A method for reducing continuous casting loss of different steel grades

Abstract

The application discloses a method for reducing loss of continuous casting of different steel grades, which comprises a refining process and a continuous casting process; each process is as follows: (1) the refining process: when smelting mixed casting steel grades, after judging whether the upper limit or the lower limit of the composition range of the next steel grade is closest to that of the previous steel grade without crossing of mixed casting furnace times, both steel grades are controlled according to the upper limit or the lower limit of the respective composition range according to the judgment result; (2) the continuous casting process: the minimum temperature of the continuous casting tundish is greater than or equal to the liquidus of the molten steel + 25 DEG C; before the previous furnace of the mixed casting furnace times is poured, full covering agent is added into the tundish; after the previous furnace is poured, the liquid level of the tundish is lowered to less than or equal to 300 mm, and the next furnace is poured again; after the next furnace is poured, the tundish is first subjected to semi-tundish casting. The method reduces the amount of judgment of the casting blank, the amount of judgment of the special steel grade and the amount of judgment of the casting blank caused by the composition of the casting blank, reduces a large amount of economic loss caused by the composition incompatibility and the judgment of the casting blank, reduces the number of small pouring times, and reduces the refractory cost, the steel material consumption and the labor intensity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of continuous casting, in particular to a method for reducing loss of continuous casting of different steel grades. BACKGROUND

[0002] Since the mixed casting process of continuous casting of different steel grades appeared, the division of mixed casting billets of different steel grades has become a problem. During the mixed casting operation of different steel grades, the composition difference and change trend of the mixed casting billet cannot be accurately grasped, and only experience is relied on for judgment, resulting in that part of the mixed casting billets should be rejudged but are not actually rejudged, and part of the mixed casting billets should not be rejudged but are rejudged by mistake, which directly leads to the increase of the rejudged amount of the casting billet, the rejected amount of the special steel grade, and the rejudged rate of the composition of the casting billet, and brings economic losses caused by a large number of composition incompatibility and casting billet rejection. Facing the current severe market situation, especially the characteristics of small use amount of high-quality steel and small order quantity, the production scheduling space is limited, some high-grade steel grades with large composition difference are frequently smelted, the number of small casting times is increased, the cost of refractory materials and the consumption of steel materials are increased, and the labor intensity is increased, so the continuous casting operator must master the casting method of the mixed casting steel grade of the caster. In order to stabilize production, adapt to the production needs of large quantities and multiple steel grades, reduce the loss caused by the judgment of the mixed casting billet while ensuring the product quality, which is a problem to be solved. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a method for reducing loss of continuous casting of different steel grades, which is suitable for large quantities and multiple steel grades.

[0004] To solve the above technical problems, the technical scheme adopted by the present application is as follows: it comprises a refining process and a continuous casting process; the process of each process is as follows:

[0005] (1) Refining process: when smelting mixed casting steel grades, the mixed casting furnace time does not cross the composition judgment, whether the composition range of the next steel grade is closest to the upper limit or the lower limit compared with the previous steel grade, and both steel grades are controlled according to the judgment result according to the upper limit or the lower limit of the respective composition range;

[0006] (2) Continuous casting process: the minimum temperature of the continuous casting tundish is greater than or equal to the liquidus of the molten steel + 25℃; the full covering agent is added into the tundish before the previous furnace of the mixed casting furnace time is finished; after the previous furnace is finished, the liquid level of the tundish is reduced to ≤300mm, and the next furnace is started to cast; after the next furnace is started to cast, the tundish is first subjected to semi-tundish casting.

[0007] Further, in the continuous casting process, after the next furnace is started to cast, the steel sample of the tundish is taken and sent in time, after the next furnace is started to cast, the mixed casting billet is marked, and the mixed casting billet is subjected to rejection treatment in combination with the composition of the steel sample detected by sampling.

[0008] Further, at least three steel samples of the tundish are taken and detected at intervals from when the next furnace is started to cast to when the molten steel of the mixed casting part is finished.

[0009] Further, the marked part of the continuously cast slab is discarded when the next furnace is cast, and the first sample of the continuously cast slab is taken.

[0010] Further, the discarding process of the marked part of the continuously cast slab is as follows: the marked part of the continuously cast slab is discarded, and L meters of the continuously cast slab is discarded per flow, wherein L is calculated according to the following formula (I):

[0011] L=(T-t)*V (I)

[0012] In formula (I),

[0013] L is the discarding length of the marked part of the continuously cast slab, in meters; T is the required sampling time of the sample, in minutes; t is the sampling time of the first sample, in minutes; and V is the casting speed, in meters per minute.

[0014] The beneficial effects of the above technical solution are as follows: 1. The problem of difficult production scheduling of steel grades with small usage and small orders is solved; 2. The amount of continuously cast slab rejudgment, the amount of special steel judgment, and the amount of judgment due to the composition of the continuously cast slab are reduced, and the economic loss caused by a large number of incompatible compositions and continuously cast slab judgment is reduced; 3. The number of small pouring times is reduced, and the refractory cost, steel material consumption, and labor intensity are reduced; 4. An effective solution is provided for the problem of ensuring the stability of the target steel composition and correctly dividing the mixed continuously cast slab under the condition of mixed casting of different casting speeds and different steel grades; 5. The process is simple, easy to operate, and has remarkable effects, effectively reducing the production cost and improving the efficiency of the enterprise, and has excellent popularization and application value in the industry. DETAILED DESCRIPTION

[0015] The application will be further described in detail below in combination with specific embodiments.

[0016] The continuous casting of different steel grades refers to the use of the same tundish to cast two steel grades with large composition differences in the continuous casting process. The method for reducing the loss of continuous casting of different steel grades adopts the following process:

[0017] (1) Refining process:

[0018] Because the continuously cast slab is marked and discarded when the next furnace is cast, the composition of the previous furnace is not affected. The main problem is that the residual composition of the previous furnace in the tundish will affect the next furnace, so the main task is to ensure that the composition of the next furnace meets the requirements as soon as possible, and the following control is adopted:

[0019] After determining the mixed cast steel grade, the composition range of the next steel grade is compared with the previous steel grade. If the composition range of the mixed cast heat has no intersection, the composition range of the next steel grade is compared with the composition range of the previous steel grade. If the lowest value of the composition range of the previous steel grade is higher than the highest value of the composition range of the next steel grade, the highest value of the composition range of the next steel grade is used as the target composition of the previous steel grade and the next steel grade. If the highest value of the composition range of the previous steel grade is lower than the lowest value of the composition range of the next steel grade, the lowest value of the composition range of the next steel grade is used as the target composition of the previous steel grade and the next steel grade. If the composition range of the mixed cast heat has intersection, the intersection is used as the target composition of the previous steel grade and the next steel grade.

[0020] The refining outstation temperature is not lower than the superheat degree of the lower liquidus steel by 65℃, and the minimum temperature of the subsequent continuous casting tundish is ensured to be not less than the liquidus of the lower liquidus steel + 25℃.

[0021] (2) Continuous casting process:

[0022] Before the previous furnace of the mixed cast heat is poured, the full covering agent is added to the tundish when 2 / 3 to 3 / 4 of the previous furnace is poured, so as to keep the temperature of the molten steel in the tundish and prevent the temperature from decreasing too fast and too much when the molten steel liquid level of the subsequent tundish is lowered.

[0023] After the previous furnace of the mixed cast heat is poured, the molten steel liquid level of the tundish is lowered to 300mm or below, and then the next furnace is poured. In this way, the molten steel liquid level of the tundish is lowered as much as possible to reduce the influence of the composition of the previous furnace on the next furnace.

[0024] After the next furnace is poured, the molten steel liquid level of the tundish is slowly raised at a speed of 20mm to 40mm / min. After the next furnace is poured, the tundish is first used for half tundish casting, and the molten steel of the previous furnace is poured as much as possible to reduce the influence of the composition of the previous furnace on the next furnace. After 7 to 8 minutes of half tundish casting, the tundish is poured to full tundish.

[0025] The ladle operator takes steel samples from the tundish at certain time intervals after the pouring of the latter furnace and performs detection, the time interval for sampling is preferably matched with the time required for component testing, preferably 3 or more steel samples are taken, preferably 3 steel samples are taken; the samples are sent in time after sampling, it is confirmed that the molten steel in the mixed pouring part has been poured, and the component meets the requirements of the latter furnace after mixed pouring. Taking an 8-machine 8-flow 150mm*150mm cross-section continuous casting machine as an example, the following Table 1 can be executed:

[0026] Table 1: Sampling time

[0027]

[0028] After the pouring of the latter furnace, the tundish operator presses the “water hole” button on each flow operation box until the ladle operator takes the first steel sample, after the button is pressed, the mixed pouring billet will be “marked” on the “online billet quality judgment system”, which facilitates the removal of unqualified billets.

[0029] The cutting worker cuts the mixed pouring billet “marked” on the “online billet quality judgment system” into short fixed-length and scraps, and takes a billet sample from the head of the first billet after the scrap to verify the component; the process of the scrap treatment is: the marked part of the billet is cut into short fixed-length and scrapped, and L meters of billet is scrapped in each flow, L is calculated by the following formula (I):

[0030] L=(T-t)*V (Ⅰ)

[0031] In formula (I),

[0032] L is the length of the scrap excluding the marked part, m; T is the sampling time of the steel sample meeting the requirements, min; t is the sampling time of the first steel sample, min; V is the pulling speed, m / min. Taking the pulling speed V=2.0 m / min as an example: if the first steel sample component meets the mixed pouring billet component determination requirements of the latter furnace, at this time T-t=0, the cutting worker cuts the “marked” part of the billet into short fixed-length and scraps; if the first steel sample component does not meet the mixed pouring billet component determination requirements of the latter furnace, and the second steel sample meets the requirements, at this time T-t=3min, the cutting worker cuts the “marked” part of the billet into short fixed-length and scraps, and scraps an additional 6 meters of billet in each flow; if the components of the first two steel samples do not meet the mixed pouring billet component determination requirements of the latter furnace, and the third steel sample meets the requirements, at this time T-t=6min, the cutting worker cuts the “marked” part of the billet into short fixed-length and scraps, and scraps an additional 12 meters of billet in each flow.

[0033] Example 1: The method for reducing the loss of continuous casting of different steel grades is described as follows.

[0034] (1) 60Si2Mn and 55SiCr are continuously cast, the components and process parameters of each steel grade are shown in Table 1;

[0035] Table 1: Components of each steel grade (wt)

[0036]

[0037] From Table 1, it can be seen that the two steel grades of 60Si2Mn and 55SiCr have no cross component of Cr.

[0038] (2) The first furnace of the mixed pouring furnace was 60Si2Mn, and the second furnace was 55SiCr; the RH vacuum refining outstation composition of the first furnace of the mixed pouring furnace was (wt): C 0.57%, Si 1.54%, Mn 0.78%, P 0.014%, S 0.006%, Cr 0.3%, and the outstation temperature was 1540℃; the RH vacuum refining outstation composition of the second furnace of the mixed pouring furnace was (wt): C 0.56%, Si 1.55%, Mn 0.68%, P 0.012%, S 0.005%, Cr 0.71%; the pulling speed of 60Si2Mn and 55SiCr was 1.8m / min.

[0039] When the ladle of 60Si2Mn was poured, the ladle worker added full covering agent into the tundish when the ladle was 2 / 3 to 3 / 4 full; after the tundish of 60Si2Mn was lowered to 300mm, the pouring of 55SiCr was started; after the pouring of 55SiCr was started, the tundish liquid level was slowly raised at a speed of 20mm / min, and the tundish liquid level was stabilized at half of the tundish; 8min later, the tundish was full; 11min, 14min and 17min after the pouring of 55SiCr was started, one tundish steel sample was taken each time, and the samples were sent in time; 11min after the pouring of 55SiCr was started, the tundish worker pressed the "water gap" button on each flow operation box, and the mixed pouring billets were "marked" on the "online billet quality judgment system"; the mixed pouring billets marked on the "online billet quality judgment system" were discarded by the cutting worker, a total of 28.8t was discarded, and the first billet head after the discarding was taken for verification of the composition. During the continuous casting process, the minimum temperature of the tundish was ≥1500℃. The steel sample and billet sample compositions are shown in Table 2.

[0040] Table 2: Steel sample and billet sample compositions (wt)

[0041]

[0042] As can be seen from Table 2, the tundish steel sample and the billet sample both meet the 55SiCr composition requirements in Table 1.

[0043] Example 2: The method for reducing the loss of continuous casting of different steel grades is specifically described as follows.

[0044] (1) SWRCH35K and SWRCH45K were continuously cast, and the compositions and process parameters of each steel grade are shown in Table 3.

[0045] Table 3: Compositions of each steel grade

[0046]

[0047] As can be seen from Table 3, the two steel grades SWRCH35K and SWRCH45K mainly have no cross component of C.

[0048] (2) The first furnace of the mixed pouring furnace was SWRCH35K and the second furnace was SWRCH45K; the LF refining out station composition of SWRCH35K of the first furnace of the mixed pouring furnace was (wt): C 0.37%, Si 0.19%, Mn 0.73%, P 0.009%, Cr 0.03%, Als 0.0356%, and the out station temperature was 1568℃; the LF refining out station composition of SWRCH45K of the second furnace of the mixed pouring furnace was (wt): C 0.47%, Si 0.19%, Mn 0.7%, P 0.01%, Cr 0.18%, Als 0.0299%; the pulling speed of SWRCH35K and SWRCH45K was 2.2m / min.

[0049] The middle ladle was supplemented with full covering agent when the first furnace SWRCH35K was poured to 2 / 3-3 / 4 of the furnace; the middle ladle liquid level was lowered to 300mm after SWRCH35K was poured, and then SWRCH45K was poured; the middle ladle liquid level was slowly raised at a speed of 40mm / min after SWRCH45K was poured, and the middle ladle liquid level was stabilized at half ladle; the middle ladle was poured full after 7min; one steel sample was taken from the middle ladle at 9min, 12min and 15min after SWRCH45K was poured, and was sent in time; the "water gap" button on each flow operation box was pressed by the middle ladle operator at 9min after SWRCH45K was poured, and the mixed pouring billets were "marked" on the "online billet quality judgment system"; the mixed pouring billets "marked" on the "online billet quality judgment system" were discarded by the cutting operator, and a total of 29.5t was discarded, and the first billet head after discarding was taken for verification of the composition. During continuous casting, the minimum temperature of the middle ladle was ≥1517℃. The steel sample and billet sample compositions are shown in Table 4.

[0050] Table 4: Steel sample and billet sample compositions (wt)

[0051]

[0052] As can be seen from Table 4, the middle ladle steel sample and the billet sample both meet the composition requirements of SWRCH45K in Table 3.

[0053] Example 3: The method for reducing the loss of continuous casting of different steel grades is specifically as follows.

[0054] (1) SWRCH35K and SWRCH25K were continuously pulled, and the compositions and process parameters of each steel grade are shown in Table 5;

[0055] Table 5: Composition of each steel grade

[0056]

[0057] As can be seen from Table 5, the two steel grades SWRCH35K and SWRCH25K have no crossover components in C and Mn.

[0058] (2) The first furnace of the mixed pouring furnace was SWRCH35K and the second furnace was SWRCH25K; the LF refining outstation composition of the first furnace SWRCH35K of the mixed pouring furnace was (wt): C 0.33%, Si 0.18%, Mn 0.71%, P 0.019%, S 0.003%, Als 0.0333%, and the outstation temperature was 1569°C; the LF refining outstation composition of the second furnace SWRCH25K of the mixed pouring furnace was (wt): C 0.24%, Si 0.17%, Mn 0.52%, P 0.013%, S 0.004%, Als 0.0307%; the pulling speed of SWRCH35K and SWRCH25K was 2.2 m / min.

[0059] The middle ladle was supplemented with full covering agent when the first furnace SWRCH35K was poured to 2 / 3 to 3 / 4 of the furnace; the middle ladle liquid level was lowered to 280 mm after SWRCH35K was poured, and then SWRCH25K was poured; the middle ladle liquid level was slowly raised at a speed of 30 mm / min after SWRCH25K was poured, and the middle ladle liquid level was stabilized at half ladle; the middle ladle was poured full after 7 min; one steel sample was taken from the middle ladle at 9 min, 12 min and 15 min after SWRCH25K was poured, and was sent in time; the middle ladle operator pressed the "water gap" button on each flow operation box at 9 min after SWRCH25K was poured, and the mixed pouring billets were "marked" on the "online billet quality judgment system"; the mixed pouring billets marked on the "online billet quality judgment system" were discarded by the cutting operator, and a total of 29.8 t was discarded, as can be seen from Table 6, the first steel sample of the middle ladle did not meet the composition requirements of SWRCH25K in Table 5, therefore, 6.6 m of the first billet was discarded in each flow, and the composition of the first billet head after discarding was verified. The minimum temperature of the middle ladle was ≥1525°C during continuous casting; the steel sample and billet sample compositions are shown in Table 6;

[0060] Table 6: Steel sample and billet sample compositions (wt)

[0061]

[0062] As shown in Table 6, the Mn composition of the first steel sample from the tundish does not meet the SWRCH25K composition requirements in Table 5; the second and third steel samples and the billet sample all meet the SWRCH25K composition requirements in Table 5.

[0063] Example 4: The specific method for reducing continuous casting losses of different steel grades is as follows.

[0064] (1) 45# steel and A350LF2 were continuously drawn together. The composition and process parameters of each steel grade are shown in Table 7.

[0065] Table 7: Composition of various steel grades

[0066]

[0067] As can be seen from Table 7, the two steel grades, 45# steel and A350LF2, are mainly composed of C and Mn with no overlap in composition.

[0068] (2) The previous heat of the mixed casting furnace was 45# steel, and the next heat was A350LF2. The composition of the LF refined steel of the previous heat of the mixed casting furnace was (wt): C 0.44%, Si 0.22%, Mn 0.63%, P 0.013%, S 0.005%, Al 0.0273%, and the outlet temperature was 1560℃. The composition of the LF refined steel of the next heat of the mixed casting furnace was (wt): C 0.16%, Si 0.23%, Mn 1.33%, P 0.014%, S 0.006%, Al 0.0292%. The casting speed of both 45# steel and A350LF2 was 2m / min.

[0069] Before the previous heat of 45# steel was finished, the ladle operator added a full layer of covering agent to the tundish when 2 / 3 to 3 / 4 of the heat was being poured. After the 45# steel was poured, the tundish liquid level was lowered to 300mm before A350LF2 was started. After A350LF2 started pouring, the tundish liquid level was slowly raised at a speed of 35mm / min until it was stabilized at half height. The tundish was then filled after 7.5 minutes. One steel sample was taken from the tundish at 10, 13, and 16 minutes after A350LF2 started pouring and sent to the tundish promptly. After the A350LF2 casting begins, the tundish operator presses the "change nozzle" button on each flow control box for 10 minutes and marks the mixed-cast slabs on the "Online Slab Quality Judgment System." The cutting operator discards the marked mixed-cast slabs, totaling 29.6 tons. As shown in Table 8, the C composition of the first and second steel samples from the tundish does not meet the A350LF2 composition requirements in Table 7. Therefore, two more 6-meter slabs are discarded from each subsequent flow, and a sample is taken from the head of the first slab after the discarding to verify its composition. During continuous casting, the minimum temperature in the tundish is ≥1520℃. The steel sample and slab sample compositions are shown in Table 8.

[0070] Table 8: Steel and bloom sample compositions (wt)

[0071]

[0072] As can be seen from Table 8, the first and second tundish steel samples do not meet the A350 LF2 composition requirements of Table 7; the third steel sample and the bloom sample do meet the A350 LF2 composition requirements of Table 7.

Claims

1. A method of reducing losses in continuous casting of different steel grades, characterized in that, It includes refining process and continuous casting process; each process technology is as follows: (1) refining process: when smelting mixed pouring steel grade, after mixed pouring furnace time composition judgment, the composition range of the next steel grade is closest to the upper limit or lower limit compared with the previous steel grade, both steel grades are controlled according to the judgment result according to the upper limit or lower limit of the respective composition range; (2) continuous casting process: the minimum temperature of continuous casting tundish is greater than or equal to liquidus of molten steel + 25 DEG C; before the previous furnace of mixed pouring furnace time is poured, the covering agent is added into the tundish; after the previous furnace is poured, the liquid level of the tundish is reduced to less than or equal to 300 mm, and the next furnace is poured; after the next furnace is poured, the tundish is first semi-tundish casting; The continuous casting process, after the next furnace is poured, the steel sample of the tundish is taken and sent in time, when the next furnace is poured, the mixed pouring billet is continuously marked, the marked mixed pouring billet is treated by discarding after the first tundish steel sample is taken, and the composition of the sampled steel sample is combined; The marked mixed pouring billet is treated by discarding; the discarding treatment process is: the marked part of the billet is discarded, and L meters of billet is discarded for each flow, L is calculated by the following formula (I): L=(T-t)*V (I) In formula (I), L is the discarding length of the marked part, m; T is the required steel sample sampling time, min; t is the first steel sample sampling time, min; V is the pulling speed, m / min.

2. The method of reducing losses in continuous casting of different steel grades according to claim 1, characterized in that: Before the molten steel of the mixed pouring part is poured, at least three tundish steel samples are taken and detected.

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