A method of obtaining a strip of high-strength steel and a device for its implementation

 

The invention relates to a method for producing a high-strength steel strip and device for its implementation. The technical result of the invention is to provide a strip with high deformation properties. A method of obtaining a high-strength steel strip, in which molten steel is poured, at least one installation for continuous casting with one or more flow lines for slab and using foundry heat transport slabs through the furnace, in an infinite or semi-infinite process, the slab is subjected to rough rolling is essentially in the austenitic range in the tool for roughing rolling, rolled in the austenitic range in the tool for finishing or rolled at least in one cage means for finish-rolling in the two-phase austenitic-ferritic range, and after the release of funds for finish rolling of strip, rolled in the austenitic or austenitic-ferritic state to the final thickness, rapidly cooled to obtain a desired structure. 2 S. and 3 C.p. f-crystals, 3 ill.

The invention relates to a method for producing a high-strength steel strip and device for its implementation. In known spycam way and subjected to two-stage cooling conveyor. At the first stage the band in the austenitic state is cooled until then, until it is in the range of austenitic-ferritic mixture, and incubated in this range until then, until it forms the desired number of ferrite. Then the strip is cooled with a high cooling rate to get in the band martensitic structure. High-strength steel of this type is known as the two-phase steel. One object of the present invention is to develop a method which provides increased flexibility in the production of high-strength steel. Another problem to be solved in the invention is to develop a method that can be performed using simple tools. These objectives and other advantages of the implement by way of obtaining high-strength steel strip, according to which the molten steel is poured in at least one installation for continuous casting of slabs and using the heat of the casting is transported through the furnace and first subjected to rolling in the tool for roughing rolling, and then rolled in a tool for finish rolling to obtain a steel strip of the desired final thickness, and in a continuous, infinite or semi-infinite mode, the slab is subjected to the second rolling rolled in the austenitic range, or at least one cage means for finish rolling, rolled in a two-phase austenitic-ferritic range, and the laminated strip of austenitic or austenitic-ferritic state after exit from the finishing rolling is rapidly cooled to obtain a desired structure.

The method is based on continuous, infinite or semi-infinite process. In the process of this type can provide very accurate control of the temperature along the length and width and the thickness of the slab or strip. In addition, reach a very high temperature uniformity as a function of time. The device for performing this method, usually equipped with means for cooling to facilitate the control and regulation of the temperature profile as a function of position in the installation and/or time functions. An additional advantage that can be noted is that the method is intended primarily for use vacuumized intermediate foundry bucket in order to prepare the composition of the steel to obtain the specified properties.

Due to the high degree of uniformity of temperature there are so many opportunities to perform rolling in the exact pre-specified dir is the difference in the percentage of austenite and ferrite in the cross section and along the length of the strip. The conventional method can only to a limited extent or with the help of special events to keep the level of uniformity of temperature, which is required to obtain uniform properties. Therefore, high-strength steel strip obtained in the usual way, there is heterogeneity in cross-section and in longitudinal direction.

One variant of the method according to the invention differs in that the strip is rolled in a tool for finish rolling at a temperature at which there is the right amount of ferrite, and the fact that the band, leaving funds for finish rolling, quickly cooled to a temperature below the Ms(the beginning of martensitic transformation) in the temperature range in which is formed martensite.

Due to the very high level of uniformity of temperature there is a possibility to achieve and maintain the necessary balance of austenite and ferrite at rolling tool for finish rolling. After exiting the means for finish-rolled strip very quickly cooled, optional after exposure, at most 10 seconds, during which cooling occurs the transformation of austenite into martensite, which results in high strength strip.

JV is uhodit of tools for finish rolling, as a band with austenitic structure. The laminated so the strip will be a very high level of temperature uniformity in cross-section and in longitudinal direction. The usual method of obtaining a two-phase steel by means of two-stage cooling can be successfully applied to the strip of this type.

Another variant of the method according to the invention differs in that the strip is rolled in a tool for finish rolling at a temperature at which there is the right amount of ferrite, and the fact that the band, leaving funds for finish rolling, quickly cooled to a temperature below the Ms(the beginning of martensitic transformation), and when the cooling rate, which is formed beinit. In this embodiment of the invention again create the right balance between austenite and ferrite, and they are evenly distributed in the band, due to the high level of temperature uniformity. The choice of cooling rate and temperature of cooling allows a portion of the austenite has transformed into banit, between which are remnants of austenite. During subsequent deformation of the steel strip in the manufacture of it products in the austenite occur dislocations, which provide the high plasticity. Due to these properties, this grade of steel is cooled in bainite range. In General, the process of education bainite and formation of residual austenite depends on the alloying elements. Thus, it is especially effective in obtaining this type of steel to use an intermediate filling the bucket, which makes it possible to prepare the composition of the steel in such a way as to obtain the desired properties immediately prior to pouring slab installation for continuous casting.

In order to obtain not only a high level of temperature uniformity, and good strain distribution in the cross section of the strip, the following variant of the method according to the invention characterized in that at least one cage, preferably in all stands tools for finish rolling and/or at least one cage, preferably in each stand means for finish rolling rolling do with lubrication. Rolling with lubrication ensures uniform distribution of the compression generated by the rollers in the part of the steel strip or steel slab, which is located between the rollers. In the patent application EP-AO-750049 described method of hot rolling to obtain a two-phase steel. The proposed combination of the Le is VKE there is no information about a single process, starting with continuous casting of liquid steel.

Similar considerations apply to the descriptions of U.S. patents 4790889, 5470529 and 4316753.

In the application EP-A-0370575 described the way in which the steel strip get on one line, starting with the continuous casting of liquid steel. However, in this application there is no information about how to obtain high-strength steel strip. In addition, the cooling band perform before the stage finish rolling, in contrast to the fact that it is carried out before the cooling of the steel strip.

The present invention also proposed a device for producing a steel strip, 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 optionally has been subjected to rough compression, and means for rolling the slab to obtain strips of the desired final thickness and a means for cooling the strip, which differs in that the cooling means with the cooling capacity of at least 2 MW/m2placed between the stand finishing mill and winder.

Below the invention is described in more detail with reference to the drawings, in which parasponia according to the invention; Fig. 2 is a graph illustrating the temperature 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 introductory 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 production lines. It is also possible to have multiple installations for the continuous casting were arranged in series one behind the other. These options are included in the scope of the claims according to 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 a tool 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 with the R 4, which serves the molten steel and in which it at least partially solidifies. If necessary, an intermediate filling the mold 4 can be equipped with an electromagnetic stirrer. 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 will provide further casting speed 8 m/min and more. Hardened thin slab enters the tunnel furnace 1, which has a total length of, 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 the continuous casting and the output side means of rolling. The present invention presented here is based on a semi-infinite process, but it is obvious that it can also be used for an 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, to store the 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 filling of a new slab, or when the installation for continuous casting is damaged, and also ensure that the installation for continuous casting could operate continuously, if damage occurs downstream. In addition, the finding in the furnace increases the time it parts of the slab that results in improved temperature uniformity in the 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 splashing water high pressure presti, when the slab passes through the means for removing the dross and supplied to the tool 10 for rolling, is approximately 0.15 m/sec. The tool 10 for rolling, which performs the function of a means for roughing rolling mill consists of two four-roll stands, which are preferably equipped with means for lubrication of the rolls. If necessary, equipment may be included a means 8 for cutting during emergency cases.

As can be seen from Fig.2, the temperature of the slab, which is the outlet of the tundish, approximately 1450oWith falls in rolling stands up to a level 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. In two stands of the rolling mill means 10 for 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 of 42 mm, steel strip, with a thickness of approximately 16,8 mm, has a temperature of approximately 950apolos with a final thickness of 0.8 mm, and the other rolled strip thickness 1,0 mm the Numbers indicate the thickness in mm downstream from the means 10 for finish rolling are the means 11 for cooling, set of 12 boxes for the rolls and, if necessary, additional furnace (not shown). 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 of the cooling box 12 for the rolls and bake, which are not shown, can be positioned differently relative to each other that 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. Using the 11 cooling the strip is cooled until then, until it is in two-phase austenitic-ferritic range. The band also can not cooling or cooling only to a limited extent, or heat, so that on the output side means 14 finishing mill to obtain a strip, stands tools for finish rolling. You can also use natural cooling, optional between the rolling stands. Second unit 13 for removing scale at a water pressure of about 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 cutting tool 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 are located one after the other and preferably equipped with means for lubrication of the rolls.

When you get the band 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 for slab thickness of 70 mm in the upper row of figures Fig.3. After exiting the line 14 for rolling strip, which then has a final temperature of approximately 850oAnd a thickness of 0.6 mm, it is intensively cooled with means 15 for cooling and wind up in the Roux is the substance of the cooling means, described in the final report ECSC 7210-EA/214. It is assumed that the content of this report is included in the content of this description. A significant advantage of this means of cooling are a wide adjustment range, high cooling capacity per unit area and the uniformity of cooling.

The means 15 for cooling configure and adjust depending on whether you want to obtain martensite or beinit. You can start with a strip in the austenitic condition and cool it using a two-stage cooling, in which the first stage cooling is performed until until it forms the desired number of ferrite, followed by rapid cooling to form martensite. You can also, if the strip was rolled in the two-phase range, quickly cooling it so as to form martensite (curve m). The band in the austenitic state, you can also cool until then, until it forms the desired number of ferrite, and then continuously cooled so as to form banit with residual austenite. You can also rolled strip in two-phase range, and then, if necessary, continuously cooled so as to form a beynite with residual authenicator output 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. The means 15 for cooling and furnace 18 can be located together or one after the other. You can also place one substance to another in a matter of austenitic or austenitic-ferritic strip must be obtained. The means 17 for cutting include equipment 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. The device is suitable for strips with a width, which is in the range from 1000 to 1500 mm and a thickness of approximately 1.0 mm in the case of strips, laminated in austenite 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. A method of obtaining a high-strength steel strip, in which molten steel is poured, at least one installation for continuous casting with one or more flow lines for slab and using the heat of the casting, convey the slab through the furnace, exposing the rough rolling tool for rough rolling and finish rolling tool for finish rolling to obtain a steel strip of the desired final thickness, characterized in that in infinite or semi-infinite process, the slab is subjected to rough rolling predominantly in the austenitic range in the tool for roughing rolling and rolled in the austenitic range in the tool for finishing or laminates, at least one cage means for finish-rolling in the two-phase austenitic-ferritic range, and after the release of the funds for finishing laminated strip is rapidly cooled to obtain a desired structure.

2. The method according to p. 1, characterized in that the strip is rolled in a device for finish rolling at a temperature, PR is ro cooled to a temperature below the Ms(beginning of the formation of martensite) in the temperature range in which is formed martensite.

3. The method according to p. 1, characterized in that the strip is rolled in a device for finish rolling at a temperature at which there is the right amount of ferrite, the strip emerging from the means for finish rolling, quickly cooled to a temperature of above Ms(beginning of the formation of martensite) in the temperature range in which is formed martensite.

4. The method according to any of paragraphs.1-3, characterized in that the rolling comply with grease at least one cage, preferably in all stands tools for roughing rolling and/or at least one cage, preferably in each stand means for finish rolling.

5. Apparatus for producing high strength steel strip containing at least one installation for continuous casting of thin slabs oven for homogenization of the slab, which may be subjected to compression prior to size, and means for rolling the slab to obtain a strip of the desired thickness, a winder for winding strip, characterized in that the means for cooling the cooling capacity of at least 2 MW/m2placed between the last Chistova the

 

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SUBSTANCE: method comprises steps of heating steel continuously cast billet until austenite temperature; further multi-pass hot rolling while providing normalized temperature of rolling termination period; performing multi-pass rolling at temperature 860-1000 C of rolling termination period and at total elongation value γ selected according to kinds of steel. Invention provides complete treatment of axial zone of billet, lowered liquation of chemical elements along cross section and length of bar, regular contour of bar cross section.

EFFECT: enhanced quality, less loss of yield.

4 ex, 1 tbl

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