Continuous Casting Equipment

Abstract

The present invention relates to a continuous casting nozzle for producing composite metal slabs, said nozzle being located between a tundish and a mold, said nozzle comprising: an upper part located downstream of the tundish, a dome located at the inlet of the upper part and provided with means for dividing the initial flow of liquid metal, an inner wall located below the dome and creating at least two mixing chambers, means for injecting powder through the dome to allow it to mix with the liquid metal, a lower part consisting of at least a central channel with two lower lateral outlets and a side channel with at least one upper lateral outlet by channels allowing the liquid metal to flow into the mold. The present invention also relates to a method for continuous casting using the continuous casting nozzle associated with the present invention.

Description

[Technical Field]

[0001] The present invention relates to continuous casting equipment, and more particularly to a continuous casting nozzle having an improved design and adapted for producing composite metal slabs. [Background technology]

[0002] Continuous casting of steel is a well-known process. It consists of pouring the liquid metal from a ladle into a tundish, intended to regulate the flow, and then pouring this metal into the top of a water-cooled, bottomless copper mold that undergoes a vertical reciprocating motion. The solidified semi-finished product is removed from the bottom of the mold by rollers. The liquid metal is introduced into the mold by a tubular duct called a nozzle, which is located between the tundish and the mold.

[0003] However, this simple equipment is not suitable for casting composite metal products. Because the nozzle is a simple duct, it can only be used as a tool to pour the liquid metal between the tundish and the mold. Therefore, the nozzle and the casting method must be modified to make it possible to cast composite metal products.

[0004] Japanese Patent Application JP11197807 describes a continuous casting nozzle for producing multi-layer cast parts, which is formed from a vertical duct having a plurality of discharge ports in the vertical direction, the duct being divided internally by partitions creating a plurality of molten steel flow passages, and which has one or more ports for adding raw materials.

[0005] The described continuous casting nozzle allows for the injection of two molten metals of different compositions into a mold at different heights, thereby creating two pools of liquid metal, an upper pool and a lower pool, each with a different composition. The metal located in the upper pool solidifies first, creating a shell with the composition of the upper pool. The metal located in the lower pool then solidifies within the shell, forming the bulk of the material, with the composition of the lower pool, thereby creating a composite metal product.

[0006] When producing composite metal products by continuous casting, to obtain a product of excellent quality it is necessary to achieve very good stability of the two pools of liquid metal in the mould and of the flow of liquid metal coming from the nozzle, as well as very good homogeneity of the pool composition.

[0007] Japanese patent application JP11197807 uses a static magnetic field and injects different flows of liquid metal above and below the field to stabilize the two pools.

[0008] However, the solutions proposed in the prior art do not provide sufficient solutions with regard to the stability of the different liquid metal flows and the homogeneity of the liquid metal pool. Furthermore, the specific magnetic fields complicate the casting operation. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 11-197807 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention discloses a continuous casting nozzle for producing composite metal slabs with an improved design, allowing for better stability of the liquid metal flow and better homogeneity of the liquid metal pool with simple equipment. [Means for solving the problem]

[0011] A first object of the present invention is a continuous casting nozzle for producing composite metal slabs, said nozzle 1 being located between a tundish 2 and a mould 3, said nozzle 1 comprising: an upper part 4, which is arranged downstream of the tundish 2 with respect to the direction of movement of the liquid metal; a dome 6 arranged at the inlet of the upper part 4, said dome 6 comprising means for dividing the initial flow of liquid metal into at least two separate flows; an inner wall 8 located below the dome 6, which creates at least two mixing chambers 9a, 9b, the separate flows of liquid metal flowing in each of the chambers 9a, 9b, means 10 for injecting powder into at least one of said chambers 9a, 9b through the dome 6, to allow it to mix with the liquid metal flowing into said chambers 9a, 9b; a lower part 5 extending from the upper part 4 to the mold 3 and consisting of at least a central channel 12a and lateral channels 12b, 12c, said central channel 12a being connected to one of said chambers 9a, 9b, said central channel 12a being longer than said lateral channels 12b, 12c, said lateral channels 12b, 12c being connected to at least one other chamber 9b, said central channel 12a allowing the liquid metal to flow into the mold 3 by at least two lateral lower outlets 14 and said lateral channels 12b, 12c allowing the liquid metal to flow into the mold 3 by at least one lateral upper outlet 13 for each channel, Equipped with.

[0012] The continuous casting nozzle according to the invention may also have any of the features listed below, considered individually or in combination: the axis of the lower outlet 14 has an angle α with respect to the horizontal plane, the axis of the upper outlet 13 has an angle β with respect to the horizontal plane, the bottom of said lateral channels 12b, 12c at the level of the upper outlet 13 has a shape chosen from among flat, concave or inclined; the bottom of the central channel 12a between the two lower outlets 14 has a shape chosen from among a flat, a recess or a dome, the dome 6 further comprises means 11 for injecting gas through the dome 6, The dome further comprises a support arm 7 .

[0013] A second object of the invention is a method for continuous casting of composite metal slabs using a continuous casting nozzle 1 according to the invention, comprising: The liquid metal is poured into a tundish 2 located above the continuous casting nozzle 1, - the liquid metal flows from the tundish 2 to the upper part 4 of the casting nozzle 1 creating an initial flow, - said initial flow impinges onto the dome 6, thereby dividing it into a defined number of separate flows; - the separate streams flow into the mixing chambers 9a, 9b of the nozzle 1, - a powder is injected into one of said chambers 9a, 9b and mixed with the flow of liquid metal flowing into said chambers 9a, 9b, thereby modifying its composition; the separated streams are then distributed into the lower channels 12a, 12b, 12c of the continuous casting nozzle 1, The liquid metal is poured into the mold 3, with the liquid metal flowing in the side channels 12b, 12c being poured into the mold by an upper outlet 13 and the liquid metal flowing into the central channel 12a being poured deeper into the mold by a lower outlet 14, thereby forming two separate pools of liquid metal 15, 16 in the mold 3.

[0014] The continuous casting method according to the invention may also have any of the following features, considered individually or in combination: -The liquid metal is steel, - the powder is injected into a chamber connected to the central channel 9a, the liquid metal in the upper pool 15 of the mold 3 is composed of base metal coming only from the tundish 2, and the liquid metal in the lower pool 16 of the mold 3 is the base metal coming from the tundish 2, which is mixed with the powder injected below the dome 6; - the powder is poured into a chamber connected to the lateral channel 9b, The liquid metal in the upper pool 15 of the mold 3 is composed of base metal coming from the tundish 2 mixed with the powder injected below the dome 6, and the liquid metal in the lower pool 16 of the mold 3 is composed of base metal coming only from the tundish 2.

[0015] The invention will now be described in a non-limiting manner with reference to the following figures: [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a general view of a nozzle according to the present invention in a use configuration; [Figure 2] FIG. 1 is a bottom view of the lower portion of the nozzle. [Figure 3] FIG. 10 is a top view of a dome for a bulk alloying embodiment. [Figure 4] FIG. 10 is a top view of the dome for an embodiment of shell alloying. [Figure 5] 2 is a cross-sectional view AA of the upper part of the nozzle under the dome in FIG. 1. [Figure 6] 10A-10C show upper outlets with different embodiments for the shape of the bottom of the side channel: a) flat, b) concave, c) slanted. [Figure 7] 10A-10C show lower outlets with different embodiments for the shape of the bottom of the central channel: a) flat, b) concave, c) dome-shaped. [Figure 8] BB is a cross-sectional view of the mold and nozzle with a representation of the flow. [Figure 9] FIG. 1 shows the immersion portion of the nozzle with a representation of the flow in the mold. [Figure 10]1 is a cross-sectional view of a composite metal slab obtained by continuous casting. [Figure 11] FIG. 2 is a cross-sectional view of the mixing chamber of the nozzle of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0017] The object of the present invention is to cast a composite metal slab, the cross section of which is a rectangle with two sides and two minor edges, as shown in Figure 10.

[0018] 1 shows a nozzle 1 having two long sides and two narrow sides, arranged between a tundish 2 and a mold 3 adapted for casting slabs. The nozzle 1 consists of an upper part 4 and a lower part 5.

[0019] The dome 6 is positioned at the entrance to the upper part 4 and closes off a portion of it. The top of the dome 6 preferably has a slope of a certain angle, for example, higher than 15°. The dome 6 also preferably has sides that form sharp, sloped edges. The dome 6 is fixed to the upper part 4 by one or more support arms 7.

[0020] An inner wall 8 located below the dome 6 creates at least two mixing chambers 9a, 9b in the upper part 4. In the configuration presented in Figure 1, there are two chambers 9a, 9b.

[0021] Also included in the upper part 4 are means 10 for injecting powder and means 11 for injecting gas, each located partially on one of the support arms 7 and passing through the dome 6. The means 10 for injecting powder may for example be a worm screw linked to a powder reservoir.

[0022] FIG. 3 shows a configuration of a dome 6 having three support arms 7, one passage 10 for powder injection located in one of the support arms 7, and two passages 11 for gas injection located in the other two support arms 7.

[0023] Figure 4 shows another configuration of the dome 6 different from that shown in Figure 3, but with three support arms 7, and with two passages 10 for powder injection located in two of the support arms 7 and one passage 11 for gas injection located in the other support arm 7. In this configuration, the two passages 10 for powder injection can be linked to two different powder injectors, each one with a different type of powder.

[0024] The dome 6 can also have other configurations with fewer or more support arms. For example, a configuration with four support arms 7 is conceivable.

[0025] As shown in FIG. 1, the lower portion 5 of the nozzle 1 consists of three channels 12a, 12b, and 12c extending from the mixing chambers 9a and 9b of the upper portion 4 and terminating in the mold 3. FIG. 2 shows an enlarged view of the bottom of the lower portion 5 of the nozzle 1 in the configuration shown in FIG. 1. The side channels 12b and 12c open into the mold 3 by two upper outlets 13, one for each channel. The central channel 12a opens into the mold by two lower outlets 14. The axes of the lower outlets 14 form an angle α with the horizontal plane. The angle α is preferably between 15° and 40°. The axis of the upper outlet 13 forms an angle β with the horizontal plane. The angle β is preferably between -10° and 10°. The angle is downward.

[0026] In this embodiment, the channels 12a, 12b, 12c are circular. In a preferred embodiment, the channels 12a, 12b, 12c have a round or oval cross section.

[0027] Figure 5 shows a cross section AA of the nozzle 1 in the configuration described in Figure 1. Figures 3 and 4 are arranged in the same orientation as Figure 5. Figure 3 can be superimposed with Figure 5 to have a cross section of the nozzle 1 above the dome 6. The same can be applied to Figure 4 with Figure 5 to obtain a view of another configuration.

[0028] As shown in Figure 5, the inner wall 8 has a V-shape, thereby creating two mixing chambers 9a, 9b of different volumes. Chamber 9a, located inside the V-shape, is linked to a central channel 12a, and chamber 9b, located outside the V-shape, is linked to side channels 12b, 12c.

[0029] In other configurations, the interior wall 8 has a different shape, creating a different number of chambers, for example a Y-shape creating three chambers of different volumes, or a single wall can create two chambers with exactly the same volume.

[0030] As shown in Figure 1, the central channel 12a is longer than the two side channels 12b, 12c, thereby opening deeper into the mold 3. In this embodiment, the three channels are aligned, as shown in Figure 5.

[0031] Other configurations may be considered, for example adding a third side channel that is not aligned with the other channels 12a, 12b, 12c, thereby creating a different geometry.

[0032] Figure 6 shows different embodiments for the shape of the bottom of the side channels 12b, 12c at the level of the upper outlet 13. Figure 6a shows a flat shape, where the bottom of the side channels 12b, 12c is flat and at the same level as the bottom of the outlet 13. Figure 6b shows a concave shape, where the bottom of the side channels 12b, 12c is also flat but lower than the bottom of the outlet 13, thereby forming a recess. Figure 6c shows a sloped shape, where the bottom of the side channels 12b, 12c forms a slope that terminates at the bottom of the outlet 13. In other embodiments, other shapes can be used.

[0033] Figure 7 shows different embodiments for the shape of the bottom of central channel 12a at the level of lower outlet 14. Figure 7a shows a flat shape, where the bottom of central channel 12a is flat and at the same level as the bottom of outlet 14. Figure 7b shows a concave shape, where the bottom of central channel 12a is also flat but lower than the bottom of outlet 14, thereby forming a recess. Figure 7c shows a dome shape, where the bottom of central channel 12a forms a dome that terminates at the bottom of outlet 14. In other embodiments, other shapes can be used.

[0034] In a preferred embodiment, the ratio between the diameter of the outlets 13, 14 and the distance between the outlets 13 and the mould 3 is greater than 0.05 and less than 0.2.

[0035] In a preferred embodiment, the ratio between the diameter of the upper outlet 13 and the diameter of the side channels 12b, 12c is greater than 0.4 and less than 1.2. In this particular embodiment, the ratio between the diameter of the lower outlet 14 and the diameter of the central channel 12a is greater than 0.4 and less than 1.

[0036] The present invention has two preferred embodiments for its use, called bulk alloying and shell alloying, respectively. Only the differences between the two preferred embodiments will be described separately. The present invention in its configuration for use is shown in Figure 1.

[0037] Liquid metal of a defined composition is poured from a ladle into a tundish 2. In a preferred embodiment, the liquid metal is steel, and the use of the nozzle 1 will be described in connection with this. The steel flows to the top 4 of the continuous casting nozzle 1, thereby creating an initial flow. A stopper rod 23 allows for control of the initial flow rate.

[0038] Dome 6 is positioned within the steel's path and causes the initial flow to impinge upon it. The slope of dome 6 causes the steel to flow toward its edges. Support arms 7 create different areas on dome 6, dividing the steel into multiple separate streams. The number of separate streams is determined by the design of dome 6 and its support arms 7. In this particular embodiment, the number of separate streams is three.

[0039] The separated streams then flow into different mixing chambers 9a and 9b. Figure 11 shows a cross-sectional view of the mixing chamber. In this configuration, part of the stream flows into the chamber 9 inside the V-shape, and the other part flows into the chamber 9b outside the V-shape. The powder is injected simultaneously into one of the mixing chambers 9a and 9b. The chamber design with a large cross-section at the top allows the steel to flow down the dome like a waterfall, allowing the powder to be injected into the stream without contacting the powder injection means. Reducing the cross-section of the chamber allows the steel to slow down and accumulate in chambers 9a and 9b. Reducing the cross-section of the chamber allows the steel to be stirred inside the chamber. As a result, the powder can be efficiently mixed with the steel to change its composition and enter chambers 9a and 9b, where it can begin to melt. This step allows the liquid steel into which the powder is injected to become homogenous. The reduction in the cross-section of the chamber can be achieved by various wall configurations. For example, the reduction can be achieved by a regular slope, in steps, or by any means for reducing the cross-section.

[0040] The powders injected into the steel can be of various compositions, for example FeSi, Ni, FeAl, FeTi, FeCr, FeNb, FeB, FeCe, FeMo, etc.

[0041] The powder addition step differs between the two preferred embodiments: for the bulk alloying embodiment, the powder is injected into the V-shaped inner chamber 9a by at least one powder injector 10, Figure 3 shows only one injector, while for the shell alloying embodiment, the powder is injected into the V-shaped outer chamber 9b by at least one powder injector 10, Figure 4 shows two powder injectors.

[0042] In both embodiments, powder injection is facilitated by gas injection 11, which creates a gas flow that keeps the steel flowing under dome 6 towards the exterior of top 4, thus creating a zone below dome 6 that is free of steel. This hollow zone prevents contact between the steel and powder injection 10, thereby avoiding potential clogging of powder injection 10.

[0043] The gas is preferably non-oxidizing, for example Ar, to prevent any reaction with the steel being cast.

[0044] After pouring, the two mixing chambers 9a, 9b contain two steels with different compositions.

[0045] The steel then flows into the channels 12a, 12b, 12c in the lower part 5 of the nozzle 1, which are connected to the chambers after reducing their cross section, as shown in Figure 1 or 11. The steel in the chamber 9a located inside the V-shape flows into the central channel 12a, and the steel in the chamber 9b located outside the V-shape flows into the side channels 12b, 12c. The different steels are then poured into the mould 3 through the outlets 13, 14 of the channels 12a, 12b, 12c.

[0046] The steel from the central channel 12a is poured deeper into the mold 3 because the central channel 12a is longer than the side channels 12b, 12c. This configuration allows two types of steel to be poured into the mold 3 at different heights, thereby creating two pools of steel with different compositions: an upper pool 15 and a lower pool 16. The upper pool 15 is formed by the steel coming from the side channels 12b, 12c, and the lower pool 16 is formed by the steel coming from the central channel 12a.

[0047] The outlets 13, 14 of the nozzle 1 are immersed in different pools of steel during use: the upper outlets 13 of the side channels 12b, 12c are immersed in an upper pool 15 and the lower outlet 14 of the central channel 12a is immersed in a lower pool 16.

[0048] According to an embodiment, the composition of the pools is different.

[0049] For the bulk alloying embodiment, the composition of the upper pool 15 is the composition of the steel coming only from tundish 2. The composition of the lower pool 16 is a combination of the composition of the steel coming from tundish 2 and the composition of the poured powder.

[0050] For the shell alloying embodiment, the composition of the upper pool 15 is a combination of the composition of the steel coming from tundish 2 and the composition of the poured powder. The composition of the lower pool 16 is the composition of the steel coming from tundish 2 only.

[0051] In both embodiments, in mold 3, the steel in upper pool 15 consolidates first, thereby creating shell 17. The steel in lower pool 16 then consolidates inside shell 17, thereby creating bulk material 18. After full consolidation, the resulting material is a composite metal slab with different compositions in its shell and its bulk.

[0052] To cast a composite metal slab of sufficient quality, each pool must have a homogeneous composition and the boundaries between them must be stable. These factors are influenced by the different flow behavior of the liquid metal coming from the nozzle 1.

[0053] The design of the nozzle 1 with at least two upper lateral outlets 13 and at least two lower lateral outlets 14 makes it possible to direct the flow of mold towards and reach the narrow faces, as shown in Figure 8, thereby ensuring the homogeneity of the two pools (15, 16).

[0054] These flows, created by the nozzle design, ensure the stability of the interface between the two pools of liquid metal (15, 16).

[0055] 9, the flow from the upper outlet 13 creates a main upward flow 19 and a smaller downward secondary flow 20 in the upper pool 15 as it fills the narrow side of the mold 3. Conversely, the flow from the lower outlet 15 creates a main upward flow 21 and a smaller downward secondary flow 22 in the lower pool 16 as it fills the narrow side of the mold 3.

[0056] The design of the outlets can affect the initial direction and velocity of the flow, and therefore the stability and homogeneity of the interface between the two pools. Those skilled in the art will determine the characteristics of the outlets 13, 14 to optimize these parameters. Among these characteristics, the diameter of the outlet relative to the diameter of the channel, the diameter of the outlet axis relative to the distance between the outlet and the mold 3, and the angles α and β of the outlet axis relative to the horizontal plane can be considered.

[0057] In a preferred embodiment, the axis of the lower outlet 14 has an angle α of 15° to 40° with respect to the horizontal plane, and the axis of the upper outlet has an angle β of -10° to 10° with respect to the horizontal plane, making it possible to reach an optimum value for the stability of the two pools.

[0058] In a preferred embodiment, the ratio between the diameter of the outlets 13, 14 and the distance between the outlets 13 and the mould 3 is greater than 0.05 and less than 0.2.

[0059] For the bulk alloying embodiment, the preferred ratio between the diameter of the upper outlet 13 and the diameter of the side channels 12b, 12c is greater than 0.8 and less than 1.2. In this particular embodiment, the ratio between the diameter of the lower outlet 14 and the diameter of the central channel 12a is greater than 0.6 and less than 1.

[0060] For the shell alloying embodiment, the preferred ratio between the diameter of the upper outlet 13 and the diameter of the side channels 12b, 12c is greater than 0.4 and less than 0.8. In this particular embodiment, the ratio between the diameter of the lower outlet 14 and the diameter of the central channel 12a is greater than 0.4 and less than 0.8.

[0061] The different shapes of the channel at the outlet level also affect the stability of the boundary.

[0062] In a preferred embodiment, the bottom of the central channel 12a at the level of the lower outlet 14 has a dome shape to allow for optimal stability of the boundary. In another embodiment, the bottom of the central channel 12a at the level of the lower outlet 14 has a flat or concave shape.

[0063] For the bulk alloying embodiment, the preferred shape for the bottom of the side channels 12b, 12c at the level of the upper outlet 13 is a flat shape to allow optimal stability of the interface. In another embodiment, the bottom of the side channels 12b, 12c at the level of the upper outlet 13 has a concave or sloping shape.

[0064] For the shell alloying embodiment, the preferred shape for the bottom of the side channels 12b, 12c at the level of the upper outlet 13 is a flat or concave shape to allow optimal stability of the interface. In another embodiment, the bottom of the side channels 12b, 12c at the level of the upper outlet 13 has a sloping shape.

[0065] In a preferred embodiment, the nozzle 1 is constructed primarily from a refractory material surrounded by a metal ring.

[0066] In its operating configuration, the continuous casting nozzle 1 meets expectations in terms of stability and homogeneity. This allows for a stable casting speed, and the differential flow of the liquid metal allows for great stability and homogeneity of the two pools in the mold 3. This stability results in a high-quality semi-finished product with a clear compositional gradient between its shell and its bulk.

Claims

1. A continuous casting nozzle (1) for producing composite metal slabs, located between a tundish (2) and a mold (3), an upper part (4) located downstream of the tundish (2) relative to the direction of movement of the liquid metal; a dome (6) placed at the inlet of the top (4), the dome (6) comprising means for dividing the initial flow of liquid metal into at least two separate flows; an inner wall (8) located below the dome (6) creating at least two mixing chambers (9a, 9b), said separate flows of liquid metal flowing respectively in each of said chambers (9a, 9b); - means (10) for injecting powder into at least one of said chambers (9a, 9b) through the dome (6), to allow it to mix with the liquid metal flowing into said chambers (9a, 9b); a lower part (5) extending from the upper part (4) to the mold (3) and consisting of at least a central channel (12a) and lateral channels (12b, 12c), said central channel (12a) being connected to one of said chambers (9a, 9b), said central channel (12a) being longer than said lateral channels (12b, 12c), said lateral channels (12b, 12c) being connected to at least one other chamber (9b), said central channel (12a) allowing the liquid metal to flow into the mold (3) by means of at least two lateral lower outlets (14) and said lateral channels (12b, 12c) allowing the liquid metal to flow into the mold (3) by means of at least one lateral upper outlet (13) for each channel; A continuous casting nozzle (1) comprising:

2. 2. The continuous casting nozzle (1) according to claim 1, wherein the axis of the lower outlet (14) is at an angle α with respect to the horizontal.

3. 3. A continuous casting nozzle (1) according to claim 1 or 2, wherein the axis of the upper outlet (13) has an angle β with respect to the horizontal.

4. 4. The continuous casting nozzle (1) according to claim 1, wherein the bottom of the side channels (12b, 12c) at the level of the upper outlet (13) has a shape selected from the group consisting of a flat surface, a recess, or an incline.

5. 5. The continuous casting nozzle (1) according to any one of claims 1 to 4, wherein the bottom of the central channel (12a) between the two lower outlets (14) has a shape selected from the group consisting of a flat surface, a recess, or a dome.

6. 6. A continuous casting nozzle (1) according to any one of claims 1 to 5, wherein the dome (6) further comprises means (11) for injecting gas through the dome (6).

7. 5. A continuous casting nozzle (1) according to any one of claims 1 to 4, wherein the dome further comprises a support arm (7).

8. 8. A method for continuous casting of composite metal slabs using a continuous casting nozzle (1) according to any one of claims 1 to 7, comprising: - liquid metal is poured into a tundish (2) located above the continuous casting nozzle (1); - the liquid metal flows from the tundish (2) to the top (4) of the casting nozzle (1) creating an initial flow; - said initial flow impinges onto a dome (6) thereby dividing it into a defined number of separate flows; - the separate streams flow into the mixing chamber (9a, 9b) of the nozzle (1), - a powder is injected into one of said chambers (9a, 9b) and mixed with the flow of liquid metal flowing into said chambers (9a, 9b), thereby modifying its composition; - the separated streams are then distributed into the lower channels (12a, 12b, 12c) of the continuous casting nozzle (1), - the liquid metal is poured into the mold (3), the liquid metal flowing in the side channels (12b, 12c) is poured into the mold by an upper outlet (13) and the liquid metal flowing into the central channel (12a) is poured deeper into the mold by a lower outlet (14), thereby forming two separate pools of liquid metal (15, 16) in the mold (3).

9. The method of claim 8 wherein the liquid metal is steel.

10. 10. The method according to claim 8 or 9, wherein the powder is injected into a chamber connected to the central channel (9a).

11. 11. The method according to claim 10, wherein the liquid metal in the upper pool (15) of the mold (3) is made up of base metal coming only from the tundish (2), and the liquid metal in the lower pool (16) of the mold (3) is made up of base metal coming from the tundish (2) mixed with the powder injected below the dome (6).

12. 10. The method according to claim 8 or 9, wherein the powder is injected into a chamber connected to a side channel (9b).

13. 13. The method according to claim 12, wherein the liquid metal in the upper pool (15) of the mold (3) is made up of base metal coming from the tundish (2) mixed with the powder injected below the dome (6), and the liquid metal in the lower pool (16) of the mold (3) is made up of base metal coming only from the tundish (2).

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