HUT66806A - A process and an apparatus for the manufacture of high quality billets from continuously cast steel - Google Patents

Abstract

A process for the manufacture of billets and blooms from continuously cast steel, allowing such long products to be directly conveyed to a finishing rolling mill in a plant supplying high quality steel and/or excellent quality steel. Said process is comprising a liquid core distortion stage, concerning the casting cross section and causing the reduction of the same cross section, the perimeter remaining unchanged (equal). Said distortion occurs in the zone comprised between the point (S), last point on the casting axis (X-X) where superheated liquid is still present, and the point (L) where the casting is completely solidified (end of the metallurgical length). Preferably, said distortion is carried out between the points respectively corresponding to 10 % and 80 % of the concentration of solid grains in the fluid mass. An apparatus is described too, essentially comprising means for bringing at least one of the sectors forming the roller train (along the casting route) near the opposite one, in at least one plane containing the casting axis (X-X), in correspondence of said distortion zone.

Description

International Publication Number:

The process ingots of the present invention are maintained at a constant cross-sectional circumference between the two points XX of the casting axis, one of which is the lowest point where the superheated melt is still present and the other is the point J i & f at the end of the metallurgical length. slightly frozen. The deformation is preferably carried out between two points where the concentration of crystal germs in the liquid core is 10% and 80% respectively. The apparatus for carrying out the process is provided with a mold for extruding roller-shaped segments in an arcuate roller section which is formed from the upper and inner segments forming a curved spindle, wherein according to the invention, at least one of the inner segments (14, 14 ', 14) the axis (XX) is provided with a means for moving the segments (14,14 ', 14) between the lowest point of the superheated melt and the end point of the complete cure at the end of the metallurgical length. (2ft tree>

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PUBLICATION LITERATURE

66 806

Represented by DANUBIA PATENT AND TRADEMARK OFFICE LTD.

£ MSvO:

PROCESS AND EQUIPMENT FOR THE PRODUCTION OF STAINLESS STEEL STEEL STOCKS

ARVEDI, Giovanni,

Inventor:

GOSIO, Giovanni,

ARVEDI, Giovanni,

Cremona, ARC Italy Cremona, ARC Cremona, ARC Italy

Priority of notification:

filed on:

PCV Filing Date:

Announcement number:

12/9/1991 (MI91A002414), Italy

1-994-: 03.0 ". 33 2. O 3- 4 TQ

9/9/1992 -H ~

PCT / IT H3 ^

International Publication Number: WO 93/04802

99045-4761 Er / An

The present invention relates to a process for producing high-quality steel ingots from continuously cast steel by deformation of the liquid core of the ingot. The present invention also relates to an apparatus for continuous casting of steels, a die, a roll of rolls and a roll of segments formed by an arc, formed from outer and inner arch segments.

It is known that continuous casting is increasingly used in steel making, due to its obvious and known advantages over other casting processes. However, it is also evident that the product thus obtained, as it is removed from the molding machine at the end of the curved molding, has characteristically molten material properties, the quality disadvantages of which are also known. Metallographic studies also show in practice that the isotropy of the particle size distribution and tissue structure is unsatisfactory and that the carbon content is not uniform but is mainly concentrated in the central zone of the product, which results in precipitation and prevents direct use of the continuously cast product. Thus, direct rolling of ingots from a continuous casting plant does not produce high-quality steels.

In the case of quality steels, continuous casting can be used to produce ingots which, after preheating, are rolled into flat ingots and then finished, if necessary with additional heating. In the production of high-quality steels, casting into molds is carried out in a continuous cycle and the ingot is cooled in a continuous cycle. The resulting stumps are also rolled: pre-rolled and pre-rolled. This technology typically involves intermediate heating between two successive forming operations. As mentioned above, steel production takes place in a rather long and complex technological cycle.

It is therefore an object of the present invention to provide a solution which enables high-quality steels to be produced directly by continuous casting so that the properties of the resulting mandrels ensure that they can be finished without further operations. It was also our intention to provide an apparatus which enables the process to be carried out.

The object of the present invention has been solved by keeping the cross-sections obtained by continuous casting at a constant cross-sectional circumference between the two points of the casting axis, one of which is the lowest point where the overheated melt is still present and the other the point at the end of the metallurgical length where the product is completely frozen.

The deformation is carried out between two points where the concentration of crystal germs in the liquid core is 10% and 80%, respectively, by deforming the circular blocks into square or rectangular blocks and the square blocks into rectangular blocks. The rectangular blocks are further shaped so that the ratio between the sides of different lengths is farther from 1 than the previous cross-section.

The basic advantage of the process according to the invention is that the particle structure of the continuous casting blocks has a fine and uniform, non-precipitating and suitable for direct finishing, which eliminates the possibility of pre-roll rolling and intermediate heating steps and consequently significant energy savings.

The apparatus of the present invention comprises a steel die-casting roll and a series of arcuate segments formed from segments forming an outer and inner arc casting axis.

wherein, according to the invention, at least one of the inner segments of the inner axis of the casting shaft is provided with a means for moving the segments towards each other between the lowest point of the casting shaft containing the superheated melt and the end of the metallurgical length.

The movable segment is the first internal segment beneath the die, which is pivotable about its axis at its upper end and connected to its lower end by a hydraulic cylinder. The apparatus is provided with lateral segments which, as part of the arc, are provided with cylindrical cylindrical axes perpendicular to the axis of rotation of the cylinders in the inner and outer segments, and the lateral segments facing the movable inner segment are also displaceable perpendicular to the movable inner segment.

The cylinders of the segments are provided with actuators also underneath the movable segment and are coupled to a finished roll, optionally by means of an induction furnace.

Further details of the invention will be illustrated by way of an exemplary embodiment. In the drawing it is

Figure 1 is a schematic sectional view of a continuously cast ingot, a

Figure 2 is a schematic diagram of a continuous casting device constructed in accordance with the present invention and a

FIG. 3 is a view showing FIG. sectional.

Figure 1 shows that the molded material shown is schematically located along a curved X-X casting axis. Inside its upper part there is a metal melt 1 and its surface is formed near the upper edge of the mold 10. The lowest point S of the superheated metal melt 1 is located on the casting axis X-X. During this time, the metal temperature reaches the liquidus temperature. The s <| and above the lines S2 and above, no crystal germs are found in the superheated metal melt 1.

• · · «

The position of the S-point can be determined separately for each die and depends on the temperature of the molten metal 1 in the die, the type of steel and the time parameter established in accordance with the casting speed. The value of the time t can be inferred from the position of the point S, which of course varies with the various casting speeds.

It is generally assumed that the S point is located below the die 10, substantially at the height of the first cylinder. The segment containing the first cylinder can be called a virtually zero segment.

L is the point where the molded product is completely solidified, and the distance is the distance between the above points S and L, which is usually called metallurgical length.

It is generally understood that the molten or plastic material between the lines S and S2 and the already solidified bark P contains crystalline germs in increasing concentrations down to the L point of complete solidification. In this viscous, semi-solidified mass M, there is practically a balance between the actual melt and the crystallized particles floating there. Concerning the casting axis X-X, the concentration of solid particles increases linearly at the S point and between 100% and two at the L point, along the metallurgical length.

The rate of growth of the P crust during casting is obviously the same at all points, while the movement of the M mass is more complex: in any case, the formation of voids or voids above the L point must be avoided as they result in cracks in the final product. In addition, the formation of the metallurgical length must be controlled such that the L point is higher than the forming roll 20 shown in Fig. 2, which is located substantially at the end of the curved casting path.

Surprisingly, our experiments have found that if the crust P is slightly compressed or deformed in cross section before the L point, the finished product will have a mandrel that has all the characteristics necessary to produce a high quality steel product.

The mechanism of this transformation is not entirely clear, but it is believed that during compression of the P cortex, a velocity gradient or acceleration occurs in the mass M, which already has crystalline germs and is in a semi-liquid state, and is formed in the mass by dendrites and dendritic branches. resulting in a breakdown. The size of the particles thus fragmented is reduced and a random distribution is obtained which results in a specific isotropy and homogeneity while eliminating the precipitation, i.e., the enrichment of carbon within the product.

However, the basic condition for the above results is that the core portion is deformed between the S and L points, such that the volume of the product changes without changing its length and its side surfaces must also remain constant. In this way, virtually no stretching or rolling occurs in the original sense of the word, that is, no creep of the solidified material as long as a viscous mass is present in the core of the product. So, as far as the cross-section is concerned, it must in any case be reduced while the circumference of the product must remain constant (in this case, the length is irrelevant as it must remain constant).

Accordingly, the following deformations are possible:

turning the circular product into a square product or a flat billet, or

forming a flat mandrel into a square product, or

- changing the size of a flat billet by increasing the ratio of the lengths of the various sides.

It is theoretically possible to deform a cast ingot from a n-sided polygonal cross-section such that, after forming, at the end of the metallurgical length it becomes an n-1 sided polygon. However, such a formation does not usually occur in practice.

It is to be emphasized that if the forming is not carried out under the above conditions, for example, the volume is increased or remains at the same level, the desired parameters which would allow the ingot to be directly rolled to a finished product without intermediate steps are obtained.

As already mentioned, the deformation according to the invention must take place within the metallurgical length, i.e. starting from the S point and preferably within a defined zone. This zone can be defined so that the concentration of the grain mass in the M mass should be 10-80%. This can easily be determined by considering that x _s = 0 and X [_ = 100. Accordingly, if l _{3 is} the distance of the point S from Iq, then X! the concentration at any point t from j is calculated as follows:

X = - fa

It would be redundant to perform deformation or volume reduction at a point too high in the melt where the concentration of the crystal nuclei is relatively low and deformation would not be sufficient if ···· ··· they are relatively far away. Therefore, moving the already frozen bark would be virtually irrelevant.

On the other hand, it can also be disadvantageous to start the deformation too low, i.e. at a point near the L point where the frozen bark portions are already so close together that joints may occur. As a result, melt-containing cavities may be formed, where shrinkage occurs during curing and casting cavities may be formed.

Figure 2 is a highly schematic diagram of an embodiment of the apparatus of the invention. The molten metal 1 in the mold 10 and then the ingot moves downwards as a result of the extraction rollers 11. The product moves between the rolls 13 formed by segments 12, 14 and 12 ', 14' ... etc. The first section following the extraction rollers 11, where it is sufficient in some cases to provide volume reduction according to the invention, is generally referred to as a zero segment. The segments 12, 12 'and 12 ... etc are located on the outside of the arc of each bank of 13, where the arc has a radius greater than that of the inner segments 14 and 14' ... etc. The rollers in segment 12 are designated by reference numeral 12a, while the rollers in segment 14 are designated by reference numeral 14a and so forth.

According to the present invention, the deformation is carried out in this first section, the inner segment 14, such that the segment 14 itself is displaceable relative to the segment 12 on the other side. The displacement can take place in any way, in the embodiment shown the hydraulic cylinder 16 moves the segment 14 towards the segment 12 which is fixed.

Figure 2 shows that at the upper corner of the segment 14 with rollers 14a it is pivotable about an axis 15 and its lower part is pushed by the hydraulic cylinder 16 towards the opposite segment 12. Of course, the movement can be effected in any other known manner, for example, by positioning the whole segment 14 on a sled and moving the sled using rollers. This type of solution can be used when a square billet is deformed to a flat billet, or when a rectangular billet is deformed to a flatter shape, such as a sheet billet.

However, if a round billet is deformed to a square or rectangular cross-section, it is no longer sufficient to deform it in a single plane as shown in Figure 2, but it must be deformed perpendicularly in this direction. Both deformation planes include the X-X casting axis of the original billet and its tangent. Such a deformation is shown in Figure 3. The circular cross-section is deformed simultaneously from two opposite directions by means of rollers 12a and 14a and 22a and 24a respectively. The rolls 22a and 24a form additional segments not shown in Figure 2, wherein the axis of rotation of the rolls 22a and 24a is perpendicular to the axis of the rolls 12a and 14a in the segments 12 and 14.

The cylinders subsequently located in the device are also preferably coupled to hydraulic cylinders, not for deformation but to keep the previously deformed ingot in the desired state and to prevent swelling relative to the deformed state.

Further details of the invention will be illustrated by way of an exemplary embodiment.

Example

In a continuous die casting machine, a circular mandrel of 130 mm diameter was cast at a speed of 2 m / min. Between 28 and 76% concentration of the crystal germs, in this case, the mandrel was deformed at an 8-meter metallurgical length and turned into a substantially 100 mm side-length square billet.

The billet was then reduced to a size of about 3 m / min and deformed between 14 and 46% at 12 m metallurgical length.

In both cases, samples were taken from the finished product after freezing and the following analysis of the samples showed that:

(a) the stump was fine and did not contain dendrites;

(b) the casting was isotropic, with no grain orientation;

(c) the substance did not show any precipitates and was found in its cross-section according to chemical analysis;

(d) all mechanical properties (tensile strength, creep, elongation at break, impact work) were isotropic;

(e) the mechanical properties measured were better than those of conventional die casting mandrels, thus allowing the production of a finished product with the same properties with less deformation during the rolling steps.

From the foregoing, it will be appreciated that the apparatus of the present invention enables the rolling of products produced by continuous casting and deformed according to the invention directly into the finished product, with the aid of only an intervening heat treatment furnace, which ensures the rolling temperature.

Of course, the illustrated embodiments and the example serve only to illustrate the invention and it is to be understood that the invention may be embodied in numerous forms within the scope of the appended claims.

Claims (10)

• * · · · • · 4 · »« »« ₉ , PATENT CLAIMS A method for producing high quality steel billets from continuously cast steel by deformation of the billet liquid core, characterized in that the billets are formed at a constant value between the two points of the casting axis XX, one of which is the lowest point (L), there is still an overheated melt and the other is the point (S) at the end of the metallurgical length (4n) where the product is completely solidified. Method according to claim 1, characterized in that the deformation is carried out between two points where the concentration of crystal germs in the liquid core is 10% and 80% respectively. Method according to claim 1 or 2, characterized in that the round billet is deformed into a square or rectangular billet. Method according to claim 1 or 2, characterized in that the square billet is deformed to a rectangular one. Method according to claim 1 or 2, characterized in that the rectangular billet is further deformed such that the ratio between the different ones is further from 1 than the previous cross-section. 6. Apparatus for continuous casting of steels, a die, a roll of rolls, and a roll of segments formed by an arc, formed from outer and inner segments forming an arc casting axis, characterized in that the inner segments (14, 14 ', 14). ) at least one of the dividing axis (XX) is the superheated melt s having a lower point {2J and ^ between the point of total cure at the end of the metallurgical length (4η) $ 5) is provided with means for moving the segments (14, 14 ', 14) towards each other. . · '; ··· ··· »*«. · * ··· ··· «. * • ♦ · · · · · · · · · · · · · · Apparatus according to claim 6, characterized in that the movable segment is a first internal segment (14) beneath the mold (10) which is pivotable about its axis at its upper end and connected to a hydraulic cylinder (16) at its lower end. Apparatus according to claim 6 or 7, characterized in that it is provided with side segments (22,24) which, as part of the arc roll (13), are provided in the inner and outer segments (12, 12 ', 14, 14'). ) are provided with cylinders (22a, 24a) perpendicular to the axis of rotation of the cylinders (12a, 14a) and the lateral segments (22, 24) facing the movable inner segment (14) are also opposed perpendicularly to the direction of movement of the movable inner segment (14). are designed. 9. A 6-8. Apparatus according to any one of the preceding claims, characterized in that the rollers (12'a, 12a, 14'a, 14a) of the segments (12, 14, 22, 24) are also provided with movable elements under the movable segment (14). 10. A 6-9. Apparatus according to any one of claims 1 to 3, characterized in that it is connected to a ready-made roll, optionally by means of an induction furnace. A-L The Trustee