Method for casting steel and distributor therefor

Abstract

The invention relates to a method for the continuous casting of metal, in particular steel, wherein liquid metal from a movably mounted ladle is guided by a shadow tube into a continuous casting distributor and is guided from the continuous casting distributor via an outlet into a casting mould, wherein the continuous casting distributor compensates for the interruptions when the ladles are changed, and wherein the ladles are stored in a movement device, characterised in that melts that are different with respect to their alloy composition and origin are cast in succession into the distributor, wherein the different melts cast in succession are LD melts on the one hand and EAF melts on the other hand.

Description

[0001] International patent application

[0002] Voestalpine Stahl GmbH

[0003] 24092 IWO

[0004] Method for casting steel and distributors for this purpose

[0005] The invention relates to a method for casting steel.

[0006] Continuous steel casting is a well-known process for the continuous casting of steel slabs.

[0007] For this purpose, steel is usually produced in a converter, transferred from the steel converter to a ladle and from the ladle via a distributor to the casting mold.

[0008] The distributor's function is to ensure a continuous flow of steel after one pan has emptied and the next pan has been fed in.

[0009] Basically, it must be ensured that there are no inclusions in the liquid steel, in particular neither slag particles nor components of the respective refractory lining or injection molding of the vessels nor reaction products from metallurgical treatment steps.

[0010] This is achieved in particular by the arrangement of appropriate components in a distribution trough, which generates a specific upward flow after the steel has been poured in, such that the steel is washed to the surface, allowing particles that are lighter than the steel to enter the slag or be bound by the slag.

[0011] A continuous casting plant is known from DE 33 37 739 A1. This continuous casting plant has a device for holding and changing ladles (ladle turntable), ladles, and a distribution trough, as well as a continuous casting mold and a strand discharge device. A distribution trough is associated with the ladle, which is filled with molten metal and in the preparation position for transport to the casting position. Preferably, in this embodiment, the distribution trough is inserted into the support arm on the ladle turntable below the ladle. The distribution trough and / or ladle are provided with means for detachable connection to one another. International patent application

[0012] Voestalpine Stahl GmbH 24092 IWO

[0013] From EP 0 119 853 A2 a distributor trough for continuous casting is known, wherein the distributor trough has a channeled induction heating device arranged on the side wall of the distributor trough, the device comprising a channel that communicates with an opening in the side walls of the distributor trough.

[0014] From EP 0 140 217 Al a method and a device for changing the casting ladle and intermediate container on a continuous casting plant are known.

[0015] From EP 0 726 115 A1, a casting trough for receiving and filtering molten ferrous metals is known, which has a discharge opening in the bottom area for drawing off the molten metal after it has passed through a deflecting and / or filtering device. A ceramic filter, which covers substantially the entire horizontal cross-section of the casting trough and is removable in a known manner, is arranged in the trough. This filter extends substantially horizontally and is provided with openings arranged in the substantially vertical flow direction of the molten metal through the trough. This is intended to enable the cleaning and filtering of molten metals, even at high casting speeds, with a simple design.

[0016] From EP 0 804 306 Bl, a device for regulating the flow of molten metal in a distribution trough to improve the separation of inclusions from the metal bath is known. For this purpose, a flow control dam is positioned downstream of a shock buffer. This dam has an upper section designed to receive a flow of molten steel that detaches from the shock buffer and to divert it into at least one secondary flow flowing downstream towards the slag cover and at least one secondary flow flowing upstream towards the slag cover. Ultimately, this is an integrated dam intended to prevent short-circuit flow.

[0017] US Patent 6,074,600 discloses a modification of a distribution channel dam for minimizing turbulence. In particular, this is intended to reduce the formation of gas bubbles and slag inclusions. This is especially advantageous during the initial filling of the distribution channel. For this purpose, a type of weir is used between the steel inlet of the distribution channel (see International Patent Application).

[0018] Voestalpine Stahl GmbH

[0019] 24092 IWO and the steel outlet of the distribution channel, which extends from the pool surface to the bottom, but is spaced away from the bottom. On the other hand, a ramp is arranged between the weir and the steel outlet, while a second ramp is arranged in front of the weir.

[0020] From DE 10 2009 009 740 Al, it is known to arrange vortex stones in the area of ​​the bottom outlets of vessels containing molten steel in such a way that their knife edges extend into the vortex in order to prevent turbulence. The vortex stones consist of a circular segment-shaped flat fixing part and a braking part with the knife edge, whereby this one-piece component can be placed on the bottom outlet or, preferably, on a perforated stone and connected to it, because the inner diameter corresponds to that of the bottom outlet.

[0021] From EP 3 496 882 Bl a baffle plate for placement in a distributor to reduce the effects of a misalignment of an incoming stream of molten steel entering the distributor is disclosed.

[0022] Furthermore, it is known to equip distribution channels with a bottom depression from the steel inlet to the steel outlet, whereby a ridge or raised section is placed on this sloping bottom, which is sometimes also stepped, such that the steel inlet area forms a kind of basin. After the basin is filled, the water flows over the ridge and then fills the entire distribution channel. This ridge also serves to ensure turbulent flow and to slightly extend the residence time of the steel in the distributor, and in particular to achieve contact with the slag layer.

[0023] From CN 103 25 465 Bl a so-called turbulent flow controller for asymmetric use in the distributor is known, in which the shadow tube is arranged above this installation, whereby this installation is arranged in a saucer-like shape with a slightly raised bottom on one side next to other waves in the distributor.

[0024] A comparable installation is known from CN 102 000 791 A, which is arranged below the shadow tube and is located next to two ridges in the base of the distributor. However, in this case, the base of this installation, which has a cuboid shape, is wavy. (International patent application)

[0025] Voestalpine Stahl GmbH

[0026] 24092 IWO formed, wherein the steel from the shadow tube is poured into this structure and then exits from this structure above.

[0027] From KR 2003 00 52 756 A, an installation is known which is arranged in a trough shape with its own vertical walls within the distributor, wherein the shadow pipe opens into a spring-like projection and from there the steel initially fills this trough-like structure before flowing into the rest of the distributor. The basic shape of the installation is approximately T-shaped, with the steel flowing into the rest of the T-shaped sub-distributor through a reduced opening.

[0028] A comparable installation is known from EP 0 804 306 Bl, in which the steel is first poured into a trough located at ground level, then exits laterally and meets conventional wall installations.

[0029] A similar trough-like installation is also known from CN 217 121 721 U, in which, however, the trough is more elongated-oval in shape, but also with a wave-shaped bottom structure, so that the steel is first poured into this trough and then flows out of it into the rest of the distributor.

[0030] From “Numerical and Physical Study on New Simple Design of Subflux Flow Controller for One-Strand Tundish”, Cwudzihski, Adam; Materials 2022, 15, 3756 ff., the influence on the flow using an asymmetric shadow roh res has been investigated, simulating various arrangements.

[0031] From “Physical and mathematical modeling of inclusion behaviour in a tundish with gas curtain”; Metallurgy and Materials 2020, 73(4), 531 - 538, the influence of gas curtains in the inlet area was investigated, whereby the inlet area was additionally designed with walls hanging from above and walls rising from below.

[0032] It was found that all these measures either calm the flow of the liquid melt, but then lead to a shorter residence time, or make it so turbulent that the particle loading is high. International patent application

[0033] Voestalpine Stahl GmbH

[0034] 24092 IWO

[0035] From WO 2025 / 109 084 Al a distributor with a movably mounted pan is known, in which a singular roller-like flow is generated in the continuous casting distributor from a shadow pipe to a casting pipe in order to shorten the mixing area.

[0036] From DE 32 46 224 Al a process for fully continuous continuous casting is known, in which, when transitioning to a subsequent melt with a higher alloy content, the remaining amount of the melt in the intermediate vessel is supplemented with the alloy components that are missing from it compared to the subsequent melt.

[0037] It was found that all these measures to increase separation efficiency and reduce the mixing range cause additional effort and complicate distribution management. The object of the invention is to create a method for casting steel that simplifies distribution management, increases separation efficiency between the batches to be cast, and reduces the mixing range.

[0038] The problem is solved by a method having the features of claim 1.

[0039] Advantageous further training courses are marked in the sub-requirements.

[0040] The invention is based on a number of insights.

[0041] In continuous casting, different batches of steel are cast continuously. After passing through the converter, each batch of steel is poured into a ladle and undergoes secondary metallurgical treatment.

[0042] To ensure a virtually uninterrupted continuous casting process, the contents of the ladle are poured into a distributor, which, however, still contains steel from the previous ladle. This is unavoidable, as otherwise the casting strand would break. The steel from the previous ladle is also referred to as pre-melt, and the steel subsequently poured into the distributor is called post-melt. International patent application

[0043] Voestalpine Stahl GmbH

[0044] 24092 IWO

[0045] Using multiple distributors would be extremely expensive. Therefore, the goal is to feed different steel grades through a single distributor one after the other.

[0046] According to the invention, the method is also intended to allow different grades of steel from different origins to be cast together using a distributor.

[0047] In particular, the invention is intended for casting steel grades produced using different methods, namely batches from the electric arc furnace (EAF) and batches from the conventional blast furnace (LD) route. These batches also exhibit, among other things, different CO₂ fingerprints, which should be readily traceable within the context of a material's CO₂ balance. However, the invention is also applicable to other steel grades, as it specifically takes into account the metallurgy of the melts.

[0048] Distribution planning (distribution management) is established well in advance. Therefore, a single distributor change for EAF or LD batches is hardly feasible.

[0049] Generally, when different steel grades are used in the subsequent casting strand and thus also in the slab, mixed areas will occur. With small differences in steel grade, this may be tolerable; otherwise, the mixed area is cut out and scrapped. A metallurgical analysis of the mixed area can also be used as a tracer for the CO2 balance.

[0050] To quantify the deviation of the respective melts from one another, the melt difference index (MDI) can be used. The MDI is calculated from the absolute deviations of individual elements between the melts (|AEj|), weighted by an element-specific weighting factor (k). The weighted deviation of an element (|AE;| * k) is calculated as the product of the absolute deviation (|AE;| ) and the weighting factor (k).

[0051] In a preferred embodiment, the melt difference index (SDKZ) can be derived from the weighted deviations (|AEj|* k) in descending order, with the resulting series being referred to as the ranking (rank). The ranking (rank) preferably includes International Patent Application

[0052] Voestalpine Stahl GmbH 24092 IWO all weighted deviations ( | A Ei | * k). A distinction must be made between the numerator for the elements (i) and the numerator for the ranking (0).

[0053] To determine the melt variation index (MSI), a defined number (x) of the largest weighted deviations can be included. For example, all elements can be included, or the selection can be limited to the three or five largest weighted deviations. The number (x) is chosen based on the process requirements. Advantageously, when all elements are included, the total MSI can be determined. In an alternative embodiment, when selecting the three or five largest deviations, the focus can be advantageously placed on the deviations of the most significant influencing factors, while other, comparatively minor (less effective) deviations are filtered out.This means that a melt which has very small deviations in numerous elements can be advantageously classified as less critical than a melt which only has deviations in three elements, but has comparatively large deviations in these three.

[0054] The largest weighted deviations (rank, ... , rank x The values ​​listed first in the ranking (rank) are shown below. The melting difference index (SDKZ) is calculated as follows.

[0055] The more different the alloy compositions of the pre- and post-melt processes are, i.e., the larger the melt difference index (SDKZ), the more pronounced the mixing range.

[0056] The invention takes into account the varying differences of successively cast melts by adapting the charging of the melts in the distributor to the melt difference index (SDKZ). The inventors have set themselves the task of minimizing the mixing range in continuous casting with different steel grades. (International patent application)

[0057] Voestalpine Stahl GmbH

[0058] 24092 IWO to maintain the required separation efficiency. This results in a reduced number of manifolds required, as it becomes possible to cast different steel grades with one and the same manifold.

[0059] An optimized manifold management system for continuous casting with different steel batches, minimizing the need for manifold changes, results in cost reductions, as fewer of the very expensive manifolds are required, as well as a reduction in the workload during the continuous casting process.

[0060] Continuous analyses are performed at the distributor to indicate the beginning and end of the mixing zone. These analyses specifically show when the first batch (pre-melt) is still present at the outlet of the continuous casting distributor, when thorough mixing has occurred, and when the second batch (post-melt) is present. This data can be used to control the slab cutting process, reliably removing the mixing zone from the casting strand.

[0061] This is expected to become even more important in the future, as conventional steel production in converters, involving the refining of a mixture of scrap and pig iron and the transfer of this crude steel into a ladle (LD steel), could be replaced by electric arc furnaces and upstream direct reduction (EAF steel). This will lead to frequent switching between LD and EAF batches in the continuous casting process.

[0062] However, it is also important to note that the successively cast melts must not differ too much in terms of their alloy composition, as otherwise various difficulties, such as hot cracks, poor butt joints, different liquidus temperatures, etc., may occur.

[0063] Critical elements, where problems can arise if there are significant differences between melts, include carbon, aluminum, niobium, vanadium, zirconium, boron, and nitrogen. Silicon, manganese, copper, titanium, chromium, nickel, and molybdenum, on the other hand, are comparatively uncritical. International patent application Voestalpine Stahl GmbH 24092 IWO

[0064] The invention thus relates in particular to a method for the continuous casting of metal, especially steel, wherein liquid metal from a ladle, which is movably mounted, is guided by a shadow pipe into a continuous casting manifold and from the continuous casting manifold is guided via an outlet into a casting mold, wherein the continuous casting manifold compensates for the interruptions when the ladles are changed, and wherein the ladles are mounted in a moving device, wherein different melts with respect to their alloy composition and origin are cast successively into the manifold, wherein the successively cast, different melts are LD melts on the one hand and EAF melts on the other, wherein deviations in the melts (AEj) are quantified with a melt difference index (SDKZ).where the melt difference index (SDKZ) is formed from the absolute deviations of individual elements between the melts | Ej | , which is weighted with an empirically determined element-specific weighting factor (k ), where the weighted deviation of an element (|AEj|* k) is formed from the product of the absolute deviation (|AEi|) and the weighting factor k ..

[0065] International patent application Voestalpine Stahl GmbH 24092 IWO

[0066] One embodiment provides that the absolute deviations of the respective alloying elements |AE ZU i,i|, preferred |AE Bev ,i|, especially preferred |AE BBe v,i| of the different melts may have a maximum of the following values: International patent application Voestalpine Stahl GmbH 24092 IWO

[0067] One embodiment provides that the empirically determined element-specific weighting factors (kj) have the following values: International patent application Voestalpine Stahl GmbH 240921 WO

[0068] One embodiment provides that the weighted deviations |AEj|* k are ordered in descending order, the resulting series being called the ranking or rank, the ranking or rank comprising all weighted deviations |AEi|* k, the following relationship between the numerator for the elements (i) and the numerator for the ranking (j) holds:

[0069] One embodiment provides that the melt difference index (SDKZ) is formed from the largest weighted deviations, where x defines a defined number of the largest weighted deviations, wherein: International patent application

[0070] Voestalpine Stahl GmbH

[0071] 24092 IWO

[0072] One embodiment provides that x >= 1, preferably x >= 3, particularly preferably x >= 7, especially x = 14.

[0073] One embodiment provides that the melt difference index (SDKZ) is divided into three categories, namely permissible SDKZzui, preferably SDKZ Bev , and especially preferred SDKZBBEV, wherein the values ​​of the three categories are derived from the product of constant melt difference index changes (SDKZ'), permissible SDKZ'zui, preferred SDKZ' Bev , especially preferred SDKZ'ßßev, and the number of largest weighted deviations (x) forms, where:

[0074] SDKZ Zut = SDKZ Zul ■ x

[0075] SDKZ Bev = SDKZ Bev ■ x

[0076] SDKZ BBev = SDKZ BBev ■ x One embodiment provides that the constant melt difference index changes (SDKZ'), permissible SDKZ'zui, preferably SDKZ' Bev, especially preferred SDKZ' BBe v exhibit the following values: International patent application

[0077] Voestalpine Stahl GmbH

[0078] 24092 IWO

[0079] One embodiment provides that the sequential filling of the distributor with the two different melts is adapted to the melt difference index (SDKZ), wherein, for a melt difference index (SDKZ), the limit values ​​for the particularly preferred melt difference index (SDKZ) BBev ) and for the preferred melt difference index (SDKZ) Be v) an adjustment is made in the distributor such that the ratio of remelt to premelt in the distributor is greater than 1.5 to 1, and wherein a melt difference index (SDKZ) is used between the limit values ​​for the preferred melt difference index (SDKZ). Bev) and permissible melt difference index (SDKZzui) an adjustment is made in the distributor so that the ratio of post-melt to pre-melt in the distributor is more than 2 to 1.

[0080] With these defined limit values ​​for the melt difference index (SDKZzui, SDKZ) Bev , SDKZ BBe A distinction can be made between permissible, preferred, and particularly preferred ranges. Instructions for action are defined for each range. The limit values ​​for the melt differential index (SDKZ) ZU i, SDKZ Bev , SDKZ BBe ) can result from the product of constant melt difference index changes (SDKZ') ZU i, SDKZ' Bev , SDKZ' BBev ) and the number (x) of largest weighted deviations.

[0081] SDKZ Zui — SDKZ Zul ■ x SDKZ Bev = SDKZ Bev ■ x iDKZ BBev = SDKZ BBev ■ x

[0082] Is the melt difference index (SDKZ) greater than the limit value for the particularly preferred melt difference index (SDKZ) BBev ) and less than or equal to the limit value for the preferred melt difference index (SDKZ) Bev ), a distributor adjustment can advantageously be made such that the ratio of remelt to premelt is more than 1.5:1 in the distributor, this can advantageously reduce the mixing area.

[0083] SDKZ BBev < SDKZ < SDKZ Bev -> Distributor adjustment 1.5:1

[0084] Is the melt difference index (SDKZ) greater than the limit value for the preferred melt difference index (SDKZ) Bev ) and less than or equal to the limit for the permissible International Patent Application Voestalpine Stahl GmbH 24092 IWO

[0085] Melt difference index (SDKZzui), a distributor adjustment can advantageously be made such that the ratio of remelt to premelt is more than 2:1 in the distributor, this can advantageously reduce the mixing area even further.

[0086] SDKZ Bev < SDKZ < SDKZ Zui -> Distributor adjustment 2: 1

[0087] If the melt difference index (SDKZ) is greater than the permissible melt difference index (SDKZzui) and / or individual elements differ too much in their absolute deviations, the differences between the various melts may be deemed too large, and the melts may be classified as unsuitable, i.e., not permissible, for the process.

[0088] SDKZ Zui < SDKZ -> Not permitted

[0089] One embodiment provides that when determining a value of a) absolute deviations of individual elements between the melts |AEi| from one or more elements above the permissible limit |AE ZU I,II and / or b) an SDKZ above the limit permissible SDKZzui, a sequential filling of the distributor with the two different melts is not carried out.

[0090] The invention is explained by way of example with the aid of a drawing. The drawing shows:

[0091] Figure 1: Highly schematic representation of a continuous casting plant; International patent application

[0092] Voestalpine Stahl GmbH

[0093] 24092 IWO

[0094] Figure 2: a table showing the maximum analysis difference of successive

[0095] Batches;

[0096] Figure 3: a table showing the element-specific factor ( ) of the individual element contents for determining the melting difference index (SDKZ);

[0097] Figure 4: a table showing pre- and post-melting, which is due to the excessively high

[0098] Deviations cannot be mixed;

[0099] Figure 5: a table showing pre- and post-melts whose melt difference index was determined with 14 largest weighted deviations (x=14) and the determined melt difference index corresponds to a particularly preferred range;

[0100] Figure 6: a table showing pre- and post-melts, whose melt difference index was determined with 8 largest weighted deviations (x=8) and the determined melt difference index corresponds to a preferred range;

[0101] Figure 7: a table showing pre- and post-melting, whose melt difference index was determined with 5 largest weighted deviations (x=5) and the determined melt difference index corresponds to a permissible range;

[0102] Figure 8: a table showing the individual melt difference index changes for calculating the limit values ​​of permissible, preferred and particularly preferred melt difference indexes;

[0103] Figure 9: a diagram showing the progression of limit values ​​of permissible, preferred and particularly preferred melt difference indices as a function of the number of largest weighted deviations considered, and in which the determined melt difference indices of the examples according to Figures 6, 7 and 8 are plotted; International patent application

[0104] Voestalpine Stahl GmbH 24092 IWO

[0105] Figure 10: highly schematic representation of two batches in a distributor, where the feed of the second batch depends on the degree of runoff of the first batch and the ratio of the two batches to each other (post-melt to pre-melt) is greater than 1.5 to 1 with a melt difference index of 0.2 to 0.5;

[0106] Figure 11: highly schematic representation of two batches in a distributor, where the feed of the second batch depends on the degree of runoff of the first batch and the ratio of the two batches to each other (remelting to premelting) is greater than 2 to 1 with a melt difference index of 0.5 to 1.4;

[0107] Figure 12: highly schematic representation of a continuous casting plant showing the casting strand with pre-melting, mixing zone and post-melting.

[0108] Figure 1 shows a highly schematic representation of a continuous casting plant 1. This plant has a first metallurgical vessel 2, for example a ladle 2, containing liquid metal. Below this is a continuous casting distributor 3, which is loaded with liquid metal via a shadow pipe 4 attached to the ladle 2. The shadow pipe 4 can have one or more outlet openings. The distributor 3 is an elongated, preferably trough-shaped container with two opposing end walls 5, 6 and two side walls connecting the end walls 5, 6.

[0109] Furthermore, the continuous casting manifold 3 has a base 7, with an inlet area 8 and an outlet area 9 provided along a central axis of the manifold 3. The inlet area 8 is located adjacent to an inlet-side end wall 5, while the outlet area 9 is located adjacent to an outlet-side end wall 6, so that, in principle, the incoming steel flows through the vessel following the longitudinal extent of the continuous casting manifold 3. However, the continuous casting manifold 3 can also be shaped differently, for example, V-shaped or with multiple fingers or multiple outlets.

[0110] The base 7 of the continuous casting manifold 3 can slope downwards from an inlet area 8 to an outlet area 9, where "sloping downwards" means that the depth is greater than a bath level 10. International patent application

[0111] Voestalpine Stahl GmbH

[0112] 24092 IWO

[0113] In the discharge area 9, a discharge outlet 11 with a casting pipe 12 is arranged in the base 7. The casting pipe 12 opens into a mold 13, in which the metal is cooled until it solidifies. The strand 14 emerges from the bottom of the mold 13, is deflected by means of refractory rollers 15, and enters a straightening zone 16. After the straightening zone 16, the strand 14 is cut into slabs 18 by means of flame cutters 17.

[0114] In the continuous casting of metal, especially steel, in such a continuous casting plant 1, liquid metal is drawn from the ladle 2, which is movably mounted, and conveyed via the shadow pipe 4 into the continuous casting manifold 3, and from the continuous casting manifold 3 via the outlet 11 into the casting mold 13. The continuous casting manifold 3 compensates for interruptions when the ladles 2, which are mounted in a moving mechanism, are changed.

[0115] According to the invention, in such a continuous casting plant 1, different grades of steel with respect to their alloy composition and origin are to be cast successively in the same distributor 3. The deviation of the respective melts from one another can be quantified by the melt difference index SDKZ, and the sequential filling of the distributor 3 with the two batches is adapted to the melt difference index.

[0116] When two different steel grades, for example from different origins such as LD and EAF batches, are cast successively in a manifold, certain maximum permissible differences in analysis with respect to the individual alloying elements must be observed. These are shown in tabular form in Figure 2.

[0117] To calculate the melt difference index (SDKZ), the deviations of the individual alloying elements between the pre- and post-melt (AEi) are multiplied by an empirically determined, element-specific factor (k), ordered in descending order to a ranking (rank), and the defined number (x) of the first (=largest) weighted deviations is summed:

[0118] Rangj = |A£) | ■ k t where rankj > rankj +1 International patent application

[0119] Voestalpine Stahl GmbH

[0120] 24092 IWO

[0121] Figure 3 shows the corresponding empirically determined factors for the individual alloying elements in tabular form. Based on the factors, which weight the deviations of the individual alloying elements, it becomes clear that the elements carbon, aluminum, niobium, vanadium, zirconium, boron, and nitrogen are particularly critical for determining the melting point differential, as their factors are comparatively high. In contrast, the elements silicon, manganese, copper, titanium, chromium, nickel, and molybdenum are comparatively less critical, as their respective factors are relatively low.

[0122] To illustrate the calculation of the melt difference index, it was calculated as an example for an LD premelt and an EAF postmelt (Figures 4, 5, 6, and 7). Naturally, these values ​​would also apply if the EAF melt had been the premelt and the LD melt the postmelt. The deviations in the alloy composition with respect to the individual alloying elements, as well as the element-specific factors from Figure 3, are incorporated.

[0123] Figure 4 shows a pre- and post-melt in which the absolute deviation of the aluminum content exceeds the maximum permissible value of 0.150 wt.%, which is 0.240 wt.%. These melts cannot be cast consecutively. Calculating the melt difference index is not necessary.

[0124] Figure 5 shows a pre- and post-melt cycle in which all elemental contents comply with the permissible absolute deviations. To calculate the melt difference index, the absolute deviations of the elemental contents were multiplied by the weighting factor (Figure 3) and ranked. In this example, 14 deviations, i.e., x = 14 of the elemental contents, were considered. The melt difference index of 0.189 corresponds to a particularly favorable range (Figure 9) as it is significantly below the SDKZBBEV limit of 0.70.

[0125] Figure 6 shows a pre- and post-melt where all elemental contents comply with the respective permissible absolute deviations. The calculation of the absolute weighted deviations is performed in the same way as for the example in Figure 5. In this example, 8 deviations (x=8) of the elemental contents were considered. The melt difference index of 0.430 corresponds to a preferred range (Figure 9) since the SDKZBBEV has a limit value of International Patent Application

[0126] Voestalpine Stahl GmbH

[0127] 24092 IWO

[0128] 0.40 is specified and this is exceeded, but the SDKZBEV value is below 0.56.

[0129] Figure 7 shows a pre- and post-melt cycle in which all elemental contents comply with their respective permissible absolute deviations. The calculation of the absolute weighted deviations is performed in the same way as for the example in Figure 5. In this example, 5 deviations (x=5) of the elemental contents were considered. The melt difference index of 0.416 corresponds to a permissible range (Figure 9), since the values ​​of SDKZBBEV (0.25) and SDKZBEV (0.35) are each exceeded, but the value of SDKZZUL (0.50) is not exceeded.

[0130] In general, the melt difference index (SDKZ) depends on the number of the largest weighted deviations (x). Limit values ​​for the melt difference index (SDKZzui, SDKZßev, SDKZßße) distinguish between permissible, preferred, and particularly preferred ranges (Figure 9). To calculate these limit values, constant changes in the melt difference index are multiplied by the number of the largest weighted deviations. Figure 8 shows the constant changes in the melt difference index for the individual ranges.

[0131] If the batches to be cast successively are very similar in composition (SDKZ < SDKZv), no specific adjustment in the manifold is necessary, and the batches can simply be cast one after the other in the same manifold without adverse effects such as hot cracking, poor butt joints, or different liquidus temperatures being expected in the resulting slab. The melt difference index (SDKZ) is in the particularly preferred range (Figure 9).

[0132] However, if the melt difference index lies between the limit values ​​for the particularly preferred melt difference index SDKZßßev and the permissible melt difference index SDKZzui, additional measures must be taken to avoid any problems arising from the differences between steel batches and to circumvent the need for a distributor change. Advantageously, a specific ratio of remelt to premelt should be set according to the melt difference index (Figure 9). This can be achieved, for example, by temporarily closing the casting pipe 12 with a plug 19 (Figures 10 and 11). International patent application Voestalpine Stahl GmbH 24092 IWO

[0133] In the case of a melt difference index between the limit values ​​for the particularly preferred melt difference index SDKZ BBev and the limit values ​​for the preferred melt difference index SDKZ BeAn adjustment is made in distributor 3 so that the ratio of remelt to premelt in distributor 3 is set to more than 1.5:1 (Figure 10). The melt difference index (SDKZ) is within the preferred range (Figure 9).

[0134] In the case of a melt difference index between the limit values ​​for the preferred melt difference index SDKZ Bev Based on the limit values ​​for the permissible melt difference index SDKZzui, an adjustment is made in distributor 3 so that a ratio of remelt to premelt of more than 2:1 is set in distributor 3 (Figure 11). The melt difference index (SDKZ) is within the permissible range (Figure 9).

[0135] Figure 12 schematically illustrates the use of one and the same distributor 3 for different batches, for example LD and EAF melts, in a continuous casting plant 1, which forms a casting strand 14 with a mixing zone.

[0136] The measures according to the invention allow different steel batches with high separation efficiency and reduced mixing range to be cast in one and the same manifold. This simplifies manifold management and contributes to reducing the overall process costs, as fewer of the very expensive manifolds are required.

[0137] International patent application Voestalpine Stahl GmbH 24092 IWO

[0138] Reference symbol list

[0139] 1 continuous casting plant

[0140] 2 metallurgical vessel / pan

[0141] 3 continuous cast manifolds

[0142] 4 shadow tube

[0143] 5 End wall

[0144] 6 Front wall

[0145] 7 Distributor base

[0146] 8 Inlet area

[0147] 9 Outlet area

[0148] 10 bathroom mirrors

[0149] 11 Exit

[0150] 12 Watering pipe

[0151] 13 molds

[0152] 14 strand

[0153] 15 fireproof rollers

[0154] 16 Guideline zone

[0155] 17 oxyfuel cutters

[0156] 18 slabs

[0157] 19 plugs

Claims

International patent application Voestalpine Stahl GmbH 24092 IWO Patent claims 1. A method for the continuous casting of steel, wherein liquid metal is conveyed from a ladle, which is movably mounted, by means of a shadow pipe into a continuous casting manifold and from the continuous casting manifold via an outlet into a casting mold, wherein the continuous casting manifold compensates for interruptions when the ladles are changed, and wherein the ladles are mounted in a moving device, characterized in that different melts with respect to their alloy composition and origin are successively poured into the manifold, wherein the successively poured, different melts are LD melts on the one hand and EAF melts on the other, wherein deviations in the melts (AEj) are quantified with a melt difference index (SDKZ), wherein the melt difference index (SDKZ) is derived from the absolute deviations of individual elements between the melts |AEi|,which is weighted with an empirically determined element-specific weighting factor (k), wherein the weighted deviation of an element ( | AEj | * k) is formed from the product of the absolute deviation ( | AEj | ) and the weighting factor k. International patent application Voestalpine Stahl GmbH 24092 IWO 2. Method according to claim 1, characterized in that the absolute deviations of the respective alloying elements |AEzui,i|, preferably |AEßev,i|, particularly preferably |AEßBev,i| of the different melts may have maximum values ​​of the following: International patent application Voestalpine Stahl GmbH 24092 IWO 3. Method according to claim 3, characterized in that the empirically determined element-specific weighting factors (k) have the following values:

4. Method according to one of claims 1 to 3, characterized in that the weighted deviations | AEJ* k are ordered in descending order, wherein the resulting series is referred to as a ranking or rank, wherein the ranking or rank comprises all weighted deviations | A Ei | * k, wherein the following relationship holds between the numerator for the elements (i) and the numerator for the ranking (0): Rangj = | A£) | ■ k t where rankj > rankj +1 5. Method according to claim 4, characterized in that the melt difference index (SDKZ) is formed from the largest weighted deviations, wherein x defines a defined number of the largest weighted deviations, wherein:

6. Method according to claim 5, characterized in that x >= 1, preferably x >= 3, particularly preferably x >= 7, in particular x = 14.

7. Method according to claims 5 to 6, characterized in that the melt difference index (SDKZ) is divided into three categories, namely in International patent application Voestalpine Stahl GmbH 24092 IWO permissible SDKZzui, preferred SDKZ Bev , and especially preferred SDKZ BBE v, where the values ​​of the three categories are derived from the product of constant melt difference index changes (SDKZ) 7 ), permissible SDKZ' ZU i, preferably SDKZ' Bev , especially preferred SDKZ' BBev , and the number of largest weighted deviations (x), where: SDKZ Zui = SDKZ Zui ■ x SDKZ Bev = SDKZ Bev ■ x SDKZ BBev = SDKZ BBev ■ x 8. Method according to claim 7, characterized in that the constant melt difference index changes (SDKZ') are permissible SDKZ', preferably SDKZ' Bev , especially preferred SDKZ' BBevexhibit the following values:

9. Method according to claims 1 to 8, characterized in that the sequential filling of the distributor with the two different melts is adapted to the melt difference index (SDKZ), wherein, for a melt difference index (SDKZ), the limit values ​​for the particularly preferred melt difference index (SDKZ) BBe v) and for the preferred melt difference index (SDKZ) Bev ) an adjustment is made in the distributor such that the ratio of remelt to premelt in the distributor is greater than 1.5 to 1, and wherein a melt difference index (SDKZ) exists between the limit values ​​for the preferred melt difference index (SDKZ). Be v) and permissible melt difference index (SDKZzui) an adjustment is made in the distributor so that the ratio of remelt to premelt in the distributor is more than 2 to 1. International patent application Voestalpine Stahl GmbH 24092 IWO 10. Method according to claims 1 to 8, characterized in that when determining a value of a) absolute deviations of individual elements between the melts |AEi| from one or more elements above the limit value Permissible |AE ZU i,i| and / or b) a permissible deviation of the SDKZ above the limit SDKZzui,

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