Method for controlling secondary cooling of high carbon steel slab continuous casting

Abstract

The application provides a high-carbon steel slab continuous casting secondary cooling control method, which comprises the following steps: along the direction of drawing the slab, the secondary cooling zone is divided into 1st zone to 5th zone, the cooling intensity ratio is 4.3-5.8, 4.1-5.3, 3.6-4.7, 2.0-2.6 and 1.0; and along the transverse width of the secondary cooling zone, the center part, the secondary center part and the edge part are distributed with the water distribution amount of T 中心 +( -1.3% -2.0% ), T 次中 +( -2.0% -3.2% ), T 边部 +( -2.5% -0 ) respectively; wherein the 1st zone, the 2nd zone, the 3rd zone, the 4th zone and the 5th zone are distributed in the secondary cooling zone in sequence and cover the secondary cooling zone completely, and the length along the direction of drawing the slab is 0.45-0.55m, 1.4-1.55m, 2.0-2.2m, 2.4-2.6m and 2.45-2.65m respectively. The application can realize the uniform cooling of the slab under the condition of the strong secondary cooling intensity, and can improve the internal crack and the surface quality simultaneously.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of continuous casting of steel, and particularly relates to a control method for secondary cooling of high-carbon steel slab continuous casting. BACKGROUND

[0002] Continuous casting is a solidification process of molten steel under specific cooling conditions. Liquid high-carbon steel is poured from a ladle to a tundish through a long nozzle, and then poured into a crystallizer through a submerged nozzle. The liquid steel cools and solidifies in the crystallizer to form a uniform-thickness shell with a liquid core. The shell cools and solidifies in the secondary cooling chamber and completes bending and straightening. Finally, the slab is pulled out of the caster. Heat transfer occurs throughout the continuous casting process, which plays a decisive role in the smooth operation of continuous casting and the quality of the continuous casting slab.

[0003] High-carbon steel has a carbon content higher than 0.6%, a wide liquid-solid two-phase region, and high crack sensitivity. In the continuous casting process, the surface transverse cracks are easily generated due to the excessive rapid surface temperature reheat rate or excessive local temperature gradient, resulting in thermal stress, which affects the product quality.

[0004] In previous studies, the high-carbon steel slab usually adopts weak cooling secondary cooling process, and the pulling speed is also low. When optimizing the cooling system in the secondary cooling zone, the optimization form is relatively single, and there is no effective means to solve the problem of high-carbon steel slab continuous casting transverse cracks. SUMMARY

[0005] To solve the technical problem of surface transverse cracks generated in the continuous casting process due to high carbon content and high crack sensitivity of high-carbon steel slab, the present application provides a control method for secondary cooling of high-carbon steel slab continuous casting, comprising the following steps:

[0006] Along the direction of slab pulling, the secondary cooling zone is divided into zone 1, zone 2, zone 3, zone 4, and zone 5. The cooling intensity ratio of zone 1, zone 2, zone 3, zone 4, and zone 5 is 4.3-5.8, 4.1-5.3, 3.6-4.7, 2.0-2.6, and 1.0, respectively. In the transverse width of the secondary cooling zone, the center part, the secondary center part, and the edge part are sequentially distributed with water distribution of T 中心 +(-1.3%-2.0%), T 次中 +(-2.0%-3.2%), and T 边部 +(-2.5%-0).

[0007] Among them, zone 1, zone 2, zone 3, zone 4, and zone 5 are sequentially distributed in the secondary cooling zone and completely cover the secondary cooling zone. The length along the direction of slab pulling is 0.45-0.55 m, 1.4-1.55 m, 2.0-2.2 m, 2.4-2.6 m, and 2.45-2.65 m, respectively. T 中心 , T 次中 , and T 边部The proportion of the spray width of the center part, the sub-center part and the edge part in the total spray width, respectively.

[0008] Further, the obtaining of the cooling intensity ratio comprises the steps of:

[0009] According to formula 1 and formula 2, the cooling intensity ratio R of the 1st zone to the 5th zone is obtained based on the cooling water flux q5 of the 5th zone. i Wherein, 1≤i≤5;

[0010] q i =Q i / S i / 60 formula 1

[0011] R i =q i / q5 formula 2

[0012] That is: Qi=S i ×R i ×q5 formula 3

[0013] In the formula, q i includes q1, q2, q3, q4 and q5, which represent the cooling water quantity per square meter per second of the 1st zone to the 5th zone, respectively, and the unit is L / m 2 / s;

[0014] Q i includes Q1, Q2, Q3, Q4 and Q5, which represent the cooling water quantity per minute of the 1st zone to the 5th zone, respectively, and the unit is L / min;

[0015] S i includes S1, S2, S3, S4 and S5, which represent the spray area of the 1st zone to the 5th zone, respectively, and the unit is m 2

[0016] R i represents the cooling intensity ratio of the 1st zone to the 5th zone.

[0017] Further, in the case that the width of the high-carbon steel slab is less than 1300mm, the center part, the sub-center part and the edge part are distributed with water in the proportions of T 中心 +(1.3% to 2.0%), T 次中 +(-2.0% to -1.3%), and T 边部 respectively; in the case that the width of the high-carbon steel slab is greater than or equal to 1300mm, the center part, the sub-center part and the edge part are distributed with water in the proportions of T 中心 +(-1.3% to -0.8%), T 次中 +(2.5% to 3.2%), and T 边部 +(-2.5% to -1.8%).

[0018] Furthermore, when the width of the high-carbon steel slab is less than 1300mm, the central portion, the secondary central portion, and the edge portion are sequentially arranged according to T... 中心 +(1.3%~2.0%), T 次中 +(-2.0% to -1.3%), T 边部 The proportional water distribution includes: when the width of the high-carbon steel slab is less than 1300 mm, the central part, the secondary central part, and the edge part are distributed sequentially according to (T 中心 +1.5%), (T) 次中 -1.5%), T 边部 The proportion of water allocation;

[0019] When the width of the high-carbon steel slab is ≥1300mm, the central portion, the secondary central portion, and the edge portion are configured according to T. 中心 +(-1.3% to -0.8%), T 次中 +(2.5%~3.2%), T 边部 The water distribution ratio of +(-2.5% to -1.8%) includes: when the width of the high-carbon steel slab is less than 1300mm, the central part, the secondary central part, and the edge part are distributed sequentially according to (T 中心 -1%), (T 次中 +3%), (T) 边部 Distribute water in a ratio of -2% (2%).

[0020] Furthermore, the step of controlling the cooling intensity ratios of zones 1, 2, 3, 4, and 5 to 4.3–5.8, 4.1–5.3, 3.6–4.7, 2.0–2.6, and 1.0 respectively, to obtain the water distribution of zones 1 to 5, includes controlling the cooling intensity ratios of zones 1, 2, 3, 4, and 5 to 4.5–5.3, 4.3–5.0, 3.6–4.4, 2.2–2.6, and 1.0 respectively.

[0021] Furthermore, the high-carbon steel molten steel is injected into the crystallizer through an immersion nozzle to form the high-carbon steel slab, and the drawing speed of the high-carbon steel slab is 3.9 to 4.6 m / min.

[0022] Furthermore, by mass percentage, the composition of the high-carbon steel molten steel includes: C: 0.5%-0.95%, Si: 0.1%-0.5%, Mn: 0.5%-1.3%, P: ≤0.02%, S: ≤0.005%, Al: 0.02%-0.06%, Cr: 0.2%-0.6%.

[0023] Further, the inverse taper of the crystallizer is 0.6%-0.9%, and the width of the high-carbon steel slab is 970-1600mm.

[0024] Further, the surface temperature recovery rate of the high-carbon steel slab when passing through the secondary cooling area is less than 80℃ / m.

[0025] Further, the cooling mode of the high-carbon steel slab in the secondary cooling area is pure water cooling, the cooling intensity adopts strong cooling, and the specific water quantity is 1.9-2.3L / kg.

[0026] The application further provides an application of the control method for the secondary cooling of the high-carbon steel slab in high-carbon steel production.

[0027] Compared with the common technology, the application at least has the following advantages:

[0028] The high-carbon steel has high carbon content, serious interdendritic segregation, low grain boundary strength, low strength and plasticity of the primary shell, and is easy to produce surface cracks, especially at the slab vibration marks; meanwhile, the liquid-solid two-phase region of the high-carbon steel is wide, and the solute elements in the interdendritic region are enriched, which makes the local temperature range brittle, and thus is easy to produce internal intermediate cracks. Therefore, the application provides a control method for the secondary cooling of the high-carbon steel slab, which realizes the uniform cooling of the steel structure in the drawing direction and the transverse direction of the high-carbon steel slab in the continuous casting process. On one hand, the uniform cooling can avoid the risk of surface cracks due to the too fast recovery rate of the local surface temperature or the too large temperature gradient; on the other hand, under the condition of the strong secondary cooling intensity, the slab realizes fast and uniform cooling, which can improve the internal cracks and also consider the surface quality. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only show some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from the drawings shown without any creative effort.

[0030] Figure 1 It is a distribution diagram of the center part, the secondary center part and the edge part in the transverse width direction in an embodiment of the application.

[0031] Figure 2 It is a temperature diagram of the surface and the cross section of the high-carbon steel slab in embodiment 1 of the application.

[0032] Figure 3 It is a longitudinal macrograph of the high-carbon steel slab in embodiment 1 of the application.

[0033] Figure 4 A schematic diagram of the surface and cross-sectional temperature of the high-carbon steel slab in the present application comparative example 1.

[0034] Figure 5 A physical diagram of the steel plate produced after hot rolling of the high-carbon steel slab produced in the present application comparative example 1.

[0035] Figure 6 A longitudinal macrograph of the high-carbon steel slab in the present application comparative example 1. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0037] In addition, the technical solutions in each embodiment of the present application can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it. When the combination of technical solutions appears to be contradictory or unachievable, it should be considered that the combination of technical solutions does not exist and is not within the scope of protection required by the present application.

[0038] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified by the present application, each numerical range has two endpoints and any number between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present application are consistent with the mastery of the prior art by those skilled in the art and the description of the present application. Any method, equipment and material of the prior art similar or equivalent to the method, equipment and material described in the embodiments of the present application can also be used to realize the present application.

[0039] In the embodiments of the present application, the slab cooling mode of the continuous casting secondary cooling zone is pure water cooling. The cooling mode of the secondary cooling zone of the continuous casting machine is usually divided into pure water cooling and gas-water cooling. The cooling intensity of gas-water cooling is more uniform, but the equipment is more complex and the cost is higher. Pure water cooling reduces the gas pipeline and other equipment, and the maintenance is relatively simple and the cost is lower. In the case of the same water quantity, the cooling intensity of pure water cooling is high, which is more likely to cause uneven cooling distribution. Therefore, it is necessary to combine the solidification and cooling characteristics of the steel grade to reasonably distribute the water quantity in the transverse and longitudinal dimensions of the entire secondary cooling zone.

[0040] The present application provides a control method for continuous casting secondary cooling of a high-carbon steel slab, comprising the steps of:

[0041] S1. Along the drawing direction, the secondary cooling zone is divided into 1st zone, 2nd zone, 3rd zone, 4th zone and 5th zone, and the cooling intensity ratio of the 1st zone, 2nd zone, 3rd zone, 4th zone and 5th zone is 4.3-5.8, 4.1-5.3, 3.6-4.7, 2.0-2.6 and 1.0.

[0042] In some embodiments, the 1st zone, 2nd zone, 3rd zone, 4th zone and 5th zone are sequentially distributed in the secondary cooling zone and completely cover the secondary cooling zone, and the length along the longitudinal drawing direction can be 0.45-0.55 m, 1.4-1.55 m, 2.0-2.2 m, 2.4-2.6 m and 2.45-2.65 m, respectively.

[0043] For example, the length of the 1st zone, 2nd zone, 3rd zone, 4th zone and 5th zone can be 0.48 m, 1.45 m, 2.05 m, 2.5 m and 2.6 m, respectively.

[0044] In some embodiments, the cooling intensity ratio can include the following steps:

[0045] According to formula 1-2, the cooling intensity ratio R of the 1st zone-5th zone is obtained based on the cooling water flux q5 of the 5th zone. i wherein 1≤i≤5;

[0046] q i =Q i / S i / 60 formula 1

[0047] R i =q i / q5 formula 2

[0048] That is, Qi=S i ×R i ×q5 formula 3

[0049] In the formula, q i includes q1, q2, q3, q4 and q5, which represent the cooling water quantity per square meter per second of the 1st zone-5th zone, respectively, and the unit is L / m 2 / s;

[0050] Q i includes Q1, Q2, Q3, Q4 and Q5, which represent the cooling water quantity per minute of the 1st zone-5th zone, respectively, and the unit is L / min;

[0051] S i includes S1, S2, S3, S4 and S5, which represent the spraying area of the 1st zone-5th zone, respectively, and the unit is m 2

[0052] R i represents the cooling intensity ratio value of the 1st zone-5th zone relative to the 5th zone, and is dimensionless.

[0053] The liquid-solid two-phase region of high carbon steel is wide, and solidification is slow. The secondary cooling process with strong cooling increases the thickness of the initial solidification shell, obtains sufficient strength to resist external force, and reduces the occurrence of surface cracks. On the other hand, it promotes rapid cooling and reduces dendritic segregation, thereby improving internal intermediate cracks. However, the strong cooling process is more prone to uneven cooling, leading to cracks. Therefore, the cooling intensity ratios of the 1st zone, 2nd zone, 3rd zone, 4th zone and 5th zone are controlled to be 4.3-5.8, 4.1-5.3, 3.6-4.7, 2.0-2.6 and 1.0, respectively, so that the high carbon steel slab is uniformly cooled in the secondary cooling area, the surface temperature rising rate is <80℃ / m, and the straightening point temperature is >1000℃.

[0054] The cooling water distribution in the longitudinal slab drawing direction of the commonly used technology and the present application is compared in Table 1. The cooling intensity ratio is different at different drawing speeds and pouring widths. As shown in Table 1, the commonly used technology has a large cooling intensity gradient in the longitudinal slab drawing direction and an unreasonable distribution, such as an excessively large 1st zone, and the cooling intensity immediately decreases by about 50% when the slab runs to the 2nd zone. Because high carbon steel cools slowly, there are still many liquid cores in the slab in the 2nd zone. The heat of the liquid cores is transferred to the surface, and after the cooling intensity suddenly decreases, the heat transfer rate of the slab surface decreases, leading to an excessively fast surface temperature rising rate of 150-210℃ / m, which is prone to produce surface transverse cracks.

[0055] Table 1 Cooling intensity ratio in the longitudinal slab drawing direction

[0056] Cooling intensity ratio of secondary cooling zone Common technique New design of the invention 1 zone 10.1-12.3 4.3-5.8 2 zone 5.2-6.1 4.1-5.3 3 zone 3.5-4.2 3.6-4.7 4 zone 1.6-2.1 2.0-2.6 5 zone 1.0 1.0

[0057] In some embodiments, the cooling intensity ratios of the 1st zone, 2nd zone, 3rd zone, 4th zone and 5th zone can also be controlled to be 4.5-5.3, 4.3-5.0, 3.6-4.4, 2.2-2.6 and 1.0, respectively.

[0058] S2. In the transverse width of each cooling zone, it is divided into three regions of center part, secondary center part and edge part, as shown in Figure 1 and the water distribution is sequentially T 中心 +(-1.3%~2.0%), T 次中 +(-2.0%~3.2%), and T 边部 +(-2.5%~0), wherein T 中心 , T 次中 , and T 边部 are the proportions of the spray widths of the center part, secondary center part and edge part in the total spray width in the transverse width, respectively.

[0059] In some embodiments, in the case where the width of the high carbon steel slab is less than 1300mm, the center part, secondary center part and edge part are sequentially T中心 +(1.3%~2.0%), T 次中 +(-2.0%~ -1.3%), T 边部 the proportion of water distribution; in the case of the high carbon steel slab width ≥1300mm, the center, the sub-center and the edge are in turn according to T 中心 +(-1.3%~ -0.8%), T 次中 +(2.5%~3.2%), T 边部 +(-2.5%~ -1.8%) proportion of water distribution.

[0060] Exemplary, in the case of the high carbon steel slab width less than 1300mm, the center, the sub-center and the edge are in turn according to T 中心 +(1.3%~2.0%), T 次中 +(-2.0%~ -1.3%), T 边部 the proportion of water distribution includes: in the case of the high carbon steel slab width less than 1300mm, the center, the sub-center and the edge are in turn according to (T 中心 +1.5%), (T 次中 -1.5%), T 边部 proportion of water distribution;

[0061] in the case of the high carbon steel slab width ≥1300mm, the center, the sub-center and the edge are according to T 中心 +(-1.3%~ -0.8%), T 次中 +(2.5%~3.2%), T 边部 +(-2.5%~ -1.8%) proportion of water distribution includes: in the case of the high carbon steel slab width ≥1300mm, the center, the sub-center and the edge are in turn according to (T 中心 -1%), (T 次中 +3%), (T 边部 -2%) proportion of water distribution.

[0062] The cooling water quantity in the prior art is mainly concentrated in the center area in the transverse width, and the water quantity is smaller and smaller towards the edge. The solidification end point of the continuous casting slab generally exists "W" shape, or even more uneven solidification condition, the design idea of the present application is based on the layout of the secondary cooling nozzle and the spraying width of each nozzle, the spraying width proportion of the center, the sub-center and the edge is calculated first, and then the pouring width is corrected secondly, so that the slab transverse heat is uniform, and the similar "W" shape is eliminated.

[0063] Meanwhile, when casting a narrow-section slab with a casting width less than 1300 mm, the corner of the slab is in the cooling area of the sub-middle part, and the cooling intensity of the area needs to be weakened to avoid the generation of corner cracks; when casting a wide-section slab with a casting width greater than or equal to 1300 mm, the 1 / 4 width area of the slab is in the cooling area of the sub-middle part, and the cooling intensity of the area needs to be increased because the heat transfer of the 1 / 4 width area of the slab is slow, and the corner of the slab is in the cooling area of the edge part, and the cooling water amount of the edge part also needs to be reduced to weaken the cooling.

[0064] Specifically, the distribution of the cooling water amount in the transverse width direction in the new design in the present application is compared with that in the conventional technology as shown in Table 2.

[0065] Table 2 Comparison of the distribution of the cooling water amount in the transverse width direction

[0066] Cooling zone in transverse width Center part Sub-center part Edge part Common technique 56％-60％ 19％-22％ 16％-19％ The proportion of the spray width of each zone, T i ]]> 45.1％-51.3％ 25.0％-27.1％ 25.5％-27.6％ New design, pouring width < 1300 mm [CAT 中心 +1.5%]] T 次中 -1.5%]] [CAT 边部 ]]> New design, casting width ≥ 1300 mm T 中心 -1%]] T 次中 +3%]] T 边部 -2%]]

[0067] In some embodiments, the width of the high-carbon steel slab can be 970-1600 mm.

[0068] Compared with the conventional technology, the present application at least has the following advantages:

[0069] The high-carbon steel has a high carbon content, serious interdendritic segregation, low grain boundary strength, low strength and plasticity of the primary shell, and is prone to surface cracks, especially at the oscillation marks of the slab. Meanwhile, the liquid-solid two-phase region of the high-carbon steel is wide, and the solute elements between the dendrites are enriched in the two-phase region, which makes them locally enter the brittle temperature range, thereby being prone to internal intermediate cracks. Therefore, the present application provides a control method for the secondary cooling of a high-carbon steel slab, which realizes the uniform cooling of the steel structure in the drawing direction and the transverse direction of the high-carbon steel slab during the continuous casting process. On the one hand, uniform cooling can avoid the risk of surface cracks due to the too fast reheat rate of the local surface temperature or the too large temperature gradient; on the other hand, under the condition of a relatively strong secondary cooling intensity, the slab realizes uniform cooling, which can improve the internal cracks and also take into account the surface quality.

[0070] In some embodiments, the high-carbon steel liquid is injected into the crystallizer through a nozzle to form the high-carbon steel slab, and the drawing speed of the high-carbon steel slab is 3.9-4.6 m / min.

[0071] Due to the crack sensitivity of high carbon steel, the high carbon steel needs to ensure uniform cooling during the secondary cooling process, and the drawing speed needs to be strictly controlled to avoid surface defects and internal cracks caused by increased thermal stress, so the common technology usually controls the slab drawing speed below 4.0 m / min during the secondary cooling process. However, the present application overcomes the technical bias of the common technology, and uses the control method of continuous casting secondary cooling to make the high carbon steel slab cool and solidify more quickly and uniformly during the continuous casting process, reduce the solute element enrichment segregation, and improve the intermediate crack and center segregation in the slab; reduce the thermal stress caused by uneven cooling to improve the surface crack defects of the slab. At the same time, the drawing speed is increased to 4.6 m / min, the production efficiency of the continuous casting section is significantly improved without increasing or modifying any hardware equipment, and the production cost is indirectly reduced.

[0072] In some embodiments, the composition of the high carbon steel liquid steel includes, in mass percentage: C: 0.5%-0.95%, Si: 0.1%-0.5%, Mn: 0.5%-1.3%, P: ≤0.02%, S: ≤0.005%, Al: 0.02%-0.06%, Cr: 0.2%-0.6%.

[0073] In order to obtain a good primary cooling effect, the solidified shell and the crystallizer copper plate must be in good contact. Since the steel liquid solidifies to form a shell in the crystallizer while accompanied by volume shrinkage, the inner cavity of the crystallizer copper plate is designed to be large at the top and small at the bottom, that is, the so-called crystallizer taper, which can reduce the air gap caused by shrinkage, thereby improving the heat conduction of the crystallizer. During the cooling and solidification process of high carbon steel, the initial phase change process is liquid phase (L)→γ phase, and the primary solidification structure is all austenite, the solidification shrinkage is small, and the shell is in close contact with the crystallizer, so the high carbon steel adopts a smaller crystallizer reverse taper to reduce the drawing resistance and avoid surface transverse cracks. Therefore, the reverse taper of the crystallizer is set to 0.6%-0.9% in the present application, while the reverse taper of the crystallizer for other ultra-low carbon steel, low carbon steel, medium carbon steel, etc. cast by the same caster is 0.8%-1.1%.

[0074] In the present application, the surface temperature rising rate of the high carbon steel slab is <80℃ / m when passing through the secondary cooling area. A large number of literature studies have shown that when the surface temperature rising rate of the slab is controlled to be <80℃ / m, the generation of surface cracks can be effectively reduced.

[0075] The application of the high carbon steel slab secondary cooling control method according to any one of the above in high carbon steel production.

[0076] In order to facilitate those skilled in the art to further understand the present application, examples are given as follows:

[0077] Example 1

[0078] The high-carbon steel liquid is smelted by converter, refined by LF furnace, and high-carbon steel liquid with temperature and composition reaching control requirements is obtained. The chemical composition of the high-carbon steel is, in mass percentage: C: 0.72%-0.78%, Si: 0.2%-0.3%, Mn: 0.5%-0.8%, P: ≤0.018%, S: ≤0.005%, Als: 0.015%-0.05%, Cr: 0.37%-0.5%.

[0079] The high-carbon steel liquid is cast on a slab continuous casting machine, and the inverse taper of the continuous casting crystallizer is 0.65%, and the casting width is set to 1250mm.

[0080] The continuous casting speed is 4.2m / min.

[0081] The cooling water amount is distributed as follows: in the slab transverse width direction, the cooling water proportion of the center part, the secondary center part and the edge part is 46.7%, 25.9% and 27.4% respectively; in the longitudinal slab drawing direction, the cooling intensity ratio of the 1st zone, the 2nd zone, the 3rd zone, the 4th zone and the 5th zone is 5.3, 4.7, 3.7, 2.3 and 1.0 respectively, wherein the length of the 1st zone, the 2nd zone, the 3rd zone, the 4th zone and the 5th zone is 0.48m, 1.45m, 2.05m, 2.5m and 2.6m respectively.

[0082] The temperature distribution of the slab surface and the cross section after the fan-shaped section is uniform, as shown in Figure 2 , the slab sample is taken, the surface oxide scale is removed by pickling, no surface transverse crack is found, and no crack defect is found on the surface of the hot-rolled steel plate, so that the surface crack defect of the high-carbon steel is effectively controlled. The longitudinal macro examination is performed on the slab sample, and no internal intermediate crack is found, as shown in Figure 3 .

[0083] Comparative Example 1

[0084] In the conventional technology, the high-carbon steel liquid is smelted by converter, refined by LF furnace, and high-carbon steel liquid with temperature and composition reaching control requirements is obtained. The chemical composition of the high-carbon steel is, in mass percentage: C: 0.72%-0.78%, Si: 0.2%-0.3%, Mn: 0.5%-0.8%, P: ≤0.018%, S: ≤0.005%, Als: 0.015%-0.05%, Cr: 0.37%-0.5%.

[0085] The high-carbon steel liquid is cast on a slab continuous casting machine, and the inverse taper of the continuous casting crystallizer is 1.0%, and the casting width is set to 1250mm.

[0086] The continuous casting speed is 3.8m / min.

[0087] The continuous casting secondary cooling zone adopts pure water cooling, and the distribution of cooling water is as follows: in the slab transverse width direction, the cooling water proportion of the center part, the secondary center part and the edge part is 58%, 21% and 17% respectively; in the longitudinal direction of the slab, the cooling intensity ratio of the 1st zone, the 2nd zone, the 3rd zone, the 4th zone and the 5th zone is 11.5, 5.7, 3.7, 1.8 and 1.0 respectively, wherein the length of the 1st zone, the 2nd zone, the 3rd zone, the 4th zone and the 5th zone is 0.48 m, 1.45 m, 2.05 m, 2.5 m and 2.6 m respectively.

[0088] The temperature distribution of the slab surface after the fan-shaped segment and the cross section is very uneven, as shown in Fig. 1; Figure 4 The surface of the steel plate after hot rolling has serious transverse crack defects, as shown in Fig. 2; Figure 5 The internal intermediate crack and center segregation of the slab sample are serious, as shown in Fig. 3. Figure 6

[0089] In the above technical solution of the present application, the above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structural transformation made under the technical concept of the present application, or direct / indirect application in other related technical fields is included in the patent protection scope of the present application.​

Claims

1. A method for controlling secondary cooling in continuous casting of high-carbon steel slabs, characterized in that, Including the following steps: Molten high-carbon steel is injected into the crystallizer through an immersion nozzle to form the high-carbon steel slab, and the drawing speed of the high-carbon steel slab is 3.9~4.6m / min; Along the throwing direction, the secondary cooling zone is divided into zone 1, zone 2, zone 3, zone 4, and zone 5, and the cooling intensity ratios of zone 1, zone 2, zone 3, zone 4, and zone 5 are 4.3~5.8, 4.1~5.3, 3.6~4.7, 2.0~2.6, and 1.0, respectively. When the width of the high-carbon steel slab is less than 1300 mm, the center, secondary center, and edge portions are sequentially arranged according to (T) 中心 +1.5%), (T 次中 -1.5%), T 边部 The proportion of water allocation; When the width of the high-carbon steel slab is ≥1300mm, the central part, the secondary central part, and the edge part are sequentially arranged according to (T) 中心 -1%), (T 次中 +3%), (T) 边部 Water volume is allocated in a proportion of -2%; Among them, zones 1, 2, 3, 4, and 5 are sequentially distributed in the secondary cooling zone and completely cover it, with lengths along the drawing direction of 0.45~0.55m, 1.4~1.55m, 2.0~2.2m, 2.4~2.6m, and 2.45~2.65m, respectively; T 中心 The T 次中 The T 边部 These represent the percentages of the spray width of the central part, the secondary central part, and the edge part in the total spray width, respectively.

2. The control method according to claim 1, characterized in that, Obtaining the cooling intensity ratio includes the following steps: Based on Equations 1 and 2, and taking the cooling water flux q5 of Zone 5 as the benchmark, the cooling intensity ratio R of Zones 1 to 5 is obtained. i Where 1≤i≤5; q i =Q i / S i / 60 Formula 1 R i =q i / q5 Formula 2 That is: Qi = S i ×R i ×q5 Equation 3 In the formula: q i Including q1, q2, q3, q4, and q5, these represent the cooling water flow rate per second per square meter for zones 1 through 5, respectively, in L / m². 2 / s; Q i Including Q1, Q2, Q3, Q4, and Q5, which represent the cooling water volume per minute for zones 1 to 5 respectively, in L / min; S i Including S1, S2, S3, S4, and S5, representing the spraying area of ​​zones 1 through 5 respectively, with the unit being m². 2 R i This represents the ratio of cooling intensity between zones 1 to 5 relative to zone 5.

3. The control method according to claim 1, characterized in that, The cooling intensity ratios of zones 1, 2, 3, 4, and 5 are controlled to be 4.5~5.3, 4.3~5.0, 3.6~4.4, 2.2~2.6, and 1.0, respectively.

4. The control method according to claim 1, characterized in that, The high-carbon steel molten steel comprises, by mass percentage: C: 0.5%-0.95%, Si: 0.1%-0.5%, Mn: 0.5%-1.3%, P: ≤0.02%, S: ≤0.005%, Al: 0.02%-0.06%, Cr: 0.2%-0.6%.

5. The control method according to claim 1, characterized in that, The inverted taper of the crystallizer is 0.6%~0.9%, and the width of the high-carbon steel slab is 970-1600mm.

6. The control method according to claim 1, characterized in that, The surface temperature recovery rate of the high-carbon steel slab in the secondary cooling zone is <80℃ / m.

7. The control method according to claim 1, characterized in that, The high-carbon steel slab is cooled by pure water in the secondary cooling zone, with a strong cooling intensity and a specific water volume of 1.9~2.3L / kg.

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