Continuous casting production method of continuous casting billet for low-temperature steel, production method and continuous casting billet

Abstract

By adjusting the insertion depth of a submersed nozzle, the length from the center position of an electromagnetic stirrer of a crystallizer to an upper opening of the crystallizer, the current value of the electromagnetic stirrer of the crystallizer and the pulling speed of a continuous casting machine, the problem that the temperature distribution of molten steel in the crystallizer is not uniform is solved. And the flow speed of molten steel on the meniscus of the crystallizer is controlled, melting of casting powder is promoted, and slag entrapment is prevented. The low-alkalinity, low-melting-point and low-viscosity continuous casting crystallizer casting powder is adopted, casting powder layer thickness control and the like are combined, the good lubricating effect of the casting powder is guaranteed, and the defects of large thermal stress, surface cracks and the like are avoided; by controlling the degree of superheat of molten steel, the water flow of a crystallizer, the taper, the specific water flow of a secondary cooling area, the distribution ratio of each area, the shrinkage amount of a fan-shaped section roll gap, the soft reduction amount and the distribution ratio, the center density of a continuous casting billet is improved, and the effects of eliminating center shrinkage cavities and looseness and relieving center segregation are achieved.

Description

Technical Field

[0001] The invention relates to a continuous casting production method of a continuous casting billet for low-temperature steel, a production method and a continuous casting billet, and belongs to the technical field of smelting. Background Art

[0002] With the diversification of global energy resources and the increasing attention paid to environmental protection, natural gas, as a clean energy source, occupies an increasingly larger proportion. The storage and transportation temperature of liquefied natural gas is below -162°C, which requires that the materials used to store liquefied natural gas have good low-temperature toughness, strength, and sufficient resistance to brittle cracking and crack arrest at ultra-low temperatures. The materials used in LNG storage and transportation equipment currently built in the world are mainly 9Ni steel with a Ni content of about 9%. The production process of this type of low-temperature steel in the prior art mainly includes: molten iron pretreatment, primary refining furnace, LF refining, RH refining, continuous casting, grinding, spraying, hot rolling, heat treatment, etc. In order to improve the yield rate and obtain finished plates with excellent performance, in the production process of low-temperature steel, in addition to controlling the number, composition and size of inclusions, it is also necessary to strictly control the surface and internal quality of the low-temperature steel slabs.

[0003] Chinese patent CN105562642A discloses a control method for typical intermediate cracks and center segregation of pipeline steel slab continuous casting, which ensures the accuracy of ±0.2mm by offline calibration and online detection of the continuous casting machine roll gap; divides the steel grades into groups to enhance the matching of the thermophysical parameters of the steel grades; strictly controls the superheat, increases the proportion of equiaxed crystals, and avoids the development of columnar crystals; adjusts the pulling speed and the secondary cooling process to optimize the basic roll gap control during the solidification of the billet; optimizes the reduction amount, and distributes the reduction amount between different fan-shaped segments to avoid large differences in reduction amount, thereby improving the internal quality of the billet. Chinese patent CN101934357A discloses a process for effectively controlling the center segregation of the continuous casting slab, which realizes effective control of the center segregation by combining the strong secondary cooling water at the end of the solidification of the continuous casting billet with the pressure control of the hydraulic cylinder of the light pressure section. To a certain extent, the degree of center segregation is controlled, the dependence of the control of the center segregation of the continuous casting billet on the pressure of the hydraulic cylinder of the light pressure section is reduced, and the service life of the light pressure equipment is increased. Chinese patent CN109940140A discloses a method for improving the quality of center segregation of hypoperitectic steel ingots, which eliminates the tensile delamination and fracture of hot rolled coils by using two pairs of electromagnetic stirring rollers and controlling the direction of the magnetic field, combined with the setting of the reduction interval and the reduction rate of dynamic soft pressure to control the center segregation of hypoperitectic steel ingots.

[0004] The above-mentioned prior art mainly focuses on the precision control of the roll gap of the fan-shaped segment, the electromagnetic stirring parameters of the secondary cooling, the superheat of the molten steel in the tundish, the drawing speed, the water content of the secondary cooling zone, the position of the reduction zone and the reduction rate, etc., to control the center quality of the continuous casting billet. After research and practice, the important factor affecting the surface and internal quality of the low-temperature steel slab is that during the continuous casting process, the molten steel in the tundish flows into the crystallizer through the side guide hole of the immersion nozzle, and the molten steel forms an upper and lower whirlpool zone in the crystallizer, resulting in a high temperature of the molten steel at the 1 / 4 position of the wide surface. This situation will affect the surface and internal quality of the continuous casting billet: (1) The uneven distribution of the temperature field of the molten steel 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 continuous casting billet; (2) In the subsequent cooling process, the temperature non-uniformity of the billet will always exist, resulting in a "W" shape at the end of the solidification of the billet. Even if the light reduction technology is used, the center quality of the continuous casting billet is difficult to control stably.

[0005] Obviously, the existing technology does not consider the goal of stably controlling the surface and internal quality of the continuous casting billet by solving the problem of inconsistent temperature distribution of molten steel in the crystallizer. Therefore, a new method is needed to ensure the surface and internal quality of the continuous casting billet. Summary of the invention

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

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

[0008] A continuous casting production method for continuous casting billets for low-temperature steel, in which molten steel is injected from a ladle through a tundish into a crystallizer during the continuous casting process, and after the molten steel is initially solidified in the crystallizer to form a billet shell, it enters a secondary cooling zone to continue solidifying; the width of the continuous casting machine is defined as l, the insertion depth of the immersion nozzle is defined as h1, the distance between the center position of the crystallizer electromagnetic stirrer and the upper mouth of the crystallizer is defined as h2, and the current of the crystallizer electromagnetic stirrer is defined as a;

[0009] The width of the continuous casting machine is 1900mm≤l≤2800mm, the insertion depth of the submerged nozzle is set to 170mm≤h1≤230mm, the current of the crystallizer electromagnetic stirrer is 450A≤a≤600A, and the length from the center position of the crystallizer electromagnetic stirrer to the upper mouth 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 the continuous caster 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 away from the upper opening of the mold, the height of the electromagnetic stirrer in the mold 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 electromagnetic stirrer in the mold to the upper opening of the mold is 550 mm ≤ h2 < 570 mm, the current of the electromagnetic stirrer in the mold 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 electromagnetic stirrer in the mold to the upper opening of the mold is 570 mm ≤ h2 < 600 mm, the current of the electromagnetic stirrer in the mold 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 electromagnetic stirrer in the mold to the upper opening of the mold is 600 mm ≤ h2 ≤ 650 mm, the current of the electromagnetic stirrer in the mold 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 taper of the mold 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 liquid level fluctuation of the mold 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 CaO / SiO2 of the mold slag is 0.79-0.94, the melting point is 1050-1150°C, and the viscosity at 1300°C 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 wall of the crystallizer tube. The thickness of the liquid slag layer is 10-13mm.

[0020] Furthermore, the secondary cooling zone includes a foot roll section, a zero section and a plurality of fan-shaped sections, wherein 14 fan-shaped sections are provided, and the secondary cooling zone includes zone 1, zone 2...zone 9;

[0021] The foot roll segment corresponds to the secondary cooling zone 1, the zero segment corresponds to the secondary cooling zone 2, zone 3 and zone 4, and the 14 sector segments are numbered 1, 2, ... 14, sector segments 1 and 2 correspond to the secondary cooling zone 5, sector segments 3 and 4 correspond to the secondary cooling zone 6, sector segments 5, 6 and 7 correspond to the secondary cooling zone 7, sector segments 8, 9 and 10 correspond to the secondary cooling zone 8, and sector segments 11, 12, 13 and 14 correspond to the secondary cooling zone 9;

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

[0023] The water volume in the secondary cooling zone 1 is distributed to the narrow side and wide side of the continuous casting billet, of which the water volume on the narrow side accounts for 30-40% and the water volume on the wide side accounts for 60-70%;

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

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

[0026] Segments 1 to 7 are located in the arc section of the continuous casting machine, segments 8 to 14 are located in the horizontal section of the continuous casting machine, and segments 6 to 7 are used to straighten the continuous casting billets; the length of segments 1 to 14 is 2.4m, and each segment has 7 pairs of rollers distributed on the wide surface;

[0027] Set the gap shrinkage of the foot roll segment and the zero roll segment to 0.10-0.20mm, the gap shrinkage of the No. 1-4 fan-shaped segments to 0.15-0.25mm, and the gap shrinkage of the No. 5-9 and No. 12-14 fan-shaped segments to 0.20-0.30mm;

[0028] Segment No. 10 and segment No. 11 perform light compression, and the compression amount is set to 4-6mm. The compression amount distribution ratio of segment No. 10 is 30-40%, and the compression amount distribution ratio of segment No. 11 is 60-70%;

[0029] A method for producing a continuous casting billet for low temperature steel comprises 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, using the continuous casting production method of the low-temperature steel continuous casting billet for processing, the corner temperature of the continuous casting billet is set to be ≥900°C before entering the No. 6 sector, and the difference between the highest and lowest surface temperatures is ≤20°C;

[0035] A continuous casting billet, wherein the continuous casting billet is produced by the production method of the continuous casting billet for low-temperature steel, and the chemical composition thereof is, in percentage by mass: 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%, and the balance is Fe and other unavoidable impurities;

[0036] Furthermore, the surface crack occurrence rate of the continuous casting billet is ≤0.1%, the surface crack depth is ≤0.1 mm, the center C segregation grade is ≤B 0.5, and there is no shrinkage cavity.

[0037] Through the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The continuous casting production method of continuous casting billets for low-temperature steel provided by the present invention, molten steel flows into the inner cavity of the crystallizer through the steel outlet hole of the submerged nozzle, and the insertion depth of the submerged nozzle and the pulling speed of the continuous casting machine are adjusted according to the width size of the continuous casting machine. After the steel flow impacts the narrow side of the crystallizer, the molten steel forms a stable double circulation (upper reflux, lower reflux) structure in the crystallizer, so that the high-temperature zone of the molten steel formed by the steel flow at the position of 1 / 4 of the width in the crystallizer is consistent with the center position of the electromagnetic stirrer of the crystallizer, and the electromagnetic stirring can better cooperate with the double circulation to control the molten steel flow rate of the meniscus of the crystallizer, so that the flow of molten steel is more stable and orderly, the activity of the steel liquid surface is improved, the melting of the protective slag is promoted, and the slag roll is prevented, which is beneficial to improving the surface quality of the product;

[0039] 2. The continuous casting production method of the continuous casting billet for low-temperature steel provided by the present invention adopts a continuous casting crystallizer protective slag with low basicity, low melting point and low viscosity, and combines the control of the thickness of the protective slag layer to make the protective slag have a good lubrication effect, avoid the formation of large thermal stress, and produce defects such as surface cracks;

[0040] 3. The method for producing low-temperature steel continuous casting slabs provided by the present invention improves the central density of the continuous casting slabs by controlling the superheat of molten steel, the water flow rate and taper of the crystallizer, the specific water volume of the secondary cooling zone and the distribution ratio of each zone, the seam shrinkage of the sector rollers, the reduction amount and distribution ratio of the light reduction, thereby playing the role of eliminating central shrinkage and looseness and reducing central segregation;

[0041] 4. The continuous casting slab provided by the present invention has a surface crack incidence rate of ≤0.1%, a surface crack depth of ≤0.1 mm, a center C segregation grade of ≤B 0.5, and no shrinkage cavity, thereby achieving the goal of stably controlling the surface and internal quality of the continuous casting slab. DETAILED DESCRIPTION

[0042] The present invention is now described in further detail. In the description of the present application, it should be understood that the terms "left side", "right side", "upper part", "lower part" and the like indicate positions or positional relationships, which 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 position, be constructed and operated in a specific position, and "first", "second" and the like do not indicate the importance of the parts, and therefore cannot be understood 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 technology, at present, regarding the control of the surface and internal quality of the slab for low-temperature steel plates, it is necessary to focus on the problem that during the continuous casting process, the molten steel in the tundish flows into the crystallizer through the side guide hole of the submerged water inlet, and the molten steel forms upper and lower whirlpool zones in the crystallizer, resulting in the high temperature of the molten steel at the 1 / 4 position of the wide surface. This will lead to the following problems: the problem of uneven solidification, the high temperature of the molten steel at the 1 / 4 position of the wide surface forms a large temperature gradient with the area with lower surrounding temperature, and the temperature difference generates thermal stress during the solidification process of the ingot. When the thermal stress exceeds the strength limit of the ingot, cracks will be generated inside the ingot. The problem of component segregation, the temperature of the molten steel at the 1 / 4 position of the wide surface is high, and its solidification process is delayed, which will lead to the enrichment of alloy elements such as manganese and silicon in the high-temperature liquid molten steel, resulting in component segregation on the cross section of the ingot. Therefore, in order to solve the above problems, starting from the temperature of molten steel at the 1 / 4 position of the wide side, the present application provides a continuous casting production method for continuous casting billets for low-temperature steel. According to the width size of the continuous casting machine, the insertion depth of the submerged water nozzle and the pulling speed of the continuous casting machine, the length of the center position of the crystallizer electromagnetic stirrer from the upper mouth 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 crystallizer electromagnetic stirrer.

[0044] When 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 crystallizer electromagnetic stirrer, electromagnetic stirring can stir the molten steel more effectively, and the alloy elements are evenly distributed in the molten steel, reducing segregation and improving the quality of the ingot. Electromagnetic stirring can better cooperate with the double circulation, which helps to stabilize the double circulation (upper reflux and lower reflux) structure of the molten steel in the crystallizer, making the flow of molten steel more stable and orderly, reducing the fluctuation of the molten steel surface, and thus reducing the risk of slag rolls.

[0045] The technical means to solve the above technical problems are: in the continuous casting process, the molten steel passes through the tundish from the ladle and then is injected into the crystallizer. After the molten steel is initially solidified in the crystallizer to form a 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 immersion nozzle is h1, the length of the center position of the crystallizer electromagnetic stirrer from the upper mouth of the crystallizer is h2, and the current of the crystallizer electromagnetic stirrer is a; the width dimension of the continuous casting machine is 1900mm≤l≤2800mm, the insertion depth of the immersion nozzle is set to 170mm≤h1≤230mm, the current of the crystallizer electromagnetic stirrer is 450A≤a≤600A, and the length of the center position of the crystallizer electromagnetic stirrer from the upper mouth 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, the thickness dimension of the continuous caster is 220 mm, and the casting speed of the continuous caster is defined as V. Then the casting speed V of the continuous caster is 1.0 m / min ≤ V ≤ 1.3 m / min; at the same time, the length of the mold selected 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 width dimension of the continuous caster, 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 are adjusted. While making the temperature field of the molten steel in the mold uniform, the flow rate of the molten steel at the meniscus of the mold is controlled, the activity of the steel liquid surface is increased, the melting of the mold powder is promoted, and slag entrainment is prevented.

[0048] Specifically, 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 mouth 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;

[0049] 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 mouth 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;

[0050] 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 mouth 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.

[0051] The crystallizer is the core component of the continuous casting machine. Its function is to make the molten steel initially solidify into a shell with a certain shape and size. In the crystallizer, the protective slag will form a layer of liquid slag film between the molten steel and the copper wall of the crystallizer. If there is no lubricating slag film, the friction between the ingot and the crystallizer wall will increase sharply, which may cause defects such as cracks on the surface of the ingot. Therefore, in this application, the protective slag used in the crystallizer is also limited, and its chemical composition includes, 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%, and the rest are unavoidable impurities. At the same time, the binary basicity CaO / SiO2 of the protective slag is set to 0.79-0.94, the melting point is 1050-1150°C, and the viscosity at 1300°C is 0.25-0.35 Pa·s; the thickness of the protective slag layer is 100-130mm, and the protective slag forms a liquid slag film between the molten steel and the wall of the crystallizer, and the thickness of the liquid slag layer is 10-13mm.

[0052] Regarding the design of the specific components and contents of the above-mentioned protective slag, low carbon content is used to reduce carbon increase during continuous casting on the one hand, and to increase the melting rate of the protective slag on the other hand; low melting point ensures that the protective slag in the crystallizer forms a stable three-layer structure and has a deeper liquid slag layer thickness; low viscosity ensures that the slag consumption of the protective slag is increased and the lubrication effect is good; low alkalinity is beneficial to increase the proportion of the glass phase, promote heat dissipation, and reduce the risk of steel leakage. The three work together, combined with the control of the protective slag layer thickness, to ensure a low incidence of surface cracks on the ingot during low-temperature steel continuous casting production, thereby improving the quality of the ingot.

[0053] In the continuous casting process of steel production, molten steel is injected from the ladle through the tundish into the crystallizer. In addition to adjusting the insertion depth of the immersion nozzle, the length of the center position of the crystallizer electromagnetic stirrer from the upper mouth of the crystallizer, the current of the crystallizer electromagnetic stirrer and the continuous casting machine pulling speed, each link needs to work together. Therefore, the following auxiliary parameters are set: the superheat of the 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 volume on the wide side of the crystallizer is 3700-4100L / min, and the water volume on the narrow side is 480-520L / min; the crystallizer liquid level fluctuation control is ±2mm.

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

[0055] The foot roll segment corresponds to the secondary cooling zone 1, the zero segment corresponds to the secondary cooling zone 2, zone 3 and zone 4, and the 14 fan-shaped segments are numbered 1, 2, ... 14, with fan-shaped segments 1 and 2 corresponding to the secondary cooling zone 5, fan-shaped segments 3 and 4 corresponding to the secondary cooling zone 6, fan-shaped segments 5, 6 and 7 corresponding to the secondary cooling zone 7, fan-shaped segments 8, 9 and 10 corresponding to the secondary cooling zone 8, and fan-shaped segments 11, 12, 13 and 14 corresponding to the secondary cooling zone 9; The water volume in the cooling zone is set to 0.4-0.6L / kg, and the water volume proportions in the secondary cooling zone 1 to the secondary cooling zone 9 are 8-13%, 24-30%, 20-25%, 13-18%, 8-13%, 6-12%, 1-3%, 1-3% and 1-3% respectively; the water volume in the secondary cooling zone 1 is distributed to the narrow side and wide side of the continuous casting billet, of which the water volume on the narrow side accounts for 30-40%, and the water volume on the wide side accounts 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] Segments No. 1 to No. 7 are located in the arc section of the continuous casting machine, segments No. 8 to No. 14 are located in the horizontal section of the continuous casting machine, and segments No. 6 to No. 7 are used to straighten the continuous casting billets. Segments No. 1 to No. 14 are 2.4 m long, and each segment has 7 pairs of rollers distributed on its wide surface.

[0058] Regarding the roll gap shrinkage, the roll gap shrinkage of the foot roll segment and the zero segment is set to 0.10-0.20mm, the roll gap shrinkage of the No. 1-4 sector segments is set to 0.15-0.25mm, and the roll gap shrinkage of the No. 5-9 and No. 12-14 sector segments is set to 0.20-0.30mm.

[0059] Regarding the light pressing amount and distribution ratio, the No. 10 and No. 11 sectors perform light pressing, and the pressing amount is set to 4-6 mm, the pressing amount distribution ratio of the No. 10 sector is 30-40%, and the pressing amount distribution ratio of the No. 11 sector is 60-70%.

[0060] By setting limits for the above-mentioned parts, the density of the center of the continuous casting billet is improved, which plays a role in eliminating center shrinkage and looseness and reducing center segregation.

[0061] Next, the present application provides a method for producing a continuous casting billet 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, adopts the above-mentioned continuous casting production method for low-temperature steel continuous casting billet for processing, and sets the corner temperature ≥900°C before the continuous casting billet enters the No. 6 sector, and the difference between the highest and lowest surface temperatures is ≤20°C.

[0067] The low-temperature steel continuous casting billet produced by the production method of the low-temperature steel continuous casting billet has the following chemical compositions in percentage by mass: 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%, and the remainder is Fe and other inevitable impurities.

[0068] The surface crack occurrence rate of the continuous casting billet is ≤0.1%, the surface crack depth is ≤0.1mm, the center C segregation level is ≤B0.5, and there is no shrinkage cavity.

[0069] Finally, the present application provides three embodiments to verify that the continuous casting billets produced by the method for producing continuous casting billets for low-temperature steel provided in the present application have better quality.

[0070] The set parameters of the continuous casting machine are as follows: the continuous casting machine is a straight arc slab continuous casting machine, the cross-sectional size is 220mm×(1900-2800)mm, the arc radius is 10m, and the continuous casting secondary cooling zone includes a foot roll segment, a zero segment and 14 fan segments, among which the foot roll segment corresponds to the secondary cooling zone 1, the zero segment corresponds to the secondary cooling zones 2, 3 and 4, the fan segments 1 and 2 correspond to the zone 5, the fan segments 3 and 4 correspond to the secondary cooling zone 6, the fan segments 5, 6 and 7 correspond to the secondary cooling zone 7, and the fan segments 8, 9 and 10 correspond to the secondary cooling zone 8. The fan-shaped segment corresponds to the secondary cooling zone 8, the fan-shaped segments No. 11, 12, 13 and 14 correspond to the secondary cooling zone 9, the length of the full roller segment is 0.52m, with 2 pairs of rollers distributed on the wide side and 3 pairs of rollers distributed on the narrow side; the length of the zero segment is 3m, with 10 pairs of rollers distributed on the wide side; the length of the fan-shaped segments No. 1-14 is 2.4m, and each fan-shaped segment has 7 pairs of rollers distributed on the wide side; the fan-shaped segments No. 1-7 are located in the arc section of the continuous casting machine, and the fan-shaped segments No. 8-14 are located in the horizontal section of the continuous casting machine; the fan-shaped segments No. 6-7 are used to straighten the continuous casting billets.

[0071] The continuous casting billet provided in the embodiment is produced for three castings (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 continuous casting billets in each casting of Example 1-Example 3

[0073] Watering times Continuous casting billet section size, mm×mm Example 1 220×2800 Example 2 220×2500 Example 3 220×1900

[0074] The production method of continuous casting billet for low temperature steel provided is as follows:

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

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

[0077]

[0078] Table 3 Molten Steel Composition

[0079]

[0080] The molten steel of Example 1 to Example 3 is hoisted to the continuous casting platform and the continuous casting process of step S5 is performed. The molten steel flows into the crystallizer from the tundish through the immersion nozzle, and the insertion depth of the immersion nozzle is defined as h1, the distance between the center position of the crystallizer electromagnetic stirrer and the upper mouth of the crystallizer is defined as h2, the current of the crystallizer electromagnetic stirrer is a, and the casting speed of the continuous casting machine is V; the above-mentioned continuous casting parameters of Example 1 to Example 3 are shown in Table 4:

[0081] Table 4 Continuous casting parameter control

[0082] Watering times <![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 of other auxiliary parameters for continuous casting are shown in Table 5, including the superheat of molten steel in the tundish, the taper of the crystallizer, the water volume on the wide side of the crystallizer, the water volume on the narrow side of the crystallizer, and the liquid level fluctuation of the crystallizer.

[0084] Table 5 Continuous casting parameter control

[0085]

[0086] The protective slag is added into the crystallizer. The chemical composition of the protective slag of Example 1 to Example 3 is expressed in mass percentage as shown in Table 6. The physical and chemical performance indexes 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 billet shell thickness and enters the secondary cooling zone of the continuous casting machine;

[0087] Table 6 Components of mold slag

[0088]

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

[0090]

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

[0092] Table 8 Secondary cooling water ratio of continuous casting machine and secondary cooling water ratio of zone 1-9

[0093]

[0094] The proportion of water volume on the narrow side and the wide side in the secondary cooling zone 1 is shown in Table 9.

[0095] Table 9 Water content ratio of narrow side and wide side of continuous casting billet in secondary cooling zone 1

[0096] Watering times Narrow side, % Wide noodles, % Example 1 30 70 Example 2 35 65 Example 3 40 60

[0097] The roll gap shrinkage of the full roll segment, zero segment, No. 1-No. 4, No. 5-No. 9, No. 12-No. 14 fan-shaped segments, No. 10 fan-shaped segments and No. 11 fan-shaped segments perform light pressing, and the pressing amount and pressing amount distribution ratio of No. 10 and No. 11 fan-shaped segments are shown in Table 10.

[0098] Table 10 Roll gap shrinkage, reduction and reduction distribution ratio of continuous casting machine

[0099]

[0100] After the continuous casting billet is produced into the No. 14 sector, it is flame cut to obtain a continuous casting billet with a billet length of 8m. Low-magnification samples are taken from the continuous casting billet, and the surface and cross-section are 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 continuous casting slab

[0102]

[0103] Obviously, the continuous casting billets produced by the continuous casting production method and production method of continuous casting billets for low-temperature steel provided in this application meet the expected set requirements, which means that the continuous casting production method and production method of continuous casting billets for low-temperature steel can improve the central density of the continuous casting billets, eliminate central shrinkage holes, looseness and reduce central segregation.

[0104] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0105] The meaning of "and / or" described in this application means that the situations where each exists alone or both exist at the same time are included.

[0106] The term “connection” as used in this application may mean a direct connection between components or an indirect connection between components via other components.

[0107] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A continuous casting production method for continuous casting billets for low temperature steel, characterized in that: In the continuous casting process, the molten steel flows from the ladle through the tundish and then into the mold. After the molten steel initially solidifies in the mold to form a shell, it enters the secondary cooling zone for further solidification. Define the width dimension of the continuous caster as l, the immersion depth of the submerged nozzle as h1, the length from the center position of the mold electromagnetic stirrer to the upper opening of the mold as h2, and the current of the mold electromagnetic stirrer as a; The width dimension of the continuous caster is 1900 mm ≤ l ≤ 2800 mm, the set immersion depth of the submerged nozzle is 170 mm ≤ h1 ≤ 230 mm, the current of the mold electromagnetic stirrer is 450 A ≤ a ≤ 600 A, and the length from the center position of the mold electromagnetic stirrer to the upper opening of the mold is 550 mm ≤ h2 ≤ 650 mm.

2. The continuous casting production method of continuous casting billet for low temperature steel according to claim 1, characterized in that: The continuous caster is a straight-arc type continuous caster with an arc radius of 10 m and a thickness dimension of 220 mm. Define the casting speed of the continuous caster as V, then 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.

3. The continuous casting production method of the continuous casting billet for low-temperature steel according to claim 2, wherein: When the width dimension of the continuous caster is 1900 mm ≤ l < 2200 mm, the set immersion depth of the submerged nozzle is 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; When the width dimension of the continuous caster is 2200 mm ≤ l < 2500 mm, the set immersion depth of the submerged nozzle is 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; When the width dimension of the continuous caster is 2500 mm < l ≤ 2800 mm, the set immersion depth of the submerged nozzle is 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.

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

5. The continuous casting production method of continuous casting billet for low temperature steel according to claim 1, characterized in that: The protective slag used in the crystallizer has the following chemical compositions 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%, and the rest are unavoidable impurities.

6. The continuous casting production method of continuous casting billet for low temperature steel according to claim 5, characterized in that: The binary basicity of the mold slag is CaO / SiO2 0.79-0.94, the melting point is 1050-1150℃, and the viscosity at 1300℃ is 0.25-0.35Pa·s; The protective slag layer has a thickness of 100-130 mm. The protective slag forms a liquid slag film between the molten steel and the wall of the crystallizer tube, and the thickness of the liquid slag layer is 10-13 mm.

7. The continuous casting production method of continuous casting billet for low temperature steel according to claim 1, characterized in that: The secondary cooling zone includes a foot roll section, a zero section and a plurality of fan-shaped sections, wherein 14 fan-shaped sections are provided, and the secondary cooling zone includes zone 1, zone 2 ... zone 9; The foot roll segment corresponds to the secondary cooling zone 1, the zero segment corresponds to the secondary cooling zone 2, zone 3 and zone 4, and the 14 sector segments are numbered 1, 2, ... 14, sector segments 1 and 2 correspond to the secondary cooling zone 5, sector segments 3 and 4 correspond to the secondary cooling zone 6, sector segments 5, 6 and 7 correspond to the secondary cooling zone 7, sector segments 8, 9 and 10 correspond to the secondary cooling zone 8, and sector segments 11, 12, 13 and 14 correspond to the secondary cooling zone 9; The water volume ratio of the secondary cooling zone is set at 0.4-0.6L / kg, and the water volume ratios of the secondary cooling zone 1 to the secondary cooling zone 9 are 8-13%, 24-30%, 20-25%, 13-18%, 8-13%, 6-12%, 1-3%, 1-3% and 1-3% respectively; The water in the secondary cooling zone 1 is distributed to the narrow side and wide side of the continuous casting billet, with the narrow side accounting for 30-40% and the wide side accounting for 60-70%.

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

9. A method for producing a continuous casting billet for low temperature steel, characterized in that: The following steps are involved: 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, adopts the continuous casting production method of low-temperature steel continuous casting billet according to claim 1 for processing, and sets the corner temperature ≥900°C before the continuous casting billet enters the No. 6 sector, and the difference between the highest and lowest surface temperatures is ≤20°C.

10. A continuous casting billet, characterized in that: The chemical composition of the continuous casting billet produced by the production method of continuous casting billet for low-temperature steel as described in claim 9 is as follows, in terms of 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%, and the remainder is Fe and other inevitable impurities.

11. The continuous casting billet according to claim 10, characterized in that: The continuous casting billet has a surface crack occurrence rate of ≤0.1%, a surface crack depth of ≤0.1 mm, a center C segregation grade of ≤B 0.5, and no shrinkage cavity.

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