Production method for improving corner cracks and surface peeling of low-carbon boron-added steel

Abstract

The invention relates to a production method for improving corner cracks and surface peeling of low-carbon boron steel, the production method aims at production of a continuous casting steel billet with the thickness of 200 mm, and the production process meets the following requirements: when the section width of the steel billet is smaller than or equal to 925 mm, weak cooling is used for crystallizer cooling intensity, and weak cooling is used for secondary cooling; when the width of the section of the steel billet is 926-1235 mm, weak cooling is used for crystallizer cooling, and weak cooling is used for secondary cooling; a pressing roller of a fan-shaped section of the secondary cooling area adopts a static roller gap; controlling the billet pulling speed according to the manganese-sulfur ratio and the boron content of the molten steel; and the temperature of the tundish is controlled to be 1545-1560 DEG C. According to the method, the defects of corner cracks and small peeling of the casting blank can be effectively reduced, the number of the defects is reduced by 80-90%, the degradation rate of the steel billet produced through the scheme is obviously reduced, and economic benefits are obviously improved.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a production method for improving corner cracking and surface peeling of low-carbon boron-added steel. Background Art

[0002] Low-carbon boron steel is a type of low-alloy steel with a boron content of about 0.0008 to 0.0025% (mass). Adding trace amounts of boron can significantly improve the hardenability of steel. Boron steel is mainly used for automotive fasteners and has very high requirements for surface quality. Boron-added steel is a crack-sensitive steel grade. Corner cracks often occur at the corners of the ingot during casting. During rolling, irregular round small warps often appear within 10 to 30 mm from the edge of the strip, resulting in strip degradation and serious impact on product quality. Specifically, it was found in production practice that after adding boron, both slabs and billets would have serious surface quality problems. The surface quality problem of boron steel has become a common problem in the industry.

[0003] This solution aims to solve the problem of corner cracks in low-carbon boron steel and optimize its production process. The traditional production process of low-carbon boron steel is: the first step is to tap the molten steel after deoxidation, add the corresponding alloy into the ladle according to the type of the target, and then pour the molten steel with qualified composition into the ladle; the second step is to let the molten steel flow into the crystallizer through the tundish for cooling; the third step is to cool it again through the secondary cooling zone to form a continuous casting billet, and finally cut the continuous slab into ingots of the required length through a flame cutting machine. Summary of the invention

[0004] The technical problem to be solved by the present invention is that corner cracks are common in continuous casting billets in the existing low-carbon boron steel production process.

[0005] The present invention solves the above-mentioned problem by adopting the following technical solution: A production method for improving corner cracking and surface peeling of low carbon boron steel. The first step is to add the corresponding type of alloy to the molten steel according to the target steel grade, and then smelt it in a converter to obtain molten steel; In the second step, the molten steel in the converter flows into the tundish through the ladle, and then enters the crystallizer for cooling. The molten steel is cooled once in the crystallizer to form a shell of a certain thickness. The third step is to cool down again in the secondary cooling zone to form a continuous casting billet, and the continuous casting billet is driven by the sector-shaped rollers in the secondary cooling zone to control the pulling speed; In the fourth step, the steel billet is cut into fixed lengths by a flame cutting machine; This production method is aimed at the production of continuous casting billets with a thickness of 200 mm. The production process meets the following requirements: Tip1: When the cross-sectional width of the billet is ≤925mm, the cooling intensity of the crystallizer should be weak cooling, and the secondary cooling should be weak cooling; When the billet section width is 926mm-1235mm, the crystallizer cooling intensity uses weak cooling, and the secondary cooling uses weak cooling; Tip2: The pressing roller of the fan-shaped section in the secondary cooling zone adopts a static roller gap; Tip3: Control the billet drawing speed according to the manganese-sulfur ratio and boron content of the molten steel; Tip4: Control the temperature of the tundish at 1545-1560℃.

[0006] Compared with the prior art, the present invention adopting the above structure has the following beneficial effects: The present invention increases the temperature of the steel billet in the secondary cooling sector by reducing the cooling intensity of the crystallizer and the secondary cooling intensity, improves the plasticity of the steel billet when in contact with the driving roller, and reduces corner cracks; by setting the pressing roller to a static roller gap to avoid pressure on the surface of the steel billet, corner cracks are reduced; the pulling speed is controlled according to the manganese-sulfur ratio of the molten steel and the boron content of the molten steel to solve the surface quality of low-carbon boron-added steel. By adjusting the parameters in the production process, this solution not only effectively solves the corner crack problem of boron-added steel, but also significantly improves the small peeling of the edge of the strip steel, and also reduces the amount of steel billets offline, improves the quality of steel billets, and further improves the quality of the strip steel; this solution is a technical innovation carried out under the premise of unchanged original process conditions and equipment accuracy, with low implementation costs and improved production efficiency.

[0007] As a preferred embodiment, a further technical solution of the above structure is: Furthermore, when the cooling intensity of the crystallizer is weak cooling, the water volume on the wide surface is 2650L / min, and the water volume on the narrow surface is 460L / min; when the cooling intensity of the crystallizer is weak cooling, the water volume on the wide surface is 3100L / min, and the water volume on the narrow surface is 460L / min.

[0008] Furthermore, when the secondary cooling uses weak cooling, the secondary cooling intensity is 0.6L / kg; when the secondary cooling uses weak cooling, the secondary cooling intensity is 0.8L / kg.

[0009] Furthermore, the reduction amount of the reduction rollers in the 6th to 12th sections of the secondary cooling zone sector is 0.

[0010] Furthermore, when the manganese-sulfur ratio of the molten steel is ≥15 and the boron content w[B]=0.0008-0.0012% (mass percentage), the drawing speed is set to 0.8-1.5 m / min for producing billets with a cross-section width of ≤925 mm; the drawing speed is set to 0.8-1.3 m / min for producing billets with a cross-section width of 926 mm to 1235 mm; when the manganese-sulfur ratio is <15, the drawing speed is reduced by 0.05-0.1 m / min for every decrease of 1 in the manganese-sulfur ratio; when the boron content W[B] is >0.0012%, the drawing speed is reduced by 0.05 m / min for every increase of 0.0001% in boron.

[0011] Furthermore, the carbon content of the molten steel is controlled to be 0.04-0.09% (mass percentage). BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic diagram of the process for producing low carbon boron steel; Figure 2 It is a schematic diagram of the structural arrangement of the fan-shaped section of the secondary cooling area; Figure 3 This is an actual photo of a corner crack in low carbon and boron steel in the prior art; Figure 4 This is an actual inspection photo of small peeling on the edge of the strip caused by corner cracks in low-carbon and boron-added ingot steel in the prior art; Figure 5 This is an actual photo of the corner of a steel billet when the present invention is used to cast low-carbon boron steel; Figure 6 The present invention is used to cast low-carbon boron-added steel, and the actual photograph of the edge surface inspection of the strip steel is shown.

[0013] Explanation of the reference numerals: 1. sector; 2. driving roller; 3. pressing roller; 4. blank shell; 5. liquid core. DETAILED DESCRIPTION

[0014] The present invention will be further described below in conjunction with embodiments, the purpose of which is only to provide a better understanding of the content of the present invention. Therefore, the examples given do not limit the protection scope of the present invention.

[0015] As attached Figure 1-6 As shown, a production method for improving corner cracking and surface peeling of low carbon boron steel is provided. The first step is to add the corresponding type of alloy into the molten steel according to the target steel grade to be smelted, and then obtain the molten steel through converter smelting.

[0016] In the second step, the molten steel in the converter flows into the tundish through the ladle, and then enters the crystallizer for cooling. The molten steel forms a shell of a certain thickness through the primary cooling of the crystallizer.

[0017] In the third step, the temperature is lowered again in the secondary cooling zone to form a continuous casting billet. The continuous casting billet passes through the secondary cooling zone sector segment 1 and the driving roller 2 controls the pulling speed.

[0018] In the fourth step, the steel billet is cut into fixed lengths by a flame cutting machine.

[0019] This production method is aimed at the production of continuous casting billets with a thickness of 200 mm. For details, see Figure 1 As shown, the following requirements should be met during the production process.

[0020] Tip1: When the cross-sectional width of the produced steel billet is ≤925mm, the cooling intensity of the crystallizer should be weak cooling, and the secondary cooling should be weak cooling; When the cross-sectional width of the produced steel billet is 926mm~1235mm, the cooling intensity of the crystallizer should be weak cooling, and the secondary cooling should be weak cooling.

[0021] The ingot is cooled twice during the production process, one in the crystallizer and the other in the secondary cooling zone.

[0022] About the crystallizer: In the original process, the billet with a cross-sectional width of ≤925mm and a thickness of 200mm was produced. The cooling intensity of the crystallizer was weak cooling, specifically the water volume of the wide surface was 3100L / min and the water volume of the narrow surface was 460L / min. Because the cross-section of this type of billet is small, the corners of the billet shell 4 are cooled by the cooling water of the wide and narrow surfaces at the same time, forming a two-dimensional heat transfer, and the uneven growth of the primary billet shell 4 causes corner cracks. After technical research, this scheme weakens the cooling intensity of the crystallizer and determines to use the crystallizer weak cooling to cool the molten steel once. Weak cooling specifically means that the water volume of the narrow surface of the crystallizer remains unchanged, and the water volume of the wide surface is reduced to 2650L / min, so that the cooling speed of the billet surface is slowed down, the primary billet shell 4 grows evenly, and corner cracks are avoided; after using weak cooling, the crystallizer reduces the temperature of the molten steel from 1545℃~1560℃ to 1000℃~1100℃, and a billet shell 4 of a certain thickness is formed on the surface of the molten steel, and there is a high-temperature liquid core 5 in the center.

[0023] About secondary cooling: Under the same cooling idea, this solution also uses weak cooling for secondary cooling, that is, the secondary cooling intensity is 0.6L / kg.

[0024] In the original process, steel billets with a cross-section width of ≤925mm and a thickness of 200mm were produced. Weak cooling was used for secondary cooling, that is, the secondary cooling intensity was 0.8L / kg. At this intensity, the temperature of the steel billet dropped from 1000℃ to 1100℃ to 820~870℃. The temperature range of 700℃ to 900℃ is the third brittle zone of low-carbon boron steel. The plasticity of the steel billet is poor, indicating that the cooling intensity of the original process was too high, causing the steel billet to be in the third brittle zone, which is very easy to cause corner cracks. This solution solves the problem of poor plasticity of the steel billet by increasing the temperature of the steel billet during straightening. Therefore, for the small-section steel billet, weak cooling is used for secondary cooling, that is, the secondary cooling intensity is 0.6L / kg, so that the straightening temperature is between 900℃ and 950℃, avoiding the third brittle zone; and for the steel billet with a cross-sectional width of 926mm to 1235mm, weak cooling (that is, 0.8L / kg) is used for the crystallizer cooling intensity, which also meets the straightening temperature above 900℃ and avoids the third brittle zone, so that the cast billet can be fully cooled, the uniformity of the primary billet shell 4 is met, and the thickening of the billet shell 4 is ensured to be uniform, bulging is prevented, and the occurrence of surface cracks is avoided.

[0025] Tip2: The fan-shaped segment 1 in the secondary cooling zone changes the dynamic roll gap into a static roll gap, eliminating the downward pressure of the pressing roller 3 on the billet shell 4.

[0026] In the original process, the secondary cooling zone includes a water cooling system and a fan-shaped segment 1. The fan-shaped segment 1 includes a driving roller 2 and a pressing roller 3. The driving roller 2 is used to provide a drawing speed for the billet and drive the billet forward. The pressing roller 3 is used to constrain the size of the billet. The fan-shaped segment 1 in the secondary cooling zone has arc segments from the 1st to the 6th segments, straightening segments from the 7th to the 8th segments, and horizontal segments from the 9th to the 12th segments. Both the driving roller 2 and the pressing roller 3 are provided in the 6th to the 12th segments. During the billet drawing process, the pressing roller 3 performs dynamic roll gap adjustment, that is, the hydraulic cylinder of the pressing roller 3 is actuated during the production process to adjust the pressing amount of the pressing roller 3. When the pulling speed exceeds 1.0m / min, the position of the liquid core 5 of the billet begins to enter the 6th section, and the dynamic roll gap begins to move. The driving roller 2 of each sector segment 1 is responsible for pulling out the cast billet, and the pressing roller 3 of each sector segment 1 is responsible for dynamically pressing down the billet. When the billet with a mushy area at the end of solidification passes through the light pressing sector segment, each pressing roller 3 in the sector segment 1 will continuously squeeze the billet shell 4 of the billet. The pressing amount of the pressing roller 3 during the dynamic roll gap is about 2.8mm / m, especially in the straightening area from the 7th to the 8th section, the squeezing force on the corner billet shell 4 is strong. When the stress distribution is uneven or the billet straightening temperature is in the brittle pocket area of ​​700-900℃, corner cracks will occur. In order to avoid the corner billet shell 4 from being subjected to additional stress, this scheme changes the dynamic light pressing to static pressing, that is, the hydraulic cylinder stroke of the pressing roller 3 does not move, the pressing amount of the pressing roller 3 is 0, and no pressing is produced on the billet shell 4, thereby avoiding corner cracks.

[0027] Tip3: Control the billet drawing speed according to the manganese-sulfur ratio and boron content of the molten steel.

[0028] 1. It is well known that sulfur in molten steel forms FeS with iron. This Fe-FeS eutectic precipitates at the grain boundary and produces hot brittleness. The higher the sulfur content, the weaker the strength of the billet shell 4 and the weaker the degree of stress resistance. On the contrary, the lower the sulfur content in the steel is controlled, the stronger the high-temperature strength of the billet shell 4 is, which is conducive to the formation of MnS and inhibits the formation of FeS. MnS has a high melting point and good plasticity. After testing and studying the composition of molten steel, the manganese-sulfur ratio of molten steel in the original process is often less than 15, the strength of the billet shell 4 is weak, the billet shell 4 cannot withstand the pressing force of the pressing roller 3, and corner cracks are prone to occur. Therefore, when the composition of molten steel is adjusted in the converter, the present invention requires the manganese-sulfur ratio in the molten steel to be ≥15 to improve the plasticity of the cast billet and avoid corner cracks.

[0029] 2. In the existing process, the boron content is w[B]=0.0008-0.0015% (mass percentage). Boron is very easy to combine with nitrogen in steel to form boron nitride (BN), which gathers at the grain boundary and causes grain boundary embrittlement, increasing the crack sensitivity of the steel. In particular, when the straightening temperature of the steel billet is in the third brittle zone of 700-900℃, the occurrence of corner cracks will be aggravated. This solution reduces the boron content in steel, and the boron content is controlled at 0.0008-0.0012% in actual production.

[0030] 3. When the manganese-sulfur ratio of molten steel is ≥15 and the boron content w[B]=0.0008-0.0012% (mass percentage), the pulling speed is set to 0.8-1.5m / min for the production of steel billets with a cross-section width of ≤925mm; the pulling speed is set to 0.8-1.3m / min for the production of steel billets with a cross-section width of 926mm~1235mm; When the manganese-sulfur ratio is less than 15, the pulling speed decreases by 0.05-0.1m / min for every 1 decrease in the manganese-sulfur ratio; When the boron content W[B] is greater than 0.0012%, the pulling speed decreases by 0.05 m / min for every 0.0001% increase in boron.

[0031] Tip4: Control the temperature of the tundish between 1545℃ and 1560℃.

[0032] It is also important to note that the carbon content of low carbon boron steel is 0.04-0.09%.

[0033] According to the existing low-carbon boron steel production technology, corner cracks appear in the ingot, which causes a large number of small peeling defects within the range of 10mm to 30mm on the edge of the hot-rolled strip. After the method of the present invention is implemented, the corner cracks are effectively reduced or even eliminated, and the number of small peelings on the hot-rolled strip is significantly reduced from 10 to 40 to 1 to 5 or even eliminated. Not only does it reduce the number of downgraded products, but it also ensures the quality of the ingot and strip, with significant economic benefits.

[0034] The following is a comparative experiment on the parameters of the method, specifically using a single variable method, that is, changing one of the six process parameters, namely, the cooling intensity of the crystallizer, the secondary cooling intensity, the manganese-sulfur ratio in the molten steel, the boron content in the molten steel, changing the dynamic light reduction to static, controlling the pulling speed, etc., and observing the corner cracks and small peeling of the hot-rolled strip. Finally, a ledger is established to record the data to verify the superiority of the data range given in the present invention.

[0035] Embodiment 1 of the present invention: The cross section of the steel billet is 925mm×200mm, the steel grade is Q195-B, the tundish temperature is 1545-1560℃, the carbon content is 0.05-0.08%, and the other five processes are unchanged. The manganese-sulfur ratio of the molten steel is changed to observe the small peeling of the edge of the hot-rolled strip. The experimental data is shown in Table 1. When the manganese-sulfur ratio in the molten steel is less than 15, the corner cracks of the ingot are serious, and the corresponding edges of the hot-rolled strip have small peeling, the number of which ranges from 15 to 30, and the strip is downgraded. When the manganese-sulfur ratio in the molten steel is ≥15, the ingot has no corner cracks, and the corresponding edges of the hot-rolled strip have no small peeling, and the strip is not downgraded.

[0036] Table 1 Steel Type Section mm Mn / S<15 Mn / S≥15 Dynamic soft pressing Static roll gap Boron content W[B]≤0.0012% Boron content W[B]>0.0012% Crystallizer cooling weak cooling Crystallizer cooling weak cooling Secondary cooling weak cooling Secondary cooling weak cooling Pulling speed m / min Corner crack of ingot Number of small peeling on the edge of the strip steel (places) Strip quality Q195-B 925 9 - use 0.0010 - - use - use 1.5 Severe horn cracks 25 Downgrade Q195-B 925 10 - use 0.0011 - - use - use 1.5 Severe horn cracks 22 Downgrade Q195-B 925 13 - use 0.0090 - - use - use 1.5 Severe horn cracks 18 Downgrade Q195-B 925 16 - use 0.0010 - - use - use 1.5 No horn crack No peeling qualified Q195-B 925 18 - use 0.0010 - - use - use 1.5 No horn crack No peeling qualified Q195-B 925 25 - use 0.0010 - - use - use 1.5 No horn crack No peeling qualified .

[0037] Embodiment 2 of the present invention: See Table 2, the cross section of the billet is 925mm, the steel grades are SPHC-B and Q195-B, the tundish temperature is 1545-1560℃, the carbon content is 0.04-0.08%, and under the premise that the other five processes remain unchanged, the dynamic light reduction is changed to the static roll gap to observe the corner cracks and small peeling on the edge of the hot-rolled strip. See Table 2, when dynamic light reduction is used, the corner cracks of the billet are serious, and the number of small peeling on the edge of the corresponding hot-rolled strip is 20-40, and the strip is downgraded. When the static roll gap is used, the billet has no corner cracks, and the number of small peeling on the edge of the corresponding hot-rolled strip is reduced to 1-3, and the strip is not downgraded.

[0038] Table 2 Steel Type Section mm Mn / S<15 Mn / S≥15 Dynamic soft pressing Static roll gap Boron content W[B]≤0.0012% Boron content W[B]>0.0012% Crystallizer cooling weak cooling Crystallizer cooling weak cooling Secondary cooling weak cooling Secondary cooling weak cooling Pulling speed m / min Corner crack of ingot Small peeling on the edge of the strip Strip quality SPHC-B 925 - 17 use - 0.0011 - - use - use 1.5 Severe horn cracks 25 Downgrade SPHC-B 925 - 19 use - 0.0011 - - use - use 1.5 Severe horn cracks 22 Downgrade SPHC-B 925 - 21 use - 0.0011 - - use - use 1.5 Severe horn cracks 20 Downgrade Q195-B 925 - 16 - use 0.0012 - - use - use 1.5 No horn crack 2 qualified Q195-B 925 - 18 - use 0.0012 - - use - use 1.5 No horn crack 2 qualified Q195-B 925 - 22 - use 0.001 - - use - use 1.5 No horn crack 1 qualified .

[0039] Embodiment 3 of the present invention: The cross-section of the steel billet is 925 mm, the steel grade is Q195-B, the tundish temperature is 1545-1560°C, the carbon content is 0.05-0.08%, and under the premise that the other five processes remain unchanged, the corner cracks and the small peeling on the edge of the hot-rolled strip are observed by changing the boron content in the molten steel. Referring to Table 3, when the boron content in the molten steel is between 0.0008 and 0.0012%, the ingot has no corner cracks, and the number of small peelings on the edge of the corresponding hot-rolled strip is 1-3, and the strip is not degraded. When the boron content in the molten steel is greater than 0.0012%, the ingot has corner cracks, and the number of small peelings on the edge of the corresponding hot-rolled strip is 10-20, and the strip is degraded.

[0040] Table 3 Steel Type Section mm Mn / S<15 Mn / S≥15 Dynamic soft pressing Static roll gap Boron content W[B]≤0.0012% Boron content W[B]>0.0012% Crystallizer cooling weak cooling Crystallizer cooling weak cooling Secondary cooling weak cooling Secondary cooling weak cooling Pulling speed m / min Corner crack of ingot Small peeling on the edge of the strip Strip quality Q195-B 925 - 24 - use 0.0008 - use use 1.5 No horn crack 1 qualified Q195-B 925 - 22 - use 0.0010 - use use 1.5 No horn crack 2 qualified Q195-B 925 - 20 - use 0.0011 - use use 1.5 No horn crack 2 qualified Q195-B 925 - 18 - use - 0.0015 use use 1.5 There is horn crack 11 Downgrade Q195-B 925 - 16 - use - 0.0017 use use 1.5 There is horn crack 15 Downgrade Q195-B 925 - 16 - use - 0.0015 use use 1.5 There is horn crack 13 Downgrade .

[0041] Embodiment 4 of the present invention: Referring to Table 4, the cross-section of the steel billet is 925 mm, the steel grade is Q195-B, the tundish temperature is 1545-1560°C, the carbon content is 0.05-0.08%, and under the premise that the other five processes remain unchanged, the corner cracks and small peeling on the edge of the hot-rolled strip are observed by changing the cooling intensity of the crystallizer and the cooling intensity of the secondary cooling zone. When the cooling intensity of the crystallizer and the secondary cooling intensity are both weakly cooled, the corner cracks of the ingot are serious, and the number of small peeling on the edge of the corresponding hot-rolled strip is 5-10, and the strip is downgraded. When the cooling intensity of the crystallizer and the secondary cooling intensity are both weakly cooled, the ingot has no corner cracks, and the number of small peeling on the edge of the corresponding hot-rolled strip is only 1-3 or even no small peeling, and the strip is not downgraded.

[0042] Table 4 Steel Type Section mm Mn / S<15 Mn / S≥15 Dynamic soft pressing Static roll gap Boron content W[B]≤0.0012% Boron content W[B]>0.0012% Crystallizer cooling weak cooling Crystallizer cooling weak cooling Secondary cooling weak cooling Secondary cooling weak cooling Pulling speed m / min Corner crack of ingot Small peeling on the edge of the strip Strip quality Q195-B 925 - 20 - use 0.0010 - use - use - 1.5 Severe horn cracks 5 Downgrade Q195-B 925 - 21 - use 0.0012 - use - use - 1.5 Severe horn cracks 9 Downgrade Q195-B 925 - 17 - use 0.0011 - use - use - 1.5 Severe horn cracks 8 Downgrade Q195-B 925 - 16 - use 0.0010 - - use - use 1.5 No horn crack 1-3 qualified Q195-B 925 - 21 - use 0.0010 - - use - use 1.5 No horn crack No peeling qualified Q195-B 925 - 17 - use 0.0010 - - use - use 1.5 No horn crack No peeling qualified .

[0043] Embodiment 5 of the present invention: Referring to Table 5, the cross section of the steel billet is 925 mm, the steel grade is Q195-B, the tundish temperature is 1545-1560°C, the carbon content is 0.05-0.08%, and the corner cracks and small peeling on the edge of the hot-rolled strip are observed by changing the pulling speed while keeping the other five processes unchanged. When the pulling speed increases from 1.5 m / min to 1.7 m / min, the corner cracks of the ingot are aggravated, and the number of small peeling on the edge of the corresponding hot-rolled strip is 10-30, and the strip is downgraded. When the pulling speed decreases from 1.5 m / min to 1.2 m / min, the corner cracks of the ingot are reduced from slight to no corner cracks, and the number of small peeling on the edge of the corresponding hot-rolled strip is 1-5 or even no small peeling 2, and the strip is not downgraded.

[0044] Table 5 Steel Type Section mm Mn / S<15 Mn / S≥15 Dynamic soft pressing Static roll gap Boron content W[B]≤0.0012% Boron content W[B]>0.0012% Crystallizer cooling weak cooling Crystallizer cooling weak cooling Secondary cooling weak cooling Secondary cooling weak cooling Pulling speed m / min Corner crack of ingot Small peeling on the edge of the strip Strip quality Q195-B 925 18 - use 0.0010 - - use - use 1.5 There is horn crack 15 Downgrade Q195-B 925 19 - use 0.0011 - - use - use 1.6 Corner cracks aggravate 18 Downgrade Q195-B 925 22 - use 0.0010 - - use - use 1.7 Corner cracks aggravate 21 Downgrade Q195-B 925 19 - use 0.0009 - - use - use 1.4 Minor horn crack 1-5 qualified Q195-B 925 19 - use 0.0010 - - use - use 1.3 No horn crack No peeling qualified Q195-B 925 17 - use 0.0011 - - use - use 1.2 No horn crack No peeling qualified .

[0045] Embodiment 6 of the present invention: The cross section of the steel billet in Table 6 is 1020 mm, the steel grade is Q195-B, the tundish temperature is 1545-1560°C, the carbon content is 0.05-0.08%, and under the premise that the other five processes remain unchanged, the manganese-sulfur ratio of the molten steel is changed to observe the corner cracks and small peeling on the edge of the hot-rolled strip. It can be seen that when the manganese-sulfur ratio in the molten steel is less than 15, the corner cracks of the ingot are serious, and the number of small peelings on the edge of the corresponding hot-rolled strip is 10-30, and the strip is downgraded. When the manganese-sulfur ratio in the molten steel is ≥15, the ingot has no corner cracks, and the corresponding hot-rolled strip has no small peeling on the edge, and the strip is not downgraded.

[0046] Table 6 Steel Type Section mm Mn / S<15 Mn / S≥15 Dynamic soft pressing Static roll gap Boron content W[B]≤0.0012% Boron content W[B]>0.0012% Crystallizer cooling weak cooling Crystallizer cooling weak cooling Secondary cooling weak cooling Secondary cooling weak cooling Pulling speed m / min Corner crack of ingot Small peeling on the edge of the strip Strip quality Q195-B 1020 8 - - use 0.0010 - use - use - 1.5 Severe horn cracks 20 Downgrade Q195-B 1020 10 - - use 0.0009 - use - use - 1.5 Severe horn cracks 17 Downgrade Q195-B 1020 7 - - use 0.0011 - use - use - 1.5 Severe horn cracks 24 Downgrade Q195-B 1020 - 16 - use 0.0010 - use - use - 1.5 No horn crack No peeling qualified Q195-B 1020 - 20 - use 0.0010 - use - use - 1.5 No horn crack No peeling qualified Q195-B 1020 - 18 - use 0.0011 - use - use - 1.5 No horn crack No peeling qualified .

[0047] Embodiment 7 of the present invention: Referring to Table 7, the cross section of the steel billet is 1235 mm, the steel grade is SPHC-B, the tundish temperature is 1545-1560°C, the carbon content is 0.04-0.06%, and under the premise that the other five processes remain unchanged, the dynamic soft pressure is changed to the static roll gap to observe the corner cracks and the small peeling of the hot-rolled strip edge. However, when the dynamic soft pressure is used, the corner cracks of the billet are serious, and the number of small peelings on the edge of the corresponding hot-rolled strip is 10-30, and the strip is downgraded. When the static roll gap is used, the billet has no corner cracks, and the number of small peelings on the edge of the corresponding hot-rolled strip is reduced to 1-3, and the strip is not downgraded.

[0048] Table 7 Steel Type Section mm Mn / S<15 Mn / S≥15 Dynamic soft pressing Static roll gap Boron content W[B]≤0.0012% Boron content W[B]>0.0012% Crystallizer cooling weak cooling Crystallizer cooling weak cooling Secondary cooling weak cooling Secondary cooling weak cooling Pulling speed m / min Corner crack of ingot Small peeling on the edge of the strip Strip quality SPHC-B 1235 - 30 use - 0.0009 - use - use - 1.5 Corner cracks aggravate 24 Downgrade SPHC-B 1235 - 27 use - 0.0001 - use - use - 1.5 Corner cracks aggravate 21 Downgrade SPHC-B 1235 - 23 use - 0.0010 - use - use - 1.5 Corner cracks aggravate 18 Downgrade SPHC-B 1235 - 18 - use 0.0011 - use - use - 1.5 No horn crack 1-3 qualified SPHC-B 1235 - 22 - use 0.0012 - use - use - 1.5 No horn crack 1-3 qualified SPHC-B 1235 - 20 - use 0.0008 - use - use - 1.5 No horn crack 1-3 qualified .

[0049] Embodiment 8 of the present invention: Referring to Table 8, the cross section of the steel billet is 1235 mm, the steel grades are Q195-B and SPHC-B, the tundish temperature is 1545-1560°C, the carbon content is 0.04-0.08%, and under the premise that the other five processes remain unchanged, the corner cracks and small peeling on the edge of the hot-rolled strip are observed by changing the boron content in the molten steel. When the boron content in the molten steel is 0.0008-0.0012%, there is no corner crack in the ingot, and the number of small peelings on the edge of the corresponding hot-rolled strip is 1-3, and the strip is not degraded. When the boron content in the molten steel is greater than 0.0012%, the corner cracks of the ingot are aggravated, and the number of small peelings on the edge of the corresponding hot-rolled strip is 10-30, and the strip is degraded.

[0050] Table 8 Steel Type Section mm Mn / S<15 Mn / S≥15 Dynamic soft pressing Static roll gap Boron content W[B]≤0.0012% Boron content W[B]>0.0012% Crystallizer cooling weak cooling Crystallizer cooling weak cooling Secondary cooling weak cooling Secondary cooling weak cooling Pulling speed m / min Corner crack of ingot Small peeling on the edge of the strip Strip quality SPHC-B 1235 - 16 use 0.0010 - use - use - 1.4 No horn crack 1-3 qualified SPHC-B 1235 - 16 use 0.0011 - use - use - 1.4 No horn crack 1-3 qualified Q195-B 1235 - 15 use 0.0010 - use - use - 1.4 No horn crack 1-3 qualified Q195-B 1235 - 16 use - 0.0015 use - use - 1.4 Corner cracks aggravate 18 Downgrade Q195-B 1235 - 18 use - 0.0015 use - use - 1.4 Corner cracks aggravate 14 Downgrade Q195-B 1235 - 19 use - 0.0017 use - use - 1.4 Corner cracks aggravate 21 Downgrade .

[0051] Embodiment 9 of the present invention, see Table 9, the cross-section of the billet is 1020mm, the steel grade is Q195-B, the tundish temperature is 1545-1560℃, the carbon content is 0.05-0.08%, and the corner cracks and small peeling on the edge of the hot-rolled strip are observed by changing the pulling speed under the premise that the other five processes remain unchanged. When the pulling speed increases from 1.5m / min to 1.7m / min, the corner cracks of the ingot are aggravated, and the number of small peeling on the edge of the corresponding hot-rolled strip is 10-30, and the strip is downgraded. When the pulling speed decreases from 1.5m / min to 1.2m / min, the corner cracks of the ingot are reduced from slight to no corner cracks, and the number of small peeling on the edge of the corresponding hot-rolled strip is 1-3 or even no small peeling, and the strip is not downgraded.

[0052] Table 9 Steel Type Section mm Mn / S<15 Mn / S≥15 Dynamic soft pressing Static roll gap Boron content W[B]≤0.0012% Boron content W[B]>0.0012% Crystallizer cooling weak cooling Crystallizer cooling weak cooling Secondary cooling weak cooling Secondary cooling weak cooling Pulling speed m / min Corner crack of ingot Small peeling on the edge of the strip Strip quality Q195-B 1020 - 18 - use 0.0010 - use - use - 1.5 There is horn crack 16 Downgrade Q195-B 1020 - 16 - use 0.0010 - use - use - 1.6 Corner cracks aggravate 21 Downgrade Q195-B 1020 - 20 - use 0.0011 - use - use - 1.7 Corner cracks aggravate 25 Downgrade Q195-B 1020 - 21 - use 0.0009 - use - use - 1.4 Minor horn crack 1-3 qualified Q195-B 1020 - 16 - use 0.0010 - use - use - 1.3 No horn crack No peeling qualified Q195-B 1020 - 18 - use 0.0010 - use - use - 1.2 No horn crack No peeling qualified .

[0053] Embodiment 10 of the present invention, see Table 10, the cross section of the steel billet is 925mm, the steel grade is Q195-B, the tundish temperature is 1545-1560℃, the carbon content is 0.05-0.08%, and under the premise that the other five processes remain unchanged, by changing the strength of the crystallizer and secondary cooling, the influence of the straightening temperature on the steel billet corner cracks and the small peeling on the edge of the hot-rolled strip is observed. When the production drawing speed is stable at 1.4m / min, the crystallizer cooling uses weak cooling, and the secondary cooling uses weak cooling, the straightening temperature of the 7th to 8th sections of the fan-shaped section of the secondary cooling zone is 834-870℃, and this straightening temperature is in the low temperature brittle zone of 700-900℃, the corner cracks of the ingot are aggravated, and the number of small peeling on the edge of the corresponding hot-rolled strip is 10-30, and the strip is downgraded. Similarly, when the pulling speed is stabilized at 1.4m / min, weak cooling is used for crystallizer cooling and weak cooling is used for secondary cooling, the straightening temperatures of the 7th to 8th sections of the secondary cooling zone fan-shaped section are all higher than 900℃, avoiding the 700-900℃ low-temperature brittle zone, and the corner cracks of the ingot are significantly reduced or even eliminated, and the number of small peelings on the edge of the corresponding hot-rolled strip is 1-3 or even no small peeling, and the strip is not degraded.

[0054] Table 10 Steel Type Section mm Mn / S<15 Mn / S≥15 Dynamic soft pressing Static roll gap Boron content W[B]≤0.0012% Boron content W[B]>0.0012% Crystallizer cooling weak cooling Crystallizer cooling weak cooling Secondary cooling weak cooling Secondary cooling weak cooling Pulling speed m / min Secondary cooling straightening temperature Corner crack of ingot Small peeling on the edge of the strip Strip quality Q195-B 925 - 17 - use 0.0010 - use - use - 1.4 870 There is horn crack 18 Downgrade Q195-B 925 - 19 - use 0.0010 - use - use - 1.4 846 There is horn crack 16 Downgrade Q195-B 925 - 22 - use 0.0009 - use - use - 1.4 834 There is horn crack 20 Downgrade Q195-B 925 - 21 - use 0.0011 - - use - use 1.4 926 Minor horn crack 1-3 qualified Q195-B 925 - 17 - use 0.0012 - - use - use 1.4 940 No horn crack No peeling qualified Q195-B 925 - 20 - use 0.0009 - - use - use 1.4 955 No horn crack No peeling qualified .

[0055] When low-carbon and boron steel is produced according to the prior art method, the corner cracks of the ingot are obvious, and there are a large number of small peeling defects within the range of 10-30mm on the edge of the corresponding hot-rolled strip, which deteriorates the quality of the ingot, increases the number of downgrades of the hot-rolled strip, and the product has a large quality risk. If low-carbon and boron steel is produced according to the method of the present invention, the ingot has no corner cracks, the corner quality is good, and the surface quality of the hot-rolled strip is good, and there is no small peeling defect within the range of 10-30mm on the edge of the strip. This method not only reduces the production cost, but also has significant economic benefits and ensures the stability of quality; the present invention successfully solves the problem that when casting low-carbon and boron steel, a large number of small peeling defects appear within the range of 10-30mm on the edge of the hot-rolled strip due to the corner cracks of the ingot, which leads to the downgrade of the strip. This method is simple to operate, and the process adjustment is finally determined after a large number of test tracking. It is highly targeted and applicable. It not only reduces the quality problems such as corner cracks of the ingot and small peeling on the edge of the strip, but also stabilizes the product quality, and has a good promotion value.

[0056] The above description is only a preferred feasible embodiment of the present invention, and does not limit the scope of rights of the present invention. All equivalent changes made using the contents of the present specification and its drawings are included in the scope of rights of the present invention.

Claims

1. A production method for improving corner cracking and surface peeling of low carbon boron steel. The first step is to add the corresponding type of alloy to the molten steel according to the target steel grade, and then smelt it in a converter to obtain molten steel; In the second step, the molten steel in the converter flows into the tundish through the ladle, and then enters the crystallizer for cooling. The molten steel is cooled once in the crystallizer to form a shell of a certain thickness. The third step is to cool down again in the secondary cooling zone to form a continuous casting billet, and the continuous casting billet is driven by the sector-shaped rollers in the secondary cooling zone to control the pulling speed; In the fourth step, the steel billet is cut into fixed lengths by a flame cutting machine; It is characterized in that This production method is aimed at the production of continuous casting billets with a thickness of 200 mm. The production process meets the following requirements: Tip1: When the cross-sectional width of the billet is ≤925mm, the cooling intensity of the crystallizer should be weak cooling, and the secondary cooling should be weak cooling; When the billet section width is 926mm-1235mm, the mold cooling intensity uses weak cooling, and the secondary cooling uses weak cooling; Tip2: The pressing roller of the fan-shaped section in the secondary cooling zone adopts a static roller gap; Tip3: Control the billet drawing speed according to the manganese-sulfur ratio and boron content of the molten steel; Tip4: Control the temperature of the tundish at 1545℃-1560℃.

2. The production method for improving corner cracking and surface peeling of low carbon boron steel according to claim 1, characterized in that: When the cooling intensity of the crystallizer is weak cooling, the water volume on the wide surface is 2650L / min, and the water volume on the narrow surface is 460L / min; when the cooling intensity of the crystallizer is weak cooling, the water volume on the wide surface is 3100L / min, and the water volume on the narrow surface is 460L / min.

3. The production method for improving corner cracking and surface peeling of low carbon and boron steel according to claim 1, characterized in that: When the secondary cooling uses weak cooling, the secondary cooling intensity is 0.6L / Kg; when the secondary cooling uses weak cooling, the secondary cooling intensity is 0.8L / Kg.

4. The production method for improving corner cracking and surface peeling of low carbon boron steel according to claim 1, characterized in that: The reduction amount of the reduction rollers in the 6th to 12th sectors of the secondary cooling zone is 0.

5. The production method for improving corner cracking and surface peeling of low carbon boron steel according to claim 1, characterized in that: When the manganese-sulfur ratio of molten steel is ≥15 and the boron content w[B]=0.0008-0.0012% (mass percentage), the drawing speed is set to 0.8-1.5m / min for producing billets with a width of ≤925mm; the drawing speed is set to 0.8-1.3m / min for producing billets with a width of 926mm~1235mm; When the manganese-sulfur ratio is less than 15, the pulling speed decreases by 0.05-0.1m / min for every 1 decrease in the manganese-sulfur ratio; When the boron content W[B] is greater than 0.0012%, the pulling speed decreases by 0.05 m / min for every 0.0001% increase in boron.

6. The production method for improving corner cracking and surface peeling of low carbon boron steel according to claim 1, characterized in that: The carbon content of molten steel is controlled to be 0.04-0.09% (mass percentage).

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