EP0761325B1 - Method and installation for production of ferritic hot-rolled strip - Google Patents

Abstract

The appts. (1) for producing flat rolled products (2, 7) consists of a multi-stand rolling section (3), an exit roller conveyor (4) with cooling units (9) and a coiling machine (5). The coiling machine is preceded by a compact rolling section (7) made up of one or several rolling stands for rolling thin strips (7). Also claimed is a method for operating such an installation comprising continuous, joint operation of the two rolling sections (3, 6) in such a way that parts of a hot strip (2) are located simultaneously in both sections.

Description

The invention relates to a production plant for the production of hot-rolled flat products, consisting of a multi-stand Rolling mill, an outfeed roller table with facilities for cooling the Hot strip and with downstream winding machines for winding of the tape.

Rolling plants for the production of hot-rolled strips are today in the generally designed and operated so that the deformation in the individual scaffolding is austenitic, which means that it is ensured that the rolling temperatures in the individual rolling stands lie above the GOS line of the iron carbon diagram. First after the last rolling pass, which is used to achieve a fine-grained Final structure should be as close as possible to the GOS line cooling to the reel temperature with structural change in the Cooling section or in the wound bundle.

For steels with a carbon content of less than 0.2% the final rolling temperature for rolling according to the method described above, that means the temperature in the last mill stand Rolling mill at 840 to 920 ° C depending on the level of carbon. The final rolling temperature is maintained by selecting the final rolling speed, with which the natural cooling of the tape in the Rolling mill and the heat supply by the drive power of the Roll stands can be controlled. This procedure is straightforward applicable for strip thicknesses above a minimum strip thickness, each is of the order of 1.3 mm depending on the road type. Will this Strip thickness is undershot, the required rolling speed is reached with values above 12 m per second, not in the free run on the roller table behind the rolling mill can be mastered more.

The development tendency existing despite this problem in the direction of lower final thicknesses has led to ways was sought to lower the finish rolling temperature to lower it To enable rolling speeds. Such rolling processes were Known under the name ferritic rolling, because they are Temperatures below the GOS line, i.e. in the area of the α , γ mixed crystals or below the GPS line in the ferritic Area.

A preferred method sees pre-rolling in austenitic Range up to an intermediate thickness of 2 to 8 mm and one finish roll in the ferritic range to the lowest final thicknesses below of 1.3 mm in front. The rolling stock must be between the two process stages from the final rolling temperature in the austenitic range to the rolling temperature be cooled in the ferritic range. This means one Cooling from the temperature range of 840 to 920 ° C to the Temperature range from 600 to 780 ° C.

The finish rolling temperature is after the second deformation stage also in the range of 600 to 780 ° C and thus on the order of magnitude, in which recrystallization of the Structure occurs in the wound bundle. A structure is created which means the use of the product without further cold forming or Allows heat treatment.

Compliance is essential for a good result a minimum cooling time for cooling from the austenitic Area in the ferritic area. So that the transformation of austenite sufficient cooling in ferrite, this minimum cooling time be respected. This lies depending on the selected temperature for entry into the first ferritic transformation at 10 to 200 seconds.

The process described above is implemented in one conventionally designed hot strip mill considerable difficulties. The transition from austenitic to ferritic Forming should be carried out in the thickness range from 2 to 8 mm, that is, in a thickness range in which the rolling stock is roughly in in the middle of a conventional finishing train. Because the lead time from scaffolding to scaffolding at this point only a few seconds is, in principle, it is possible to implement cooling, however, adherence to the time required for the conversion cannot be realized. Carrying out ferritic rolling according to the method described is conventional for that designed hot strip mill impossible.

EP-A-226 446, which also belongs to the prior art a production plant for the production of hot-rolled flat products described with a final thickness of 2 to 6 mm. In the production plant is at very high speeds, namely not rolled less than 1,500 m / min. That in this production facility The end product produced has in no way a structure that is similar to a cold rolled product. Essential objective this previously known production facility is the increase in throughput and the production of a rolled product with good properties for further treatment. However, the rolled product itself is not of too high quality. A process is known from EP-A2-0 524 162 known for rolling out hot strip to a thickness of 0.5 to 2 mm, in a last roll stand, the steel at or below 750 ° is rolled out and this rolling temperature by roller cooling in last scaffold is set. From the German published application 1 903 554 is a process for producing hot rolled Strip steel is known, being after a conventional hot rolling steel strip on a normal hot rolling mill similar to the document EP-A2-0 524 162 an additional Hot rolling operation at below 700 ° C follows. An austenitic Rolling process and / or a ferritic rolling process is with this previously known methods not possible.

In this prior art, the object of the invention therein, a production plant for the ferritic rolling of hot strip to create with the aforementioned disadvantages and problems be eliminated. The object of the invention is also a method To provide with the finishing rolling of hot strip in ferritic Range is easily enabled.

The task is solved in a production plant of type mentioned with the invention in that in the rolling direction seen behind the winding machines for continuous passage an additional compact forming stage in the form of a single or Multi-stand rolling mill arranged for rolling thin strips is and that the first multi-stand rolling mill seen in the rolling direction for rolling in the austenitic temperature range and seen in the rolling direction second single or multi-stand rolling mill can be used for rolling in the ferritic temperature range and that the cooling device for cooling the hot strip the austenitic in the ferritic temperature range in the range of the roller table is arranged between the two rolling mills (cf. Figure). This rolling mill is specially designed for ferritic forming Area designed. This includes equipping with work roll diameters of less than 500 mm and with positioning and Control loops to achieve strip tolerances for thickness and flatness, as required by cold rolled products.

The conventional process takes over the entire rolling process designed hot strip mill 3 to create an intermediate thickness through rolling in the austenitic area and the compact ferritic Forming stage 6 the final rolling in the ferritic range. The cooling of the strip with intermediate thickness from the austenitic area in the The ferritic range occurs in the simplest way when passing through the run-out roller table 4 between the austenitic forming step 3 and the ferritic forming stage 6. Due to the length of this Roller table, which is used for cooling austenitic rolled strips Reel temperature is to be designed, lead times result in the case of ferritic rolling, the cooling normally required and ensure the conversion of austenite to ferrite. The for the austenitic rolling process existing cooling devices 9 can, if necessary, in addition to achieving the required Cooling rate can be used. Should the lead time of the last austenitic transformation 3.1 to the first ferritic Forming 6.1 for a sufficient conversion of austenite into Ferrite will not be sufficient, so a heated loop storage (not shown) provided the immediately between the conventional coiler 5 and the compact ferritic Forming stage 6 is to be arranged.

Immediately behind the compact ferritic forming stage 6 specially designed reel 8 for winding thin strip 7. As for the local conditions no longer matters thicker belts must be considered is the construction such facilities easily possible.

The hot strip production plant shown in the single figure 1 for austenitic and ferritic rolling is before the first multi-stand mill 3 a roughing mill, not shown 12 or a thin slab furnace with casting machine 13 upstream.

The invention results in an overall system concept, which in optimally both the austenitic process and the allows ferritic rolling process.

Claims (6)

1. Production plant (1) for production of hot-rolled flat products (2, 7) consisting of a multi-stand rolling train (3), an outlet roller path (4) with devices (9) for cooling of the hot strip and downstream coiling machines (15) for winding up the strip, wherein an additional compact reshaping stage (6) in the form of a single-stand or multi-stand rolling mill for the rolling of thin strips (7) is arranged behind the coiling machines (5), as seen in rolling direction (14), for continuous transit, and that the first multi-stand rolling train (3) as seen in rolling direction (14) is usable for rolling in the austenitic temperature range and the second single-stand or multi-stand rolling train (6) as seen in rolling direction (14) is usable for rolling in the ferritic temperature range and the cooling device (9) for cooling the hot strip (2) from the austenitic to the ferritic temperature range is arranged in the region of the cooling roller path (4) between the two rolling trains (3, 6), wherein in addition the diameter of the working rolls (10) of the second stand group (6) is less than 800 mm, preferably less than 400 mm, and the second stand group (6) for the rolling of the hot strip (2) in the ferrite temperature range is equipped with setting and regulating circuits for attainment of strip tolerances for thickness and planarity as in cold rolling stands.
2. Production plant according to claim 1, characterised in that special coiling machines (8) for winding up thin strips (7) are arranged directly behind the compact reshaping stage (6).
3. Production plant according to claim 1 or 2, characterised in that a heated storage device is provided directly in front of the second single-stand or multi-stand rolling train (6).
4. Production plant according to at least one of claims 1 to 3, characterised in that the roll stands of the compact reshaping stage (6) are constructed as a four-high stand (6.1) or six-high stand (6.2).
5. Production plant according to at least one of claims 1 to 4, characterised in that in the case of use of working roll diameters less than 400 mm the working rolls (10) are drivable by way of the backing rolls (11) or by way of the intermediate rolls (14).
6. Method of producing hot-rolled flat products by a production plant consisting of a multi-stand rolling train (3), an outlet roller path (4) with devices (9) for cooling of the hot strip and with downstream coiling machines (5) for winding up the strip, according to at least one of the preceding claims 1 to 7, characterised in that for the purpose of rolling the flat product in the austenitic and ferritic range a second stand group (6) is arranged downstream of the coiling machine (5) and that the two roll stand groups (3, 6) continuously work together in the manner that parts of a hot strip (2) are simultaneously disposed in both stand groups (3, 6), wherein in the first stand group (3) the hot strip (2) is reshaped in the austenitic temperature range and subsequently the hot strip (2) is reshaped in the second stand group (6) in the ferrite temperature range.

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