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
  • 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
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/16—Controlling or regulating processes or operations
• • 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
  • B22D11/0622—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels

Definitions

• the invention relates to a process for the continuous casting of a thin metal strip in a two-roll process, in particular a steel strip, preferably with a thickness of less than 10 mm, molten metal being poured into a casting gap formed by two casting rolls in the thickness of the metal strip to be cast, with the formation of a molten bath.
• the invention aims to avoid these disadvantages and difficulties and has as its object to provide a continuous casting method of the type described in the introduction, which makes it possible for the metal strip to adhere to predetermined quality features, such as in particular the formation of a desired structure of the metal or the securing of a specific one Enable geometry, etc. for metals with different chemical compositions, i.e. for a variety of steel qualities or steel grades to be cast.
• the object of the invention is to avoid deviations in the quality of the metal strip from the outset, etc. by creating the possibility of intervening in production stages in which an actual value of the metal strip that determines the quality and is not yet easily recognizable or cannot be determined directly.
• This object is achieved in that for the formation of a certain structure in the cast metal strip and / or for influencing the geometry of the metal strip, the continuous casting with on-line calculation on the basis of the formation of the specific structure of the metal and / or the formation of the geometry of the metal strip describing calculation model is carried out, the Microstructure formation or variables influencing the geometry of the continuous casting process can be set on-line dynamically, ie during the ongoing casting.
• the structure of the casting roll surfaces is an important factor in solidification or microstructure formation. This structure is only reproduced to a certain extent by the liquid metal, i.e. Depending on the structure of the surface of the casting rolls, solidification occurs in certain surface areas and in other surface areas it is delayed.
• the structuring of the surface of the casting rolls is preferably recorded, preferably recorded online, and integrated into the computing model, taking into account the resulting solidification and segregation conditions, in particular in the case of primary solidification.
• the solidification of the metal on the surfaces of the casting rolls it is essential to condition these surfaces, such as by cleaning, spraying, coating, in particular by flushing with gas or with gas mixtures.
• This gas or these gas mixtures determine the heat transfer from the melt or already solidified metal to the casting rolls, and therefore, according to a preferred embodiment, the chemical composition of the gas or the gas mixture and the amount and optionally the distribution over the length of the Casting rolls recorded, preferably recorded online, and integrated into the calculation model, taking into account the resulting solidification and segregation conditions, particularly in the case of primary solidification.
• thermodynamic changes in the state of the entire metal strip are constantly included in the calculation model by solving a heat conduction equation and solving an equation or equation systems describing the phase conversion kinetics, and the temperature setting of the metal strip and, if appropriate, of the casting rolls is dependent of the calculated value of at least one of the thermodynamic state variables, the thickness of the metal strip, the chemical analysis of the metal and the casting speed being taken into account for the simulation, the values of which are preferably measured repeatedly during the casting, in particular the thickness is continuously measured.
• a continuous phase conversion model of the metal is preferably integrated into the computing model, in particular according to Avrami.
• the Avrami equation describes all diffusion-controlled conversion processes for the respective temperature under isothermal conditions.
• ferrite, pearlite and bainite fractions can be set very specifically in continuous steel casting, etc. also taking into account a holding time at a certain temperature.
• the method is preferably characterized in that, with the computing model, thermodynamically changes in the state of the entire metal strip, such as changes in temperature, by solving a heat conduction equation and solving an equation or system of equations describing the excretion kinetics during and / or after solidification, in particular non-metallic and intermetallic precipitations are constantly included in the calculation and the temperature setting of the metal strip and, if applicable, of the casting rolls is set as a function of the calculated value of at least one of the thermodynamic state variables, the thickness of the metal strip, the chemical analysis of the metal and the casting speed, the values of which are preferably taken into account during the simulation Pouring can be measured repeatedly, especially regarding the thickness.
• thermodynamic basic variables in particular Gibb's energy, and the germ growth according to Zener are integrated into the calculation model.
• Structural quantity relationships are expediently integrated into the calculation model in accordance with multi-material system diagrams, such as, for example, in accordance with the Fe-C diagram.
• Grain growth properties and / or grain formation properties are advantageously integrated into the computational model, possibly taking into account recrystallization of the metal.
• a dynamic and or delayed and / or post-recrystallization, ie a recrystallization that later takes place in an oven, can be taken into account in the calculation model.
• thermomechanical rolling for example high-temperature thermomechanical rolling
• Thickness reductions according to the invention even after reeling the strip and also in low-temperature ranges (for example at 200-300 ° C.), which can also be carried out on-line, ie without prior reeling, are considered as rolling tongues.
• the mechanical state such as the deformation behavior
• the mechanical state is preferably also constantly included in the calculation model by solving further model equations, in particular by solving the basic continuum-technical equations for the visco-elasto-plastic material behavior.
• a preferred embodiment is characterized in that a quantity-defined structure is set by applying an on-line strand deformation, which causes the structure to recrystallize.
• a thermal influence of the molten metal and already solidified metal by the casting rolls is expediently integrated into the calculation model, with the casting roll cooling being recorded online.
• thermo influence on the metal strip such as cooling and / or heating, is integrated in the computing model. Differences between the edge and the central area of the metal strip may have to be taken into account.
• An advantageous variant of the method according to the invention is characterized in that a rolling process model, preferably a hot rolling process model, is integrated in the computing model, the rolling process model expediently carrying out a rolling force calculation and / or a roll bending force calculation and / or a roll displacement calculation and / or a roll deformation calculation and / or a deformation calculation for thermally caused changes in the roll geometry has been integrated for specially profiled rolls.
• a rolling process model preferably a hot rolling process model
• mechanical properties of the metal strip such as yield strength, tensile strength, elongation, etc.
• yield strength tensile strength
• elongation elongation
• corrective action can be taken in good time, etc. in the most suitable generation stages, i.e. during solidification and subsequent thermal influencing or during subsequent rolling, recrystallization etc.
• a continuous casting mold formed by two casting rolls 2 arranged parallel to one another and next to one another is used.
• the casting rolls 2 form a casting gap 3, the so-called “kissing point”, at which the strip 1 emerges from the continuous casting mold.
• a space 4 is formed, which is shielded from above by a cover plate 5 forming a cover and which serves to receive a weld pool 6.
• the molten metal 7 is fed through an opening 8 of the cover through which an immersion tube projects into the molten bath 6 to below the bath level 9.
• the casting rolls 2 are provided with internal cooling, not shown.
• side plates are provided for sealing the space 4 which receives the weld pool 6.
• a strand shell is formed on the surfaces 10 of the casting rolls 2, these strand shells in the casting gap 3, i.e. at the kissing point, to be combined into a volume 1.
• a specific rolling force distribution e.g. in rectangular shape or barrel shape.
• a computer 11 is used, in the machine data, the desired format of the metal strip, material data, such as the chemical analysis of the molten steel, the casting condition, the casting speed, the molten steel temperature at which the molten steel enters between the casting rolls, and that desired structure and, if necessary, a deformation of the steel strip, which can take place on-line or outside the continuous caster.
• the computer calculates various parameters influencing the quality of the hot strip, such as a temperature influence of the steel melt and / or the steel strip, as well as further the internal cooling of the casting rolls, the gas loading of the casting rolls, the degree of deformation of the roll stand 12 arranged on-line in the example shown, as well as possibly reeling conditions for the reel 13, etc.
• the computing model used according to the invention is essentially based on a strip casting model and a rolling model.
• the former includes a casting roll, solidification, segregation, primary structure, phase change and precipitation model.
• the rolling model includes a thermophysical model, a phase change, hot rolling, precipitation, recrystallization and grain size model as well as a model for predicting mechanical parameters.
• the structuring of the casting roll surfaces 10 is decisive for the initial solidification on the casting rolls 2.
• the surface profile of the casting rolls 2 is simulated by the steel 7, but only to a certain extent. Due to the surface tension of the liquid steel 7, "valleys" are often spanned, in which media (e.g. gases) are stored. Since the gases reduce the heat dissipation from the liquid steel 7 to the casting rolls 2, the solidification is delayed.
• media e.g. gases
• the interplay between specially created casting roll surfaces 10 and different gas mixtures is used to set a temperature suitable for the casting process. To do this, it is necessary to know and describe exactly the nature of the casting roll surfaces 10. This is done by measuring the surface of the casting roll after finishing the surface at several points (ideally several times in the axial direction, eg with a highly sensitive measuring pin). The surface profiles obtained in this way are now filtered and divided into classes. For each of these classes, heat transfers are determined off-line by flow simulations and tests, and thus a specific distribution of heat flows is assigned to each surface class. These heat flow / temperature distributions are transferred to the downstream program parts.
• Presetting the (integral) heat flows can be made possible by setting the casting roll temperature. This in turn is determined by the casting roll materials, the cooling water temperature and the cooling water quantity.
• the first step of this calculation model is to describe the condition of the casting roll surface and to calculate the associated heat transfers (surface "mountains”, gas-filled “valleys”, transition areas) and to divide them into classes (fuzzification) and to transmit the respective temperatures.
• the primary solidification for the different classes is calculated.
• the primary solidification dendrite growth, orientations, lengths, arm distances
• the goal of this step is to calculate the size distribution and direction of growth of the dendrites.
• a segregation model and an elimination model serve to determine segregations and excretions.
• the latter in combination with the temperature model, determines the degree of excretion processes that are fuzzyfied for the respective belt position.
• All fuzzified parameters are transferred to an on-line calculation model which determines the current conditions for the steel strip 1 on the basis of the continuously running temperature model and, if necessary, influences the control parameters by means of control circuits.
• Quality characteristics are returned from tapes that have already been produced and saved, and correlated with the manufacturing parameters.
• New process parameters are proposed in a self-learning loop.

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

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