EP0611610B1 - Process for the production of a strip, a pre-strip or a slab - Google Patents

Description

• mit einer Durchlaufkokille mit einem durchlaufend gleichbleibenden Querschnitt einer Bramme,
• einer ersten Verformungsstufe, die im Bereich unterhalb der Kokille, in dem der Strang einen flüssigen Kern aufweist, vorgesehen ist,
• einer zweiten Verformungsstufe, die in dem Bereich, in dem der Strang bereits durcherstarrt ist, vorgesehen ist,
• einer dritten Verformungsstufe, die von einem ein- oder mehrgerüstigen Warmwalzgerüst gebildet ist, und
• einer zwischen der zweiten und der dritten Verformungsstufe angeordneten Trenneinrichtung zur Herstellung von vom Strang abgetrennten Strangstücken.

The invention relates to a method for operating a system

• with a continuous mold with a constant cross-section of a slab,
• a first deformation stage, which is provided in the area below the mold, in which the strand has a liquid core,
• a second deformation stage, which is provided in the area in which the strand has already solidified,
• a third deformation stage, which is formed by a single or multi-stand hot rolling stand, and
• a separating device arranged between the second and the third deformation stage for producing strand pieces separated from the strand.

A method for producing a hot-rolled strip with the smallest possible thickness Help of the continuous casting process and subsequent rolling of the continuous cast product is over PCT publication WO 92/00815. Here, the cast product after it leaves subjected to a first deformation step from the continuous mold, in which the Cast product still has a liquid core. After solidification there is another Deformation step by rolling the solidified cast product, which then on Hot rolling temperature is heated and wound into a bundle. Then there is one Finish hot rolling.

The known method not only requires a complex construction, but is also complicated in terms of control technology and requires a large number to achieve control equipment. Accordingly, it requires a considerable amount Investment. Furthermore, it brings with it a large degree of production uri security, because of the large number of continuously intervening drive units in the event of failure part of the whole process is stopped and the casting process is stopped must become.

In the known method there is no flexibility with regard to product quality and quality given the manufactured products. For example, the first Deformation step must always be carried out, otherwise one necessary for winding Thinness of the product and therefore production cannot be guaranteed. So that is the known method for certain steel grades not feasible. Furthermore is targeted and flexible temperature control with regard to the quality of the finished product hardly possible, especially in transient conditions. If the winding unit fails the overall process also comes to a standstill immediately; this also includes the standstill of the Pouring process.

A similar process, as described in WO 92/00815, is also known from US Pat EP-A 0 504 999 is known. In this process, the cast product is also after the second Deformation stage coiled, and it must therefore have the necessary thinness.

A method for producing a tape in a thickness of 2 to 25 mm is known from the EP-B 0 286 862 known. In this known method, a steel strand is cast formed by melt in a funnel-shaped continuous mold and while passing through the same already deformed. The strand, which still has a liquid core, becomes after Exit from the continuous mold so compressed that there is a weld of inner walls of the already solidified strand shells comes. This will create a Thickness reduction to a thickness of less than 25 mm achieved. This known method leaves however, only apply to very specific steel grades, namely those that have a allow such deformation just below the continuous mold.

Another disadvantage here is that the still thin strand shell on its way through the The mold is badly squeezed, causing wrinkling and overstretching of the Strand shell can come. Also, the relative movement between the Chill copper wall and the strand shell liquid exogenous or endogenous non-metallic Components are pressed into the soft strand shell.

In addition, the deformation in the mold increases the frictional forces uncontrollably. The funnel-shaped continuous mold does not allow an even flow distribution, i.e. it can by the pouring jet emerging from the dip tube already strong stressed strand shell at the critical deformation points by melting weakened, which manifests itself in increased risk of breakthrough. Another disadvantage lies in the very low flexibility in terms of production capacity and in terms of the utilization of the full casting speed range.

EP-B - 0 327 854 describes a method for rolling on a continuous strip caster cast pre-strips known, the cast pre-strip in a continuous Work step brought to the rolling temperature and rolled out into the finishing mill is introduced.

In the event of a malfunction in the finishing mill or in the coiler To avoid production interruptions, it is known from this document, the cast Support strip in the finishing mill as an alternative to hot strip rolling to heavy plate thickness rolling, then cooling, dividing and stacking. With this well-known However, it is not possible to proceed from a relatively large, thin strand To produce tapes.

The invention aims to avoid the disadvantages and described above Difficulties and the task arises to create a procedure which is high Product quality enables the production of tapes as thin as possible, with a very high Operational flexibility is given. In particular, continuous casting should start in the event of a malfunction a deformation stage downstream of the continuous mold can be continued.

• daß zum alternativen Herstellen eines warmgewalzten Bandes aus Stahl oder eines warmverformten Vorstreifens aus Stahl oder einer unverformten Bramme aus Stahl unterschiedliche Verformungsstufen aktiviert bzw. deaktiviert werden,
• zur Herstellung eines möglichst dünnen Bandes sämtliche Verformungsstufen in Summe aktiviert werden,
• zur Herstellung eines Bandes mit etwas größerer Dicke nur die zweite und dritte Verformungsstufe einzeln oder in Summe aktiviert werden, und
• zur Herstellung einer unverformten Bramme alle drei Verformungsstufen deaktiviert werden.

This object is achieved according to the invention by the combination of the following features:

• that different deformation stages are activated or deactivated for the alternative production of a hot-rolled steel strip or a hot-formed steel pre-strip or an undeformed steel slab,
• all deformation stages are activated in total to produce the thinnest possible strip,
• for the production of a tape with a somewhat greater thickness, only the second and third deformation stages are activated individually or in total, and
• all three deformation stages must be deactivated to produce an undeformed slab.

According to the method according to the invention, plate molds with plane-parallel ones Walls. This has the consequence in connection with a dip tube that an even strand shell is formed. This is neither in the continuous mold deformed or squeezed because it has a constant cross-section. The strand emerging from the continuous mold has as a result of the inside of the Continuous mold stable operating conditions (homogeneous conditions such as uniform Lubrication and uniform cooling) a strand shell of the highest quality, so that the risk of breakthrough is minimized and a deformation of the still liquid core having strand is possible without the risk of breakthrough.

The high flexibility of the process is evident in the achievability of small ones Hot strip thicknesses with the same system and with the same number of Roll stands, etc. by reducing the thickness of the pre-strip according to Requirements.

Preferably, the first and second are used to make a tape Deformation level individually or together depending on the steel quality Consideration of their deformation properties in the case of these deformation levels prevailing temperature conditions activated, expedient for high-alloy or high-carbon structural steels, for high-strength tubular steels, for austenitic steels and for Duplex steels only the second and third deformation stages can be activated.

According to a preferred embodiment, the deformation in the first Deformation stage in a manner known per se immediately after the strand emerges from the Mold is carried out, advantageously the deformation in the first deformation stage in is known to be carried out in a plurality of substeps.

Descaling is expediently the second deformation stage in a manner known per se upstream.

Before the third deformation stage, a temperature homogenization of the separated strand pieces carried out.

The high flexibility of the method according to the invention enables that, preferably by the first two stages of the process, applied individually or together, reduce the Thickness of the strand down to a minimum thickness of 30 mm is carried out. Consequently the severed strand has a thickness of at least 30 mm before it Further rolling is fed. This thickness can be in the case of switching off the first two Deformation stages up to the casting thickness, i.e. up to a maximum of 150 mm, in particular 100 mm.

The invention is based on an exemplary embodiment Schematic sketch explained in more detail.

1 with a continuous mold for steel casting is referred to, the one continuous has a constant cross section and is preferably designed as a plate mold. With this continuous mold, cast strands with a thickness 2 between 60 and 150 mm, preferably in a thickness between 60 and 100 mm (so-called thin slabs) become. For continuous molds of this thickness, the use of a conventional one Dip tube 3 possible, resulting in stable operating conditions, which cooling and Melt distribution concerns, so that the leaving the continuous mold 1 Strand 4 is a uniform and stable strand shell having.

Below the continuous mold 1, which is preferably straight Mold is designed to form a first Deformation stage arranged a vertical support structure 5, the hydraulic (- as indicated by pressure cylinder 6 -) the strand shell has adjustable support rollers 7. This Vertical support frame is divided into two sub-segments 5 ', 5' ', so that with each sub-segment different forces on the Strand 4 can be applied. With the help of this Vertical support frame 5 becomes a so-called "soft reduction" of the solidifying strand 4 with the still liquid core as the first Deformation step performed, the load on the Strand shell in the two-phase boundary layer under one Ultimate elongation influencing end product quality remains. With With the help of this so-called "soft reduction" one can Reduction of the strand thickness by up to 30 mm without Achieve quality losses. Subsequent to the vertical segment 5, further arc segments 8, 9 are provided, which optionally also hydraulically adjustable support rollers 7 exhibit.

After the strand 4 has been deflected into the horizontal, it becomes through a simple (possibly multi-stage) Deformation scaffold 10 passed, which is used to deform the now already solidified strand 4 as the second Deformation stage (second deformation step) can be activated can. This corresponds to a thickness 12 of a pre-strip the required hot strip thickness with a stitch acceptance up to reached a maximum of 60% (e.g. 70 to 30 mm).

Before it passes through the deformation framework 10, the strand 4 descaling in a descaling device 11 subjected to soft descaling by means of rotating Descaling nozzles and with special water wipers for the descaling water enables.

The thickness pre-reduction allows one before the temperature compensation Influencing the end product quality especially for microalloyed steels, which are usually replaced by appropriate Stitch decreases above the recrystallization stop temperature Precipitation and recrystallization processes are influenced.

After the pre-reduction, the strand 4 preferably has the format a roughing strip, i.e. a (non-wrapable) raw material for tape production. The thickness 12 is preferably 30 mm and more.

A separating device is arranged downstream of the deformation framework 7 13 for the transverse division of the cast strand 4, which depends on Requirements for the end product in the continuous caster deformed strand 4 using hydraulic scissors in the Coil weights corresponding lengths are separated.

The resulting strand pieces 14 with a thickness of 30 to 150 mm (the latter in the case of an undeformed strand of maximum thickness) then run into a transport and homogenization facility, e.g. a roller hearth furnace 15, depending on the slab temperature is also able to heat a thin slab. In this Roller hearth furnace 15 is the entire cross section of the strand piece 14, in particular their edges, to a uniform temperature brought. In this furnace unit 15, the strand pieces can are buffered (stored, e.g. by stacking), i.e. in the In the event of brief malfunctions in a part of the facility Thin slabs or strand pieces 14 added until it Resumption of the manufacturing process is coming.

Following the roller hearth furnace 15 is another Separating device, which is designed as hydraulic scissors 16 is provided, in the event of a malfunction in the following Rolling mill stage 17 functioning as the third deformation stage is activated. Before entering rolling mill stage 17 descaling in a descaling device 18, the preferably a rotor descaling with low water consumption and the resulting low temperature drop excellent descaling effect.

Subsequently, the strand pieces are rolled in the Rolling mill stage 17, which consists of finishing stands 19. The number of the finishing stands 19 of the finishing train results from the thickness 12 of the strand pieces 14 after separation from the cast strand 4 and of the strip thickness to be rolled 20. Experience the strand pieces 14 no γ-α conversion until that point in time Manufacturing process to which the γ-α conversion is due material science processes to achieve the required mechanical-technological characteristics and toughness for the steel grade is required.

For smaller capacities, the finishing train can be Steckel rolling mill to be replaced. This possibility will preferably for the production of hot strips made of stainless steel Steel or special steel made from thin slabs.

After leaving the rolling mill stage 17, the rolled Strand piece 14 in a cooling section 21 (laminar cooling section) Cooled reel temperature and by means of a reel device 22 wound into a bundle 23. The finished rolled strip is 24 designated.

The possible combinations of the three deformation levels increase the overall system flexibility, since also without "soft reduction" (first deformation step) liquid sump or rolling after solidification (second Deformation step) the overall process without quality and Performance loss in operation remains. For example, at the activation of all of the present system Deformation levels only for approx. 15 to 20% of the total production necessary, namely for that part of the production which is based on a Final thickness to be rolled with the finishing train otherwise not reachable.

Furthermore, the arrangement allows the energy to be optimized Overall process by balancing the casting thickness (D) and Final thickness (P) with the aim of achieving the greatest possible enthalpy Bring strand pieces in the roller hearth furnace 15. Reached this is achieved through a dynamic cooling regime using air-water jets to increase the exit temperature of the strand as well as "soft descaling".

In the process proposed according to the invention, the structural changes that usually take place are eliminated since the steel temperature does not drop below the transition temperature Ar ₃ . The processes required for a fine and homogeneous structure, which do not take place in the case of specific steel grades, are compensated for by the proposed system parts with the help of the pre-deformation. This advantageously opens up new perspectives for the production of microalloyed steels with the help of thin slab technology.

The variety of the method according to the invention is documented in the table below. In this table, the smallest achievable strip thicknesses with a casting thickness of 70 mm are given in horizontal lines for different steel qualities, whereby it is additionally indicated which of the first two deformation stages is activated. The first deformation stage - with a thickness reduction of 10 mm - is designated I and the second deformation stage - with a thickness reduction of 20 mm - with II. If the corresponding deformation level is activated, this is marked with an X, if it is not activated, it is marked with a 0. An N indicates that these strip thicknesses should not be produced solely by the process steps according to the invention. The third deformation stage (rolling mill stage 17) is always in operation with five to seven finishing stands 19 for the dimensional ranges specified in the table.

Claims (8)

1. A method of operating a plant

   comprising an open-ended mold (1) having a continuously constant cross section of a slab,

   a first forming stage (5 to 9) provided in the region below the mold, in which the strand (4) has a liquid core,

   a second forming stage (10) provided in the region in which the strand (4) has already completely solidified,

   a third forming stage (17) constituted by a one- or multi-stand hot-rolling stand (19), and

   a separating means (13) provided between the second and third forming stages for producing strand pieces (14) separated from the strand (4),
   characterized in that

   for alternatively producing a hot-rolled strip (24) of steel or a hot-formed pre-strip (14) of steel or an unformed slab of steel, different forming stages are activated or deactivated, respectively,

   for producing a strip (24) as thin as possible, all of the forming stages are activated in sum,

   for producing a strip (14) having a slightly larger thickness, only the second and third forming stages are activated individually or in sum, and

   for producing an unformed slab, all of the three forming stages are deactivated.
2. A method according to claim 1, characterized in that, for producing a strip (24), the first and second forming stages are activated individually or jointly as a function of the steel grade and under consideration of the forming properties of the latter at the temperature conditions prevailing during these forming stages.
3. A method according to claim 1 or 2, characterized in that only the second and third forming stages are activated for high-alloy or high-carbon structural steels, for high-strength tube steels, for austenitic steels and for duplex steels.
4. A method according to claim 1 or 2, characterized in that forming in said first forming stage is carried out in a manner known per se immediately upon emergence of the strand (4) from the mold (1).
5. A method according to claim 4, characterized in that forming in said first forming stage is carried out in a plurality of partial steps in a manner known per se.
6. A method according to one or several of claims 1 to 5, characterized in that said second forming stage is preceded by descaling in a manner known per se.
7. A method according to one or several of claims 1 to 6, characterized in that temperature homogenization of the separated strand pieces (14) is effected before said third forming stage.
8. A method according to one or several of claims 1 to 7, characterized in that a reduction of the thickness of the strand (4) down to a minimum thickness of 30 mm is effected by the first two method stages applied individually or jointly.

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