Casting-rolling system for batch and continuous operation

Abstract

A method for producing an ultra-thin strip of less than 0.8 mm from cast steel in batch/continuous operation with a casting-rolling system. The method includes casting a thin slab having a casting thickness of 90-150 mm and width of at least 1000 mm at a casting speed of 7 m/min. The thin slab is heated/homogenized to a first temperature in a continuous furnace and subsequently rolled by at least seven final roll stands into an ultra-thin band. Neither the thin slab nor strip undergo inductive heating during production. The thin slab rolling steps include rough rolling the thin slab at the heated/homogenized first temperature by a roughing stand; heating/homogenizing the rough-rolled thin slab to a second temperature by a further continuous furnace; and finally rolling the rough-rolled thin slab at the second temperature to the ultra-thin strip by the final roll stands arranged downstream of the further continuous furnace.

Claims

1. A method for producing an ultra-thin strip of or less than 0.8 millimeter (mm) from cast steel in a batch mode or a continuous mode of operation with a casting-rolling system which includes at least one casting plant and at least seven final roll stands, the method comprising the steps of: casting a thin slab having a slab casting thickness of 90 mm to 150 mm and a casting width of at least 1200 mm at a casting speed of 7 m/min; heating and/or homogenizing the thin slab to a first temperature in a continuous furnace; and rolling the thin slab by the at least seven final roll stands, wherein the thin slab undergoes no inductive heating during production of the ultra-thin strip; wherein the step of rolling the thin slab includes: rough rolling the thin slab at the heated and/or homogenized first temperature by at least one roughing roll stand; heating and/or homogenizing the rough-rolled thin slab to a second temperature by a further continuous furnace, the first and second temperatures being greater than an austenite-to-ferrite transition temperature; and finally rolling the rough-rolled thin slab at the second temperature, to the ultra-thin strip with a thickness of or less than 0.8 mm by the at least seven final roll stands, which are arranged downstream of the further continuous furnace.

2. The method according to claim 1, wherein a leading portion or edge of the thin slab is cut off by a cutter positioned between a last of the at least one roughing roll stand and a first of the at least seven final roll stands.

3. The method according to claim 1, wherein the casting-rolling system is switchable between the batch mode and the continuous mode depending on a mass flow of the at least one casting plant which is calculated as a product of the slab casting thickness and the casting speed.

4. The method according to claim 3, wherein the casting-rolling system is operable in the continuous mode of operation above a threshold value for the mass flow of 350 mm*m/min.

5. The method according to claim 1, wherein an annual output of the casting-rolling system is between 4.0 and 5.0 million tons.

6. The method according to claim 1, wherein casting-rolling system produces the ultra-thin strip of LC, MC, HC, HSLA, DP, API, Si grades, AHSS and Corten steels.

7. The method according to claim 1, wherein a final rolling temperature in a last roll stand of the at least seven final roll stands is set above 820 C.

8. The method according to claim 1, wherein a trailing portion or edge of the thin slab is cut off by a cutter positioned between a last of the at least one roughing roll stand and a first of the at least seven final roll stands.

Description

5. BRIEF DESCRIPTION OF THE FIGURES

(1) The invention will be explained in more detail below with reference to the FIGS. which show preferred embodiments of the invention.

(2) It is shown in

(3) FIG. 1 a schematic view of an extended system configuration according to the invention.

(4) FIG. 2 a schematic illustration of an embodiment of the inventive casting-rolling system with eight roll stands arranged one behind the other and an example calculation for the operation of the inventive casting-rolling system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(5) FIG. 2 shows a schematic illustration of an embodiment of the inventive casting-rolling system and a table with results of exemplary experiments for producing thin strips from different steel grades with a casting-rolling system 1 according to the invention, here with a system layout having a casting plant, a downstream continuous furnace 7 and eight final roll stands 9, 10, 14-19, followed by a cooling section 21 and two reels 25a, 25b. After the first two stands 9, 10, shears 13 are arranged to cut off the strip head after exit from the second roll stand 10 and to straighten the strip on the head side.

(6) An S315MC grade steel was cast into a thin slab having a thickness of 100 mm or 110 mm and width of 1200 mm, at a withdrawal rate of 7.9 m/min. or 7.2 m/min. This thin slab was rolled in continuous operation into a thin strip with a thickness of 1.0 mm and width of 1,200 mm. In a further experiment, the same steel grade was cast at a casting speed of 9.1 m/min. or 8.4 m/min. in continuous operation to a thin slab having a thickness of 100 mm or 110 mm and a width of 1,550 mm, and was rolled, also in continuous operation, to a thin strip having a thickness of 1.3 and a width of 1,550 mm. The mass flow (Flow) was 700 to about 925 mmm/min, thus above the threshold for using continuous operation. The final rolling temperatures were above 900 C., thus significantly above the transformation temperature austenite.fwdarw.ferrite.

(7) In another series of tests, steel grade HDT580X was cast into thin slabs with a thickness of 100 mm or 110 mm and a width of 1,200 mm at casting speeds of 9.6 m/min. or 8.8 m/min. Forming in the continuous operation resulted in a thin strip with a thickness of 1.2 mm and a width of 1,200 mm. In a further pair of experiments, the same steel was cast into a thin slab with a thickness of 100 mm or 110 mm and a width of 1,550 mm at a casting speed of 11.5 m/min. or 10.7 m/min. The mass flow (Flow) was 960 to 1,180 mmm/min., thus also clearly above the threshold for continuous operation, the final rolling temperatures for the test series with the steel grade HDT580X were above 900 C.

(8) With the same system layout, in a further series of tests, grade S315MC steel was cast into a thin slab with a thickness of 100 mm and a width of 1200 mm. From the thin slab, a thin strip of 2.30 mm thickness was rolled in batch operation. A thin slab of S315MC grade steel was also cast with a thickness of 100 mm and a width of 1,550 mm, and finally rolled in batch operation to a thin strip with a thickness of 2.80 mm.

(9) In a further series of tests, HDT580X grade steel was cast into a thin slab with a thickness of 100 mm and a width of 1,200 mm or 1,550 mm, and finally rolled into a thin strip with a thickness of 2.75 mm or 3.50 mm in batch operation. Also in batch mode, the final rolling temperatures were above the austenite.fwdarw.ferrite transition temperature to obtain a hot rolled microstructure in the final rolled strip.

(10) FIG. 1 shows a casting-rolling system 1 in a further system layout according to the invention, wherein the casting-rolling system 1 has two casting plants 2a, 2b with respective casting molds 3a, 3b. After exit from the strand guide 4a, 4b, the solidified strand is cut by means of shears 6a, 6b, if a batch operation is to be performed on the casting-rolling system 1, and then enters a continuous furnace 7a, 7b. Between the continuous furnaces 7a, 7b, a device 8 for transferring a slab (not shown) from the continuous furnace 7b into the continuous furnace 7a is provided. After exit from the continuous furnace 7a, the slab enters a pair of roughing stands 9, 10 and is rolled in these roughing stands 9, 10 to a strip, which then enters a further continuous furnace 11 where it is reheated. After exit from the further continuous furnace 11, the pre-rolled strip can be straightened on the head side by means of shears 13, to then enter a series of final roll stands 14 to 20. Upon exiting the last roll stand 20, the strip has the desired final thickness and the desired final rolling temperature, whereupon the rolled strip is then cooled in the cooling section 21 to the temperature required for reeling. Downstream of the cooling section 21, a high speed shear 24 is provided which is used when thin strip is rolled in continuous mode and in this case has to be cut to the length of the reel without interrupting the casting-rolling process. The rolled and optionally cut thin strip can then be alternatingly wound up on two reels 25a, 25b on the fly.

LIST OF REFERENCE NUMBERS

(11) 1 cast rolling mill 2a, 2b casting plants 3a, 3b casting molds 4a, 4b strand guide 6a, 6b shear 7a, 7b continuous furnace 8 device for transferring a slab 9 roughing stand 10 roughing stand 11 continuous furnace 13 shears 14-20 finishing roll stands 21 cooling section 23 cooling section 24 high-speed shears 25a, 25b reel