Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D2/00—Arrangement of indicating or measuring devices, e.g. for temperature or viscosity of the fused mass

Definitions

• the invention relates to a method for predicting and controlling the castability of liquid steel by analyzing the chemical composition of a melt to be cast, performing an alloy calculation and determining alloying elements and / or additives to achieve certain material properties of the steel and defining • driving diagrams for the further treatment of the Melt.
• Such processes are used in steel production.
• the molten steel is delivered by a steel mill.
• the secondary metallurgy is carried out in a ladle furnace upstream of a thin strip caster.
• certain secondary metallurgical devices are provided in or on the ladle furnace in order to treat the liquid steel metallurgically.
• precise analyzes of the melt can be carried out, and the melt can also be precisely thermally conditioned.
• the liquid steel is treated in the ladle furnace by adding alloying agents, slag formers, reducing agents, desulfurizing agents, etc., whereby these additives are added automatically or manually.
• the slag can be added by adding oxygen or by flushing with an inert gas such as e.g. Be treated with argon.
• the liquid steel can be stirred electromagnetically in the pan, and electrical energy can also be supplied to it via carbon electrodes. The arc running from the electrodes to the melt causes the alloying elements to melt and enables the thermal conditioning of the melt.
• Steel strip with a strip thickness of up to 10 mm is usually produced in thin strip casting plants. Conditioning the
• Liquid steel is said to be non-castable if the cast strip breaks, for example when casting in the thin strip casting plant, the cast material has surface defects or structural defects of a general nature and causes system malfunctions as a result of the non-castable liquid steel, e.g. sticking on the casting rolls, etc. So far, attempts have been made , this Problems related to the castability are essentially to be solved in the thin strip caster itself. However, these attempts were only partially successful, since many melts proved to be non-pourable.
• the invention is therefore based on the problem of improving the method for predicting and controlling the castability of liquid steel in such a way that the error rate is significantly reduced.
• the invention is based on the surprising finding that interactions exist between the alloy and / or additive elements, which not only see the mechanical properties but also the castability of the
• the current proportions of the two alloying elements shown are entered in the coordinate system, this instantaneous value being symbolized by a point.
• the graphic shows immediately whether the melt is within the tolerance range or not.
• those interactions that have an influence on the castability of the melt must also be taken into account.
• the method according to the invention provides that the information “pourable” or “non-pourable” is assigned to each poured melt.
• the method according to the invention provides that, based on the data collection of cast melts and the alloy elements and / or additives related to one another, at least one permissible range of values for the proportions of the alloy elements and / or additives is defined within which a castable Melt is expected.
• This permissible value range is a subset of the value range mentioned above, in which only those interactions are taken into account that have an influence on the material properties.
• the range of values which specifies the permissible proportions of the individual alloying elements and aggregates, must already be cast, taking into account the data collection
• the permissible range of values for the proportions is defined as the intersection of a plurality of inequalities. Due to an inequality, the entire x-y area of the coordinate system can be divided into two parts, namely a valid and an invalid area. Graphically, a surface on one side of a straight line corresponds to an inequality.
• the coordinate axes can be used to determine permissible value ranges, since the alloy elements can only take positive numbers, only the first quadrant has to be considered.
• the permissible range of values it will generally be necessary to determine the permissible range of values as an intersection of several intersecting straight lines. If the axes of the coordinate system are not taken into account, at least three straight lines are required in order to clearly define a range of values. In practice, it has been found that more than three inequalities, in particular four, are often required for a meaningful determination of the value range.
• the method according to the invention can be carried out particularly quickly and in part automatically if the changing Effects of the alloy and / or addition elements can be implemented as mathematical models in a computer system.
• the calculation and graphical representation of the value ranges requires comparatively little computing time, so that immediately after a melt analysis has been carried out it can be determined whether the proportions of the individual alloying elements and additives are within the permissible value range or whether further treatment steps are required.
• the method according to the invention for predicting and controlling the castability of liquid steel is carried out iteratively automatically by the computer system.
• fuzzy logic methods are used for the mathematical models in the method according to the invention.
• neural networks are used for the mathematical models.
• the alloy calculation can be carried out by preselecting those alloy and / or additive elements which have an influence on the castability of the melt. Studies have shown that only some of the alloying elements influence the castability. If a melt has ten elements, one would have to examine the first element with the remaining nine elements. The second element with eight elements etc., so that a large number of element pairs would have to be taken into account. It is therefore expedient to consider only those alloy elements or pairs of alloy and / or additive elements that actually affect the castability of the melt. In this way, the number of element pairs to be taken into account can be considerably reduced. This also reduces the number of inequalities to be taken into account or boundary conditions, which makes it easier to solve the systems of equations.
• the method according to the invention can be designed such that interactions of the following pairs of alloy elements and / or additives are taken into account in the alloy calculation: N / ⁇ 2 , Zn / ⁇ 2 , S / Zn, C / Zn, Mn / S, Mn / N , Si / C, Al / C, in particular Si / 0 2 , S / ⁇ 2 , Al / 0 2 , S / C, N / C. From the eight selected alloy elements mentioned, 28 pairs can theoretically be combined. However, it has been shown that only 13 of these pairs have an influence on the castability. Of these, five pairs of alloying elements or additives have a serious influence on the castability. If only these five pairs are taken into account with regard to a rational process, excellent results can already be achieved in terms of predicting and controlling the castability.
• the permissible value range for a or each alloy element or one or each additive and the actual value measured in the melt result in a castable melt.
• the actual value can be indicated in the graphic as a point or cross or the like, so that it can be seen at a glance whether it is within the permissible value range or not.
• This graphic representation is displayed for each of the pairs of values taken into account, so that an operator can knows whether all boundary conditions that have an influence on the castability are fulfilled. Otherwise, it recognizes which alloy elements require further treatment, for example by adding the alloy element further.
• the permissible value range for an alloy element or an additive, which results from the desired material properties is displayed.
• an updated actual value of an alloy element or an additive is displayed after a treatment step carried out on the melt. In this way it can be checked immediately whether the treatment step has led to the desired success.
• the method according to the invention can be used particularly advantageously in a thin strip casting installation which works according to the two-roll casting method.
• the invention relates to a control device for a secondary metallurgical plant, in particular a ladle furnace, with a means for analyzing the chemical composition of a melt to be cast, a means for performing an alloy calculation for determining alloying elements and / or additives to achieve certain material properties of the steel and a means for establishing driving diagrams for the further treatment of the melt.
• the control device is designed to carry out the described method.
• Fig. 1 shows schematically the sequence of the method according to the invention
• Fig. 4 is a diagram showing the proportions of the elements silicon and oxygen and the pourable area.
• FIG. 1 schematically shows the sequence of the method for predicting and controlling the pourability of liquid steel.
• the starting point of the process is a melt analysis to determine the chemical composition of the melt to be cast.
• the melt is located in a ladle furnace, which is upstream of a thin strip caster.
• the metallurgical treatment of the liquid steel takes place in the ladle furnace in order to set the required material parameters. Electrical or thermal energy can be supplied to the melt via graphite electrodes in order to trigger certain chemical reactions.
• the melt can be stirred electromagnetically in the ladle furnace.
• the addition of alloying elements and additives such as slag Formers, reducing agents, desulfurizing agents, etc. is done automatically or manually. It is also possible to purge the liquid steel with an inert gas such as argon or to add oxygen.
• an alloy calculation 1 is carried out in order to set metallic and non-metallic alloy elements in a defined range.
• the alloy calculation is used to calculate the type and quantity of additives and alloying elements so that the batch of liquid steel currently in the ladle furnace can be modified and treated in such a way that it meets the requirements.
• the individual alloy elements must be present in the correct quantity ratio, that is, in the correct concentration, with tolerance bands with a lower and upper limit for each element.
• this method takes into account interactions between the alloying elements and additives that have an influence on the castability.
• the mathematical models used in alloy calculation 1 take these interactions into account, so that the melt is very likely to be cast after treatment.
• melt fulfills the requirements regarding the material properties of the finished steel, but e.g. Surface defects on or the steel stuck to the casting rolls, so that the melt had to be discarded as not pourable.
• the process is continued by determining driving diagrams 2 for the electric furnace rack and the ladle furnace. If the result Alloy calculation 1 reads "not castable", for example further alloy elements or additives have to be added or treatment steps such as the addition of an inert gas or oxygen are required.
• the driving diagrams for driving the ladle furnace are determined and specifications are made about the addition of metallic and non-metallic additives and the further treatment. The consideration of the interactions that have an influence on the castability leads to additional conditions for the driving diagrams or to a switching of a driving diagram.
• the driving diagrams are determined for the ladle furnace and the secondary metallurgy.
• This procedure is advantageous with regard to the selection of the melts. If a melt proves not to be pourable or if the measures to produce the castability are too complex, it can be decided to reject the melt. In this case, the melt would have to be treated again in the steel mill. This procedure avoids errors in production costs and conserves resources.
• the melt can be brought into a castable state by means of metallic or non-metallic additives and if this procedure is not too complex, then the cast diagrams for the ladle furnace and the secondary metallurgy can be used to achieve the castability of the melt. In this case, too, there is the advantage of avoiding production errors and conserving resources.
• the melt can be treated in the ladle furnace with the travel diagram planned for it and released for the thin strip casting plant. If one recognizes that the melt can be adjusted even more favorably metallurgically, taking into account the interactions affecting the material properties, this can be implemented while maintaining the castability. This has the advantage that the melt can be optimally adjusted metallurgically, taking into account the castability. In this case too, errors in production costs are avoided and resources are spared.
• control parameters for the further treatment of the melt are obtained by determining the driving diagrams.
• the value ranges for the proportions of the elements x and y are plotted on the x and y axes, respectively.
• the value range of each element is limited by two axially parallel straight lines, which indicate the minimum or maximum concentration of the respective substance in the melt. If the analysis value of the melt lies within the intersection of these straight lines, the requirements for the material properties are met.
• Fig. 2 the pourable area is represented by the straight sections 3, 4, 5.
• a melt that meets the requirements for material properties on the one hand and the requirements for castability on the other must lie in the intersection of both surfaces.
• This valid area 6 is shown hatched in FIG. 2.
• a value 7 is known from a melt analysis which fulfills the conditions for conventional casting operation, since it lies within the range of values of the elements x and y, provided the material properties are affected. However, it is not within the valid range 6, so it can be expected that this melt is not pourable.
• This examination which is exemplarily explained on the basis of the elements x and y, is to be carried out for all relevant value pairs, all of which must lie within the valid value range. At least the following pairs of values should be checked: Si / 0, S / ⁇ 2 , Al / 0 2 , S / C, N / C. If the examination of these conditions leads to the result that all elements lie within the valid ranges, the melt is very likely to be pourable. If any value is not within the valid range, a further treatment step is necessary, for example by adding an alloying element. However, it should be noted that when adding an alloy element, the proportions or concentrations of the other alloy elements and additives to be taken into account are also influenced. These relationships are generally not linear and complex.
• the mathematical models that take account of these interactions, which have an influence on the castability, therefore include methods such as neural networks or fuzzy logic.
• an iterative calculation or an optimization calculation is therefore carried out in order to achieve the target with the minimum amount of alloy achievement elements or as inexpensively as possible.
• FIG. 3 shows a diagram of the proportions of the elements sulfur and carbon.
• the concentration of carbon in the melt is plotted on the x-axis, and the concentration of sulfur on the y-axis.
• the triangular surface 9 shown in FIG. 3 shows the region of the castability of the sulfur / carbon element pair.
• the first analysis value 10 lies outside the triangular area 9, that is to say the melt cannot be cast in this state.
• the melt is therefore treated, for example by adding an additive, in order to increase the proportion of carbon and to reduce the proportion of sulfur.
• an analysis is carried out again and the analysis value 11 results.
• a second treatment step is necessary until the analysis value 12 results.
• the analysis value 12 lies within the triangular area 9, ie within the pourable area. At the same time, however, it must also be ensured that the other elements or pairs of elements to be taken into account are within their valid ranges.
• Fig. 4 shows the proportions of the elements silicon and oxygen and the pourable area.
• the pourable region 13 in FIG. 4 is indicated by a plurality of sections of the furnace which do not form a closed surface.
• the castable area can also be specified by parabola sections or sections of trigonometric functions.
• the aim should be to define the valid ranges using straight line sections in order to keep the calculation effort within limits.
• the first analysis value 14 lies outside the pourable area 13. After the treatment of the melt, the analysis value 15 was determined, in which the oxygen content was increased, but was too high, so that the value 15 was again outside the pourable area 13 , The analysis value 16, which complies with the conditions for the elements silicon and oxygen, was only measured after a further treatment step.
• the method provides that the operator is shown the diagrams for the five most important pairs of elements simultaneously on a display.
• the analysis values for individual alloying elements or aggregates can be shown as numerical values in a table. In this way, the operator can see at a glance which values are already in order and which require further treatment.
• the measured values of this melt are stored in a database, so that the mathematical models can access an ever-growing database, which increases the probability of prediction.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Continuous Casting (AREA)
• Investigating And Analyzing Materials By Characteristic Methods (AREA)

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• 2003
  • 2003-08-26 DE DE10339595A patent/DE10339595A1/de not_active Withdrawn
• 2004
  • 2004-07-23 US US10/569,781 patent/US7543628B2/en not_active Expired - Fee Related
  • 2004-07-23 CN CN200480024272XA patent/CN1842384B/zh not_active Expired - Lifetime
  • 2004-07-23 EP EP04763467A patent/EP1667806A1/de not_active Ceased
  • 2004-07-23 WO PCT/EP2004/008300 patent/WO2005021186A1/de active Search and Examination

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