DE102012009870A1 - Method and strand guide for influencing the solidification of the partially still liquid core during continuous casting - Google Patents

Abstract

1. Method for influencing the solidification of the partially still liquid core of slabs and blooms of steel during continuous casting 2.1. The invention relates to a method for influencing the solidification of the still partially liquid core of slabs and blooms of steel during the continuous casting, 2.2. It is provided that periodically takes place a force or Weginwirkung on the broad sides of the strand.

Description

The invention relates to a method for influencing the solidification of the still partially liquid core of slabs and billets of steel during the continuous casting, and a strand guide for carrying out the method.

Methods for influencing the solidification of the still liquid core in continuous casting are known. These include, for example, those in which mechanically acting hammer vibrators are used, which are integrated into the strand guide ( EP 2 174 734 A1 . EP 2 258 499 A1 ).

Common to these is that an impact on the narrow sides takes place.

Furthermore, segments are known whose upper frame can be moved in a controlled manner during casting in the thickness direction (position-controlled segments, in the case of SMS: CyberLink segments, in the case of VAI: smart segments). Some of these segments are able to perform this position control dynamically (CyberLink segments).

A disadvantage of the first-mentioned devices or methods is the considerable additional expenditure on equipment and the considerable metallurgical effect. Of the second-mentioned devices or methods, only applications are known that have a static effect on the cast strand or whose dynamic effect on the cast strand serves metrological tasks and is designed only for such.

The object of the invention is to influence the structure during continuous casting by comparatively simpler means effectively.

This object is achieved according to the invention with a method for influencing the solidification of the still partially liquid core of slabs and billets of steel during the continuous casting, which is characterized in that periodically takes place a force or Weginwirkung on the broad sides of the strand

Embodiments emerge from the dependent claims 2-7, as well as directed to the strand guide claims 8 and 9.

According to the invention a positive influence on the solidification process and the associated phenomena (accumulation of impurities, segregation and unwanted structure formation before the solidification front, loosening and cavitations in the field of Enderstarrung) are exercised, namely with the widest possible use of the already existing strand guiding components and without adverse metallurgical Effects (periodic pouring mirror fluctuations).

The volume change in the liquid core region resulting from the periodic application of force or change in position exerted according to the invention produces a flow in the direction of the meniscus (bath level), which leads to breakage of the dendrite tips on the solidus front of the strand shell. The required flow rate is estimated in the literature at about 0.3 to 0.6 m / s.

v

Strömungsgeschwindigkeit

V

Verstärkungsfaktor = Verhältnis der wirksamen Flächen bzw. Längen

e

Oszillationsamplitude

ω

Kreisfrequenz der Oszillation

f

Oszillationsfrequenz

A_Seg

Klemmfläche des Segments

A_fl

Querschnittsfläche des flüssigen Stranginhaltes

l

Klemmlänge des Segmentes

d_fl

Querschnittshöhe des flüssigen Stranginhaltes

b_fl

Querschnittsbreite des flüssigen Stranginhaltes

kann unter Voraussetzung einer Oszillationsfrequenz von z. B. 2 Hz die erforderliche Oszillationsamplitude zu mindestens 0,24 mm ermittelt werden.In order to achieve a minimum value corresponding to this estimate (0.3 m / s), the following pump oscillation movement of the upper frame can be determined:
When moving together, the volume of liquid under the top frame is compressed along the entire length of the segment (eg l = 2000 mm). Dodge it can only perpendicular to the direction of action, so on the bathroom mirror too. The available cross-section is determined by the thickness of the liquid sump (average). This results from the strand thickness and the average shell thickness in the considered interval and is close to the sump tip, for example, 20 mm. About the relationships v = V · e · ω = V · 2 · π · e · f and V = A _Seg / A _fl = (l * b _fl ) / (d _fl * b _fl ) = 1 / d _fl With

v

flow rate

V

Gain factor = Ratio of the effective areas or lengths

e

oscillation

ω

Angular frequency of the oscillation

f

oscillation

A _Seg

Clamping surface of the segment

A _fl

Cross-sectional area of the liquid strand content

l

Clamping length of the segment

d _fl

Cross-sectional height of the liquid strand content

b _fl

Cross-sectional width of the liquid strand content

can under the condition of an oscillation frequency of z. B. 2 Hz the required oscillation amplitude to at least 0.24 mm can be determined.

In the upper part of the continuous casting plant, the ratio of the effective areas is less favorable because of a generally shorter segment length significantly greater height of the flow cross section is opposite. It follows in this area that in order to obtain the same effect stroke amplitude, frequency or their product must be about 10 times larger than in the area of the sump tip.

The volume change described results in a corresponding periodic change of the casting level. Their negative effects can be compensated for by always oscillating two (or more) segments in push-pull mode and thus restricting the flow to (one) region (e) within the strand guide.

Strong jaw width changes may result in impermissible jumps in the reference lines of the segments at the boundary of a stationary or counter-oscillatory segment. These "segment jumps" are avoided if the upper frames of the segments are not moved parallel, but only tilted.

The aim of the tilting movement is to avoid sudden changes in the passline between each two adjacent oscillating segments in favor of a local slight bending stress in the strand shell at this point.

The resulting halved volume change must then be absorbed by a larger deflection.

• • einer Verbesserung der Innenqualität ähnlich einer Softreduction ohne Beschränkung auf die enderstarrungsnahe Zone im Bereich der Solid Fraction (Festphasenanteil) zwischen 0,1 und 0,9 sowie
• • der Möglichkeit einer Gefügeverfeinerung auch im oberen Bereich der Anlage bzw. in den randnäheren Zonen des Stranges.

Advantages of the invention are in

• • an improvement in the internal quality similar to a soft reduction without restriction to the near-solidification zone in the range of solid fraction (solid phase fraction) between 0.1 and 0.9 and
• • the possibility of microstructural refinement also in the upper part of the plant or in the nearer zones of the strand.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2174734 A1 [0002]
• EP 2258499 A1 [0002]

Claims (9)

Method for influencing the solidification of the still partially liquid core of slabs and blooms of steel during the continuous casting, characterized in that periodically a force or Weginwirkung on the broad sides of the strand takes place A method according to claim 1, characterized in that the force or Weginwirkung is vibrating. Method according to one of the preceding claims, characterized in that the force or Weginwirkung is controlled such that in the area of action - based on the still liquid core of the strand - a periodic change in volume is generated, which leads to a against the continuous casting in the direction of the Badspiegel directed flow of the liquid core leads. A method according to claim 3, characterized in that the product of oscillation frequency and oscillation amplitude is greater than / equal to 0.48 mm / s (2 Hz x 0.24 mm) up to 20 mm / s. Method according to one of the preceding claims, characterized in that the force or Weginwirkung takes place in the production flow successive adjacent areas in push-pull. Method according to one of the preceding claims, characterized in that the upper frame of the force or path effecting effecting segments do not move parallel, but are tilted movable. Method according to one of the preceding claims, characterized in that the segments generate the Oszillationsvorgänge against the resistances of the strand. Strand guide of a continuous casting plant for influencing the solidification of the still partially liquid core of slabs and blooms of steel during continuous casting according to one of the preceding claims 1 to 7, characterized in that at least one segment of the strand guide whose holding cylinders are designed so that during casting the upper frame can assume a dynamically variable in strand thickness direction position, which allows an oscillatory movement. Strand guide according to claim 8, characterized in that, in the case of several segments, the upper frame can assume a variable position, wherein the segments can be influenced in a coordinated manner via regulators.