Continuous casting method of composite metal product

Abstract

A continuous casting method of a composite metal product having different shells and a body of different composition, the shells having a constant thickness, comprising the following steps: A. injecting an initial flow of liquid metal from a tundish into a crystallizer using a continuous casting nozzle at an initial flow rate FRini; B. injecting at least one of the raw materials into at least one of the mixing chambers to mix with the liquid metal flowing into the mixing chamber, thereby changing its composition; C. injecting a gas under the dome at a determined gas flow rate GFR; D. adjusting the initial flow rate FRini, the gas flow rate GFR, the outlet immersion depths D1 and D2 and the casting speed Vc to obtain a composite metal product.

Description

Technical Field

[0001] This invention relates to a continuous casting process. In particular, this invention relates to a continuous casting process for manufacturing composite metal products. Background Technology

[0002] Continuous casting of steel is a well-known process. It involves pouring molten metal from a ladle into an tundish designed to regulate the flow, and then pouring the metal into the upper part of a water-cooled, bottomless copper crystallizer that undergoes vertical reciprocating motion. The solidified semi-finished product is removed from the lower part of the crystallizer by rollers. The molten metal is introduced into the crystallizer through tubular conduits called nozzles, which are placed between the tundish and the crystallizer.

[0003] However, this simple process is not suitable for casting composite metal products. The nozzle is a simple conduit that can only be used as a pouring tool for molten metal between the tundish and the crystallizer. Therefore, improvements must be made to both the nozzle and the casting method to allow for the casting of composite metal products.

[0004] Japanese patent application JP11197807 describes a continuous casting method for producing multi-layered billets, which uses a nozzle formed by a vertical conduit having multiple discharge ports in the vertical direction. The conduit is internally separated by partition walls to form multiple molten steel flow channels and has one or more ports for adding raw materials.

[0005] The described continuous casting process involves injecting two types of molten metal with different compositions into a crystallizer at different heights, thereby forming two liquid metal pools, an upper pool and a lower pool, each with a different composition. The metal in the upper pool solidifies first, forming a shell with the composition of the upper pool. The metal in the lower pool then solidifies inside the shell, forming the bulk of the material and having the composition of the lower pool, thus forming a composite metal product.

[0006] When manufacturing composite metal products by continuous casting, the stability of the interface between the molten pools is one of the main parameters defining the separation quality between the shell and the body of the composite product.

[0007] Japanese patent application JP11197807 uses a static magnetic field and injects different streams of liquid metal above and below the magnetic field. The magnetic field acts as a brake on the liquid metal, thereby reducing the mixing of the two molten pools and stabilizing the boundary.

[0008] However, this method relies solely on the equipment to achieve boundary stability, thus it cannot adapt to different casting conditions. Furthermore, the magnetic field does not prevent sufficient remixing of the product, thus failing to achieve adequate separation quality between the shell and the body. Summary of the Invention

[0009] This invention discloses a continuous casting method for manufacturing composite metal products, which allows the casting of products with shells and bodies having different compositions, resulting in products with maximized compositional variation and good definition, and therefore better quality.

[0010] The object of this invention is a continuous casting method for composite metal products, which are shells 16 and bodies 17 with different compositions, wherein the shells 16 have a constant thickness, and the method includes the following steps:

[0011] A. An initial flow of liquid metal is injected from the tundish 2 into the crystallizer 3 at an initial flow rate FRini using a continuous casting nozzle 1, wherein the continuous casting nozzle 1 comprises at least:

[0012] - Dome 6, which is used to divide the initial liquid metal flow into multiple independent flows.

[0013] - Two mixing chambers 9a and 9b, separated by an inner wall 8, to allow the independent flow of liquid metal in each of the chambers 9a and 9b, the inner wall 8 being designed to determine the redistribution of the independent flow into each chamber 9a and 9b.

[0014] - A device for injecting raw material 10 into at least one of the mixing chambers 9a and 9b through the dome 6.

[0015] - A device for injecting gas 11 through dome 6,

[0016] - Two channels 12a, 12b, 12c, each channel connected to at least one chamber 9a, 9b and leading to the crystallizer 3 via at least one outlet 13, allowing liquid metal from chambers 9a, 9b to be injected into the crystallizer, wherein at least one of the channels 12a has a different length than the other channels 12b, 12c, thereby allowing the outlet 13 of the channels 12a, 12b, 12c to be immersed in the crystallizer 3 at two different immersion depths D1 and D2, thereby forming two types of liquid metal flows 20, 21 within the crystallizer 3, the upper flow 20 having a total flow rate FRup = Q*FRini, where Q is the ratio, and the lower flow 21 having a total flow rate FRlow = (1-Q)*FRini, wherein for each outlet, the ratio between the channel diameter and the outlet diameter is designed to set the velocity of the liquid metal flow exiting the outlet;

[0017] B. The raw material is injected into at least one of the mixing chambers 9a and 9b to mix with the liquid metal flowing into the mixing chambers 9a and 9b, thereby changing its composition and forming two liquid metal pools 14 and 15 in the crystallizer 3, namely an upper pool 14 and a lower pool 15 with different compositions, the two liquid metal pools 14 and 15 being separated by an interface 19 located at a depth Li in the crystallizer 3;

[0018] C. Gas is injected below the dome 6 at a defined gas flow rate GFR to facilitate the injection of raw materials into the chambers 9a and 9b;

[0019] D. Adjust the initial flow rate FRini, the gas flow rate GFR, the immersion depths D1 and D2 of the outlet 13, and the casting speed Vc to adjust the depth Li of the interface 19 between the two molten pools 14 and 15 in the crystallizer 3, thereby obtaining a composite metal product.

[0020] The continuous casting method according to the invention may also have the following optional features, either individually or in combination:

[0021] - Liquid metal is steel.

[0022] - The initial flow rate FRini is adjusted using stopper rod 18.

[0023] - The initial flow rate FRini is set from 0.3 T / min to 6 T / min.

[0024] - Gas flow rate (GFR) is regulated using valves or mass flow meters.

[0025] - The gas flow rate (GFR) is set from 0.1 Nl / min to 5 Nl / min.

[0026] - The casting speed Vc is set from 0.4 m / min to 6 m / min.

[0027] - The ratio Q is set to 0.2 to 0.8.

[0028] - The raw material is injected in the direction of the metal flow flowing down the dome.

[0029] - The raw material is injected at an angle of 30° to 90° relative to the horizontal plane. Attached Figure Description

[0030] The invention will be described in a non-limiting manner with reference to the following figures:

[0031] - Figure 1 : An overall view of one embodiment of the device used in this invention

[0032] - Figure 2Examples of composite metal products that can be manufactured using this invention

[0033] - Figure 3 A view of one embodiment of the nozzle immersion section and crystallizer used in this invention.

[0034] - Figure 4 A redistribution view of the flow entering the nozzle and crystallizer in one embodiment.

[0035] - Figure 5 Cross-sectional view of one embodiment of an apparatus for injecting raw material into a nozzle.

[0036] - Figure 6 Example of the bottom shape of the channel and its outlet. Detailed Implementation

[0037] Figure 1 An embodiment of an apparatus used in the continuous casting method according to the present invention is shown. The apparatus includes a continuous casting nozzle 1 disposed between a tundish 2 and a crystallizer 3. The nozzle 1 is composed of an upper part 4 and a lower part 5.

[0038] A dome 6 is positioned at the entrance of the upper part 4 and partially closes it. The top of the dome 6 preferably has a sloped surface at an angle, for example, greater than 15°. The dome 6 also has sides, preferably forming sharp edges with the sloped surface. The dome 6 is secured to the upper part 4 by one or more support arms 7.

[0039] The inner wall 8 located below the dome 6 divides the upper part 4 into at least two mixing chambers 9a and 9b. These chambers 9a and 9b include portions with reduced cross-sections. Figure 1 The configuration shown contains two chambers, 9a and 9b.

[0040] Devices for injecting raw material 10 into at least one of the mixing chambers 9a and 9b, and devices for injecting gas 11, are also included in the upper part 4, each partially located in one of the support arms 7 and passing through the dome 6. In this configuration, the device for injecting raw material 10 is a powder injector. The powder injector may be, for example, an endless spiral connected to a powder container. The diameter of the powder injector is preferably in the range of 10 to 30 mm. In the usage configuration, the powder injector preferably has an angle in the range of 30° to 90° relative to the horizontal plane. More preferably, the powder injector has an angle in the range of 30° to 50° relative to the horizontal plane.

[0041] The lower part 5 of the nozzle 1 is composed of at least two channels 12a, 12b, and 12c, which extend from the chambers 9a and 9b of the upper part 4 after their reduced cross-sections and lead to the crystallizer 3 through at least one outlet 13 of each channel 12a, 12b, and 12c. In this embodiment, there are three channels 12a, 12b, and 12c.

[0042] In this embodiment, channels 12a, 12b, and 12c have a circular shape. In a preferred embodiment, channels 12a, 12b, and 12c have a circular, elliptical, or oblong cross-section.

[0043] At least one of channels 12a, 12b, and 12c has a different length than the other channels 12a, 12b, and 12c. Figure 1 As shown, channel 12a is longer than other channels 12b and 12c, but other configurations with only two channels or two longer channels can be considered.

[0044] Channels 12a, 12b, and 12c of different lengths connect to different chambers 9a and 9b, but more than one channel 12a, 12b, and 12c can connect to a single chamber 9a and 9b. For example, in this embodiment, there are two chambers 9a and 9b and three channels 12a, 12b, and 12c. The longer channel 12a connects to one chamber 9a, and the other two shorter channels 12b and 12c connect to the other chamber 9b.

[0045] For each channel 12a, 12b, 12c, each channel 12a, 12b, 12c has at least one outlet 13, but the number of outlets 13, the location of the outlets 13, the angle of their axes, and the shape of the bottom of the channels 12a, 12b, 12c can vary depending on the implementation. The outlets 13 between the longer channels 12a and the shorter channels 12b, 12c can also be different. Figure 1 In one embodiment, the longer channel 12a has only one outlet 13 located at the bottom of the channel 12a, which is vertical, while the shorter channels 12b and 12c each have an outlet 13 located on their side, without any angle relative to the horizontal plane, and the bottoms of channels 12b and 12c have a flat shape. In another embodiment, not shown, the longer channel 12a has two outlets 13 located on the side of the channel 12a, which are angled relative to the horizontal plane, and the bottom of the channel 12a has a dome shape. In a preferred embodiment, when the outlets 13 are located on the sides of channels 12a, 12b, and 12c, the bottoms of channels 12a, 12b, and 12c have a flat, recessed, sloping, or dome shape.

[0046] Figure 6Various shapes of the bottom of channels 12a, 12b, and 12c are shown. Figure 6 a shows the flat shape of channels 12a, 12b, and 12c with only one outlet 13. Figure 6 b shows the concave shape of channels 12a, 12b, and 12c with only one outlet 13. Figure 6 c shows the slope shape of channels 12a, 12b, and 12c with only one outlet 13. Figure 6 d shows the flat shape of channels 12a, 12b, and 12c with two outlets 13. Figure 6 e illustrates the recessed shape of channels 12a, 12b, and 12c with two outlets 13, and Figure 6 f shows the dome shape of channels 12a, 12b, 12c with two outlets 13. Figure 6 The shapes shown are given as examples only, and the bottoms of channels 12a, 12b, and 12c can have any shape.

[0047] The continuous casting method of the present invention includes manufacturing composite metal products having different shells 16 and bodies 17 with different compositions, maximizing the compositional differences between the shells 16 and the bodies 17, while allowing the thickness of the shells 16 to remain equal to a target value in the final product. The method comprises four steps.

[0048] The first step involves injecting a liquid metal of a defined composition from a ladle into an intermediate ladle 2, and then filling a previously described nozzle 1 to dispense the liquid metal into a crystallizer 3. In a preferred embodiment, the liquid metal is steel, and the invention will be described with steel as the liquid metal.

[0049] An initial flow of steel with an initial flow rate of FRini flows from the tundish 2 into the upper part 4 of the nozzle 1.

[0050] A dome 6, placed within the trajectory of the steel, forces the initial flow to impact it. The slope of the dome 6 directs the steel flow toward its edge. Supporting arms 7 form distinct zones on the dome 6, dividing the initial steel flow into multiple independent streams. The number of independent streams is determined by the design of the dome 6 and its supporting arms 7.

[0051] Independent flows then flow into different mixing chambers 9a and 9b. The design of the inner walls 8 of the separating chambers 9a and 9b determines the redistribution of the independent flows into each chamber 9a and 9b by determining their respective volumes. Due to the reduction in their cross-section, steel subsequently accumulates inside chambers 9a and 9b. The steel is then distributed into channels 12a, 12b, and 12c and injected into the crystallizer 3 through the outlets 13 of channels 12a, 12b, and 12c.

[0052] Because channels 12a, 12b, and 12c have different lengths, their outlets 13 have different immersion depths in the crystallizer 3. The shorter channels 12b and 12c have outlets 13 at an immersion depth D1, while the longer channel 12a has an outlet 13 at an immersion depth D2. This difference in immersion depth allows liquid steel to be injected at two different depths, D1 and D2, thereby forming two types of liquid steel flows 20 and 21 within the crystallizer 3.

[0053] The liquid steel flow 20 from outlet 13 with an immersion depth D1 is the upper flow 20. The total flow rate FRup of the upper flow is a portion Q of the initial flow rate FRini at the top of injection nozzle 1. FRup can be calculated using the following formula: FRup = Q * FRini.

[0054] The liquid steel flow 21 from outlet 13 with an immersion depth D2 is the lower flow 21. The total flow rate FRlow of the lower flow is another part (1-Q) of the initial flow rate FRini. FRlow can be calculated using the following formula: FRlow = (1-Q)*FRini.

[0055] Figure 4 It shows according to Figure 1 The implementation uses a ratio Q for the redistribution of the liquid steel flow. In this implementation, FRup is distributed between two upper outlets 13, where the flow rate flowing out of each upper outlet 13 is (Q / 2)*FRini. Typically, the flow rate is distributed between outlets 13 with the same immersion depth. The flow rate FRup is distributed between all outlets 13 with an immersion depth D1, and the flow rate FRlow is distributed between all outlets 13 with an immersion depth D2.

[0056] The outlet diameter, relative to the channel diameter, is defined as the velocity of the liquid metal flow exiting the outlet.

[0057] The second step involves injecting raw material into at least one of chambers 9a and 9b to alter the composition of the steel flowing into said chambers 9a and 9b. Chambers 9a and 9b are designed with a large cross-section at the top, allowing the steel to flow down the dome 6 like a waterfall, and allowing the raw material to be injected into the flow without contacting the device 10 used for injecting the raw material. The design of chambers 9a and 9b allows the steel to slow down and accumulate within the chambers. The reduced cross-section of the chambers causes the steel to be agitated within the chambers. Therefore, the injected raw material can be effectively mixed with the steel in said chambers 9a and 9b to alter its composition and initiate melting.

[0058] In a preferred embodiment, the raw material injected into the steel is in powder form. It can have various compositions, such as FeSi, Ni, FeAl, FeTi, FeCr, FeNb, FeB, FeCe, FeMo, etc.

[0059] Figure 5 A cross-sectional view of the top of the dome 6 and mixing chambers 9a and 9b is shown, along with one embodiment of the device 10 for injecting raw materials. The end portion of the device 10 for injecting raw materials is located inside the dome 6 and one of its supporting arms 7, and opens below the dome 6. It injects the raw materials into one of the mixing chambers 9a and 9b. In a preferred embodiment, the injection direction of the raw materials is towards the flow of metal steel flowing down the dome 6. This allows for better mixing of the raw materials in the mixing chambers 9a and 9b. For this purpose, the device 10 for injecting raw materials has an angle relative to the horizontal plane, preferably between 30° and 90°. More preferably, the angle is between 30° and 50°.

[0060] For the injection step, different chambers 9a and 9b contain two types of steel with different compositions.

[0061] Because channels 12a, 12b, and 12c have different lengths, the two types of steel are injected into the crystallizer 3 at two different heights. The upper flow 20 and the lower flow 21 form two steel molten pools, namely the upper molten pool 14 and the lower molten pool 15 with different compositions, and these two steel molten pools are separated by an interface 19 at a depth Li.

[0062] The composition of the molten pools 14 and 15 varies depending on the chambers 9a and 9b into which the raw material is injected. If the raw material is injected into chambers 9a and 9b connected to the longer channel 12a, the composition of the upper molten pool 14 is solely the composition of the steel from the tundish 2, while the composition of the lower molten pool 15 is a combination of the steel from the tundish 2 and the composition of the injected raw material. On the other hand, if the raw material is injected into chambers 9a and 9b connected to the shorter channels 12b and 12c, the composition of the upper molten pool 14 is a combination of the steel from the tundish 2 and the composition of the injected raw material, while the composition of the lower molten pool 15 is solely the steel from the tundish 2.

[0063] Therefore, the raw material can be injected into either chamber 9a or 9b, according to the needs of those skilled in the art.

[0064] The third step involves injecting gas below the dome 6 at a defined gas flow rate GFR. This step facilitates the injection of raw material into the chambers 9a and 9b by creating a gas flow that causes steel to flow downwards along the dome 6 towards the outside of the upper part 4, thereby creating a steel-free region below the dome 6. This hollow region prevents any contact between the steel and the raw material injection device 10, thus avoiding potential blockage of the injection device.

[0065] The gas is preferably non-oxidizing, such as Ar, to prevent any reaction with the steel during casting. In a preferred embodiment, the gas flow is regulated using a valve or mass flow meter. In a preferred embodiment, the gas flow rate (GFR) is set to 0.1 Nl / min to 5 Nl / min.

[0066] The fourth step involves adjusting and stabilizing different parameters to limit the depth Li of the interface 19 between the two molten pools 14 and 15 in the crystallizer 3, thereby maximizing the compositional difference between the shell 16 and the body 17 of the composite metal product, and maintaining a constant shell 16 thickness. The main adjustable parameters are the initial steel flow rate FRini, the gas flow rate GFR, the immersion depths D1 and D2 at outlet 13, and the casting speed Vc.

[0067] In the crystallizer, the thickness of the solidified portion can be determined by a formula, where e is the solidification thickness:

[0068]

[0069] e: Solidification thickness (mm)

[0070] L: Casting length (m)

[0071] Vc: Casting speed (m / min)

[0072] k: A constant that depends on the cooling rate of the casting machine.

[0073] The casting length L is a variable representing the distance from the meniscus of the liquid steel to a variable depth in the crystallizer 3.

[0074] Because there are two molten pools 14 and 15, the steel in the upper molten pool 14 solidifies first, forming a solidified portion with one composition. The thickness of the solidified portion increases until it reaches the interface 19 between the two molten pools 14 and 15, where the second component in the lower molten pool 15 begins to solidify until the product is completely solidified. The first solidified component from the upper molten pool 14 represents the shell 16 of the product, and the second component from the lower molten pool 15 represents the body 17 of the product. After complete solidification, the resulting material is a composite metal product, the composition of which differs from the composition of its body 17, such as... Figure 2 As shown.

[0075] Using the formula given above, the thickness of the shell 16 of the composite metal product can be calculated. Under a defined casting speed, the thickness of the shell 16 is calculated using the distance Li between the meniscus of the molten steel and the position of the interface 19 between the upper molten pool 14 and the lower molten pool 15. By defining and adjusting the casting speed Vc and the position of the interface between the molten pools, the thickness of the shell 16 of the solidified product can thus be kept constant.

[0076] Figure 3 An embodiment of a nozzle 1, the lower part 5 of which is used in a continuous casting process, and the crystallizer 3 immersed therein are shown. The outlets 13 of the shorter channels 12b and 12c are immersed in the crystallizer 3 at an immersion depth D1, while the outlet 13 of the longer channel 12a is immersed in the crystallizer 3 at an immersion depth D2 > D1. For the lateral outlet 13, the immersion depth D1 or D2 represents the distance from the meniscus of the molten steel to the top of the outlet 13, such as... Figure 3 As shown. For outlet 13 located at the bottom of channels 12a, 12b, and 12c, distance D1 or D2 represents the distance from the meniscus of the molten steel to the bottom of channels 12a, 12b, and 12c. D1 and D2 are parameters defined by casting conditions. The gap Δ between outlet 13 of shorter channels 12b and 12c and outlet 13 of longer channel 12a, unlike D1 and D2, is a fixed distance determined solely by the design of nozzle 1. Its value can be calculated using the following formula:

[0077]

[0078] Δ is a fixed distance, determined by the nozzle design.

[0079] Considering this process, the steel used for the upper molten pool 14 is injected into the crystallizer 3 through the outlet 13 of the shorter channels 12b and 12c, forming an upper flow 20 at depth D1, while the steel used for the lower molten pool 15 is injected into the crystallizer 3 through the outlet 13 of the longer channel 12a, forming a lower flow 21 at depth D2. The interface 19 between the two molten pools is formed at the junction of the upper flow 20 and the lower flow 21.

[0080] D1 and D2 are defined by the immersion of nozzle 1 in the molten steel. The two parameters affecting immersion are the height of the tundish 2 to which nozzle 1 is attached relative to the crystallizer 3, and the height of the meniscus of the molten steel in the crystallizer 3. These parameters should be defined before casting and kept constant during casting to avoid fluctuations in the interface 19 between the molten pools 14 and 15, thereby achieving a constant thickness of the shell 16 of the solidified product. To modify them, the operator can adjust the initial flow rate FRini by using stopper 18 to adjust the level of molten steel in the crystallizer 3, or move the tundish 2 up and down to change the immersion of nozzle 1 in the crystallizer 3.

[0081] To consistently ensure good casting quality, it is preferable to set limits on the depths D1 and D2 of the outlet 13. If the immersion depth D1 is too low, the upper flow 20 approaches the meniscus of the liquid steel, potentially entraining mold flux into the liquid steel. On the other hand, if the immersion depth D1 is too high, the upper flow 20 may not be able to transfer sufficient heat to the top of the mold 3, causing the casting operation to malfunction. Regarding D2, a minimum immersion depth is preferred, ensuring an acceptable gap Δ so that the upper flow 20 and lower flow 21 do not mix. A maximum immersion depth is also preferred, ensuring that the bottom of the nozzle 1 does not contact the solidification thickness of the product, thereby avoiding potential breakage.

[0082] In view of these factors, in the preferred embodiment, D1 is set to 100 to 150 mm, D2 is set to 250 to 500 mm, and Δ is set to 100 to 500 mm.

[0083] During casting, remixing between the two molten metal pools 14 and 15 is unavoidable due to the merging of the upper flow 20 and the lower flow 21, as well as the gas flow from the injection nozzle. However, to achieve good separation quality between the shell 16 and the body 17 of the final product, it is important that the elements added with the raw materials do not mix with the molten pools 14 and 15; addition in the molten pools 14 and 15 is undesirable. If addition in the body 17 is desired, it is important that the added elements do not mix with the upper molten pool 14. However, molten steel from the upper molten pool 14 can flow downwards into the lower molten pool 15 without affecting the separation between the shell 16 and the body 17. In another case where addition in the shell 16 is desired, it is important that the added elements do not mix with the lower molten pool 15. However, in the same manner as in the other case, molten steel from the lower molten pool 15 can flow upwards into the upper molten pool 14. Therefore, depending on the type of addition, remixing is acceptable in only one manner.

[0084] This invention takes into account this fact, maximizing the compositional difference and separation between the shell 16 and the body 17 by forcing a remixing process to limit the diffusion of added elements into the undesirable molten pool. This is achieved by adjusting the flow rates FRup and FRlow of the molten steel from the nozzle 1 outlet 13. These parameters cannot be directly controlled, but they all depend on the controllable initial flow rate FRini and the redistribution of this initial flow rate FRini to the two flow rates FRup and FRlow flowing out of the nozzle 1. The ratio Q represents this redistribution and is determined by the design of the nozzle 1.

[0085] To adjust the ratio Q, various parameters of nozzle 1 must be considered. The first parameter is the initial separation of the liquid metal flow into multiple independent streams, accomplished by dome 6. The design of dome 6 determines the number of independent streams. For example, dome 6 with three support arms 7 will separate the initial flow into three independent streams. The second parameter is the chambers 9a and 9b for collecting the independent streams. The inner walls 8 separating the different chambers 9a and 9b are designed such that the different chambers 9a and 9b have a defined volume to collect a defined number of independent streams. Figure 1 In this implementation, there are two chambers 9a and 9b. The first chamber 9a collects one independent flow, while the other chamber 9b collects two other independent flows. The final parameter is the passages 12a, 12b, and 12c connected to each chamber 9a and 9b, as their lengths determine the molten pools 14 and 15 into which the molten steel is injected. By adjusting these parameters, the operator can thus regulate Q according to the desired type of addition.

[0086] For addition to body 17, Q is preferably 0.5 to 0.7.

[0087] For addition to shell 16, Q is preferably 0.3 to 0.5.

[0088] With a defined Q value, the initial flow rate FRini can be adjusted to limit the flow rates FRup and FRdown in the crystallizer. In a preferred embodiment, a stopper rod is used to adjust the initial flow rate FRini. In a preferred embodiment, the initial flow rate FRini is set to 0.3 T / min to 6 T / min.

[0089] However, even if remixing is forced in one manner, it should be limited to a minimum to maximize the compositional difference between the shell 16 and the body 17 in the final product. The final product must also have sufficient quality. For this purpose, the composite metal product must have a clear and constant separation between the body 16 and the shell 17. Therefore, the thickness of the shell 16 must be maintained at the target value throughout the product. To achieve this, the interface 19 between the molten pools 14 and 15 must be as stable as possible during casting, thus other parameters, namely the liquid metal flows 20 and 21 themselves and the gas flow, must be considered.

[0090] The liquid metal flows 20 and 21 are characterized by their velocity and direction, which are defined by their angle and velocity at the nozzle 1 outlet. The angle of the flow is defined by the angle of the axis of the outlet 13. The velocity of the flow at the nozzle 1 outlet is determined by the diameter of the outlet 13 and the flow rate in the channels 12a, 12b, and 12c, and therefore depends on the initial flow rate FRini and the ratio Q.

[0091] To achieve good stability at interface 19 between molten pools 14 and 15 and to obtain the desired product quality, the liquid metal flows 20 and 21 are balanced with the gas flows, while allowing sufficient remixing in a manner that prevents added elements from mixing with incorrect molten pools 14 and 15. Since the geometry of the crystallizer 3 and the casting parameters vary according to the desired product, the nozzle 1 and process parameters must be modified accordingly. The angle and velocity of the flows must be adjusted to reach the edges of the crystallizer 3 without mixing. Velocity also affects the gas flow. Insufficient velocity can cause the gas to flow directly upwards at the outlet 13, which may be detrimental to stability. However, with sufficient velocity, the gas flow is entrained by the metal flows 20 and 21, resulting in better flow balance.

[0092] Table 1 lists the preferred values ​​for different parameters considering different implementation methods.

[0093]

[0094] In a preferred embodiment, Vc is set to 0.4 m / min to 6 m / min.

[0095] The products obtained by this method are preferably small square billets, large square billets, or slabs.

[0096] This continuous casting process meets expectations in terms of the quality of the semi-finished products. It allows for the stable casting of composite metal products with different shells 16 and bodies 17, maximizing the compositional differences between the shells 16 and bodies 17, and ensuring that the thickness of the shells 16 is constant in the final product.

Claims

1. A continuous casting method for a composite metal product, the composite metal product having shells (16) and a body (17) of different compositions, the shells (16) having a constant thickness, the method comprising the following steps: A. An initial flow of liquid metal is injected from a tundish (2) into a crystallizer (3) at an initial flow rate FRini using a continuous casting nozzle (1), said continuous casting nozzle (1) comprising at least: - A dome (6), which is used to divide the initial liquid metal flow into multiple independent flows. - Two mixing chambers (9a, 9b), separated by an inner wall (8), to allow the independent liquid metal flow to flow in each of the chambers (9a, 9b), the inner wall (8) being designed to determine the redistribution of the independent flow into each chamber (9a, 9b). - A means for injecting raw material (10) into at least one of the mixing chambers (9a, 9b) through the dome (6), - A device for injecting gas (11) through the dome (6), - Two channels (12a, 12b, 12c), each channel being connected to at least one chamber (9a, 9b) and leading to the crystallizer (3) through at least one outlet (13), allowing liquid metal from the chambers (9a, 9b) to be injected into the crystallizer (3), wherein at least one of the channels (12a) has a different length than the other channels (12b, 12c), thereby allowing the outlet (13) of the channel (12a, 12b, 12c) to be immersed in the crystallizer (3) at two different immersion depths D1 and D2, thereby forming two types of liquid metal flows (20, 21) within the crystallizer (3), the upper flow (20) having a total flow rate FRup = Q*FRini, the lower flow (21) having a total flow rate FRlow = (1-Q)*FRini, and wherein for each outlet, the ratio between the channel diameter and the outlet diameter is designed to set the velocity of the liquid metal flow exiting the outlet; B. The raw material is injected into at least one of the mixing chambers (9a, 9b) to mix with the liquid metal flowing into the mixing chamber (9a, 9b), thereby changing its composition and forming two liquid metal pools (14, 15) in the crystallizer (3), namely an upper pool (14) and a lower pool (15) with different compositions, the two liquid metal pools (14, 15) being separated by an interface (19) located at a depth Li in the crystallizer (3); C. Gas is injected below the dome (6) at a defined gas flow rate GFR to facilitate the injection of raw materials into the chambers (9a, 9b). D. Adjust the initial flow rate FRini, the gas flow rate GFR, the outlet immersion depths D1 and D2, and the casting speed Vc to adjust the depth Li of the interface (19) between the two molten pools (14, 15) in the crystallizer (3), thereby obtaining a composite metal product.

2. The continuous casting method according to claim 1, wherein the liquid metal is steel.

3. The continuous casting method according to any one of the preceding claims, wherein the initial flow rate FRini is adjusted using a stopper rod (18).

4. The continuous casting method according to claim 3, wherein the initial flow rate FRini is set to 0.3 T / min to 6 T / min.

5. The continuous casting method according to any one of the preceding claims, wherein the gas flow rate GFR is regulated using a valve or a mass flow meter.

6. The continuous casting method according to claim 5, wherein the gas flow rate GFR is set to 0.1 Nl / min to 5 Nl / min.

7. The continuous casting method according to any one of the preceding claims, wherein the casting speed Vc is set to 0.4 m / min to 6 m / min.

8. The continuous casting method according to any one of the preceding claims, wherein the ratio Q is set to 0.2 to 0.

8.

9. The continuous casting method according to any one of the preceding claims, wherein the direction of the injection of raw materials is toward the metal flow flowing down along the dome.

10. The continuous casting method according to claim 9, wherein the raw material is injected at an angle of 30° to 90° relative to the horizontal plane.

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