A continuous casting method for a continuous casting slab of a low-temperature steel, a production method, and a continuous casting slab

Abstract

The present application relates to a continuous casting production method of a low-temperature steel continuous casting billet, a production method and a continuous casting billet, which solves the problem of uneven distribution of molten steel temperature in a crystallizer by adjusting the immersion depth of a submerged nozzle, the length of the center position of a crystallizer electromagnetic stirrer from the upper opening of the crystallizer, the current value of the crystallizer electromagnetic stirrer and the pulling speed of the continuous casting machine, controls the molten steel flow rate of the meniscus of the crystallizer, promotes the melting of the protective slag and prevents slag entrapment. Low alkalinity, low melting point and low viscosity continuous casting crystallizer protective slag is used, and combined with protective slag layer thickness control, to ensure good lubrication effect of the protective slag, avoid the formation of large thermal stress and surface cracks and other defects; by controlling the superheat of the molten steel, the water flow of the crystallizer, the taper, the specific water quantity of the secondary cooling zone and the distribution ratio of each zone, the fan-shaped segment roll gap shrinkage, the soft reduction amount and the distribution ratio, the center density of the continuous casting billet is improved, which plays a role in eliminating center shrinkage, porosity and reducing center segregation.

Description

Technical Field

[0001] This invention relates to a continuous casting production method for low-temperature steel continuously cast billets, the production method, and the continuously cast billets, belonging to the field of metallurgical technology. Background Technology

[0002] With the diversification of global energy resources and increasing emphasis on environmental protection, natural gas, as a clean energy source, is playing an increasingly important role. However, liquefied natural gas (LNG) is stored and transported at temperatures below -162°C, requiring materials used for LNG storage to possess excellent low-temperature toughness, strength, and sufficient resistance to brittle fracture and crack arrest at ultra-low temperatures. Currently, the materials used in LNG storage and transportation facilities worldwide are primarily 9Ni steel with a Ni content of approximately 9%. Existing production processes for this type of low-temperature steel mainly include: hot metal pretreatment, primary refining furnace, LF refining, RH refining, continuous casting, grinding, spraying, hot rolling, and heat treatment. To improve yield and obtain high-performance finished plates, in addition to controlling the quantity, composition, and size of inclusions, strict control of the surface and internal quality of the low-temperature steel slabs is also necessary during the production process.

[0003] Chinese patent CN105562642A discloses a method for controlling typical intermediate cracks and center segregation in continuous casting of pipeline steel slabs. This method ensures accuracy within ±0.2mm by offline calibration and online detection of the continuous casting machine roll gap; it also involves classifying steel grades to enhance the matching of their thermal properties; strictly controlling superheat to increase the proportion of equiaxed crystals and avoid developing columnar crystals; adjusting the casting speed and secondary cooling process to optimize the control of the basic roll gap during slab solidification; and optimizing the reduction amount, avoiding large differences in reduction amount between different sector sections to improve the internal quality of the slab. Chinese patent CN101934357A discloses an effective process for controlling center segregation in continuously cast slabs. This method combines a strong secondary cooling water flow at the end of the slab solidification with pressure control of the hydraulic cylinder in the light reduction section to effectively control center segregation. This method controls the degree of center segregation to a certain extent, reduces the reliance on the hydraulic cylinder pressure in the light reduction section for controlling center segregation in continuously cast slabs, and increases the service life of the light reduction equipment. Chinese patent CN109940140A discloses a method for improving the center segregation quality of peritectic steel billets. By using two pairs of electromagnetic stirring rollers and controlling the direction of the magnetic field, combined with setting the reduction range and controlling the reduction rate under dynamic light pressure, the center segregation of peritectic steel billets is eliminated, thus eliminating tensile delamination and fracture of hot-rolled coils.

[0004] The above-mentioned existing technologies mainly focus on the control of the precision of the roll gap in the fan-shaped section, the electromagnetic stirring parameters of the secondary cooling zone, the superheat of the molten steel in the tundish, the casting speed, the specific water volume in the secondary cooling zone, the position of the reduction zone and the reduction rate, etc., to control the center quality of the continuously cast billet. Through research and practice, the important factor affecting the surface and internal quality of the slab for low-temperature steel is that during the continuous casting process, the molten steel in the tundish flows into the crystallizer through the side guide hole of the submerged entry nozzle, forming upper and lower swirling zones in the crystallizer, resulting in a high temperature of molten steel at the 1 / 4 position of the wide face. This situation will affect the surface and internal quality of the continuously cast billet: (1) The uneven distribution of the molten steel temperature field in the crystallizer will lead to different temperature gradients between the molten steel and the copper plate of the crystallizer and different melting rates of the protective slag at the meniscus position, further causing defects such as cracks to form on the surface of the continuously cast billet; (2) During the subsequent cooling process, the unevenness of the billet temperature will always exist, resulting in the billet solidification endpoint morphology being "W" shaped, and even with the use of light reduction technology, the center quality of the continuously cast billet is difficult to control stably.

[0005] Clearly, existing technologies do not address the issue of inconsistent steel temperature distribution within the crystallizer, thus failing to achieve stable control over the surface and internal quality of continuously cast billets. Therefore, new methods are needed to guarantee the surface and internal quality of continuously cast billets. Summary of the Invention

[0006] This invention provides a continuous casting production method for low-temperature steel continuously cast billets, a production method, and a continuously cast billet, which can effectively improve the surface and internal quality of the continuously cast billet and enhance the quality of low-temperature steel.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A continuous casting production method for low-temperature steel billets, wherein in the continuous casting process, molten steel is poured from the ladle through the tundish and then into the crystallizer. After the molten steel initially solidifies in the crystallizer to form a billet shell, it enters the secondary cooling zone to continue solidification. The width dimension of the continuous casting machine is defined as l, the insertion depth of the submerged entry nozzle is h1, the distance from the center position of the electromagnetic stirrer in the crystallizer to the top opening of the crystallizer is h2, and the current of the electromagnetic stirrer in the crystallizer is a.

[0009] The width of the continuous casting machine is 1900mm≤l≤2800mm, the insertion depth of the submerged entry nozzle is set to 170mm≤h1≤230mm, the current of the crystallizer electromagnetic stirrer is 450A≤a≤600A, and the distance from the center of the crystallizer electromagnetic stirrer to the top of the crystallizer is 550mm≤h2≤650mm.

[0010] Further, the continuous caster is a straight-arc continuous caster with an arc radius of 10 m, a thickness dimension of 220 mm. Defining the casting speed of the continuous caster as V, the casting speed V of the continuous caster is 1.0 m / min ≤ V ≤ 1.3 m / min; the length of the mold is 900 mm, the position of the molten steel meniscus in the mold is 200 mm from the upper opening of the mold, the height of the mold electromagnetic stirrer is 400 mm, and the frequency is 3 Hz.

[0011] Further, when the width dimension of the continuous caster is 1900 mm ≤ l < 2200 mm, the immersion nozzle insertion depth is set to 170 mm ≤ h1 < 190 mm, the length from the center position of the mold electromagnetic stirrer to the upper opening of the mold is 550 mm ≤ h2 < 570 mm, the current of the mold electromagnetic stirrer is 550 A < a ≤ 600 A, and the casting speed of the continuous caster is 1.2 m / min < V ≤ 1.3 m / min;

[0012] When the width dimension of the continuous caster is 2200 mm ≤ l < 2500 mm, the immersion nozzle insertion depth is set to 190 mm ≤ h1 < 210 mm, the length from the center position of the mold electromagnetic stirrer to the upper opening of the mold is 570 mm ≤ h2 < 600 mm, the current of the mold electromagnetic stirrer is 500 A < a ≤ 550 A, and the casting speed of the continuous caster is 1.1 m / min < V ≤ 1.2 m / min;

[0013] When the width dimension of the continuous caster is 2500 mm < l ≤ 2800 mm, the immersion nozzle insertion depth is set to 210 mm ≤ h1 ≤ 230 mm, the length from the center position of the mold electromagnetic stirrer to the upper opening of the mold is 600 mm ≤ h2 ≤ 650 mm, the current of the mold electromagnetic stirrer is 450 A ≤ a ≤ 500 A, and the casting speed of the continuous caster is 1.0 m / min ≤ V ≤ 1.1 m / min;

[0014] Further, in the continuous casting process, the superheat of the molten steel in the tundish of the continuous caster is 20 - 30 °C, and the mold taper is 1.1% - 1.2%;

[0015] The water flow on the wide face side of the mold is 3700 - 4100 L / min, and the water flow on the narrow face side is 480 - 520 L / min;

[0016] The mold liquid level fluctuation is controlled within ±2 mm;

[0017] Further, for the mold powder used in the mold, its chemical composition in mass percentage includes: SiO2: 34 - 38%, CaO: 29 - 36%, MgO: 0.5 - 1.0%, Al2O3: 3 - 7%, Na2O: 8 - 10%, F: 8 - 10%, C: 1 - 3%, and the rest are inevitable impurities;

[0018] Furthermore, the binary basicity of the protective slag, CaO / SiO2, is 0.79-0.94, the melting point is 1050-1150℃, and the viscosity at 1300℃ is 0.25-0.35 Pa·s;

[0019] The thickness of the protective slag layer is 100-130mm. The protective slag forms a liquid slag film between the molten steel and the crystallizer wall, and the thickness of the liquid slag layer is 10-13mm.

[0020] Furthermore, the second cooling zone includes a foot roller section, a zero section, and several fan-shaped sections, wherein 14 fan-shaped sections are provided, and the second cooling zone includes zone 1, zone 2... zone 9;

[0021] The foot roller section corresponds to Zone 1 of the second cooling system, and the zero section corresponds to Zones 2, 3, and 4 of the second cooling system. The 14 sector sections are numbered 1, 2, ... 14. Sector sections 1 and 2 correspond to Zone 5 of the second cooling system, sector sections 3 and 4 correspond to Zone 6 of the second cooling system, sector sections 5, 6, and 7 correspond to Zone 7 of the second cooling system, sector sections 8, 9, and 10 correspond to Zone 8 of the second cooling system, and sector sections 11, 12, 13, and 14 correspond to Zone 9 of the second cooling system.

[0022] The specific water volume of the secondary cooling zone is set at 0.4-0.6 L / kg, and the water volume proportions of secondary cooling zones 1 to 9 are 8-13%, 24-30%, 20-25%, 13-18%, 8-13%, 6-12%, 1-3%, 1-3%, and 1-3%, respectively.

[0023] In the second cooling zone 1, the water volume is distributed to the narrow side and the wide side of the continuously cast billet, with the narrow side accounting for 30-40% and the wide side accounting for 60-70%.

[0024] Furthermore, in the foot roller section of the second cooling zone, its length is set to 0.52m, with 2 pairs of rollers distributed on the wide side and 3 pairs of rollers distributed on the narrow side;

[0025] In the zero section of the second cooling zone, its length is set to 3m, with 10 pairs of rollers distributed on the wide side;

[0026] Sectors 1-7 are located in the arc section of the continuous casting machine, sector sections 8-14 are located in the horizontal section of the continuous casting machine, and sector sections 6-7 are used for straightening the continuous casting billet; sector sections 1-14 are 2.4m long, and each sector section has 7 pairs of rollers distributed on its wide side;

[0027] The roll gap shrinkage of the foot roll section and the zero roll section is set to 0.10-0.20mm, the roll gap shrinkage of the No.1-4 fan-shaped sections is set to 0.15-0.25mm, and the roll gap shrinkage of the No.5-9 and No.12-14 fan-shaped sections is set to 0.20-0.30mm.

[0028] Segment 10 and segment 11 are lightly pressed down, with a pressing amount set at 4-6mm. The pressing amount distribution ratio of segment 10 is 30-40%, and the pressing amount distribution ratio of segment 11 is 60-70%.

[0029] A method for producing continuously cast billets for low-temperature steel includes the following steps:

[0030] Step S1, molten iron pretreatment;

[0031] Step S2, primary refining furnace process;

[0032] Step S3, LF refining process;

[0033] Step S4, RH refining process;

[0034] Step S5, continuous casting process, is carried out using the continuous casting production method of the low temperature steel continuous casting billet. Before the continuous casting billet enters the No. 6 sector section, the corner temperature is set to ≥900℃, and the difference between the highest and lowest surface temperatures is ≤20℃.

[0035] A continuously cast billet, produced by the aforementioned method for producing continuously cast billets for low-temperature steel, has the following chemical composition by mass percentage: 0.05%≤C≤0.10%, 0.10%≤Si≤0.40%, 0.50%≤Mn≤2.00%, 8.0%≤Ni≤12.0%, P≤0.0050%, S≤0.0030%, 0.01%≤Al≤0.06%, Ti≤0.0030%, O≤0.0015%, N≤0.0030%, H≤0.0002%, with the balance being Fe and other unavoidable impurities;

[0036] Furthermore, the surface crack incidence rate of the continuously cast billet is ≤0.1%, the surface crack depth is ≤0.1mm, the center C segregation grade is ≤B 0.5, and there are no shrinkage cavities.

[0037] By employing the above technical solutions, the present invention has the following beneficial effects compared to the prior art:

[0038] 1. The continuous casting production method for low-temperature steel billets provided by this invention involves molten steel flowing into the inner cavity of the crystallizer through the immersion nozzle. The insertion depth of the immersion nozzle and the casting speed of the continuous casting machine are adjusted according to the width of the continuous casting machine. After the steel flow impacts the narrow side of the crystallizer, a stable double circulation (upper reflux and lower reflux) structure is formed in the crystallizer. This makes the high-temperature zone of the molten steel formed at 1 / 4 of the width of the crystallizer consistent with the center position of the electromagnetic stirrer in the crystallizer. The electromagnetic stirrer can better cooperate with the double circulation to control the flow rate of molten steel on the meniscus of the crystallizer, making the flow of molten steel more stable and orderly, improving the activity of the molten steel surface, promoting the melting of the protective slag, and preventing slag entrapment, which is beneficial to improving the surface quality of the product.

[0039] 2. The continuous casting production method for low-temperature steel billets provided by the present invention uses a continuous casting mold protective slag with low basicity, low melting point and low viscosity, and combines it with the control of the thickness of the protective slag layer, so that the protective slag has a good lubrication effect, avoids the formation of large thermal stress, and avoids defects such as surface cracks.

[0040] 3. The production method of low-temperature steel continuous casting billet provided by the present invention improves the central density of the continuous casting billet by controlling the superheat of molten steel, the water flow rate and taper of the crystallizer, the specific water volume and distribution ratio of the secondary cooling zone, the gap shrinkage of the fan-shaped section roll, the reduction amount and distribution ratio of the light pressing, thereby eliminating central shrinkage cavities, porosity and reducing central segregation.

[0041] 4. The continuous casting billet provided by this invention has a surface crack incidence rate of ≤0.1%, a surface crack depth of ≤0.1mm, a center C segregation grade of ≤B 0.5, and no shrinkage cavities, thus achieving the goal of stable control over the surface and internal quality of the continuous casting billet. Detailed Implementation

[0042] The present invention will now be described in further detail. In the description of this application, it should be understood that the terms "left side," "right side," "upper part," "lower part," etc., indicating orientation or positional relationships, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. "First," "second," etc., do not indicate the importance of components and therefore should not be construed as limiting the present invention. The specific dimensions used in this embodiment are only for illustrating the technical solution and do not limit the scope of protection of the present invention.

[0043] As described in the background section, current methods for controlling the surface and internal quality of slabs used in low-temperature steel plates primarily address the issue of high temperatures at the widest quarter of the slab during continuous casting. This occurs because molten steel from the tundish flows into the crystallizer through the side guide hole of the submerged entry nozzle, creating upper and lower swirling zones within the crystallizer. This leads to several problems: uneven solidification, as the high temperature at the widest quarter creates a significant temperature gradient with the surrounding cooler areas. This temperature difference generates thermal stress during slab solidification, which can cause cracks if it exceeds the slab's strength limit. Compositional segregation, due to the delayed solidification process at the widest quarter, leads to the enrichment of alloying elements such as manganese and silicon in the high-temperature liquid steel, resulting in compositional segregation across the slab's cross-section. Therefore, in order to solve the above problems, starting from the temperature of molten steel at the 1 / 4 position of the width, this application provides a continuous casting production method for low-temperature steel continuous casting billets. Based on the width of the continuous casting machine, the insertion depth of the submerged entry nozzle, and the casting speed of the continuous casting machine, the distance between the center position of the electromagnetic stirrer in the crystallizer and the top opening of the crystallizer is adjusted so that the high-temperature zone of molten steel formed at the 1 / 4 position of the width of the steel flow in the crystallizer is consistent with the center position of the electromagnetic stirrer in the crystallizer.

[0044] When the high-temperature zone of molten steel formed at one-quarter of the width of the crystallizer aligns with the center of the electromagnetic stirrer, the electromagnetic stirring can more effectively agitate the molten steel, resulting in a more uniform distribution of alloying elements, reduced segregation, and improved billet quality. Electromagnetic stirring can also better coordinate with the dual-circulation flow, helping to stabilize the dual-circulation (upper and lower reflux) structure of the molten steel within the crystallizer, making the flow of molten steel more stable and orderly, reducing surface fluctuations, and thus lowering the risk of slag entrapment.

[0045] The technical solution to the above-mentioned technical problems is as follows: In the continuous casting process, molten steel is poured from the ladle through the tundish and then into the crystallizer. After the molten steel initially solidifies to form a billet shell in the crystallizer, it enters the secondary cooling zone to continue solidifying. The width of the continuous casting machine is defined as l, the insertion depth of the submerged entry nozzle is h1, the distance from the center of the crystallizer electromagnetic stirrer to the top opening of the crystallizer is h2, and the current of the crystallizer electromagnetic stirrer is a. The width of the continuous casting machine is 1900mm≤l≤2800mm, the insertion depth of the submerged entry nozzle is set to 170mm≤h1≤230mm, the current of the crystallizer electromagnetic stirrer is 450A≤a≤600A, and the distance from the center of the crystallizer electromagnetic stirrer to the top opening of the crystallizer is 550mm≤h2≤650mm.

[0046] It should be noted here that the thickness of the continuous caster can be adjusted according to factors such as the steel grade to be produced and the requirements of product specifications. For the low-temperature steel of this application, the continuous caster used is a straight-arc continuous caster with an arc radius of 10 m and a thickness dimension of 220 mm. Defining the casting speed of the continuous caster as V, the casting speed V of the continuous caster is 1.0 m / min ≤ V ≤ 1.3 m / min; at the same time, the selected mold length is 900 mm, the position of the molten steel meniscus in the mold is 200 mm away from the upper mouth of the mold, the height of the mold electromagnetic stirrer is 400 mm, and the frequency is 3 Hz.

[0047] As a relatively prominent innovation point of this application, according to the different ranges of the continuous caster width dimensions, adjust the immersion nozzle insertion depth, the length from the center position of the mold electromagnetic stirrer to the upper mouth of the mold, the current of the mold electromagnetic stirrer, and the casting speed of the continuous caster. While homogenizing the temperature field of the molten steel in the mold, control the flow rate of the molten steel at the meniscus of the mold, improve the activity of the steel liquid surface, promote the melting of the mold powder, and prevent slag entrainment.

[0048] Specifically, when the continuous caster width dimension is 1900 mm ≤ l < 2200 mm, set the immersion nozzle insertion depth as 170 mm ≤ h1 < 190 mm, the length from the center position of the mold electromagnetic stirrer to the upper mouth of the mold as 550 mm ≤ h2 < 570 mm, the current of the mold electromagnetic stirrer as 550 A < a ≤ 600 A, and the casting speed of the continuous caster as 1.2 m / min < V ≤ 1.3 m / min;

[0049] When the continuous caster width dimension is 2200 mm ≤ l < 2500 mm, set the immersion nozzle insertion depth as 190 mm ≤ h1 < 210 mm, the length from the center position of the mold electromagnetic stirrer to the upper mouth of the mold as 570 mm ≤ h2 < 600 mm, the current of the mold electromagnetic stirrer as 500 A < a ≤ 550 A, and the casting speed of the continuous caster as 1.1 m / min < V ≤ 1.2 m / min;

[0050] When the continuous caster width dimension is 2500 mm < l ≤ 2800 mm, set the immersion nozzle insertion depth as 210 mm ≤ h1 ≤ 230 mm, the length from the center position of the mold electromagnetic stirrer to the upper mouth of the mold as 600 mm ≤ h2 ≤ 650 mm, the current of the mold electromagnetic stirrer as 450 A ≤ a ≤ 500 A, and the casting speed of the continuous caster as 1.0 m / min ≤ V ≤ 1.1 m / min.

[0051] The mold is the core component of the continuous casting machine. Its function is to initially solidify molten steel into a billet shell with a certain shape and size. Inside the mold, the protective slag forms a liquid slag film between the molten steel and the copper wall of the mold. Without this lubricating slag film, the friction between the billet and the mold wall would increase dramatically, potentially leading to defects such as cracks on the billet surface. Therefore, this application further specifies the protective slag used in the mold, whose chemical composition, by mass percentage, includes: SiO2: 34-38%, CaO: 29-36%, MgO: 0.5-1.0%, Al2O3: 3-7%, Na2O: 8-10%, F: 8-10%, C: 1-3%, with the remainder being unavoidable impurities. Meanwhile, the binary basicity of the protective slag (CaO / SiO2) is set to 0.79-0.94, the melting point to be 1050-1150℃, and the viscosity at 1300℃ to be 0.25-0.35 Pa·s; the thickness of the protective slag layer is 100-130 mm, and a liquid slag film is formed between the molten steel and the crystallizer wall, with a liquid slag layer thickness of 10-13 mm.

[0052] The design of the specific components and contents of the above-mentioned protective slag involves using a low carbon content to reduce carbon gain during continuous casting and to increase the melting rate of the protective slag. A low melting point ensures that the protective slag in the crystallizer forms a stable three-layer structure with a relatively deep liquid slag layer thickness. Low viscosity ensures increased slag consumption and good lubrication. Low alkalinity helps to increase the proportion of glass phase, promotes heat dissipation, and reduces the risk of steel leakage. The combined effect of these three factors, along with the control of the protective slag layer thickness, ensures a low incidence of surface cracks in the billet during low-temperature steel continuous casting production, thereby improving the quality of the billet.

[0053] In the continuous casting process of steel production, molten steel is poured from the ladle through the tundish and then into the crystallizer. In addition to adjusting the insertion depth of the submerged entry nozzle, the distance between the center position of the crystallizer electromagnetic stirrer and the top opening of the crystallizer, the current of the crystallizer electromagnetic stirrer, and the casting speed of the continuous casting machine, the combined action of various links is required. Therefore, the following auxiliary parameters are set: the superheat of molten steel in the tundish of the continuous casting machine is 20-30℃, the taper of the crystallizer is 1.1%-1.2%, the water flow rate on the wide side of the crystallizer is 3700-4100L / min, the water flow rate on the narrow side is 480-520L / min, and the crystallizer liquid level fluctuation is controlled within ±2mm.

[0054] Regarding the specific water volume and distribution ratio of the secondary cooling zone, the secondary cooling zone includes a foot roller section, a zero section, and several fan-shaped sections, wherein 14 fan-shaped sections are provided, and the secondary cooling zone includes zone 1, zone 2... zone 9;

[0055] The foot roller section corresponds to Zone 1 of the secondary cooling system, and the zero section corresponds to Zones 2, 3, and 4 of the secondary cooling system. The 14 sector sections are numbered 1, 2...14. Sector sections 1 and 2 correspond to Zone 5 of the secondary cooling system, sector sections 3 and 4 correspond to Zone 6, sector sections 5, 6, and 7 correspond to Zone 7, sector sections 8, 9, and 10 correspond to Zone 8, and sector sections 11, 12, 13, and 14 correspond to Zone 9. The specific water volume in the cooling zone is set at 0.4-0.6 L / kg. The water volume proportions of the secondary cooling zones 1 to 9 are 8-13%, 24-30%, 20-25%, 13-18%, 8-13%, 6-12%, 1-3%, 1-3%, and 1-3%, respectively. In the secondary cooling zone 1, the water volume is distributed to the narrow side and the wide side of the continuously cast billet, with the narrow side accounting for 30-40% and the wide side accounting for 60-70%.

[0056] In the foot roller section of the second cooling zone, its length is set to 0.52m, with 2 pairs of rollers distributed on the wide side and 3 pairs of rollers distributed on the narrow side; in the zero section of the second cooling zone, its length is set to 3m, with 10 pairs of rollers distributed on the wide side.

[0057] Sectors 1-7 are located in the arc section of the continuous casting machine, sector 8-14 are located in the horizontal section of the continuous casting machine, and sector 6-7 are used for straightening the continuous casting billet. Sectors 1-14 are 2.4m long, and each sector has 7 pairs of rollers distributed on its wide side.

[0058] Regarding the roll gap shrinkage, the roll gap shrinkage for the full roll section and the zero roll section is set to 0.10-0.20mm, the roll gap shrinkage for the No.1-4 sector sections is set to 0.15-0.25mm, and the roll gap shrinkage for the No.5-9 and No.12-14 sector sections is set to 0.20-0.30mm.

[0059] Regarding the light pressing amount and distribution ratio, light pressing is performed on sector segments 10 and 11, with a pressing amount set to 4-6mm. The pressing amount distribution ratio for sector segment 10 is 30-40%, and the pressing amount distribution ratio for sector segment 11 is 60-70%.

[0060] By setting limits in each of the above parts, the density of the continuous casting billet at the center is improved, which helps to eliminate central shrinkage cavities, porosity, and reduce central segregation.

[0061] Next, this application provides a method for producing continuously cast billets for low-temperature steel, comprising the following steps:

[0062] Step S1, molten iron pretreatment;

[0063] Step S2, primary refining furnace process;

[0064] Step S3, LF refining process;

[0065] Step S4, RH refining process;

[0066] Step S5, continuous casting process, is carried out using the aforementioned continuous casting production method for low-temperature steel billets. Before the billet enters the No. 6 sector section, the corner temperature is set to ≥900℃, and the difference between the highest and lowest surface temperatures is ≤20℃.

[0067] The low-temperature steel continuous casting billet produced by the aforementioned production method has the following chemical composition by mass percentage: 0.05%≤C≤0.10%, 0.10%≤Si≤0.40%, 0.50%≤Mn≤2.00%, 8.0%≤Ni≤12.0%, P≤0.0050%, S≤0.0030%, 0.01%≤Al≤0.06%, Ti≤0.0030%, O≤0.0015%, N≤0.0030%, H≤0.0002%, with the balance being Fe and other unavoidable impurities.

[0068] The continuous casting billet has a surface crack incidence rate of ≤0.1%, a surface crack depth of ≤0.1mm, a center C segregation grade of ≤B0.5, and no shrinkage cavities.

[0069] Finally, this application provides three embodiments to demonstrate that the continuous casting billet produced by the production method for low-temperature steel billets provided in this application has better quality.

[0070] The set parameters for the continuous casting machine are as follows: the continuous casting machine is a straight-arc slab continuous casting machine with a cross-sectional dimension of 220mm × (1900-2800)mm and an arc radius of 10m. The secondary cooling zone includes a foot roll section, a zero section, and 14 sector sections. The foot roll section corresponds to secondary cooling zone 1; the zero section corresponds to secondary cooling zones 2, 3, and 4; sector sections 1 and 2 correspond to zone 5; sector sections 3 and 4 correspond to secondary cooling zone 6; sector sections 5, 6, and 7 correspond to secondary cooling zone 7; and sector sections 8, 9, and 10 correspond to secondary cooling zone 1. The first section corresponds to Zone 8 of the secondary cooling system; the second section (sectors 11, 12, 13, and 14) corresponds to Zone 9 of the secondary cooling system. The length of the foot roller section is 0.52m, with 2 pairs of rollers on the wide side and 3 pairs of rollers on the narrow side. The zero section is 3m long, with 10 pairs of rollers on the wide side. The length of sector sections 1-14 is 2.4m, with 7 pairs of rollers on the wide side of each sector section. Sector sections 1-7 are located in the arc section of the continuous casting machine, and sector sections 8-14 are located in the horizontal section of the continuous casting machine. Sector sections 6-7 are used for straightening the continuous casting billet.

[0071] The continuous casting billet provided in the embodiments is used to produce three casting cycles (corresponding to Embodiment 1, Embodiment 2 and Embodiment 3), and the cross-sectional dimensions of the continuous casting billet are shown in Table 1.

[0072] Table 1. Cross-sectional dimensions of continuously cast billets for each casting cycle in Examples 1-3.

[0073] Pouring Dimensions of continuous casting billet cross section, mm × mm Example 1 220×2800 Example 2 220×2500 Example 3 220×1900

[0074] The production method for continuously cast billets for low-temperature steel is as follows:

[0075] Molten iron undergoes pretreatment in step S1, primary refining in step S2, LF refining in step S3, and RH refining in step S4 to obtain molten steel with qualified composition and temperature. The composition of the molten steel obtained from the primary refining furnace in step S2 is shown in Table 2, and the composition of the molten steel obtained from the RH refining in step S4 is shown in Table 3.

[0076] Table 2 Composition of molten steel tapped from the primary smelting furnace

[0077]

[0078] Table 3 Steel Composition

[0079]

[0080] The molten steel from Examples 1-3 is hoisted to the continuous casting platform for the continuous casting process in step S5. The molten steel flows from the tundish into the crystallizer via a submerged entry nozzle. The insertion depth of the submerged entry nozzle is defined as h1, the distance from the center of the crystallizer's electromagnetic stirrer to the top opening of the crystallizer is h2, the current of the crystallizer's electromagnetic stirrer is a, and the continuous casting machine speed is V. The various continuous casting parameters for Examples 1-3 are shown in Table 4.

[0081] Table 4 Continuous Casting Parameter Control

[0082] Pouring <![CDATA[h1,mm]]> <![CDATA[h2,mm]]> a, A V, m / min Example 1 230 650 450 1.0 Example 2 210 600 500 1.1 Example 3 170 550 600 1.3

[0083] The settings for other continuous casting auxiliary parameters are shown in Table 5, including the superheat of molten steel in the tundish, the taper of the crystallizer, the water flow rate on the wide side of the crystallizer, the water flow rate on the narrow side of the crystallizer, and the fluctuation of the liquid level in the crystallizer.

[0084] Table 5 Continuous Casting Parameter Control

[0085]

[0086] A protective slag is added to the crystallizer. The chemical composition of the protective slag in Examples 1-3 is shown in Table 6 by mass percentage. The physicochemical properties of the protective slag and the thickness of the protective slag layer are shown in Table 7. The continuous casting billet in the crystallizer has a certain shell thickness and enters the secondary cooling zone of the continuous casting machine.

[0087] Table 6 Composition of protective slag

[0088]

[0089] Table 7 Physicochemical properties and slag layer thickness of protective slag

[0090]

[0091] The proportion of secondary cooling water in zones 1, 2...9 of the secondary cooling zone is shown in Table 8.

[0092] Table 8. Secondary Cooling Water Quantity and Proportion of Secondary Cooling Water Quantity in Zones 1-9 of the Continuous Casting Machine

[0093]

[0094] Table 9 shows the proportions of water volume on the narrow side and the wide side in Zone 1 of the secondary cooling system.

[0095] Table 9. Proportion of water volume on the narrow and wide sides of the continuously cast billet in Zone 1 of the secondary cooling area.

[0096] Pouring Narrow side, % Wide face, % Example 1 30 70 Example 2 35 65 Example 3 40 60

[0097] The roll gap shrinkage of the foot roll section, zero section, and sector sections 1-4, 5-9, and 12-14, and the light reduction applied to sector sections 10 and 11, are shown in Table 10.

[0098] Table 10. Shrinkage, Reduction, and Reduction Distribution Ratio of Continuous Casting Machine Roll Gap

[0099]

[0100] After the No. 14 sector section of the continuous casting billet is cut by flame, a continuous casting billet with a length of 8m is obtained. Low magnification samples of the continuous casting billet are taken and surface and cross-section pickled. The surface crack incidence, surface crack depth and center segregation of the low magnification samples of the continuous casting billet are observed, as shown in Table 11.

[0101] Table 11. Surface crack incidence, surface crack depth, and center segregation of continuously cast billets

[0102]

[0103] Obviously, the continuous casting production method and production method for low-temperature steel billets provided in this application produce continuously cast billets that meet the expected requirements, which means that the continuous casting production method and production method for low-temperature steel billets can improve the central density of the continuously cast billet and play a role in eliminating central shrinkage cavities, porosity and reducing central segregation.

[0104] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0105] The meaning of "and / or" as used in this application includes situations where each exists alone or both exist simultaneously.

[0106] The term "connection" as used in this application can mean a direct connection between components or an indirect connection between components through other components.

[0107] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A continuous casting production method for low-temperature steel billets, characterized in that: In the continuous casting process, molten steel is poured from the ladle through the tundish and then into the crystallizer. After initial solidification in the crystallizer to form a billet shell, the steel enters the secondary cooling zone for further solidification. The width dimension of the continuous casting machine is defined as... l The insertion depth of the submersible sprue is h 1 The distance from the center of the electromagnetic stirrer in the crystallizer to the top opening of the crystallizer is... h 2 The current of the electromagnetic stirrer in the crystallizer is a The binary basicity (CaO / SiO2) of the protective slag used in the crystallizer is 0.79-0.

94. The continuous casting machine is a straight-arc type, with an arc radius of 10m and a thickness of 220mm. The casting speed of the continuous casting machine is defined as follows: V The continuous casting machine speed V 1.0 m / min ≤ V ≤1.3m / min; the length of the crystallizer is 900mm, the distance between the meniscus of molten steel inside the crystallizer and the top opening of the crystallizer is 200mm, the height of the electromagnetic stirrer in the crystallizer is 400mm, and the frequency is 3Hz; When the width of the continuous casting machine is 1900mm or less l When the diameter is less than 2200mm, the insertion depth of the submersible nozzle should be set to 170mm or less. h 1 <190mm, the distance from the center of the electromagnetic stirrer in the crystallizer to the top opening of the crystallizer is 550mm≤ h 2 <570mm, crystallizer electromagnetic stirrer current is 550A< a ≤600A, continuous casting machine speed is 1.2m / min< V ≤1.3m / min; When the width of the continuous casting machine is 2200mm ≤ l < 2500mm, the insertion depth of the submerged entry nozzle is set to 190mm ≤ h 1 <210mm, the distance from the center of the electromagnetic stirrer in the crystallizer to the top opening of the crystallizer is 570mm≤ h 2 <600mm, crystallizer electromagnetic stirrer current is 500A< a ≤550A, continuous casting machine speed is 1.1m / min< V ≤1.2m / min; When the width of the continuous casting machine is 2500mm l When the diameter is ≤2800mm, the insertion depth of the submersible nozzle is set to ≤210mm. h 1 ≤230mm, the distance from the center of the electromagnetic stirrer in the crystallizer to the top opening of the crystallizer is 600mm≤ h 2 ≤650mm, the current of the electromagnetic stirrer for the crystallizer is 450A≤ a ≤500A, continuous casting machine casting speed is 1.0m / min≤ V ≤1.1m / min.

2. The continuous casting production method for low-temperature steel continuously cast billets according to claim 1, characterized in that: In the continuous casting process, the superheat of molten steel in the tundish of the continuous casting machine is 20-30℃, and the taper of the crystallizer is 1.1%-1.2%. The water flow rate on the wide side of the crystallizer is 3700-4100 L / min, and the water flow rate on the narrow side is 480-520 L / min; The liquid level fluctuation in the crystallizer is controlled within ±2mm.

3. The continuous casting production method for low-temperature steel continuous casting billets according to claim 1, characterized in that: The protective slag used in the crystallizer has the following chemical composition by mass percentage: SiO2: 34-38%, CaO: 29-36%, MgO: 0.5-1.0%, Al2O3: 3-7%, Na2O: 8-10%, F: 8-10%, C: 1-3%, with the remainder being unavoidable impurities.

4. The continuous casting production method for low-temperature steel continuous casting billets according to claim 3, characterized in that: The melting point of the protective slag is 1050-1150℃, and the viscosity at 1300℃ is 0.25-0.35 Pa·s; The thickness of the protective slag layer is 100-130mm. The protective slag forms a liquid slag film between the molten steel and the crystallizer wall, and the thickness of the liquid slag layer is 10-13mm.

5. The continuous casting production method for low-temperature steel continuously cast billets according to claim 1, characterized in that: The second cooling zone includes a foot roller section, a zero section, and several fan-shaped sections, of which 14 fan-shaped sections are provided, and the second cooling zone includes zone 1, zone 2... zone 9; The foot roller section corresponds to Zone 1 of the second cooling system, and the zero section corresponds to Zones 2, 3, and 4 of the second cooling system. The 14 sector sections are numbered 1, 2, ...

14. Sector sections 1 and 2 correspond to Zone 5 of the second cooling system, sector sections 3 and 4 correspond to Zone 6 of the second cooling system, sector sections 5, 6, and 7 correspond to Zone 7 of the second cooling system, sector sections 8, 9, and 10 correspond to Zone 8 of the second cooling system, and sector sections 11, 12, 13, and 14 correspond to Zone 9 of the second cooling system. The water volume of the secondary cooling zone is set at 0.4-0.6 L / kg, and the water volume proportions of secondary cooling zones 1 to 9 are 8-13%, 24-30%, 20-25%, 13-18%, 8-13%, 6-12%, 1-3%, 1-3%, and 1-3%, respectively. In the second cooling zone 1, the water volume is distributed to the narrow side and the wide side of the continuously cast billet, with the narrow side accounting for 30-40% and the wide side accounting for 60-70%.

6. The continuous casting production method for low-temperature steel continuously cast billets according to claim 5, characterized in that: In the foot roller section of the second cooling zone, its length is set to 0.52m, with 2 pairs of rollers distributed on the wide side and 3 pairs of rollers distributed on the narrow side; In the zero section of the second cooling zone, its length is set to 3m, with 10 pairs of rollers distributed on the wide side; Sectors 1-7 are located in the arc section of the continuous casting machine, sector sections 8-14 are located in the horizontal section of the continuous casting machine, and sector sections 6-7 are used for straightening the continuous casting billet; sector sections 1-14 are 2.4m long, and each sector section has 7 pairs of rollers distributed on its wide side; The roll gap shrinkage of the foot roll section and the zero roll section is set to 0.10-0.20mm, the roll gap shrinkage of the No.1-4 fan-shaped sections is set to 0.15-0.25mm, and the roll gap shrinkage of the No.5-9 and No.12-14 fan-shaped sections is set to 0.20-0.30mm. Segment 10 and segment 11 are lightly pressed, with a pressing amount set to 4-6mm. The pressing amount distribution ratio of segment 10 is 30-40%, and that of segment 11 is 60-70%.

7. A method for producing continuously cast billets for low-temperature steel, characterized in that: Includes the following steps: Step S1, molten iron pretreatment; Step S2, primary refining furnace process; Step S3, LF refining process; Step S4, RH refining process; Step S5, continuous casting process, is carried out using the continuous casting production method for low-temperature steel continuous casting billets as described in claim 1. Before the continuous casting billet enters the No. 6 sector section, the corner temperature is set to ≥900℃, and the difference between the highest and lowest surface temperatures is ≤20℃.

8. A continuously cast billet, characterized in that: The continuously cast billet produced by the production method of the low-temperature steel continuously cast billet according to claim 7 has the following chemical composition by mass percentage: 0.05%≤C≤0.10%, 0.10%≤Si≤0.40%, 0.50%≤Mn≤2.00%, 8.0%≤Ni≤12.0%, P≤0.0050%, S≤0.0030%, 0.01%≤Al≤0.06%, Ti≤0.0030%, O≤0.0015%, N≤0.0030%, H≤0.0002%, with the balance being Fe and other unavoidable impurities.

9. The continuously cast billet according to claim 8, characterized in that: The continuous casting billet has a surface crack incidence rate of ≤0.1%, a surface crack depth of ≤0.1mm, a center C segregation grade of ≤B 0.5, and no shrinkage cavities.

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