WO1997001401A1

WO1997001401A1 - Plant for the manufacture of steel strip

Info

Publication number: WO1997001401A1
Application number: PCT/EP1996/002873
Authority: WO
Inventors: Cornelis Pronk
Original assignee: Hoogovens Staal B.V.
Priority date: 1995-06-29
Filing date: 1996-06-28
Publication date: 1997-01-16
Also published as: ZA965574B; NL1000693C2; AU6516596A

Abstract

A plant for the manufacture of steel strip, comprises a continuous casting machine (1) for casting a steel slab, and at least one furnace apparatus (13, 14) receiving the steel slab. The furnace apparatus has an entry port and an exit port for the slab and an enclosed path for the slab. A coiling apparatus (27, 28) receives the steel slab from the furnace apparatus. The coiling apparatus has an enclosure providing an enclosed space and an entry port for entry of the slab into said enclosed space. A rolling apparatus (40) receives the steel slab uncoiled from said coiling apparatus and rolls the slab into strip of a desired thickness. A non-oxidising gas atmosphere is provided in the furnace apparatus and in the enclosed space of the coiling apparatus, and the exit port of the surface apparatus is gas-tightly and detachably connectable to the entry port of the coiling apparatus. This minimizes oxide formation and allows flexible operation of the plant.

Description

PLANT FOR THE MANLTFACTLTRE OF STEEL STRIP

Field of the invention

The invention relates to a plant for the manufacture of steel strip, in which steel slabs are cast in a continuous casting maching and are thereafter rolled into strip. It also relates to a furnace apparatus and a coiling apparatus for use in the plant.

Description of the prior art

There have been many proposals for a strip-making plant of the above type. In O92/00815 there is proposed a plant having in succession a continous casting machine for casting slab, a first hot-rolling train for reducing the thickness of the fully solidified slab, an induction furnace for re-heating the slab and a coiler. From the coiler, the steel is fed into a hot-rolling train, then to a water-cooling means and to a cold-rolling mill. A similar plant is described in EP-A-504999.

This apparatus is for use in a method in which, starting with molten steel being cast into a slab, a strip of formable steel is manufactured in a continuous or virtually continuous process . Such a method and the associated apparatus by which that method may be carried out offers the advantage that it achieves a high material yield for relatively low investment costs . In addition it enables good correspondence between the capacity of the continuous casting machine and the rolling capacity of the mill stands, leading to short waiting times and thus a high return on investment. A drawback of the installation and of the method which may be used with it is that for the reasons described below it can only be used for manufacturing low steel grades .

Important properties in determining the grade of a steel sheet are the formability and the appearance, i.e. the surface quality. The oxide that forms on exposure of the hot steel through contact with the surrounding atmosphere has an important disadvantageous influence on the surface quality. For this reason the normal method with steel which is rolled in the austenitic range is removal of oxide from it beforehand by water spraying, cooling down to the ferritic range and then pickling to remove the newly formed oxide scale. The pickled steel is cold rolled to reduce the thickness to a desired value, to improve the surface and, in combination with a heat treatment, to improve the crystal structure.

Even when the plant described above is used the disadvantageous oxide formation occurs, first of all in the continuous casting machine. This means that in any event this oxide has to be removed because the slab is being rolled and otherwise oxide particles would be rolled into the material. For this, it is known to use high pressure water sprays with pressures of up to 200 bar. Moreover, during homogenisation in the furnace and during possible reheating prior to rolling, a tenacious oxide occurs which cannot be removed even by water spraying with water pressures of 400 bar and which ultimately has to be removed by pickling. However, a part of the tenacious oxide has already been rolled in thereby affecting the quality of the surface. By its nature a pickling procedure works to the detriment of material yield because of material loss . Also the pickling installation necessitates an extra investment thereby reducing the return on capital. Pickling is a slow process that reduces the capacity of the entire apparatus . The result is that use of the known apparatus does not make possible the achievement of the advantage that in theory should be possible with it .

Proposals have been made for providing a low- oxidation or non-oxidation atmosphere around the steel when it is at high temperature in such a plant . This is described in JP-A-62-114701 for the homogenization furnace and for a buffer furnace for holding coils prior to the hot finishing mill. It is specifically proposed here to achieve a low-oxidation atmosphere by a low air ratio combustion in recuperators for pre¬ heating the air in the furnaces. In JP-A-62-89501 it is proposed to subject many parts of a strip plant to nitrogen sealing. Particularly shown with enclosures for nitrogen sealing are the continuous casting machine, a slab cutter, a slab conveying line and a slab buffer store. It seems to be proposed also that other parts, such as a roughing mill and subsequent devices are also subject to nitrogen sealing. No coiler for slab after the roughing mill is shown. Such proposals however do not appear sufficient to solve the problem described above of oxide arising in the slab furnace in an efficient and economical manner.

It is mentioned for completeness that US-A-4675974 also proposes an inert or reducing atmosphere in an insulated run-out furnace for the slab from a continous casting machine. This furnace is connected to a hot reversing mill provided with upstream and downstream coiling furnaces, rather than to a continuous hot strip mill.

Summary of the invention

The object of the invention is to create a plant for manufacture of an apparatus of steel strip which avoids or at least reduces the drawbacks described above, and can achieve other advantages.

According to the invention there is provided a plant for the manufacture of steel strip, comprising

(a) a continuous casting machine for casting a steel slab, (b) a furnace apparatus arranged for receiving the steel slab cast in the continuous casting machine (optionally with thickness reduction of the solidified slab prior to entry to the furnace apparatus) , for adjusting the temperature of the steel slab, the furnace apparatus having an entry port and an exit port for the slab and an enclosed path for the slab from the entry port to the exit port,

(c) a coiling apparatus for receiving the steel slab from the furnace apparatus, coiling the slab and subsequently uncoiling the slab, the coiling apparatus having an enclosure providing an enclosed space in which the slab is coiled and an entry port for entry of the slab into the enclosed space, (d) rolling apparatus for receiving the steel slab uncoiled from the coiling apparatus and rolling the slab into strip of a desired thickness, and

(e) means for providing a non-oxidising gas atmosphere in the furnace apparatus at the path thereof and in the enclosed space of the coiling apparatus, wherein the exit port of the furnace apparatus is gas-tightly and detachably connectable to the entry port of the coiling apparatus.

By this plant there is achieved the effect that from the time when the slab runs into the furnace apparatus until the time ic is conveyed out of the coiling apparatus, the slab does not come into contact with the outside air, but rather it is continually surrounded by a gaseous atmosphere of a non-oxidizing composition. For this purpose the gaseous atmosphere in the furnace apparatus and in the coiling apparatus may be the same or different.

The gas atmosphere provided in the furnace apparatus and the coiling apparatus is substantially non-oxidizing, though inevitably it may include a small amount of oxygen due to leakage of air. Preferably it is based on nitrogen, although an inert gas such as argon may be used if its high cost allows. The nitrogen may contain additive for inhibiting nitriding of the steel surface, as is known in the process of batch annealing of steel. The gas atmosphere may contain water vapour.

Typically the furnace apparatus is built as an electric furnace in which, by means of resistance or inductive heating, energy is supplied to the slab, so that in any event the surface of the slab is heated again after having cooled as a consequence of the descaling by high pressure water sprays and because of heat loss to the surroundings. In the case of conventional plants, during this heating the surface is exposed to the normal outside atmosphere along a relatively great distance and thus for a relatively long time, so that an oxide scale again forms on the surface, which under these conditions is a thin, tenacious layer which in practice cannot be completely removed with available very high water pressures and which ultimately must be removed by pickling.

The furnace apparatus may be employed only for homogenizing the temperature of the steel slab, or may be arranged to alter at least the core of the slab in temperature.

In the plant in accordance with the invention the slab is prevented from coming into contact with the outside atmosphere as it passes through even a relatively long furnace apparatus, so that oxide scale thereby forming on the outer surface of the slab is minimized.

As stated, the coiling apparatus is provided an enclosure, i.e. screening means, for maintaining the desired gaseous atmosphere in the coiling apparatus. In the case of a conventional plant, the slab is coiled at a relatively high temperature in the coiling apparatus and stored there for some time for temperature homogenising or for waiting for further processing in the rolling apparatus. With the invention, the slab is prevented from still oxidising or oxidising further during its stay in the coiling apparatus. The coiling apparatus preferably has sealing means, such as a door for closing its entry port and maintaining the desired atmosphere in it, when it is detached from the furnace apparatus . Because of the need to attain a desired internal structure of the steel strip it may be desirable to select an advancing speed of the strip in the rolling apparatus which is considerably higher than the casting speed in the continuous casting machine. In that case a stoppage may occur in the rolling apparatus while feeding of a fresh coil is awaited. To avoid this waiting time in a rolling apparatus, it is known to place in parallel two continuous casting machines or a continuous casting machine with two strands and thereby to cast two slabs virtually simultaneously and synchronously. In that case the slabs arriving from the different casting machines are rolled one after the other which means that a waiting time for a coil can now occur in a coiling apparatus . To prevent oxygen still reaching the coil from the outside atmosphere while this waiting time elapses, the coiling apparatus is as mentioned preferably provided with sealing means for sealing its entry port gas-tightly. By sealing off the entry of the coiling apparatus for detaching it from the furnace apparatus, it is possible to preserve the desired gaseous atmosphere in the coiling apparatus for a sufficiently long time, even if the coiling apparatus does not have its own means for providing a non-oxidizing atmosphere. This feature also creates the same advantage of temporary storage in a conditioned gaseous atmosphere in the event that no waiting time occurs but the coiling apparatus is moved from the furnace apparatus to the rolling apparatus.

Together with other measures in accordance with the invention this feature also contributes to the particular advantage that the strip can be rolled into a smaller thickness. With the conventional apparatuses for hot rolling a steel strip it is not possible in any effective manner to achieve a finished thickness smaller than approximately 1.3 mm. The reason for this is that the maximum exit speed of the strip is restricted because of the risk that due to airflow it will fly uncontrollably. This fact combined with the inevitable cooling during the rolling process and the requirement that the final rolling stage in hot-rolling has to take place in the austenitic range, means that the entry temperature of the slab as it enters the rolling apparatus must be set as high as possible. However, an entry temperature set too high causes a rapid growth of an oxide scale on the surface which during rolling is then rolled into the material causing surface defects. All this in combination means that in conventional plants it is not efficient to make hot rolled steel with a thickness smaller than 1.3 mm in sizeable quantities . With the plant in accordance with the invention it is possible to move the exit of the coiling apparatus, filled with a chosen gas, close to the entry of the rolling apparatus. Thus, at the point when it is at a high temperature, the slab is only in contact with the outside air along a very short distance. The entry speed can now be reduced without oxide occurring on the surface, so that, in its turn, the slab may be rolled to a smaller thickness before the risk of flying occurs. Finished thicknesses smaller than 1.0 mm can be obtained with the plant in accordance with the invention. This allows considerable advantages to be attained not only in the range of application of steel sheet but also in subsequent processing.

In practice it is known for a continuous casting machine for casting thick slabs to be located in the vicinity of a steel plant and to set up a rolling apparatus for rolling a slab, pre-reduced or not pre- reduced, in a separately situated rolling mill complex.

Of particular advantage is therefore an embodiment of the invention in which the coiling apparatus is mobile, e.g. is movable, carrying a coiled slab, relative to the furnace apparatus and the rolling apparatus. This arrangement achieves the effect that the casting machine, optionally with roughing means, and the furnace apparatus may be physically located at a far distance from the rolling apparatus . The coiled- up coil in the coiling apparatus may be conveyed from the continuous casting machine to the rolling mill without the coil being affected by the outside atmosphere. Consequently the apparatus and the method to be carried out with it can fit with ease in existing steel production facilities.

In another preferred embodiment of the plant in accordance with the invention, the conditioning means are provided with recirculation means for discharging gas forming the gaseous atmosphere out of the furnace apparatus and if desired, processing and reconveying it back into the furnace apparatus . In doing this it is possible to suck away the gas, optionally to modify the gas composition, and then to convey the gas back into the furnace apparatus. The forced motion achieves a better transfer of heat and thereby a better temperature homogenisation. For modifying the gas composition it is possible to conceive the removal of inward-leaking oxygen or the addition of a component which exerts a metallurgical effect such as decarbonisation. It is also possible to heat the gas so that, in this manner heat is added directly to the slab. Other possibilities are provided with an embodiment of the plant in which the furnace apparatus is provided with cooling means for cooling the gas of the gaseous atmosphere. With this embodiment it is possible to cool the slab, if desired following roughing in the austenitic region, in a conditioned gaseous atmosphere down to the ferritic region preferably above 200 °C or to the lower part of the two- phase austenitic-ferritic region, and to coil the slab at such a temperature without a harmful amount of oxide forming on the surface. When still in the temperature range indicated, the slab may be rolled in the rolling apparatus into the steel strip of a desired thickness. This embodiment thereby opens up the possibility of making a formable steel strip having cold strip properties as regards forming behaviour and surface quality, in a very compact installation. Where still higher demands are placed on those properties, the strip may, if desired, be further processed in the conventional manner, whether or not in-line, or in a following continuous process.

In order to avoid influencing the gaseous atmosphere in the coiling apparatus and possibly also in the furnace apparatus, it is preferable for the coiling apparatus to be provided with electrical heating means, if desired with^' an adjustable or controllable capability. It is known to heat a coiling apparatus to prevent the slab within it from cooling during storage. For this gas heating is normally chosen. The combustion gases of such gas heating still contain oxygen and so can cause oxide scale. This drawback is avoided with electrical heating. With this embodiment it is preferable to provide, for supply of electrial power to the electrical heating means of the coiling apparatus, stationary electrical conductors and, on the coiling apparatus, current collectors movable in contact with said stationary electrical conductors when the coiling apparatus moves. Current conductors are relatively simple and relatively inexpensive components and may be laid over great distances. This makes it possible, at low cost and with great reliability and safety, physically to split a plant in accordance with the invention into at least two parts situated at a distance from one another, so that each part is accommodated in the optimum place for that part . The coiling apparatus may be adapted to travel on rails or may be placed on a transport means such as the chassis of a truck or a car. It is possible to provide the transport means by which the coiling apparatus is conveyed with a generator for generating electrical energy.

A particularly great freedom of movement of the coiling apparatus is obtained when the plant is provided with rotation means for rotating the coiling apparatus around a vertical axis. This makes it possible to move the coiling apparatus in a horizontal plane between the different positions which it has to adopt during normal operation. The necessary means of driving and control of the transport can be executed with simplicity. Another feature which provides greater flexibility in use is that the coiling apparatus is provided with a mandrel onto which the coil can be coiled. The crop end of a slab, whether or not subjected to roughing, is clamped onto the mandrel and then coiled in the coiling apparatus into the coil in a path determined by the mandrel. This forced path makes it possible to coil a wide range of thicknesses reliably. This achieves a great freedom in the part of the process taking place prior to coiling, and it is also possible to coil thin, rolled slabs. Such slabs have a relatively large exposed surface. With the plant in accordance with the invention this surface is screened from oxygen from the outside atmosphere. Consequently it is possible to profit from the plant to the maximum.

The invention also provides a coiling apparatus and a furnace apparatus as described above, useful as components of the plant in accordance with the invention.

Introduction of the drawings

The invention will be illustrated in the following by a non-limitative example of an embodiment, with reference to the drawings. In the drawings: -

Fig. 1 is a schematic top-view of a plant in accordance with the invention, and

Fig. 2 is a schematic side-view of the plant of Fig. 1. Description of the embodiment

Fig. 1 shows a continuous casting machine 1 for two strands. The continuous casting machine 1 comprises a ladle turret 2 in which two ladles 3 and 4 can be accommodated. Each of the two ladles can contain approximately 300 tons of liquid steel. The continuous casting machine is provided with a tundish 5 which is filled from the ladles 3 and 4 and kept filled. The liquid steel runs out of the tundish into two moulds (not drawn) from where the steel, now in the form of a partially solidified slab with its core still liquid, passes between the rolls of curved roller tables 6 and 7. For some grades of steel it can be an advantage to reduce the steel slab in thickness in roller tables 6 and 7 while its core is still liquid. This is known as squeezing.

Descaling sprays 8 are located on the exit side of the two roller tables 6 and 7, by which oxide scale is sprayed from the slab with a water pressure of approximately 200 bar. Starting with a cast thickness of for example approximately 60 mm, the slab typically still has a thickness following squeezing of approximately 45 mm. By the 3-stand roll trains 9 and 10 the slab is further reduced to a thickness ranging from 10 to 15 mm. If desired the head and the tail may be cut off the slab by the shears 11 and 12, or the slab sheared into parts of a desired length. Instead of casting a thin slab with a thickness of less than 100 mm, it is also possible to cast a thicker slab and by means of rolling, in particular by means of reversible rolling, to reduce the thickness of the slab to a value ranging from 10 to 15 mm.

The method of using the rest of the apparatus depends on whether it is to make cold-rolled or hot- rolled steel.

When used for making hot-rolled steel the slab will generally be rolled into an intermediate slab with a thickness of 15 mm, as mentioned above. This rolled slab is conveyed into the furnace apparatus 13 or 14. The furnace apparatuses are each provided with heating means (not drawn) , for example induction heating means, for heating the rolled slab up to a desired temperature in the austenitic region. The furnace apparatuses are in the form of enclosures and are provided with conditioning means for creating^' and preserving a desired non-oxidizing gaseous atmosphere in the furnace apparatus . In the embodiment shown the conditioning means of a furnace apparatus comprise a suction line 15, a pump 17, gas metering and gas scrubbing means 19 and a supply line 21 along which the gas is pumped into the furnace apparatus. If desired the gas metering and gas scrubbing means 19 may also comprise a gas heating apparatus for compensating for any heat loss . Thus heat exchangers can be employed to control the gas temperature, using gas combustion to supply heat, and water for cooling.

The furnace apparatus is provided on its entry and exit sides with ports 23, 25 having sealing means to substantially prevent any undesired penetration of gas from the surrounding atmosphere. A suitable value for the temperature of the reduced slab on exiting the furnace apparatus is 1080 "C. The furnace apparatus is coupled essentially gas-tightly to the coiling apparatus 27, which coiling apparatus 27 itself comprises an essentially gas-tight enclosure in which the slab is coiled into a coil. The coiling apparatus is preferably provided with a mandrel 29 which supports the coil as it is being coiled. In this embodiment, the gas atmosphere provided in the furnace apparatus also enters the coiling apparatus when the latter is connected to it. Alternatively both the furnace apparatus and the coiling apparatus may be provided with conditioning means, as described above, for providing the desired atmosphere.

As appropriate, virtually synchronously with coiling of a slab onto coiling apparatus 27, a slab cast on the other strand is coiled in coiling apparatus 28 provided with a mandrel 30 (not drawn) . Coiling apparatuses 27 and 28 and furnace apparatuses 13 and 14 are each provided with sealing means 33, 35, 34, 36 respectively, by which the coiling apparatuses and the furnace apparatuses may be sealed for uncoupling, so that following uncoupling no gas can penetrate from the outside atmosphere and the gaseous atmosphere in the coiling apparatuses and the furnace apparatuses remains preserved. The sealing means for the ports of the furnace apparatuses and the coiling apparatuses are suitably steel flaps, biassed to the closed position, or they may be doors which are driven. To minimize gas leakage, flexible curtains may additionally be provided.

As soon as the coiling apparatus 27 is filled with a slab coiled into a coil, this coiling apparatus 27 is uncoupled from the furnace apparatus 13 and driven from position A (see Figure 1) past position B to position C. At position C there is a turnstile 31 (not drawn) by which at position C the coiling apparatus may be rotated through 180° around a vertical axis. Following rotation the coiling apparatus is driven past waiting position D to entry position E. As a coiling apparatus travels from position A to position E, an empty coiling apparatus is driven from position E to a turnstile 37 at position F. Following rotation through 180^* around a vertical axis by the turnstile 37, the coiling apparatus is driven past position G to the starting position A and there it is ready for taking up a fresh slab.

A corresponding working method is applicable for the second strand, whereby the coiling apparatus 28 filled with a coil is driven from position B to position C and following 180° rotation to position D. The coiling apparatus stays parked in this position until a coiling apparatus which is currently uncoiling, for example coiling apparatus 27, is empty at position E and driven off to the now vacated position F. As soon as coiling apparatus 28 leaves position B, an empty coiling apparatus from position I, following rotation through 180° around a vertical axis by means of a turnstile 38, is moved via position K to take up the position of the coiling apparatus 28 now driven off. The new slab fed out of the furnace apparatus 14 can be coiled in the empty coiling apparatus. Devices, preferably electrical current conductors (not shown) , are fitted along the paths over which the coiling apparatuses travel for providing power for internally heating the coiling apparatuses according to need. For this purpose, the coiling apparatus contains electrical heaters for heating the coils and contacts for pick-up of power from the fixed conductors. Path B, C, D, E is common and used as described by coiling apparatuses of both strands. Position C has a rotation facility and position D is a waiting position in which a coiling apparatus filled with a coil is ready to be moved to position E as soon as it becomes free. Positions C and D may be swapped or may coincide.

In the manner described, a coiling apparatus 27 arrives at position E with its sealing means 33 closed and filled with a coil with a temperature of approximately 1080^*C. After the sealing means 33 have been opened the extremity of the outer winding corresponding to the tail of the coiled slab is fed into the rolling train. If desired the head may be cut off by crop shears if it does not have a suitable shape or composition for further processing. Should some oxide still have occurred, this can then be removed easily using the high pressure spray 42. In practice oxide formation will be negligible because the slab has been almost constantly in a conditioned gaseous atmosphere. Because the coiling apparatus rotates through 180°, its original infeed which is now the outfeed can be brought up very close to the entry of the rolling train. This also minimizes oxide formation.

In the example shown, the rolling train 40 is provided with four mill stands and is so designed that the slab can be rolled in the austenitic range, or at least at such a temperature that only a small part converts to ferrite. A minimum target temperature of approximately 820 'C applies for low-carbon steel. For controlling thickness, width and temperature, a measuring and control apparatus 43 may be incorporated in the rolling train, after or between the mill stands. As described above, the apparatus in accordance with the invention achieves the effect that less oxide forms as the slab and the strip are being processed. Because of this and because of the lower entry speed in - 91 -

the last rolling train 40 which this achieves as an additional advantage, it is possible to attain a smaller than conventional finished thickness of the hot rolled steel. Exit thicknesses of 1.0 mm and less from the rolling train 40 can be attained with the plant described.

After exiting the rolling train 40, the hot-rolled strip passes through a cooling line 44 in which the strip is cooled to a desired temperature in the ferritic range by means of water cooling. Finally the strip is coiled into a coil on the coiling apparatus 45. By selecting the cooling on the cooling line it is possible in a manner known in itself to influence the recrystallisation in the ferritic range and thereby influence the mechanical properties of the hot rolled strip.

With this apparatus in accordance with the invention it is alternatively possible to make a ferritically rolled strip. In such an application the slabs will preferably be rolled in rolling trains 9 and 10 to a thickness of approximately 10 mm. Furnace apparatuses 13 and 14 are now used primarily as cooling apparatus, possibly in combination with extra heating to compensate for heat losses, or to heat the slab locally as required. To obtain the cooling effect the gas is sucked from the furnace apparatus through suction line 15, arranged into a desired composition and cooled in the conditioning apparatus, and then conveyed back into the furnace apparatus through line 21. Both furnace apparatuses are equipped with such a conditioning apparatus. A suitable value for the temperature of the slab on exiting the furnace apparatus is 780°C.

The slab is coiled in the manner described above into a coil which is moved to position E stored in one of the coiling apparatuses .

Following any desired cutting off the crop end with shears 41, and if desired, following oxide removal by means of high pressure sprays, the ferritic slab is rolled in the ferritic region in the rolling train 40 to a finished thickness which, as is conventional, ranges between 0.7 mm and 1.5 mm. For most steel grades further cooling is not necessary and the ferritic strip can be coiled into a coil on the coiling apparatus 46 which may be placed at a short distance after the rolling train.

Therefore, using the plant in this manner it is possible using the casting heat to manufacture in a successive series of process stages a ferritically rolled steel strip with good properties in particular in terms of the surface quality. External heating after casting may be avoided (except any heat generated by the rolling) .

The proposed paths of movement of the coiling apparatus between the furnace apparatus and the rolling train allow for a very compact construction, in particular in a direction transverse to the direction of passage of the steel through the apparatus. This makes it possible to cast simultaneously two strands from just one tundish while using just one ladle turret. This achieves a considerable reduction of the financial capital which needs to be invested in the plant.

Claims

1. A plant for the manufacture of steel strip, comprising (a) a continuous casting machine (1) for casting a steel slab,

(b) a furnace apparatus (13,14) arranged for receiving the steel slab cast in said continuous casting machine, for adjusting the temperature of the steel slab, said furnace apparatus having an entry port and an exit port for the slab and an enclosed path for the slab from said entry port to said exit port,

(c) a coiling apparatus (27,28) for receiving the steel slab from said furnace apparatus, coiling the slab and subsequently uncoiling the slab, said coiling apparatus having an enclosure providing an enclosed space in which the slab is coiled and an entry port for entry of the slab into said enclosed space,

(d) rolling apparatus (40) for receiving the steel slab uncoiled from said coiling apparatus and rolling the slab into strip of a desired thickness, and (e) means (15,17,19,21) for providing a non- oxidising gas atmosphere in said furnace apparatus at said path thereof and in said enclosed space of said coiling apparatus, wherein said exit port of said furnace apparatus is gas-tightly and detachably connectable to said entry port of said coiling apparatus.

2. A plant according to claim 1 further having means for reducing the slab thickness, during passage of the slab from said continuous casting machine to said furnace apparatus.

3. Apparatus according to claim 1 or claim 2 wherein said coiling apparatus is mobile and is adapted to be moved, carrying a coiled slab, relative to said exit port of said furnace apparatus.

4. A plant according to claim 1, 2 or 3 wherein said means for providing a non-oxidising atmosphere comprises recirculation means for extracting gas from said atmosphere in said furnace apparatus, treating gas so extracted and returning the treated gas to said atmosphere in said furnace apparatus.

5. A plant according to any one of claims 1 to 4 wherein said coiling apparatus has sealing means (33,34) for sealing said entry port thereof, when detached from said exit port of said furnace apparatus.

6. A plant according to any one of claims 1 to 5 wherein said furnace apparatus has means for cooling gas of said gas atmosphere therein.

7. A plant according to any one of claims 1 to 6 wherein said coiling apparatus has electrical heating means for heating a coiled slab therein.

8. A plant according to claim 7 having, for supply of electric power to said electrical heating means of said coiling apparatus, stationary electrical conductors and, on said coiling apparatus, current collectors movable in contact with said stationary electrical conductors when said coiling apparatus moves.

9. A plant according to any one of claims 1 to 8 having means for rotating said coiling apparatus about a vertical axis,

10. A plant according to any one of claims 1 to 9 wherein said coiling apparatus has at least one mandrel for coiling said slab thereon.

11. A furnace apparatus (13,14) for use in a plant for the manufacture of steel strip, having an enclosure defining a path for traversing by a steel slab which is later to be rolled into strip, an entry port (23) for entry of a steel slab into said enclosure, an exit port (35,36) for exit of a steel slab therefrom, means (15,17,19,21) for providing a non-oxidising atmosphere in said enclosure at said path thereof, and means for gas-tightly and detachably connecting said exit port to an entry port of a coiling apparatus for said slab.

12. A coiling apparatus (27,28) for use in a plant for the manufacture of steel strip, having an enclosure defining a space, coiling means in said space for coiling of a slab which is later to be rolled into strip, at least an entry port into said space for entry of a slab thereto and means for detachably and gas- tightly connecting said entry port to an exit port of a furnace apparatus for temperature adjustment of said slab.