The method of obtaining steel strips are laminated in the ferritic condition, and a device for its implementation

 

The invention relates to rolling to obtain a steel strip. The technical result of the invention is to provide a strip with high deformation properties. To achieve a technical result, the molten steel is poured into the installation for continuous casting with obtaining slab and using foundry heat transport slabs through the furnace, rolled slab in the austenitic range in the tool for roughing rolling mill, cooled to a temperature of obtaining a ferritic structure and rolled strip tool for finish rolling at a speed corresponding to the speed at which it is introduced into the tool for finishing and in the subsequent stages of rolling on the thickness of rolled strip in the ferritic condition at a temperature of from 850 to 600oFrom and after the exit from the finishing strip is rapidly cooled to a temperature below 500oIn order to avoid recrystallization. 2 C. and 8 C.p. f-crystals, 3 ill.

The invention relates to a method for producing laminated in the ferritic condition of the steel strip, in which molten steel is poured into the installation for continuous casting of slabs and using the heat of the casting, convey the slab through the furnace, Rocade to obtain a steel strip with a ferritic structure of the desired final thickness. A method of this type is described in patent application PCT/NL 97/00325, the contents of which are included in the present patent application by reference. The invention relates also to a device intended in particular for performing the method according to the invention, comprising at least one installation for continuous casting of thin slabs oven for homogenization of the slab, which may be subjected to rough compression tool rolling for rolling the slab to obtain strips of the desired final thickness and a winder for winding strip. A device of this type is known from patent application PCT/NL 97/00325.

In the patent application PCT/NL 97/00325 described fully continuous, infinite or semi-infinite way to obtain a steel strip, which is subjected to at least one stage of rolling in the ferritic range. The strip emerging from the means for finish rolling, wound into a roll on the winder, which is located downstream from the means for finish rolling at a temperature at which recrystallization occurs in the roll.

Discovered that the above method is especially suitable for producing steel strip with special properties. This method uses specific features of the device, apoanagyrus slab or strip in the width direction, and in the thickness direction. The temperature is uniform in the longitudinal direction, since the rolling is carried out with a constant speed, and therefore, in the rolling process does not require acceleration or deceleration due to the choice of continuous, semi-infinite or infinite modes, which can operate the device for rolling in the ferritic condition.

Temperature uniformity as a function of time is also better than that which can be obtained using conventional equipment. In addition, the device allows you to perform a rolling using grease on one or more stands of the rolling mill. In addition, in different parts of the device is provided by means of cooling for more reliable control of the temperature profile of the steel slab or steel strip during its passage and exits.

In addition, especially when using vacuumized intermediate bottling bucket, can be particularly accurately prepare the chemical composition of the steel to obtain the required properties of the product. In addition, due to the high degree of uniformity of temperature in the device, you can get ferritic range, which is very wide, i.e. it is detected, that known method provides for receiving a steel strip with a particularly high deformation properties option, which according to the invention is characterized by the fact that in a fully continuous, infinite or semi-infinite process, the slab is rolled in the austenitic range in the tool for roughing rolling and after rolling in the austenitic range cooled to a temperature at which the steel has a predominantly ferritic structure, and the strip is rolled in a tool for finish rolling speed, which mainly corresponds to the speed at which the strip exits the means for finish rolling and the following stages of compression in thickness, and in at least one cage means for finish rolling of the rolled strip in the ferritic condition at a temperature of from 850 to 600oWith, and when you exit from the finishing rolling quickly cooled to a temperature below 500oPredominantly in order to avoid recrystallization.

The invention is based on the fact that due to the fast cooling laminated in the ferritic state band after its release of funds for finish rolling recrystallization does not occur or is negligible recrystallization, and hence the orbital band in the ferritic condition, thus obtained can be subjected to cold compression in the ferritic condition as is known per se (in itself), for example, thus, the total compression in the ferritic condition was approximately 70 to 80%, part of which is produced by heating in the ferritic condition, and some cold ferritic condition. The result of cold rolled steel strip with a high r value and a low value ofr. For clarity, we can imagine that the thickness of the slab can be 70 mm, and the thickness of the slab after compression in the transition from the austenitic range to the ferrite is in the range from 15 to 40 mm Rapid cooling of the hot rolled strip in the ferritic condition to a temperature of 500oTo prevent the loss of deformation patterns as a result of recrystallization.

In the patent application DE-A-19520832 also describes a method for rolled steel strip in the ferritic condition of the molten steel is poured into the installation for continuous casting. Rolled steel strip is cooled prior to winding into a roll. However, there is no information that is related to the fact that the cast slab is transported through the furnace and the cooling is done with such speed, that the house is output from the last stand of the rolling mill. However, there is also no information about fast cooling, which allows to avoid recrystallization.

Patent application DE-A-19600990 relates to a combined rolling in the austenitic state, and then in the ferritic condition. Before rolling in the ferritic condition the strip is cooled. Further cooling after rolling in the ferritic condition not specified.

In addition to uniform distribution of temperature is particularly important is also a good distribution of the value of compression during rolling by the thickness and width of the slab or strip. Therefore, it is preferable to perform the way so that at least one stand of a rolling mill, which are rolling in the ferritic condition, rolling was performed with lubrication, and even more preferably so that all stands of the rolling mill, which are rolling in the ferritic condition, rolling to do with lubrication.

Additional improvements of the stress distribution and the distribution of compression on the cross section of the slab or strip is achieved through a method which is characterized by the fact that the rolling of the at least one stand of a rolling mill tools for finish rolling comply with /chr/916.gif">r, get in a variant of the method, which is characterized by the fact that steel is a steel of class IF. Steel of this type allows you to reach the value of g is approximately 3. It is preferable to use steel class IF with a complex chemical composition with a high content of titanium and acceptable content, and sulfur so that in the process of rolling in the ferritic condition no breaks. The strip of steel of this type is particularly suitable for deep drawing, and as source material for receiving the strip with a coating, especially for galvanized bands.

Another variant of the method according to the invention differs in that the steel is a low carbon steel. A method of obtaining steel DWI allows you to reach values of about 1.1 g. Upon receipt steel, intended for the manufacture of cans, the desired r value is 1.2. When using the method according to the invention can easily achieve r values of 1.3 or more. The prerequisites for this is that unlike the traditional method of production of steel DWI method according to the invention allows to achieve a good initial value of the texture, increasing the value of r to the desired B0,01 to 0.1%, preferably from 0.01 to 0.07%.

To achieve the required high cooling rate following variant according to the invention differs in that the strip exit means for finish rolling is cooled by using the cooling with a cooling capacity greater than 2 MW/m2. In order to maintain the distance between the means for finish rolling and means for cooling as low as possible and to achieve a high level of flexibility regarding the cooling rate, the following variant of the method according to the invention differs in that the means for cooling is the cooling capacity of at least 3 MW/m2.

Such cooling rates can be achieved using the method according to the invention is characterized in that the means for cooling using water you spray on the slab in the form of intersecting jets arranged with high density.

Coolant, which allows to obtain the required cooling rate in accordance with the present invention, are described inter alia (among other things) the final report of the ECSC project 7210-EA/214, the content of which is incorporated into the present application by reference. A significant advantage of the awn, the uniformity of cooling and high cooling capacity per unit surface area. The high cooling capacity of this type allows to achieve a desired cooling rate when the velocity at the exit of the device, which occur in a continuous, infinite or semi-infinite rolling process.

It was found that it is possible to avoid so-called "close winder immediately downstream from the mill stand of a rolling mill using a variant of the device, which is characterized by the fact that between the last stand of the rolling mill and the coiler is coolant in the cooling capacity of at least 2 MW/m2.

Would have been numerous proposals to create a device and method to achieve high cooling rate of the steel strip downstream from the means of rolling and upstream from the winder. In the case of the device described in the patent application PCT/NL 97/00325, can be obtained as laminated in the ferritic state band, which recrystallized roll and the strip is rolled in the austenitic state. In addition, the device is particularly suitable for producing laminated in the ferritic condition of the strip according to the invention. When on the strip as slowly as possible after its exit from the rolling mill and the coiler, which is located downstream, as close as possible to the tool for finishing (approximate winder). If you get the steel strip is rolled in the austenitic state, then it is cooled before winding. Thus, the nearby winder that just mentioned, not suitable for this purpose, and the necessary second winder located after the cooling means. If the cooling capacity of the cooling medium is high, the length along which to perform the cooling, is short, and close winder can exclude that provides an additional advantage of significant savings.

This high cooling ability of this type, the distance between the output means for finish rolling and coiling, located after the cooling medium is so short that the temperature of ferritic rolled into the status bar changes slightly, allowing the band is still possible to get cracking at a temperature at which recrystallization occurs in the roll.

Below the invention is described in more detail with reference to the drawings showing an embodiment of the invention, where Fig.1 is a schematic view sboc atorny profile steel as a function of position in the device; Fig.3 is a graph illustrating the profile of the thickness of steel as a function of position in the device.

In Fig.1 position 1 is the installation for continuous casting of thin slabs. In this description, the term adopted to refer to installation for continuous casting of thin slabs with a thickness of less than 150 mm, preferably less than 100 mm, more preferably less than 80 mm Installation for continuous casting may contain one or more lines. You can have multiple installations for the continuous casting one after another. These options are included in the scope of the invention. Position 2 indicated teeming ladle, from which the molten steel to be poured, enters the intermediate filling the bucket 3, which in this design is of the form vacuumized in the tundish. Intermediate teeming ladle is preferably provided with means, such as a measuring tool and a tool for analysis, to bring the chemical composition of the steel to the desired composition, as in the present invention composition is an important factor. Below the intermediate filling of the bucket 3 is the casting mold 4, which serves the molten steel and in which it at least partly sakalai. Standard installation for continuous casting is the casting speed of approximately 6 m/min; additional measures, such as vacuumized the tundish and/or electromagnetic stirrer, which provide further casting speed 8 m/min and more. Hardened thin slab enters the tunnel kiln 7, which is full-length, for example, 250-330 m as soon As the cast slab reaches the end of the furnace 7, it is cut into pieces in a semi-infinite process using a cutting tool 6. The term semi-infinite process means a process in which one slab or part of the slab by rolling get a few rolls, preferably more than three rolls, more preferably more than five rolls of standard size, in a continuous rolling process at least in the medium for finish rolling to the final thickness. In the process of endless rolling slabs or strips after tools for finish rolling are combined together so as to perform a process of endless rolling tool for finish rolling.

In the continuous process, the slab is moved continuously along the path between the installation for continuous casting and the output side means of rolling. Nastoyarshi for endless or continuous process. Each part of the slab contains a number corresponding to the five or six regular rolls. In the furnace includes a chamber for holding a number of slabs of this type, for example, extracts of three slabs. As a result, those components that are downstream from the furnace can be operated continuously, while the installation for continuous casting replaces bottling bucket and begin casting a new weak, ensure that the installation for continuous casting could continue if damage occurs downstream. In addition, the finding in the furnace increases the time it parts of the slab, which results in increasing the uniformity of temperatures in parts of the slab. The speed at which the slab is supplied into the furnace corresponds to the speed of casting and is approximately 0.1 m/sec downstream from the furnace 7 has the means 9 for removing scale, in this case in the form of spraying high-pressure water at a pressure of about 400 atmospheres, for controlling oxides that have formed on the surface of the slab. The speed at which the slab passes through the means for removing the dross and supplied to the tool 10 for rolling, is approximately 0.1 is halkovic stands, which is preferably equipped with means for lubrication of the rolls. If necessary, equipment can be included tool 8 cutting for emergency cases.

As can be seen from Fig. 2, the temperature of the slab, which is the outlet of the tundish is approximately 1450oWith decreases in rolling stands to approximately 1150oC, and homogenized slab in the furnace at this temperature. Intensive water spray means 9 for removing scale causes a decrease in the temperature of the slab from approximately 1150 to 1050oC. It is applicable for both austenitic and ferritic process a and f, respectively. In two stands of the rolling mill means 10 finish rolling temperature of the slab is reduced in each iteration in the rolling mill approximately the 50oWith, so the slab, the thickness of which originally was 70 mm and which is deformed in two passes, with intermediate thickness 42 mm steel strip with a thickness of approximately 16,8 mm has a temperature of approximately 950oC. the thickness Profile as a function of the position shown in Fig.3. The numbers indicate the thickness in mm downstream from the means 10 for rough rolling are the means 11 for cooling, wasps, rolled in the austenitic state, the strip emerging from the means 10 for rolling, may be temporarily left on the shutter speed and homogenization in boxes of 12 for the rolls, and if necessary to raise the temperature, the heating can be performed in the heating means (not shown), which is located downstream from the boxes for the rolls. Specialists in the art it should be clear that the tool 11 for cooling, duct 12 for the rolls and bake, which are not shown, can be positioned differently relative to each other from those mentioned above. As a result of compression in the thickness of rolled strip is included in the box for rolls with a speed of approximately 0.6 m/s Second unit 13 for removing scale at a water pressure of approximately 400 atmospheres is located downstream from the means 11 of the cooling ducts 12 coil or furnace (not shown) for removing a layer of oxides that may be formed on the surface of the rolled strip. If necessary, other means for cutting may be part of the equipment for trimming the front and rear end of the strip. Then the band comes on the line rolling, which may consist of six four-roll stands of the rolling mill, which is in the austenitic state, the desired final thickness, for example from 1.0 to 0.6 mm, can be achieved using only five of the stands of the rolling mill. Thickness, which is obtained after each stand of the rolling mill shown in Fig.3 for a slab thickness of 70 mm in the top row of numbers. After exiting the line 14 for rolling a strip, which then has a final temperature of approximately 900oAnd a thickness of 0.6 mm, intensively cooled by using the 15 cooling and wound into a roll in the winder 16. The rate at which it enters the winder, is approximately 13-25 m/s

If you want to get a steel strip, rolled in the ferrite region, the steel strip emerging from the means 10 rough rolling, intensively cooled with means 11 for cooling. The means for cooling can be installed between the rolling stands tools for finish rolling. You can also use cooling in the environment does not necessarily between the rolling stands. Then the strip is introduced into the duct 12 for the rolls and, if necessary, into a furnace (not shown), and then remove the dross in the installation of 13 to remove oxides. The band, which is now in the ferritic condition, is then a temperature of approximately 750

As in the case of rolling of austenitic strip for rolling ferritic bandwidth is used essentially equal compression in thickness in each stand of the rolling mill, with the exception of compression obtained in the finishing stand of the rolling mill. All this is shown in the temperature profile in Fig.2 and the thickness profile in accordance with the lower number of digits in Fig.3 for rolling steel strip in the ferritic region as a function of position. The temperature profile shows that the band at the output has a temperature that is considerably higher than the recrystallization temperature. Thus, to prevent the formation of scale, it may be necessary to use the tool 15 for cooling the strip to the desired temperature, which may still occur recrystallization. If the temperature at the outlet from line 14 rolling is too low, you can bring laminated in the ferritic region of the strip to the desired temperature coiling when using the oven 18, which is located downstream from the line of rolling. In accordance with the present invention the strip, laminated in ferritic pleasure to temperature, which still at least a significant part of the structure formed in the rolling process. For this purpose it is enough cooling to a temperature below 500oC.

Due to the high speed at which the strip is rolled in the ferritic condition goes from 14 secondary rolling, and to maintain a small distance along which perform the cooling means 15 cooling has a very high cooling capacity is more than 2, and preferably more than 3 MW/m2.

Because the tool 15 cooling is very short, the distance from the output side means 14 secondary rolling to the reel 16, which in this case has the form of a so-called "loose winder", also very short. In the winder 15 can also be used in the normal process of getting a band in the ferritic condition in which the recrystallization of the steel occurs in the roll. To limit the temperature drop of the so-called close winder immediately downstream from the exit side of the means 14 for the secondary rolling in this regard is not required.

The means 15 for cooling and furnace 18 can be located together or one after the other. You can also place one tool with another Witney strip rolling carry out continuous or semi-continuous. This means that the band goes from 14 rolling and, if necessary, a means for cooling or furnace 15 or 18, respectively, may be of greater length than is usual in the formation of one roll, and that the segment of slab with length equal to the length of the furnace, or even a longer period of slab rolled continuously in the tool for finish rolling. The means 17 for cutting set for cutting the strip to the desired length corresponding to the standard size rolls.

With appropriate selection of the various components of the device and steps of the process performed by a device, such as homogenization, rolling, cooling and residence time, it is possible to ensure the operation of this device using a single installation for continuous casting, whereas in the preceding technical solutions use two units for continuous casting, in order to agree on a limited casting speed with substantially higher speeds of rolling, which is usually used. If desirable, additional so-called close winder can be placed immediately downstream from the line 14 rolling to contribute to the regulation of the movement and temperature of the strip, one that ranges from 1000 to 1500 mm, and a thickness of approximately 1.0 mm in the case of strips, rolled in the austenitic region, and from about 0.5 to 0.6 mm in the case of strips, laminated in the ferritic condition. The time of homogenization in the furnace 7 is approximately ten minutes at a speed of three slabs along the length of the furnace. The basket of rolls suitable for storing whole two bands in the case of rolling in the austenitic state.

Claims

1. The method of obtaining laminated in the ferritic condition of the steel strip, in which molten steel is poured into the installation for continuous casting with obtaining slab and using the heat of the casting, convey the slab through the furnace, subjected to rough rolling tool for rough rolling and finish rolling tool for finish rolling to obtain a steel strip in the ferritic condition desired final thickness, characterized in that in an infinite or semi-infinite process, the slab is subjected to rough rolling in the austenitic range in the tool for roughing rolling and after rolling in the austenitic range cooled to a temperature at which the steel is mainly ferritic structure, and rolled bar in the tool for finishing probatova rolling on the subsequent stages of compression in thickness, and rolled strip in the ferritic condition, at least one cage means for finish rolling at a temperature of from 850 to 600C, and after the release of funds for finish rolling of the rolled strip is rapidly cooled to a temperature below 500C, in order largely to avoid recrystallization.

2. The method according to p. 1, characterized in that the rolling comply with lubricant, at least one rolling stand, which performs rolling in the ferritic condition.

3. The method according to p. 1 or 2, characterized in that the rolling comply with lubrication in all mill stands, which carry rolling in the ferritic condition.

4. The method according to any of paragraphs.1-3, characterized in that the rolling comply with lubricant, at least one stand of a rolling mill tools for roughing rolling.

5. The method according to any of paragraphs.1-4, characterized in that the steel is a steel of class IF.

6. The method according to any of paragraphs.1-4, characterized in that the steel is a low carbon steel.

7. The method according to any of paragraphs.1-6, characterized in that after the release of the funds finishing strip is cooled by using the cooling with a cooling capacity greater than 2 MW/m2.

8. The method according to p. 1, the b under item 7 or 8, characterized in that the means for cooling using water you spray on the slab overlapping jets with high positional density.

10. The device receiving laminated in the ferritic condition of the steel strip containing at least one installation for continuous casting of thin slabs, furnace (7) for the homogenization of the slab, means (10) for roughing rolling and means (14) for rolling slab up to strip the desired final thickness, the tool (16) of the strip winding, characterized in that the means (15) for cooling the cooling capacity of at least 2 MW/m2placed between the last crate means (14) for rolling strip, and means (16) for winding strip.

 

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4 ex, 1 tbl

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