EP0098214A1 - Process and device for the electro-magnetic stirring of continuously cast metals, especially steel - Google Patents

Abstract

Process in which the cast metal is subjected to a stirring action with the aid of a mobile magnetic field rotating about the axis (2) of the cast product and acting downstream of the ingot mould (12), and in which the magnetic field is applied at least over a portion ( delta h) of the metallurgical height ( DELTA H) between the level TL, where the still liquid core (4) reaches the liquidus temperature, and the level Ti, at which the proportion of solid material in the liquid phase reaches approximately 40% by weight. Moreover, the direction of rotation of the magnetic field is periodically reversed, it being possible for this to be performed advantageously with the aid of an array of electromagnetic inductors (20, 20', 20'') supplying, in pairs, magnetic fields rotating in opposite directions. The invention makes it possible to improve the internal quality of cast products, particularly in the central segregation plane. It applies especially to the continuous casting of steels or other metal alloys having a wide solidification range. <IMAGE>

Description

The present invention relates to the electromagnetic stirring of metals, in particular steels, continuously cast. It is particularly applicable to metals, or steels, having a wide solidification range.

It is known that the continuous casting operation consists schematically of continuously pouring the molten metal into a bottomless, energetically cooled ingot mold, generally made of copper or copper alloy, from which is extracted, also continuously, a bar having a crust external solidified and whose core still liquid gradually solidifies during its extraction, downstream of the mold, in the area called "secondary cooling" of the casting machine. The distance over which the poured product passes from a completely liquid state (surface of the liquid metal in the mold, or "meniscus") to a completely solidified state (bottom of the solidification well) is usually called "metallurgical height" and this whatever the trajectory of the casting bar, vertical or curved.

It is also known that the metallurgical quality of the products obtained is improved, both in terms of inclusion cleanliness and that of the solidification structure, by means of controlled stirring of the molten metal during casting. For example, for long products in particular (billets, blooms, etc.), it is known that this mixing is advantageously carried out by rotating the liquid metal by means of a mobile magnetic field, rotating around the axis of casting and acting in the secondary cooling zone (French patent n ° 2,236,584 from IRSID), or at the level of the ingot mold (French patent n ° 2,279,500 from USINOR, n ° 2,315,344 from IRSID , IRSID n ° 2.340.789), this last provision having the advantage of being able to quickly interrupt, as soon as it leaves the ingot mold, the solidification with dendritic growth (solidification of the "basaltic" type) started in the ingot mold, for the benefit of an "equiaxed" solidification, by crystalline germination within the liquid phase.

On the other hand, some grades of high-carbon, low-alloy steel are very poorly continuous castable at present, mainly due to axial segregation. which are particularly important for long products. The known techniques in continuous casting to mitigate these defects (weak overheating of the metal before casting, electromagnetic stirring in the ingot mold or in the secondary cooling zone, as mentioned above, etc.) seem, in fact, to find their limitation for this type of steel. These techniques, valid for carbon steels (up to about 0.5% of C) with low alloys or stainless steels, do not give fully satisfactory results for steels where the carbon content goes beyond about 0.5 Â (hyper-architectural steels). Steel of grade 100C6, for example, intended for the manufacture of parts subjected to contact fatigue, clearly embodies the difficulties encountered in continuous casting for steels of this type.

The object of the present invention is precisely to allow, by continuous casting of steel, or other metal alloys with a large solidification interval, the production of semi-finished products having a low axial segregation, or at least, an axial segregation substantially less than that which would be obtained by the known techniques of continuous casting.

To this end, the subject of the invention is an electromagnetic stirring process, during the continuous casting of metals, in particular steels having a large solidification interval, according to which the molten molten metal is rotated about the axis. casting using a magnetic field rotating around said axis and which acts downstream of the mold in the secondary cooling zone of the casting machine, process characterized in that the rotating magnetic field is applied to a portion of the metallurgical height included, at least, between the level where the still liquid core of the cast product reaches the liquidus temperature of the cast metal and the level where said core has a proportion of solid in the liquid phase of the order of 40 % by weight approximately and in that the action of the magnetic field is regulated so that the metal is subjected, during casting, to a magnetic field rotating in an accelerated direction of rotation.

According to a variant, a magnetic field is implemented consisting of a plurality of successive rotating elementary magnetic fields, arranged in a stepped fashion on said portion of the metallurgical height and whose directions of rotation are opposite two by two.

Preferably, the rotating magnetic field is already made to act slightly upstream of said portion of the metallurgical height, in order to compensate for the delay in rotation which the liquid metal opposes due to its inertia.

In another variant, the direction of rotation of the magnetic field is periodically reversed over time.

The invention also relates to a continuous casting installation for the implementation of the method, which is characterized in that it comprises, in the secondary cooling zone, a battery of inductors with mobile magnetic field for the mixing of the liquid metal, arranged in a staggered manner, successively one after the other along the metallurgical height, on a portion of the latter extending, at least, from the level at which the liquid core of the cast product reaches the temperature of liquidus of the cast metal, up to the level at which the proportion of solid in the still liquid phase is about 40 Å by weight.

As can be understood, the invention consists in its essential characteristics, of brewing the metal when the state of progress of the solidification of the latter gives it a consistency which is not yet completely solid, or more completely liquid and that we will qualify, to fix the idea, of "pasty".

According to a more precise definition, the term “paste-like” consistency, zone or solidification is intended to characterize the state of solidification of a continuously cast metal, the enthalpy of which lies between the enthalpy of the completely solid metal and the enthalpy of completely liquid metal. The position and extent of the "pasty" zone are determined from the determination of the temperature of the metal on the casting axis and it is considered that the "pasty" zone is the portion of the metallurgical height between the levels upper and lower temperature corresponding respectively to the liquidus temperature and the solidus temperature of the cast metal.

To fully understand the above, it should be borne in mind that the solidification of a continuously cast steel progresses from the periphery towards the axis of the product, not according to a well-planar front separating the liquid phase from the solid phase , but according to a very uneven surface on a small scale, formed by peaks (dendrites) and hollows. These peaks and valleys define two successive fronts progressing together: respectively a front called "starting solidification" and representing the envelope passing through the peaks of the peaks and a front said "of solidification ending" representing the envelope passing through the base of the hollows. The intersections of these two fronts with the pouring axis (which moreover merges with the product axis) determine between them, in magnitude and position, the portion of the metallurgical height where solidification of the type takes place. "pasty", and in which according to the invention, the magnetic field (s) of alternating rotation are acted upon.

It should be emphasized that this pasty solidification zone is characterized by the birth of a solid phase within the liquid phase itself and by the increase in the proportion of this solid phase as the cast product cools down to '' to total solidification corresponding to the closing of the solidification well (intersection of the pouring axis with the ending solidification front).

As the proportion of solid progresses in the liquid phase, an increasingly dense aggregate of crystals is formed in the solidification well until a sort of quasi-rigid skeleton is formed, giving the heterogeneous liquid-solid mass a very high pseudo-viscosity, close to that of a solid. It is easy to understand that this "skeleton" ends up reaching a degree of rigidity such that it then becomes useless, even impracticable, with the electromagnetic means currently available, to stir the metal.

The inventors have found that it can be considered that such immobility is achieved when the proportion of the solid fraction in the liquid matrix reaches about 40% by weight and that it was therefore sufficient to limit the stirring to this value and generally unnecessary to extend beyond 60%.

• - la figure 1 représente très schématiquement, en demi-coupe longitudinale, la progression de la solidification d'un acier coulé en continu,
• - la figure 2 représente une vue schématique en coupe axiale d'une installation de coulée continue équipée des moyens de l'invention,
• - les figures 3a, 3b et 3c sont des reproductions de clichés d'analyse métallographique (empreintes Baumann) d'un acier coulé en continu vu en coupe longitudinale partielle, et correspondant respectivement à un produit de référence non brassé (figure 3a), un produit brassé à l'aide d'un champ magnétique tournant permanent (figure 3b), et un produit brassé à l'aide d'un champ magnétique tournant avec inversion alternative du sens de rotation (figure 3c).

The invention will be better understood, and other aspects and advantages will appear more clearly in the light of the description which follows, given with reference to the accompanying drawing plates in which:

• FIG. 1 very schematically represents, in longitudinal half-section, the progression of the solidification of a continuously cast steel,
• FIG. 2 represents a schematic view in axial section of a continuous casting installation equipped with the means of the invention,
• - Figures 3a, 3b and 3c are reproductions of photos metallographic analysis (Baumann footprints) of a continuously cast steel seen in partial longitudinal section, and corresponding respectively to a reference product not stirred (Figure 3a), a product stirred using a permanent rotating magnetic field (Figure 3b), and a product stirred using a rotating magnetic field with alternative reversal of the direction of rotation (Figure 3c).

Figure 1 illustrates well what has been said previously about the progress of solidification in continuous casting. On this axial longitudinal section of the casting bar, the vertical arrow pointing downwards indicates the direction of extraction of the product. We see in 1 the side surface of the product - which is energetically cooled -, in 2 the product axis (merged with the pouring axis), in 3 the free surface of the metal in the mold, in 4 the completely liquid metallic phase , in 5 the metal completely solidified and, in 6 and 7, respectively the fronts of starting and ending solidification delimiting between them a zone 8 semi-solid, semi-liquid (whose liquid phase is besides strongly segregated in elements of 'alloy). It is precisely this zone 8, the consistency of which recalls in certain respects that of a sponge, which is described as "pasty". In addition, the beginning solidification front 6 defines, with very good approximation, the isothermal surface of liquidus T _L of the cast metal. It is the same for the ending solidification front 7 as regards the solidus temperature T ₅ . As already said, the intersections of the casting axis 2 respectively with the beginning solidification front 6 and the ending solidification front 7, intersections identified in the figure by the two points T _L and T _S , define between they the portion, denoted ¿h of the metallurgical height (denoted ΔH) and which, in accordance with the invention, constitutes the field in which the stirring magnetic field or fields are made to act.

The graph of FIG. 1, in addition to its purely illustrative role of the phenomena explained above, also reflects the quantitative results obtained during test runs of steels of grade 100 C6 for which the physicochemical data and the operating conditions are recorded. respectively in the tables of values 1 and 2 below.

Under these conditions, the metallurgical height ΔH is approximately 15.5 m and the level of T _L has been determined at a height of 4.5 m. We therefore calculate a zone Δh, corresponding to the pasty zone, of length: 15.5 - 4.5 = 11 m, initiating at 4.5 m under the meniscus 3.

In addition, using a thermal solidification model solving the heat diffusion equation in transient regime, one can calculate the temperature field at any level of the metallurgical height. From, for example, a simple enthalpy diagram - temperature "of the casting grade, it is then easy to construct the curve, referenced 9 in FIG. 1, intermediate between the fronts of finishing and beginning solidification, and representing the place of the points in the liquid phase where the proportion of liquid phase is 40% by weight. More simply, one can be satisfied with determining the point of intersection T. of this curve with the pouring axis 2, this point T _i then defining, with the point T _L placed upstream, the portion denoted 6h, of the pasty zone Δh, along which, in accordance with the invention, the metal is stirred.

As can be seen in the figure, in the case of a grade 100C6 steel cast under the conditions specified above, the point T _i , defines the temperature point at 1430 ° C on the casting axis, and is located at 9 m below the meniscus. It thus defines with point T _L , a 6h brewing portion of length 9-4.5 = 4.5 m approximately, from the dimension at 4.5 m under the meniscus 3.

Of course, the preceding information on the method of determining the point T _i on the casting axis is given for purely indicative and illustrative purposes. Other methods exist, which are known to those skilled in the metallurgical profession and which fall entirely within its field of competence. Thus for example, if one wishes a more precise determination of the dimension of T _i , one can, instead of using the enthalpic curve, call upon the phase diagram of the cast shade, associated with the relation of SCHEIL- GULLIVER connecting, for each temperature value, the solid fraction to its 5concentration within the liquid phase. This method could moreover be advantageously used in the case of shades with very large solidification intervals for which, as we know, the enthalpy diagram, constructed by linear interpolation between T _L and T _s , does not always provide the desired precision.

This being the case, we will now make a few additional comments on the considerations at the origin of the invention.

The liquid segregated into alloying elements which forms at the solidification front (a single average front is considered here) tends, by density, to descend towards the bottom of the solidification well. This phenomenon establishes a natural convection of the liquid in the pasty zone and the extent of which depends in particular on L 3, where L is the number of GRASTHOFs for the liquid metal poured. Now, we know that L is all the greater the wider the solidification interval of the metal is. We are therefore entitled to admit that, in the case of nuances to large solidification interval, significant convection movements of the liquid phase are established within the solidification well. As this well becomes enriched in equiaxed crystals as one approaches the bottom, the segregated liquids, which percolate between these crystals while circulating at high flow, tend to melt the crystals on contact . Privileged passage areas are thus formed, which are generally called "canals". Since the segregated liquids circulate from the top to the bottom and from the periphery to the center of the cast product, enriched in aggregated elements, these channels appear in the form of successive "V" with a central collector in the axis of the product. and are directly responsible for the internal quality problems mentioned at the start.

The primary result sought by the invention is precisely, as will have already been understood, to suppress the desires of highly segregated liquids to circulate in the channels which they form in the solidification well. To achieve this, the proposed solution consists in electromagnetically mixing the liquid metal in the pasty zone dh, more simply along the portion Sh (fig 1) of this zone, in order to counteract the tendency of the metal to form these segregated channels. Preferably, the brewing is initiated slightly upstream of the ₆ h portion in order to, as already pointed out, to compensate for the delay which the inertia of the liquid metal opposes to the brewing movement, in particular when the brewing consists in making rotate the liquid metal around the casting axis. Furthermore, the inventors have been able to show that it is advantageous to seek a shearing effect of the liquid metal against the solidification front, this effect being obtainable, in accordance with the invention, by means of repetitive reversals of the direction of movement of the stirring magnetic field.

• dans le temps, notamment à l'aide d'un inducteur de brassage à champ magnétique alterné, cet inducteur pouvant être du type monobloc couvrant toute la portion 6h voulue, ou constitué d'une succession d'inducteurs autonomes synchronisés,
• dans l'espace (i.e. le long de l'axe de coulée) à l'aide d'une batterie d'inducteurs successifs, couvrant la portion 6h et délivrant des champs magnétiques mobiles dans des

According to two variant embodiments of the invention, these inversions can be carried out, either in time or in space:

• over time, in particular using an alternating magnetic field stirring inductor, this inductor being able to be of the monobloc type covering the entire desired 6h portion, or consisting of a succession of synchronized autonomous inductors,
• in space (ie along the casting axis) using a battery of successive inductors, covering the 6h portion and delivering mobile magnetic fields in

FIG. Z shows, in correspondence of scale and dimensions with the diagram of FIG. 1, the location of the stirring inductors for the implementation of the invention according to a variant with successive rotating and alternating magnetic fields along the axis of: oulée. In this FIG. 2, a so-called “vertical” continuous casting installation has been schematically represented (ie entirely straight trajectory of the casting bar) comprising, from the top of the installation, a distributor 10 supplying molten metal continuously, by a pouring jet 11, a bottomless ingot mold 12. From the latter is extracted, also continuously, a bar 13 having a solidified outer crust 5 and the still liquid core 4 of which progressively solidifies during its extraction ( in the direction indicated by the arrow) over the total distance ΔH called "metallurgical height". Downstream of the point marking the end of solidification (closing of the solidification well) - point T _s in FIG. 1 - a shear symbolized at 14 cuts the bar by accompanying it in its descent. Once cut, the section is tilted and immediately removed to allow the casting process to continue.

The ingot mold 12 is a boxed mold of known type, essentially comprising an internal tubular element 14, made of copper, defining a passage for the cast product and energetically cooled on its external face by a casing of water 15 in upward circulation from a chamber of supply 16 to an upper evacuation chamber 17.

As can be seen, the upper evacuation chamber 17 has been sufficiently dimensioned to be able to immerse therein an electromagnetic stirring inductor 18. The role of this inductor, the presence of which is desirable but in no way essential for the implementation of the invention , will be specified later. The same remark also applies to the inductor 19 placed downstream of the mold and acting, as can be seen, already upstream the pasty solidification zone Δh.

In accordance with an essential characteristic of the invention, a battery of stepped inductors (here three in number) 20, 20 ′, 20 "surrounds the bar cast on the 6h portion of the metallurgical height ΔH. These inductors with rotating magnetic field, annular in shape and polyphase static type, are stirring devices electromagnetic known and used in the field of continuous casting. A detailed description can be found, if necessary, by referring, for example, to French patent No. 2,211,305 (CEM).

According to the invention, each inductor delivers a rotating magnetic field whose direction of rotation is opposite to that of, or inductors which are immediately adjacent to it. This arrangement, as already explained, makes it possible to improve the results obtained with respect to a uniform rotating field over the entire 6h stirring portion.

In another variant, the inductors 20, 20 ′, 20 ″ deliver magnetic fields rotating in the same direction at the same time, in which case it is advantageous, for the reasons already mentioned, to periodically reverse the direction of rotation of the field. In this regard, the rule to be observed is that any elementary volume of liquid metal which, during the extraction of the cast product, penetrates into the portion 6h is, before leaving it, subjected to a magnetic field whose direction of rotation reverses at least once.

The application of this rule obviously depends on the local operating conditions and, in particular, on the speed of extraction of the cast product, in connection with the length of the brewed portion 6 hours. Thus in the example considered where the extraction speed is 0.7 n / min and .6h of 4.5m, the minimum residence time of any elementary volume of metal in the stirred portion 6h is therefore approximately 6 and a half minutes. Under these conditions, the aforementioned rule is observed if one brews in each direction for example for about 3 minutes, an exposure time of a few tens of seconds. between the two shuffling sequences then being provided for the natural attenuation of the movement before turning back in the direction of circulation. Nothing heard, we can reduce the duration of each sequence, which has the effect of multiplying the number of field inversions during the time of stay of the metal in the 6h portion and, consequently, of increasing the shearing effect. research. It is understood, however, that it is not desirable to reduce the duration of the brewing sequences below a certain threshold, (generally of the order of 20 to 40 sec. Depending on the operating conditions), from which the action of the field is no longer sufficiently maintained to overcome the inertia of the liquid mass to be stirred.

As such, it is entirely advantageous, as shown in Figure 2, to provide, just upstream of the portion δh, the inductor ie additional stirring 19, the magnetic field produced of which rotates in synchronism with that delivered by the inductor 20 in order precisely to alleviate the resistance to movement which the liquid metal opposes and in this way to ensure a rotation of the latter already at the entrance to the brewing area 6am

It is emphasized that, in FIG. 2, the size of the inductor 19 has been voluntarily reduced compared to that of the inductors 20, 20 ′, 20 ", with the sole aim of clearly differentiating it so as not to harm the understanding of the It is clear that its size, as well as its implementation, can be quite similar to that of the inductors 20.

It goes without saying that what has just been said about the periodic reversals of the magnetic field can be achieved, not only with the battery of structurally independent inductors, 20, 20 ′, 20 ", but also with a single inductor sufficiently dimensioned so that its useful air gap length (field action height) can cover the portion δh. It is understood, however, that a battery of independent inductors will often be preferred, for simple reasons of convenience, when the portion 6h at brewing has a curved trajectory.

In accordance with a preferred implementation of the invention, the liquid metal is further subjected. to a stirring already within the mold 12. As shown in Figure 2, this can be done using the electromagnetic inductor 18 housed in the upper water chamber 17. The inductor 18, retained in this example is of the polyphase static type surrounding the cast product and delivering a rotating magnetic field. It will be recalled that the production of inductors of this kind, as well as their use within a continuous casting mold as a device for stirring the metal, as well as the favorable results of such stirring on the metallurgical quality of the products obtained, are already part of the known state of the art (aforementioned patents). The originality of the variant of the invention presented here lies in the combination of mixing in an ingot mold and mixing in a pasty zone Ah, leading to a beneficial conjugation of their effects, which are manifested in particular by obtaining a well of shallower solidification and flattened bottom, so that the portion δh to be brewed is, on the one hand, shortened in height and, on the other hand, widened in section, which goes in the direction of stirring in the times more economical and more efficient.

Furthermore, we are also entitled to admit an increased efficiency of stirring in the ₆ h zone, against the formation of segregated channels, by the fact that the liquid metal put into circulation is loaded with solid particles which, thanks to the action of mixing in an ingot mold, originated upstream of the zone ₆ h by pruning of the heads of dendrites, or by crystalline germination within the liquid phase 4.

The modification of the profile of the solidification well caused by the commissioning of the inductor 18 within the ingot mold has not been shown in FIG. 2 so as not to overload it unnecessarily.

FIGS. 3 are photographic reproductions of "Raumann" impressions made in longitudinal axial section of the cast product (grade 100C6 steel). They illustrate, by highlighting the segregation of sulfur, the comparative metallurgical results obtained between an unmixed product (Figure 3a) and a product brewed, on the one hand, using a permanent rotating magnetic field (Figure 3b), on the other hand, using an alternating rotating magnetic field (Figure 3c).

We are well aware that the segregated channels 21 (in black) in the shape of a "V" as well as the central collector 22, very marked in FIG. 3a, are clearly attenuated when the metal is stirred in the zone 6h in accordance with the invention (figure 3b) and practically absent - or at least without appreciable consequences on the quality of the product - when the direction of rotation of the magnetic field is alternated (figure 3c).

It will be noted in FIGS. 3b and 3c the presence of clear lateral bands 23, therefore very depleted in segregated elements, and which, as is known, are very characteristic of the brewed products continuously cast. We also know that the location of these bands 23, usually called "white areas", as well as their thickness, can be related in some way to the location and extent of the stirring action on the metallurgical height.

It goes without saying that the invention cannot be limited to the examples described, but extends to multiple variants or equivalents as long as the characteristics set out in the appended claims are respected.

Thus, the term "at least" should be understood as used above in the expression "... it is important that the liquid metal be brewed ... at least in the 6h portion ... ", the possibility, not only to initiate brewing upstream of this portion to compensate for the inertia of the metal, but also to continue the brewing action downstream of the level Ti on the metallurgical height where the proportion by weight of solid in the liquid phase reaches 40%. It will be understood, however, that there is little point, in the context of the results targeted by the invention, of continuing to be stirred up to the close vicinity of the bottom Ts of the solidification well.

In fact, tests have shown that there is no longer any significant improvement in the internal quality of the product when the brewing is prolonged beyond the level where the solid / liquid proportion is approximately 60% by weight and that the main part of this improvement is obtained, as shown in particular in FIG. 3c, when a proportion of approximately 40% is reached.

Claims (10)

1) electromagnetic stirring process of metals, in particular steels, continuously cast, method according to which the molten molten metal is rotated about the casting axis using a magnetic field rotating around said axis and which acts downstream of the mold, in the secondary cooling zone of the casting machine, and characterized in that the rotating magnetic field is applied at least over a portion (6h) of the metallurgical height (ΔH), included between the level (T _L ) where the core (4) still liquid of the cast product reaches on the casting axis (2) the liquidus temperature of the cast metal and the level (Ti) where said core has a proportion of solid in the liquid phase of about 40% by weight approximately, and in that the action of the magnetic field is regulated so that the metal is subjected, during casting, to a magnetic field rotating in a direction of alternating rotation. 2 °) A method according to claim 1 characterized in that, in order to compensate for the delay in movement that opposes the liquid metal due to its inertia, it initiates the action of the mobile magnetic field already upstream of the level (T _L ) at which the liquid core (4) reaches on the axis (2) the liquidus temperature of the cast metal. 3 °) A method according to claim 1 characterized in that periodically reverses the direction of movement of the magnetic field. 4 °) Method according to claims 1 or 3 characterized in that one implements a mobile magnetic field, consisting of a plurality of elementary magnetic fields spanning the metallurgical height and whose directions of movement are opposite two to of them. 5 °) Method according to any one of the preceding claims, characterized in that the liquid metal which is already poured into the same mold is stirred. 6 °) Method according to claim 5 characterized in that said mixing is carried out by acting a mobile magnetic field at the level of the mold. 7) continuous metal casting installation for the implementation of the method according to claims 1 and 4 characterized in that it comprises, in the secondary cooling zone, a battery of inductors with rotating magnetic fields (20, 20 ', 20 "), which surround the cast product and which are arranged in a staggered fashion along) the metallurgical height (eH) on a portion (6h) thereof extending, at least, from the level at which the liquid core (4) of the cast product (13) reaches on the pouring axis (2) the liquidus temperature (T ₁ ) of the cast metal, up to the level ( Ti) in which the proportion of solid in the still liquid phase is approximately 40% by weight. 8 °) continuous casting installation according to claim 7 characterized in that it is equipped with a stirring inductor (19) disposed in the upper extension of the inductor battery (20, 20 ', 20 "). 9 °) continuous casting installation according to claims 7 or 8 characterized in that it is equipped with a stirring inductor (18) disposed at the mold (12). 10 °) A method according to any one of claims 1 to 6 characterized in that it is applied to the continuous casting of metals, in particular steels, having a wide solidification interval.

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