal yield of mixed-cast billets according to claim 3, characterized in that, The formula for calculating the theoretical size of the top opening of the crystallizer is: W 上= W 下 ×(1+T); The theoretical taper is a narrow-face millimeter taper, and the calculation formula for the narrow-face millimeter taper is: (W 上 -W 下 ) / 2; where W 下 denoted as the lower opening size of the crystallizer, and T as the percentage taper of the crystallizer.

5. A method for improving the metal yield of mixed-cast billets according to any one of claims 1-4, characterized in that, The percentage taper of the crystallizer is (0.9-1.2)%.